Chapter 23 respiratory Flashcards
The respiratory system contributes to homeostasis by
providing for the exchange of gases—oxygen and carbon dioxide—among the atmospheric air, blood, and tissue cells. It also helps adjust the pH of body fluids.
Your body’s cells continually use oxygen (O2) for
the metabolic reactions that generate ATP from the breakdown of nutrient molecules.
Because an excessive amount of CO2 produces acidity that can be toxic to cells,
excess CO2 must be eliminated quickly and efficiently.
The cardiovascular and respiratory systems cooperate to
supply O2 and eliminate CO2
Failure of eitherthe cardiovascular system or the respiratory system disrupts homeostasis by
causing rapid death of cells from oxygen starvation and buildup of waste products.
In addition to functioning in gas exchange, the respiratory system also participates in
regulating blood pH, contains receptors for the sense of smell, filters inspired air, produces sounds, and rids the body of some water and heat in exhaled air.
As in the digestive and urinary systems, which will be covered in subsequent chapters, in the respiratory system there is
an extensive area of contact between the external environment and capillary blood vessels.
respiration is
The process of supplying the body with O2 and removing CO2
respiration has three basic steps
Pulmonary ventilation
external (pulmonary) respiration
internal (tissue) respiration
Pulmonary ventilation (pulmon- = lung), or breathing, is
the inhalation (inflow) and exhalation (outflow) of air and involves the exchange of air between the atmosphere and the pulmonary alveoli of the lungs. Inhalation permits O2 to enter the lungs and exhalation permits CO2 to leave the lungs.
External (pulmonary) respiration is
the exchange of gases between the pulmonary alveoli of the lungs and the blood in pulmonary capillaries across the respiratory membrane. In this process, pulmonary capillary blood gains O2 and loses CO2.
Internal (tissue) respiration is
the exchange of gases between blood in systemic capillaries and tissue cells. In this step the blood loses O2 and gains CO2. Within cells, the metabolic reactions that consume O2 and give off CO2 during the production of ATP are termed cellular respiration
The respiratory system (RES-pi-ra-tōr-ē) consists of
the nose, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs
Structurally, the respiratory system consists of two parts:
(1) The upper respiratory system
(2) the lower respiratory system
The upper respiratory system includes
the nose, nasal cavity, pharynx, and associated structures;
the lower respiratory system includes
the larynx, trachea, bronchi, and lungs.
Functionally, the respiratory system also consists of two parts.
(1) The conducting zone
2) the respiratory zone
The conducting zone consists of
a series of interconnecting cavities and tubes both outside and within the lungs. These include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles
What is the function of the conducting zone
to filter, warm, and moisten air and conduct it into the lungs.
The respiratory zone consists of
tubes and tissues within the lungs where gas exchange occurs. These include the respiratory bronchioles, alveolar ducts, alveolar saccules (sacs), and pulmonary alveoi
What is the main function of the respiratory zone
the main sites of gas exchange between air and blood.
During respiration
the body is supplied with O2 and CO2 is removed.
otorhinolaryngology
The branch of medicine that deals with the diagnosis and treatment of diseases of the ears, nose, and throat (ENT)
What are the functions of the respiratory system
Provides for gas exchange: intake of O2 for delivery to body cells and removal of CO2 produced by body cells.
Helps regulate blood pH.
Contains receptors for sense of smell, filters inspired air, produces vocal sounds (phonation), and excretes small amounts of water and heat.
The nose is
a specialized organ at the entrance of the respiratory system that consists of a visible external portion (external nose) and an internal portion inside the skull called the nasal cavity (internal nose).
The external nose is
the portion of the nose visible on the face and consists of a supporting framework of bone and hyaline cartilage covered with muscle and skin and lined by a mucous membrane.
the bony framework of the external nose consists of
The frontal bone, nasal bones, and maxillae
The cartilaginous framework of the external nose consists of
several pieces of hyaline cartilage connected to each other and certain skull bones by fibrous connective tissue.
The components of the cartilaginous framework are
the nasal septal cartilage, which forms the anterior portion of the nasal septum; the lateral nasal cartilages inferior to the nasal bones; and the alar cartilages (Ā-lar), which form a portion of the walls of the nostrils.
Because it consists of pliable hyaline cartilage, the cartilaginous framework of the external nose is
somewhat flexible.
On the undersurface of the external nose are
two openings called the nostrils (external nares) which lead into cavities called the nasal vestibules.
The interior structures of the external nose have three functions:
(1) warming, moistening, and filtering incoming air; (2) detecting olfactory stimuli; and (3) modifying speech vibrations as they pass through the large, hollow resonating chambers.
Resonance refers to
prolonging, amplifying, or modifying a sound by vibration.
Rhinoplasty (RĪ-nō-plas′-tē; rhin = nose; -plasty = to mold or to shape), or “nose job,” is
a surgical procedure in which the shape of the external nose is altered.
The nasal cavity (internal nose) is
a large space in the anterior aspect of the skull that lies inferior to the nasal bone and superior to the oral cavity; it is lined with muscle and mucous membrane
A vertical partition, the nasal septum,
divides the nasal cavity into right and left sides.
The anterior portion of the nasal septum consists primarily of
hyaline cartilage;
The anterior portion of the nasal septum consists primarily of hyaline cartilage; the remainder is formed by
the vomer and the perpendicular plate of the ethmoid, maxillae, and palatine bones
Anteriorly, the nasal cavity merges with the
external nose,
posteriorly the nasal cavity communicates with
the pharynx through two openings called the choanae (kō-Ā-nē) or internal nares
Ducts from the paranasal sinuses (which drain mucus) and the nasolacrimal ducts (which drain tears)
open into the nasal cavity.
the paranasal sinuses are
cavities in certain cranial cavity and facial bones lined with mucous membrane that are continuous with the lining of the nasal cavity.
Skull bones containing the paranasal sinuses are
the frontal, sphenoid, ethmoid, and maxillae
Besides producing mucus, the paranasal sinuses serve as
resonating chambers for sound as we speak or sing.
The lateral walls of the internal nose are formed by
the ethmoid, maxillae, lacrimal, palatine, and inferior nasal conchae bones (see Figure 7.9); the ethmoid bone also forms the roof.
__________________________ form the floor of the internal nose.
The palatine bones and palatine processes of the maxillae, which together constitute the hard palate,
As air passes through the nose,
it is warmed, filtered, and moistened, and olfaction occurs.
The external nose has
a cartilaginous framework and a bony framework.
The bony and cartilaginous framework of the nose help
to keep the nasal vestibule and nasal cavity patent, that is, open or unobstructed.
The nasal cavity is divided into
a larger, inferior respiratory region and a smaller, superior olfactory region.
The respiratory region of the nasal cavity is lined with
ciliated pseudostratified columnar epithelium with numerous goblet cells, which is frequently called the respiratory epithelium
The anterior portion of the nasal cavity just inside the nostrils,
is called the nasal vestibule,
the nasal vestibule,
is surrounded by cartilage
the superior part of the nasal cavity is
surrounded by bone.
When air enters the nostrils,
it passes first through the nasal vestibule
the nasal vestibule is lined by
skin containing coarse hairs that filter out large dust particles.
Three shelves are formed by projections of the
superior nasal conchae, middle nasal conchae, and inferior nasal conchae bones (KON-kē) extend out of each lateral wall of the nasal cavity.
The conchae, almost reaching the nasal septum,
subdivide each side of the nasal cavity into a series of groovelike air passageways—the superior, middle, and inferior nasal meatuses
Mucous membrane lines
the nasal cavity and its shelves
The arrangement of conchae and meatuses
increases surface area in the internal nose and prevents dehydration by trapping water droplets during exhalation.
As inhaled air whirls around the conchae and meatuses,
it is warmed by blood in the capillaries.
Mucus secreted by the goblet cells in the nasal conchae and meatuses
moistens the air and traps dust particles.
The cilia in the nasal conchae and meatuses
move the mucus and trapped dust particles toward the pharynx, at which point they can be swallowed or spit out, thus removing the particles from the respiratory tract.
The olfactory sensory neurons, supporting epithelial cells, and basal epithelial cells lie
in the respiratory region, which is near the superior nasal conchae and adjacent septum.These cells make up the olfactory epithelium. It contains cilia but no goblet cells
The pharynx (FAR-inks), or throat, is
a funnel-shaped tube about 13 cm (5 in.) long that starts at the choanae and extends to the level of the cricoid cartilage, the most inferior cartilage of the larynx (voice box)
The pharynx lies
just posterior to the nasal and oral cavities, superior to the larynx, and just anterior to the cervical vertebrae.
The pharynx´s wall is composed of
skeletal muscles and is lined with a mucous membrane.
Relaxed skeletal muscles help keep the pharynx
patent
Contraction of the skeletal muscles in the pharynx
assists in deglutition (swallowing).
The pharynx functions as
a passageway for air and food, provides a resonating chamber for speech sounds, and houses the tonsils, which participate in immunological reactions against foreign invaders.
The pharynx can be divided into three anatomical regions:
(1) nasopharynx, (2) oropharynx, and (3) laryngopharynx.
The muscles of the entire pharynx are
arranged in two layers, an outer circular layer and an inner longitudinal layer.
The superior portion of the pharynx, called the nasopharynx, lies
posterior to the nasal cavity and extends to the soft palate.
The soft palate, which forms the posterior portion of the roof of the mouth, is
an arch-shaped muscular partition between the nasopharynx and oropharynx that is lined by mucous membrane.
There are five openings in the wall of the soft palate:
two choanae, two openings that lead into the auditory (pharyngotympanic) tubes (commonly known as the eustachian tubes), and the opening into the oropharynx
The posterior wall of the soft palate also contains
the pharyngeal tonsil (fa-RIN-je-al), or adenoid
Through the choanae, the nasopharynx
receives air from the nasal cavity along with packages of dust-laden mucus.
The nasopharynx is lined with
ciliated pseudostratified columnar epithelium, and the cilia move the mucus down toward the most inferior part of the nasopharynx.
The nasopharynx also exchanges small amounts of air with
the auditory tubes to equalize air pressure between the tympanic cavity and the atmosphere.
The intermediate portion of the pharynx, the oropharynx, lies
posterior to the oral cavity and extends from the soft palate inferiorly to the level of the upper border of the epiglottis.
The oropharynx
has only one opening into it, the fauces (FAW-sēz = throat), the opening from the mouth.
the oropharynx has both
respiratory and digestive functions, serving as a common passageway for air, food, and drink.
Because the oropharynx is subject to abrasion by food particles,
it is lined with nonkeratinized stratified squamous epithelium.
Two pairs of tonsils, are found in the oropharynx.
the palatine and lingual tonsils,
The inferior portion of the pharynx, the laryngopharynx (la-RING-gō-far-ingks) begins
at the level of the hyoid bone.
At its inferior end the laryngopharynx opens into
the esophagus (food tube) posteriorly and the larynx (voice box) anteriorly
Like the oropharynx, the laryngopharynx is both
a respiratory and a digestive pathway and is lined by nonkeratinized stratified squamous epithelium.
The larynx (LAR-ingks), or voice box, is
a short passageway that connects the laryngopharynx with the trachea.
The larynx lies
in the midline of the neck anterior to the esophagus and the fourth through sixth cervical vertebrae (C4–C6).
The wall of the larynx is composed of
nine pieces of cartilage
Three of the pieces of cartilage that line the wall of the larynx ________________ and three occur _______________________
occur singly (thyroid cartilage, epiglottic cartilage, and cricoid cartilage),
in pairs (arytenoid, cuneiform, and corniculate cartilages).
Of the paired cartilages, the arytenoid cartilages are
the most important because they influence changes in position and tension of the vocal folds (true vocal cords for speech).
The extrinsic muscles of the larynx connect
the cartilages to other structures in the throat;
the intrinsic muscles of the larynx
connect the cartilages to one another.
The laryngeal cavity is
the space that extends from the entrance into the larynx down to the inferior border of the cricoid cartilage
the laryngeal vestibule.
The portion of the laryngeal cavity above the vestibular folds (false vocal cords)
the infraglottic cavity
The portion of the cavity of the larynx below the vocal folds is called
The thyroid cartilage (laryngeal prominence or Adam’s apple) consists of
two fused plates of hyaline cartilage that form the anterior wall of the larynx and give it a triangular shape.
the thyroid cartilage
is present in both males and females but is usually larger in males due to the influence of male sex hormones on its growth during puberty
the thyrohyoid membrane.
The ligament that connects the thyroid cartilage to the hyoid bone
The epiglottic cartilage (epi- = over; -glottic = tongue) is
a large, leaf-shaped piece of elastic cartilage
The term epiglottis refers to
the epiglottic cartilage and its mucous membrane covering
The “stem” of the epiglottis is
the tapered inferior portion that is attached to the internal surface of the thyroid cartilage.
The broad superior “leaf” portion of the epiglottis is
unattached and is free to move up and down like a trap door.
During swallowing,
the pharynx and larynx rise.
Elevation of the pharynx
widens it to receive food or drink
elevation of the larynx causes
the epiglottis to move down and form a lid over the glottis, closing it off.
The glottis consists of
a pair of folds of mucous membrane, the vocal folds (true vocal cords) in the larynx, and the space between them called the rima glottidis (RĪ-ma GLOT-ti-dis).
The closing of the larynx during swallowing
routes liquids and foods into the esophagus and keeps them out of the larynx and airways.
When small particles of dust, smoke, food, or liquids pass into the larynx,
a cough reflex occurs, usually expelling the material.
The cricoid cartilage (KRĪ-koyd = ringlike) is
a ring of hyaline cartilage that forms the inferior wall of the larynx.
the cricoid cartilage is attached to
the first ring of cartilage of the trachea by the cricotracheal ligament (krī′-kō-TRĀ-kē-al).
The thyroid cartilage is connected to
the cricoid cartilage by the cricothyroid ligament.
The cricoid cartilage is the landmark for
making an emergency airway called a tracheotomy
The paired arytenoid cartilages (ar′-i-TĒ-noyd = ladlelike) are
triangular pieces of mostly hyaline cartilage located at the posterior, superior border of the cricoid cartilage. They form synovial joints with the cricoid cartilage and have a wide range of mobility.
The paired corniculate cartilages (kor-NIK-ū-lāt = shaped like a small horn),
horn-shaped pieces of elastic cartilage, are located at the apex of each arytenoid cartilage.
The paired cuneiform cartilages (KŪ-nē-i-form = wedge-shaped),
club-shaped elastic cartilages anterior to the corniculate cartilages, support the vocal folds and lateral aspects of the epiglottis.
The lining of the larynx superior to the vocal folds is
nonkeratinized stratified squamous epithelium.
The lining of the larynx inferior to the vocal folds is
ciliated pseudostratified columnar epithelium consisting of ciliated columnar cells, goblet cells, and basal cells.
The mucus produced by the goblet cells in the larynx
helps trap dust not removed in the upper passages
The cilia in the upper respiratory tract
move mucus and trapped particles down toward the oropharynx;
the cilia in the lower respiratory tract
move mucus and trapped particles up toward the laryngopharynx.
The mucous membrane of the larynx forms
two pairs of folds
the twopairs of folds formed by the mucous membrane of the larynx are
a superior pair called the vestibular folds (false vocal cords) and an inferior pair called the vocal folds (true vocal cords).
The space between the vestibular folds is known as the
rima vestibuli.
The laryngeal ventricle is a
lateral expansion of the middle portion of the laryngeal cavity inferior to the vestibular folds and superior to the vocal folds
When the vestibular folds are brought together, they function in
holding the breath against pressure in the thoracic cavity, such as might occur when a person strains to lift a heavy object.
The vocal folds are
the principal structures of voice production
Deep to the mucous membrane of the vocal folds, which is nonkeratinized stratified squamous epithelium, are
bands of elastic ligaments stretched between the rigid cartilages of the larynx like the strings on a guitar.
Intrinsic laryngeal muscles
attach to both the rigid cartilages and the vocal folds. When the muscles contract they move the cartilages, which pulls the elastic ligaments tight, and this stretches the vocal folds out into the airways so that the rima glottidis is narrowed.
Contracting and relaxing the intrinsic laryngeal muscles
varies the tension in the vocal folds, much like loosening or tightening a guitar string.
Air passing through the larynx vibrates the folds and produces sound (phonation) by
setting up sound waves in the column of air in the pharynx, nose, and mouth. The variation in the pitch of the sound is related to the tension in the vocal folds. The greater the pressure of air, the louder the sound produced by the vibrating vocal folds.
When the intrinsic muscles of the larynx contract,
they pull on the arytenoid cartilages, which causes the cartilages to pivot and slide.
Contraction of the posterior cricoarytenoid muscles
moves the vocal folds apart (abduction), thereby opening the rima glottidis
contraction of the lateral cricoarytenoid muscles
moves the vocal folds together (adduction), thereby closing the rima glottidis
Other intrinsic muscles can
elongate (and place tension on) or shorten (and relax) the vocal folds.
The glottis consists of
a pair of folds of mucous membrane in the larynx (the vocal folds) and the space between them (the rima glottidis).
Pitch is controlled by
the tension on the vocal folds. If they are pulled taut by the muscles, they vibrate more rapidly, and a higher pitch results. Decreasing the muscular tension on the vocal folds causes them to vibrate more slowly and produce lower-pitched sounds.
Due to the influence of androgens (male sex hormones),
vocal folds are usually thicker and longer in males than in females, and therefore they vibrate more slowly. This is why a man’s voice generally has a lower range of pitch than that of a woman.
Sound originates from
the vibration of the vocal folds, but other structures are necessary for converting the sound into recognizable speech.
The pharynx, mouth, nasal cavity, and paranasal sinuses all act as
resonating chambers that give the voice its human and individual quality.
We produce the vowel sounds by
constricting and relaxing the muscles in the wall of the pharynx.
Muscles of the face, tongue, and lips
help us enunciate words.
Whispering is accomplished by
closing all but the posterior portion of the rima glottidis. Because the vocal folds do not vibrate during whispering, there is no pitch to this form of speech.
we can still produce intelligible speech while whispering by
changing the shape of the oral cavity as we enunciate. As the size of the oral cavity changes, its resonance qualities change, which imparts a vowel-like pitch to the air as it rushes toward the lips
Laryngitis is
an inflammation of the larynx that is most often caused by a respiratory infection or irritants such as cigarette smoke.
Cancer of the larynx is found
almost exclusively in individuals who smoke
The trachea (TRĀ-kē-a = sturdy), or windpipe, is
a tubular passageway for air that is about 12 cm (5 in.) long and 2.5 cm (1 in.) in diameter.
The trachea
is located anterior to the esophagus (Figure 23.7) and extends from the larynx to the superior border of the fifth thoracic vertebra (T5), where it divides into right and left primary bronchi
The trachea is located
anterior to the esophagus and extends from the larynx to the superior border of the fifth thoracic vertebra.
The bronchial tree consists of .
macroscopic airways that begin at the trachea and continue through the terminal bronchioles
The layers of the tracheal wall, from deep to superficial, are
the (1) respiratory mucosa, (2) submucosa, (3) hyaline cartilage, and (4) adventitial layer (composed of areolar connective tissue).
The respiratory mucosa of the trachea consists of
an epithelial layer of ciliated pseudostratified columnar epithelium and an underlying layer of lamina propria that contains elastic and reticular fibers.
The respiratory mucosa of the trachea
provides the same protection against dust as the membrane lining the nasal cavity and larynx.
The submucosa consists of
areolar connective tissue that contains seromucous glands and their ducts.
The 16–20 incomplete, horizontal rings of hyaline cartilage on the trachea
resemble the letter C, are stacked one above another, and are connected by dense connective tissue.They may be felt through the skin inferior to the larynx.
The open part of each C-shaped cartilage ring
faces posteriorly toward the esophagus (Figure 23.7) and is spanned by the membranous wall of the trachea.
Within themembranous wall of the trachea are
transverse smooth muscle fibers, called the trachealis muscle (trā-kē-Ā-lis), and elastic connective tissue that allow the diameter of the trachea to change subtly during inhalation and exhalation, which is important in maintaining efficient airflow.
The solid C-shaped cartilage rings provide
a semirigid support to maintain patency so that the tracheal wall does not collapse inward (especially during inhalation) and obstruct the air passageway.
The adventitial layer of the trachea consists of
areolar connective tissue that joins the trachea to surrounding tissues.
tracheostomy
a surgical procedure in which a skin incision is followed by a short longitudinal incision into the trachea below the cricoid cartilage. Then, an endotracheal (within the trachea) tube (en-dō- TRĀK- ē-al) is placed through the opening to provide an airway when the usual route for breathing is obstructed or impaired and to remove secretions from the lungs
endotracheal intubation, or simply intubation.
In this procedure, also done in a hospital setting under anesthesia, an endotracheal tube is advanced through the mouth (or sometimes the nose), pharynx, and larynx into the trachea
A mechanical ventilator or simply a ventilator, is
a machine that is used to support ventilation (breathing). It is a form of life support
At the superior border of the fifth thoracic vertebra,
the trachea divides into a right main (primary) bronchus (BRONG-kus = windpipe), which goes into the right lung, and a left main (primary) bronchus, which goes into the left lung
The right main bronchus is
more vertical, shorter, and wider than the left
an aspirated object is more likely to enter and lodge in the
right main bronchus than the left
Like the trachea, the main bronchi (BRONG-kī) contain
incomplete rings of cartilage and are lined by ciliated pseudostratified columnar epithelium.
At the point where the trachea divides into right and left main bronchi
an internal ridge called the carina (ka-RĪ-na = keel of a boat) is formed by a posterior and somewhat inferior projection of the last tracheal cartilage.
The mucous membrane of the carina is
one of the most sensitive areas of the entire larynx and trachea for triggering a cough reflex.
Widening and distortion of the carina is a serious sign because
it usually indicates a carcinoma of the lymph nodes around the region where the trachea divides.
On entering the lungs, the main bronchi
divide to form smaller bronchi—the lobar (secondary) bronchi, one for each lobe of the lung.
The right lung has
three lobes; the left lung has two.)
The lobar bronchi continue to
branch, forming still smaller bronchi, called segmental (tertiary) bronchi (TER-shē-e-rē), that supply the specific bronchopulmonary segments within the lobes.
There are _________________ segmental bronchi in the right lung and __________ segmental bronchi in the left lung.
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The segmental bronchi
divide into bronchioles
Bronchioles
branch repeatedly, and the smallest ones branch into even smaller tubes called terminal bronchioles.
terminal bronchioles contain
exocrine bronchiolar (Clara) cells, which are nonciliated columnar cells, interspersed among ciliated simple columnar cells.
The exocrine bronchiolar cells may
protect against harmful effects of inhaled toxins and carcinogens, produce surfactant (discussed shortly), and function as stem cells, which give rise to various cells of the epithelium
The terminal bronchioles represent
the end of the conducting zone of the respiratory system.
The extensive branching from the trachea through the terminal bronchioles
resembles an inverted tree and is commonly referred to as the bronchial tree.
Beyond the terminal bronchioles of the bronchial tree,
the branches become microscopic. These branches are called the respiratory bronchioles and alveolar ducts,
The respiratory passages from the trachea to the alveolar ducts contain
about 23 generations of branching; branching from the trachea into main bronchi is called first-generation branching, that from main bronchi into lobar bronchi is called second-generation branching, and so on down to the alveolar ducts
How does the epithelium of the bronchial tree change as branching becomes more extensive
The mucous membrane in the bronchial tree changes from ciliated pseudostratified columnar epithelium in the main bronchi, lobar bronchi, and segmental bronchi to ciliated simple columnar epithelium with some goblet cells in larger bronchioles, to mostly ciliated simple cuboidal epithelium with no goblet cells in smaller bronchioles, to mostly nonciliated simple cuboidal epithelium in terminal bronchioles.
ciliated epithelium of the respiratory membrane removes inhaled particles in two ways
1 mucus produced by goblet cells traps the particles, and the cilia move the mucus and trapped particles toward the pharynx for removal.
2 In regions where nonciliated simple cuboidal epithelium is present, inhaled particles are removed by macrophages.
Describe the structural changes in cartilage as branching becomes more extensive in the bronchial tree
Plates of cartilage gradually replace the incomplete rings of cartilage in main bronchi and finally disappear in the distal bronchioles.
Describe the relationship between cartilage and smooth muscle as branching becomes more extensive in the bronchial tree
As the amount of cartilage decreases, the amount of smooth muscle increases. Smooth muscle encircles the epithelial-lined lumen in spiral bands and helps maintain patency. However, because there is no supporting cartilage, muscle spasms can close off the airways.
During exercise, activity in the sympathetic part of the autonomic nervous system (ANS)
increases and the suprarenal medulla releases the hormones epinephrine and norepinephrine; both of these events cause relaxation of smooth muscle in the bronchioles, which dilates the airways.Because air reaches the pulmonary alveoli more quickly, lung ventilation improves.
The parasympathetic part of the ANS and mediators of allergic reactions such as histamine
cause contraction of bronchiolar smooth muscle, which results in constriction of distal bronchioles.
A pulmonologist (pul-mō-NOL-ō-gist; pulmo- = lung) is
a specialist in the diagnosis and treatment of lung diseases.
The lungs (= lightweights, because they float) are
paired cone-shaped organs in the thoracic cavity
The lungs are separated from each other by
the heart and other structures of the mediastinum, which divides the thoracic cavity into two anatomically distinct chambers.
if trauma causes one lung to collapse,
the other may remain expanded.
Each lung is enclosed and protected by
a double-layered serous membrane called the pleural membrane (PLOOR-al; pleur- = side) or pleura
The superficial layer, called the parietal pleura,
lines the wall of the thoracic cavity
the deep layer, the visceral pleura,
covers the lungs themselves
Between the visceral and parietal pleurae is
a small space, the pleural cavity, which contains a small amount of lubricating fluid secreted by the membranes.
What is the function of pleural fluid
pleural fluid reduces friction between the membranes, allowing them to slide easily over one another during breathing. Pleural fluid also causes the two membranes to adhere to one another just as a film of water causes two glass microscope slides to stick together, a phenomenon called surface tension.
Separate pleural cavities
surround the left and right lungs.
Inflammation of the pleural membrane, called pleurisy or pleuritis,
may in its early stages cause pain due to friction between the parietal and visceral layers of the pleura. If the inflammation persists, excess fluid accumulates in the pleural space, a condition known as pleural effusion.
In certain conditions, the pleural cavities may fill with
air (pneumothorax; noo′-mō-THOR-aks; pneumo- = air or breath), blood (hemothorax), or pus.
collapse of a part of a lung, or rarely an entire lung, is called
atelectasis
The lungs extend from
the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly
The broad inferior portion of the lung,
the base, is concave and fits over the convex area of the diaphragm.
The narrow superior portion of the lung is the
apex
The surface of the lung lying against the ribs,
the costal surface, matches the rounded curvature of the ribs.
The mediastinal (medial) surface of each lung contains a region,
the hilum, through which bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit These structures are held together by the pleura and connective tissue and constitute the root of the lung.
Medially, the left lung also contains a concavity,
the cardiac notch, in which the apex of the heart lies.
Due to the space occupied by the heart,
the left lung is about 10% smaller than the right lung.
Although the right lung is thicker and broader,
it is also somewhat shorter than the left lung because the diaphragm is higher on the right side, accommodating the liver that lies inferior to it.
The oblique fissure
divides the left lung into two lobes.
The oblique and horizontal fissures
divide the right lung into three lobes.
The apex of the lungs lies
superior to the medial third of the clavicles, and this is the only area that can be palpated.
The anterior, lateral, and posterior surfaces of the lungs
lie against the ribs.
The base of the lungs extends from
the sixth costal cartilage anteriorly to the spinous process of the tenth thoracic vertebra posteriorly.
The pleura extends
about 5 cm (2 in.) below the base from the sixth costal cartilage anteriorly to the twelfth rib posteriorly. Thus, the lungs do not completely fill the pleural cavity in this area.
Removal of excessive fluid in the pleural cavity can be accomplished without injuring lung tissue by
inserting a needle anteriorly through the seventh intercostal space, a procedure called thoracentesis (thor′-a-sen-TĒ-sis; -centesis = puncture).The needle is passed along the superior border of the lower rib to avoid damage to the intercostal nerves and blood vessels. Inferior to the seventh intercostal space there is danger of penetrating the diaphragm.
One or two fissures divide each lung
into sections called lobes
Both lungs have
an oblique fissure, which extends inferiorly and anteriorly;
the right lung also has
a horizontal fissure
The oblique fissure in the left lung
separates the superior lobe from the inferior lobe.
In the right lung, the superior part of the oblique fissure
separates the superior lobe from the inferior lobe;
in the right lung the inferior part of the oblique fissure
separates the inferior lobe from the middle lobe, which is bordered superiorly by the horizontal fissure.
Each lobe receives
its own lobar bronchus.
the right main bronchus gives rise to three lobar bronchi called the superior, middle, and inferior lobar bronchi,
three lobar bronchi called the superior, middle, and inferior lobar bronchi,
the left main bronchus gives rise to
two lobar bronchi called the superior and inferior lobar bronchi
Within the lung, the lobar bronchi give rise to
the segmental bronchi, which are constant in both origin and distribution
there are ________________segmental bronchi in each lung
10
bronchopulmonary segment
The portion of lung tissue that each segmental bronchus supplies
Each bronchopulmonary segment of the lungs
has many small compartments called lobules
each lobule
is wrapped in elastic connective tissue and contains a lymphatic vessel, an arteriole, a venule, and a branch from a terminal bronchiole
Terminal bronchioles in a lobule subdivide into
microscopic branches called respiratory bronchioles
respiratory bronchioles
have pulmonary alveoli (described shortly) budding from their walls
Pulmonary alveoli participate in
gas exchange
respiratory bronchioles begin
the respiratory zone of the respiratory system.
As the respiratory bronchioles penetrate more deeply into the lungs, the epithelial lining changes
from simple cuboidal to simple squamous
Respiratory bronchioles in turn subdivide into
several (2–11) alveolar ducts (al-vē-Ō-lar), which consist of simple squamous epithelium.
The terminal dilation of an alveolar duct is called
an alveolar saccule or alveolar sac and is analogous to a cluster of grapes.
Each alveolar saccule is composed of
outpouchings called pulmonary alveoli (al-vē-Ō-Iī), analogous to individual grapes
There are about _______________at the end of each alveolar duct and each alveolar saccule contains ___________________
100 alveolar saccules
about 20–30 pulmonary alveoli,
The wall of each pulmonary alveolus (singular) consists of
two types of alveolar epithelial cells
What is the name and function of the most numerous aveolar cell
The more numerous (about 95%) pneumocyte type I (type I alveolar cell) are simple squamous epithelial cells that form a nearly continuous lining of the pulmonary alveolar wall
Describe Pneumocyte type II
(type II alveolar cell), also called septal cells, are fewer in number and are found between pneumocytes type I
The thin wall of pneumocytes type I
are the main sites of gas exchange.
Pneumocytes type I are
rounded or cuboidal epithelial cells with free surfaces containing microvilli, secrete pulmonary alveolar fluid, which keeps the surface between the cells and the air moist.
Included in the pulmonary alveolar fluid is
surfactant (sur-FAK-tant), a complex mixture of phospholipids and lipoproteins
Surfactant function
lowers the surface tension of pulmonary alveolar fluid, which reduces the tendency of pulmonary alveoli to collapse and thus maintains their patency (described later).
An alveolar saccule is
the terminal dilation of an alveolar duct and is composed of pulmonary alveoli.
Also present in the aveolar wall is
aveolar macrophages and fibroblasts
What is the function of aveolar macrophages
phagocytes that remove fine dust particles and other debris from the pulmonary alveolar spaces
What is the function of fibroblasts in the aveolar wall
produce reticular and elastic fibers.
Underlying the layer of pneumocytes type I is
an elastic basement membrane
On the outer surface of the pulmonary alveoli,
the lobule’s arteriole and venule disperse into a network of blood capillaries (see Figure 23.11a) that consist of a single layer of endothelial cells and basement membrane.
The exchange of O2 and CO2 between the air spaces in the lungs and the blood takes place
by diffusion across the pulmonary alveolar and capillary walls, which together form the respiratory membrane
Extending from the pulmonary alveolar air space to blood plasma,
the respiratory membrane consists of four layers
Describe the four layers of the respiratory membrane
A layer of pneumocytes type I and type II and associated alveolar macrophages that constitutes the alveolar wall
An epithelial basement membrane underlying the pulmonary alveolar wall
A capillary basement membrane that is often fused to the epithelial basement membrane
The capillary endothelium
Despite having several layers,
the respiratory membrane is very thin
It has been estimated that both lungs contain
300–500 million pulmonary alveoli, providing an immense surface area of about 75 m2 (807 ft2)—about the size of a racquetball court or slightly larger—for gas exchange.
The hundreds of millions of pulmonary alveoli account for
the spongy texture of the lungs.
The lungs receive blood via
two sets of arteries: pulmonary arteries and bronchial arteries
Deoxygenated blood
passes through the pulmonary trunk, which divides into a left pulmonary artery that enters the left lung and a right pulmonary artery that enters the right lung.
(The pulmonary arteries are the only arteries in the body
that carry deoxygenated blood.)
Return of the oxygenated blood to the heart occurs by way of
the four pulmonary veins, which drain into the left atrium
A unique feature of pulmonary blood vessels is
their constriction in response to localized hypoxia (low O2 level).
In all body tissues besides the pulmonary blood vessels,
hypoxia causes dilation of blood vessels to increase blood flow
In the lungs in response to hypoxia
vasoconstriction diverts pulmonary blood from poorly ventilated areas of the lungs to well-ventilated regions for more efficient gas exchange.This phenomenon is known as ventilation–perfusion coupling (per-FYU-zhun) because the perfusion (blood flow) to each area of the lungs matches the extent of ventilation (airflow) to alveoli in that area.
Bronchial arteries, which branch from the aorta,
deliver oxygenated blood to the lungs This blood mainly perfuses the muscular walls of the bronchi and bronchioles.
Connections do exist between
branches of the bronchial arteries and branches of the pulmonary arteries, however; most blood returns to the heart via pulmonary veins
Some blood drains into
bronchial veins, branches of the azygos system, and returns to the heart via the superior vena cava.
coryza (kō-RĪ-za),
the common cold
List the structures dedicated to maintaining the patency of the respiratory system
the bony and cartilaginous frameworks of the nose, skeletal muscles of the pharynx, cartilages of the larynx, C-shaped rings of cartilage in the trachea and bronchi, smooth muscle in the bronchioles, and surfactant in the pulmonary alveoli.
Unfortunately, there are also factors that can compromise patency. These include
crushing injuries to bone and cartilage, a deviated nasal septum, nasal polyps, inflammation of mucous membranes, spasms of smooth muscle, and a deficiency of surfactant.
List the structures of the respiratory system that are lined by nonkeratinized stratified squamous epithelium
Nasal vestbule
oropharynx
laryngopharynx
larynx (above vocal folds)
List the structures of the respiratory system that are lined by ciliated pseudostratified columnar epithelium
Respiratoey region of the nose
nasopharynx
Larynx below the vocal folds
trachea
main bronchi
Lobar bronchi
segmental bronchi
The olfactory region of the nose is lined by
Olfactory epithelium (olfactory sensory neurons)
Which respiratory system structures are lined by ciliated simple columnar epithelium
Larger bronchioles
smaller bronchioles
What type of epithelium lines the terminal bronchioles
nonciliated simple columnar
What type of epithelium lines the respiratory bronchioles
simple cuboidal to simple squamous
Which respiratory system structures are lined by simple squamous epithelium
alveolar ducts
pulmonary alveoli
List all of the respiratory system structures that contain goblet cells
Respiratory region of the nose
nasopharynx
larynx (below vocal folds)
trachea
main bronchi
lobar bronchi
segmental bronchi
larger bronchioles
what are the only gas exchange structures in the respiratory system
respiratory bronchioles
alveolar ducts
pulmonary alveoli
Pulmonary ventilation, or breathing, is
the flow of air into and out of the lungs.
In pulmonary ventilation,
air flows between the atmosphere and the pulmonary alveoli of the lungs because of alternating pressure differences created by contraction and relaxation of respiratory muscles.
The rate of airflow and the amount of effort needed for breathing are also influenced by
alveolar surface tension, compliance of the lungs, and airway resistance.
Air moves into the pulmonary alveoli of the lungs when
the air pressure inside the lungs is less than the air pressure in the atmosphere
Air moves out of the pulmonary alveoli of the lungs when
the air pressure inside the lungs is greater than the air pressure in the atmosphere.
Breathing in is called
inhalation (inspiration).
Just before each inhalation,
the air pressure inside the lungs is equal to the air pressure of the atmosphere,
For air to flow into the lungs,
the pressure inside the pulmonary alveoli must become lower than the atmospheric pressure. This condition is achieved by increasing the size of the lungs.
The pressure of a gas in a closed container is
inversely proportional to the volume of the container.
if the size of a closed container is increased,
the pressure of the gas inside the container decreases, and that if the size of the container is decreased, then the pressure inside it increases.
The inverse relationship between volume and pressure, is called
Boyle’s law
Differences in pressure caused by changes in lung volume
force air into our lungs when we inhale and out when we exhale
For inhalation to occur,
the lungs must expand, which increases lung volume and thus decreases the pressure in the lungs to below atmospheric pressure
The first step in expanding the lungs during normal quiet inhalation involves
contraction of the main muscle of inhalation, the diaphragm, with resistance from external intercostals
The most important muscle of inhalation is
the diaphragm, the dome-shaped skeletal muscle that forms the floor of the thoracic cavity
the diaphragm
is innervated by fibers of the phrenic nerves, which emerge from the spinal cord at cervical levels 3, 4, and 5.
Contraction of the diaphragm causes
the diaphragm to flatten, lowering its dome.This increases the vertical diameter of the thoracic cavity
During normal quiet inhalation,
the diaphragm descends about 1 cm (0.4 in.), producing a pressure difference of 1–3 mmHg and the inhalation of about 500 mL of air.
In strenuous breathing,
the diaphragm may descend 10 cm (4 in.), which produces a pressure difference of 100 mmHg and the inhalation of 2–3 liters of air.
Contraction of the diaphragm is responsible for
about 75% of the air that enters the lungs during quiet breathing.
The second most important muscles of inhalation are
the external intercostals. When these muscles contract, they elevate the ribs. As a result, there is an increase in the anteroposterior and lateral diameters of the chest cavity.
Contraction of the external intercostals is responsible for
about 25% of the air that enters the lungs during normal quiet breathing.
During normal, quiet inhalation,
the diaphragm and external intercostals contract, the lungs expand, and air moves into the pulmonary alveoli of the lungs
during normal, quiet exhalation,
the diaphragm and external intercostals relax and the lungs recoil, forcing air out of the pulmonary alveoli of the lungs
Intrapleural pressure is
the pressure within the pleural cavity.
Intrapleural pressure is always
a negative pressure (lower than atmospheric pressure), ranging from 754–756 mmHg during normal quiet breathing.
since the pleural cavity has a negative pressure,
it essentially functions as a vacuum. The suction of this vacuum attaches the visceral pleura to the chest wall. Thus, if the thoracic cavity increases in size, the lungs also expand; if the thoracic cavity decreases in size, the lungs recoil (become smaller).
Just before inhalation, intrapleural pressure is
about 4 mmHg less than atmospheric pressure, or about 756 mmHg at an atmospheric pressure of 760 mmHg
As the diaphragm and external intercostals contract and the overall size of the thoracic cavity increases,
the volume of the pleural cavity also increases, which causes intrapleural pressure to decrease to about 754 mmHg.
As the thoracic cavity expands, the parietal pleura lining the cavity
is pulled outward in all directions, and the visceral pleura and lungs and pulled along with it.
As the volume of the lungs increases the pressure of air within the pulmonary alveoli of the lungs, called the alveolar (intrapulmonic) pressure,
drops from 760 to 758 mmHg. A pressure difference is thus established between the atmosphere and the pulmonary alveoli. since air always flows from a region of higher pressure to a region of lower pressure, inhalation takes place. Air continues to flow into the lungs as long as a pressure difference exists
Although the lungs enlarge in all directions during inhalation,
most of the increase in volume appears to be due to the lengthening and expansion of the alveolar ducts and the increase in size of the openings into the alveoli.
During deep, forceful inhalations,
accessory muscles of inspiration also participate in increasing the size of the thoracic cavity
accessory muscles of inhalation are so named because
they make little, if any, contribution during normal quiet inhalation, but during exercise or forced breathing they may contract vigorously.
The accessory muscles of inhalation include
the sternocleidomastoid muscles, which elevate the sternum; the scalene muscles, which elevate the first two ribs; and the pectoralis minor muscles, which elevate the third through fifth ribs
since both normal quiet inhalation and inhalation during exercise or forced breathing involve muscular contraction,
the process of inhalation is said to be active.
Breathing out, called exhalation (expiration), is also due to
a pressure gradient, but in this case the gradient is in the opposite direction: The pressure in the lungs is greater than the pressure of the atmosphere.
Normal exhalation during quiet breathing, unlike inhalation
, is a passive process because no muscular contractions are involved. Instead, exhalation results from elastic recoil of the chest wall and lungs, both of which have a natural tendency to spring back after they have been stretched.
Two inwardly directed forces contribute to elastic recoil:
1) the recoil of elastic fibers that were stretched during inhalation and (2) the inward pull of surface tension due to the film of intrapleural fluid between the visceral and parietal pleurae.
Exhalation starts
when the inspiratory muscles relax.
As the diaphragm relaxes,
its dome moves superiorly owing to its elasticity.
As the external intercostals relax,
the ribs are depressed. These movements decrease the vertical, lateral, and anteroposterior diameters of the thoracic cavity, which decreases lung volume.
As lung volume decreases
the alveolar pressure increases to about 762 mmHg. Air then flows from the area of higher pressure in the pulmonary alveoli to the area of lower pressure in the atmosphere
Exhalation becomes active
only during forceful breathing, as occurs while playing a wind instrument or during exercise.
During active exhalation,
muscles of exhalation—the abdominal and internal intercostals (see Figure 23.14a)—contract, which increases pressure in the abdominal region and thorax.
Contraction of the abdominal muscles
moves the inferior ribs downward and compresses the abdominal viscera, thereby forcing the diaphragm superiorly.
Contraction of the internal intercostals, which extend inferiorly and posteriorly between adjacent ribs
, pulls the ribs inferiorly
Although intrapleural pressure is always less than alveolar pressure,
it may briefly exceed atmospheric pressure during a forceful exhalation, such as during a cough.
three other factors affect the rate of airflow and the ease of pulmonary ventilation:
surface tension of the alveolar fluid, compliance of the lungs, and airway resistance.
a thin layer of alveolar fluid coats the luminal surface of pulmonary alveoli and
exerts a force known as surface tension.
Surface tension arises
at all air–water interfaces because the polar water molecules are more strongly attracted to each other than they are to gas molecules in the air
When liquid surrounds a sphere of air, as in a pulmonary alveolus or a soap bubble,
surface tension produces an inwardly directed force.
In the lungs, surface tension causes
the pulmonary alveoli to assume the smallest possible diameter.
During breathing, surface tension must be
overcome to expand the lungs during each inhalation.
Surface tension also accounts for
two-thirds of lung elastic recoil, which decreases the size of pulmonary alveoli during exhalation.
The surfactant (a mixture of phospholipids and lipoproteins) present in alveolar fluid
reduces its surface tension below the surface tension of pure water.
A deficiency of surfactant in premature infants causes respiratory distress syndrome, in which
the surface tension of pulmonary alveolar fluid is greatly increased, so that many pulmonary alveoli collapse at the end of each exhalation. Great effort is then needed at the next inhalation to reopen the collapsed pulmonary alveoli.
Respiratory distress syndrome (RDS) is
a breathing disorder of premature newborns in which the pulmonary alveoli do not remain open due to a lack of surfactant.
Compliance refers to
how much effort is required to stretch the lungs and chest wall.
High compliance means that
the lungs and chest wall expand easily; low compliance means that they resist expansion.
In the lungs, compliance is related to two principal factors:
elasticity and surface tension.
The lungs normally have
high compliance and expand easily because elastic fibers in lung tissue are easily stretched and surfactant in alveolar fluid reduces surface tension.
Decreased compliance is a common feature in pulmonary conditions that
(1) scar lung tissue (for example, tuberculosis), (2) cause lung tissue to become filled with fluid (pulmonary edema), (3) produce a deficiency in surfactant, or (4) impede lung expansion in any way
Increased lung compliance occurs in
emphysema due to destruction of elastic fibers in alveolar walls
Airflow equals
the pressure difference between the pulmonary alveoli and the atmosphere divided by the resistance.
The walls of the airways, especially the bronchioles,
offer some resistance to the normal flow of air into and out of the lungs
As the lungs expand during inhalation,
the bronchioles enlarge because their walls are pulled outward in all directions. Larger-diameter airways have decreased resistance
Airway resistance increases during
exhalation as the diameter of bronchioles decreases.
Airway diameter is also regulated by
the degree of contraction or relaxation of smooth muscle in the walls of the airways
Signals from the sympathetic division of the autonomic nervous system (ANS) cause
relaxation of bronchiolar smooth muscle (bronchodilation), which results in decreased resistance.
Signals from the parasympathetic part of the ANS cause
contraction of bronchiolar smooth muscle (bronchoconstriction) resulting in increased resistance.
Any condition that narrows or obstructs the airways
increases resistance, so that more pressure is required to maintain the same airflow.
The hallmark of asthma or chronic obstructive pulmonary disease (COPD)—emphysema or chronic bronchitis—is
increased airway resistance due to obstruction or collapse of airways.
The term for the normal pattern of quiet breathing is
eupnea (ūp-NĒ-a; eu- = good, easy, or normal; -pnea = breath). Eupnea can consist of shallow, deep, or combined shallow and deep breathing.
A pattern of shallow (chest) breathing, called costal breathing, consists of
an upward and outward movement of the chest due to contraction of the external intercostal muscles.
A pattern of deep (abdominal) breathing, called diaphragmatic breathing (dī′-a-frag-MAT-ik), consists of
the outward movement of the abdomen due to the contraction and descent of the diaphragm.
Coughing.
A long-drawn and deep inhalation followed by a complete closure of the rima glottidis, which results in a strong exhalation that suddenly pushes the rima glottidis open and sends a blast of air through the upper respiratory passages. Stimulus for this reflex act may be a foreign body lodged in the larynx, trachea, or epiglottis
Sneezing
Spasmodic contraction of muscles of exhalation that forcefully expels air through the nose and mouth. Stimulus may be an irritation of the nasal mucosa
Sighing
A long-drawn and deep inhalation immediately followed by a shorter but forceful exhalation.
Yawning
A deep inhalation through the widely opened mouth producing an exaggerated depression of the mandible. It may be stimulated by drowsiness or someone else’s yawning, but the precise cause is unknown.
Sobbing
A series of convulsive inhalations followed by a single prolonged exhalation. The rima glottidis closes earlier than normal after each inhalation so only a little air enters the lungs with each inhalation.
Crying
An inhalation followed by many short convulsive exhalations, during which the rima glottidis remains open and the vocal folds vibrate; accompanied by characteristic facial expressions and tears.
Laughing
The same basic movements as crying, but the rhythm of the movements and the facial expressions usually differ from those of crying. Laughing and crying are sometimes indistinguishable.
Hiccupping
Spasmodic contraction of the diaphragm followed by a spasmodic closure of the rima glottidis, which produces a sharp sound on inhalation. Stimulus is usually irritation of the sensory nerve endings of the digestive canal.
Valsalva (val-SAL-va) maneuver
Forced exhalation against a closed rima glottidis as may occur during periods of straining while defecating.
Pressurizing the middle ear
The nose and mouth are held closed and air from the lungs is forced through the auditory meatus into the middle ear. Employed by those snorkeling or scuba diving during descent to equalize the pressure of the middle ear with that of the external environment.
The different amounts of air moving into and out of the lungs can be classified into two types:
(1) lung volumes, which can be measured directly by use of a spirometer (described shortly) and (2) lung capacities, which are combinations of different lung volumes.
The apparatus used to measure volumes and capacities is called a spirometer
spirometer
in a spirogram.
Inhalation is recorded as an upward deflection and exhalation is recorded as a downward deflection (Figure 23.16).
In general, lung volumes and capacities are larger in
males, taller individuals, younger adults, people who live at higher altitudes, and those who are not obese.
Lung capacities are
combinations of various lung volumes.
While at rest, a healthy adult averages
12 breaths a minute, with each inhalation and exhalation moving about 500 mL of air into and out of the lungs
The volume of one breath is called the
tidal volume (VT)
In a typical adult, about 70% of the tidal volume (350 mL)
actually reaches the respiratory zone of the respiratory system—the respiratory bronchioles, alveolar ducts, alveolar saccules, and alveoli—and participates in external respiration. The other 30% (150 mL) remains in the conducting airways of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles.
anatomic (respiratory) dead space.
Collectively, the conducting airways with air that does not undergo respiratory exchange
Not all of the inhaled air can be used in gas exchange because
some of it remains in the anatomic dead space.
By taking a very deep breath, you can inhale a good deal more
than 500 mL. This additional inhaled air, called the inspiratory reserve volume (IRV), is about 3100 mL in an average adult male and 1900 mL in an average adult female
If you inhale normally and then exhale as forcibly as possible
, you should be able to push out considerably more air in addition to the 500 mL of tidal volume The extra 1200 mL in males and 700 mL in females is called the expiratory reserve volume (ERV).
The forced expiratory volume in 1 second (FEV1) is
the volume of air that can be exhaled from the lungs in 1 second with maximal effort following a maximal inhalation
Even after the expiratory reserve volume is exhaled,
considerable air remains in the lungs because the subatmospheric intrapleural pressure keeps the alveoli slightly inflated, and some air remains in the noncollapsible airways. This volume, which cannot be measured by spirometry, is called the residual volume
residual volume (re-ZID-u-al) (RV) amounts to
about 1200 mL in males and 1100 mL in females.
If the thoracic cavity is opened, the intrapleural pressure rises to equal the atmospheric pressure and forces out some of the residual volume. The air remaining is called the
minimal volume.
Minimal volume provides a medical and legal tool for
determining whether a baby is born dead (stillborn) or died after birth
The presence of minimal volume can be demonstrated
by placing a piece of lung in water and observing if it floats. Fetal lungs contain no air, so the lung of a stillborn baby will not float in water.
Inspiratory capacity (IC) is
the sum of tidal volume and inspiratory reserve volume (500 mL + 3100 mL = 3600 mL in males and 500 mL + 1900 mL = 2400 mL in females).
Functional residual capacity (FRC) is
the sum of residual volume and expiratory reserve volume (1200 mL + 1200 mL = 2400 mL in males and 1100 mL + 700 mL = 1800 mL in females).
Vital capacity (VC) is
the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume (4800 mL in males and 3100 mL in females).
total lung capacity (TLC) is
the sum of vital capacity and residual volume (4800 mL + 1200 mL = 6000 mL in males and 3100 mL + 1100 mL = 4200 mL in females).
Another way to assess pulmonary function is to determine
the amount of air that flows into and out of the lungs each minute. The minute ventilation ()—the total volume of air inspired and expired each minute
the minute ventilation can be calculated by
tidal volume multiplied by respiratory rate.
In a typical adult at rest, minute ventilation is about
6000 mL/min ( = 12 breaths per minute × 500 mL = 6000 mL/min). A lower-than-normal minute ventilation usually is a sign of pulmonary malfunction.
The alveolar ventilation (A) is
the volume of air per minute that actually reaches the respiratory zone (350 mL). Alveolar ventilation is typically about 4200 mL/min (A = 12 breaths per minute × 350 mL = 4200 mL/min).
The exchange of oxygen and carbon dioxide between alveolar air and pulmonary blood occurs via
passive diffusion, which is governed by the behavior of gases as described by two gas laws, Dalton’s law and Henry’s law.
Dalton’s law is important for understanding
how gases move down their pressure gradients by diffusion
Henry’s law helps explain
how the solubility of a gas relates to its diffusion.
According to Dalton’s law,
each gas in a mixture of gases exerts its own pressure as if no other gases were present
The pressure of a specific gas in a mixture is called
its partial pressure (Px); the subscript is the chemical formula of the gas.
The total pressure of the mixture is calculated simply by
adding all of the partial pressures.
Atmospheric air is
a mixture of gases—nitrogen (N2), oxygen (O2), argon (Ar), carbon dioxide (CO2), variable amounts of water vapor (H2O), plus other gases present in small quantities.
We can determine the partial pressure exerted by each component in the mixture by
multiplying the percentage of the gas in the mixture by the total pressure of the mixture
describe the concentration of different gases in atmospheric air
Atmospheric air is 78.6% nitrogen, 20.9% oxygen, 0.093% argon, 0.04% carbon dioxide, and 0.06% other gases; a variable amount of water vapor is also present.
partial pressures determine the movement of
O2 and CO2 between the atmosphere and lungs, between the lungs and blood, and between the blood and body cells
Each gas diffuses across a permeable membrane
from the area where its partial pressure is greater to the area where its partial pressure is less. The greater the difference in partial pressure, the faster the rate of diffusion.
Compared with inhaled air, alveolar air has
less O2 (13.6% versus 20.9%) and more CO2 (5.2% versus 0.04%)
Compared with inhaled air, alveolar air has less O2 (13.6% versus 20.9%) and more CO2 (5.2% versus 0.04%) for two reasons.
First, gas exchange in the alveoli increases the CO2 content and decreases the O2 content of alveolar air. Second, when air is inhaled it becomes humidified as it passes along the moist mucosal linings.
exhaled air contains
more O2 than alveolar air (16% versus 13.6%) and less CO2 (4.5% versus 5.2%) because some of the exhaled air was in the anatomic dead space and did not participate in gas exchange.
Exhaled air is
a mixture of alveolar air and inhaled air that was in the anatomic dead space.
Henry’s law states that
the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility.
In body fluids, the ability of a gas to stay in solution is
greater when its partial pressure is higher and when it has a high solubility in water.
The higher the partial pressure of a gas over a liquid and the higher the solubility,
the more gas will stay in solution.
In comparison to oxygen, much more CO2 is dissolved in blood plasma because
the solubility of CO2 is 24 times greater than that of O2.
Even though the air we breathe contains mostly N2,
this gas has no known effect on bodily functions, and at sea level pressure very little of it dissolves in blood plasma because its solubility is very low.
A major clinical application of Henry’s law is
hyperbaric oxygenation (hyper- = over; -baros = pressure), the use of pressure to cause more O2 to dissolve in the blood
What causes nitrogen narcosis or rapture of the deep
When a scuba diver breathes air under high pressure, the nitrogen in the mixture can have serious negative effects. Because the partial pressure of nitrogen is higher in a mixture of compressed air than in air at sea level pressure, a considerable amount of nitrogen dissolves in plasma and interstitial fluid. Excessive amounts of dissolved nitrogen may produce giddiness and other symptoms similar to alcohol intoxication
If a diver comes to the surface slowly, the dissolved nitrogen can be eliminated by exhaling it. However, if the ascent is too rapid,
nitrogen comes out of solution too quickly and forms gas bubbles in the tissues, resulting in decompression sickness (the bends).
External respiration or pulmonary gas exchange
is the diffusion of O2 from air in the pulmonary alveoli of the lungs to blood in pulmonary capillaries and the diffusion of CO2 in the opposite direction
External respiration in the lungs converts
deoxygenated blood (depleted of some O2) coming from the right side of the heart into oxygenated blood (saturated with O2) that returns to the left side of the heart
As blood flows through the pulmonary capillaries,
it picks up O2 from pulmonary alveolar air and unloads CO2 into pulmonary alveolar air. Although this process is commonly called an “exchange” of gases, each gas diffuses independently from the area where its partial pressure is higher to the area where its partial pressure is lower.
O2 diffuses from pulmonary alveolar air, where its partial pressure is 105 mmHg, into
the blood in pulmonary capillaries, where PO2 is only 40 mmHg in a resting person. If you have been exercising, the PO2 will be even lower because contracting muscle fibers are using more O2. Diffusion continues until the PO2 of pulmonary capillary blood increases to match the PO2 of alveolar air, 105 mmHg
Since blood leaving pulmonary capillaries near pulmonary alveolar air spaces mixes with a small volume of blood that has flowed through conducting portions of the respiratory system, where gas exchange does not occur,
the PO2 of blood in the pulmonary veins is slightly less than the PO2 in pulmonary capillaries, about 100 mmHg.
While O2 is diffusing from pulmonary alveolar air into deoxygenated blood,
CO2 is diffusing in the opposite direction.
The PCO2 of deoxygenated blood is 45 mmHg in a resting person,
and the PCO2 of pulmonary alveolar air is 40 mmHg
Because of this difference in PCO2, between deoxygenated blood and pulmonary aveolar air,
carbon dioxide diffuses from deoxygenated blood into the pulmonary alveoli until the PCO2 of the blood decreases to 40 mmHg. Exhalation keeps alveolar PCO2 at 40 mmHg. Oxygenated blood returning to the left side of the heart in the pulmonary veins thus has a PCO2 of 40 mmHg.
The number of capillaries near pulmonary alveoli in the lungs is
very large, and blood flows slowly enough through these capillaries that it picks up a maximal amount of O2.
During vigorous exercise, when cardiac output is increased,
blood flows more rapidly through both the systemic and pulmonary circulations. As a result, blood’s transit time in the pulmonary capillaries is shorter. Still, the PO2 of blood in the pulmonary veins normally reaches 100 mmHg.
In diseases that decrease the rate of gas diffusion,
the blood may not come into full equilibrium with pulmonary alveolar air, especially during exercise. When this happens, the PO2 declines and PCO2 rises in systemic arterial blood.
The left ventricle
pumps oxygenated blood into the aorta and through the systemic arteries to systemic capillaries.
The exchange of O2 and CO2 between systemic capillaries and tissue cells is called
internal respiration or systemic gas exchange
As O2 leaves the bloodstream,
oxygenated blood is converted into deoxygenated blood.
Unlike external respiration, which occurs only in the lungs, internal respiration
occurs in tissues throughout the body.
The PO2 of blood pumped into systemic capillaries is higher (100 mmHg) than
the PO2 in tissue cells (40 mmHg at rest) because the cells constantly use O2 to produce ATP. Due to this pressure difference, oxygen diffuses out of the capillaries into tissue cells and blood PO2 drops to 40 mmHg by the time the blood exits systemic capillaries.
While O2 diffuses from the systemic capillaries into tissue cells,
CO2 diffuses in the opposite direction. Because tissue cells are constantly producing CO2, the PCO2 of cells (45 mmHg at rest) is higher than that of systemic capillary blood (40 mmHg). As a result, CO2 diffuses from tissue cells through interstitial fluid into systemic capillaries until the PCO2 in the blood increases to 45 mmHg. The deoxygenated blood then returns to the heart and is pumped to the lungs for another cycle of external respiration.
In a person at rest, tissue cells, on average, need
only 25% of the available O2 in oxygenated blood; despite its name, deoxygenated blood retains 75% of its O2 content.
During exercise,
more O2 diffuses from the blood into metabolically active cells, such as contracting skeletal muscle fibers. Active cells use more O2 for ATP production, causing the O2 content of deoxygenated blood to drop below 75%.
The rate of pulmonary and systemic gas exchange depends on several factors.
Partial pressure difference of the gases.
Surface area available for gas exchange
Diffusion distance.
Molecular weight and solubility of the gases.
Alveolar PO2 must be higher than blood PO2 for
oxygen to diffuse from pulmonary alveolar air into the blood.
The rate of diffusion is faster when
the difference between PO2 in pulmonary alveolar air and pulmonary capillary blood is larger; diffusion is slower when the difference is smaller.
many capillaries surround
each pulmonary alveolus, so many that as much as 900 mL of blood is able to participate in gas exchange at any instant
The respiratory membrane is very thin, so
diffusion occurs quickly. Also, the capillaries are so narrow that the red blood cells must pass through them in single file, which minimizes the diffusion distance from a pulmonary alveolar air space to hemoglobin inside red blood cells.
Because O2 has a lower molecular weight than CO2, it could be expected to diffuse across the respiratory membrane about 1.2 times faster. However,
the solubility of CO2 in the fluid portions of the respiratory membrane is about 24 times greater than that of O2. Taking both of these factors into account, net outward CO2 diffusion occurs 20 times more rapidly than net inward O2 diffusion. Consequently, when diffusion is slower than normal—for example, in emphysema or pulmonary edema—O2 insufficiency (hypoxia) typically occurs before there is significant retention of CO2 (hypercapnia).
When O2 and CO2 enter the blood,
certain chemical reactions occur that aid in gas transport and gas exchange.
Oxygen does not dissolve easily in water, so
only about 1.5% of inhaled O2 is dissolved in blood plasma, which is mostly water.
About 98.5% of blood O2
is bound to hemoglobin in red blood cells (Figure 23.18). Each 100 mL of oxygenated blood contains the equivalent of 20 mL of gaseous O2. Using the percentages just given, the amount dissolved in the plasma is 0.3 mL and the amount bound to hemoglobin is 19.7 mL.
Most O2 is transported by hemoglobin as
oxyhemoglobin (Hb–O2) within red blood cells;
most CO2 is transported in blood plasma as
bicarbonate ions (HCO3−)
The heme portion of hemoglobin contains
four atoms of iron, each capable of binding to a molecule of O2
Oxygen and hemoglobin
bind in an easily reversible reaction to form oxyhemoglobin:
The 98.5% of the O2 that is bound to hemoglobin is trapped inside RBCs, so
only the dissolved O2 (1.5%) can diffuse out of tissue capillaries into tissue cells.
The most important factor that determines how much O2 binds to hemoglobin is
the PO2: the higher the PO2, the more O2 combines with Hb.
When reduced hemoglobin (Hb) is completely converted to oxyhemoglobin (Hb–O2),
the hemoglobin is said to be fully saturated;
when hemoglobin consists of a mixture of Hb and Hb–O2
, it is partially saturated.
The percent saturation of hemoglobin expresses
the average saturation of hemoglobin with oxygen
if each hemoglobin molecule has bound two O2 molecules,
then the hemoglobin is 50% saturated because each Hb can bind a maximum of four O2.
The relationship between the percent saturation of hemoglobin and PO2 is illustrated in
the oxygen–hemoglobin dissociation curve
when the PO2 is high,
hemoglobin binds with large amounts of O2 and is almost 100% saturated.
When PO2 is low,
hemoglobin is only partially saturated.
the greater the PO2,
the more O2 will bind to hemoglobin, until all the available hemoglobin molecules are saturated.
in pulmonary capillaries, where PO2 is high,
a lot of O2 binds to hemoglobin.
In tissue capillaries, where the PO2 is lower,
hemoglobin does not hold as much O2, and the dissolved O2 is unloaded via diffusion into tissue cells
As PO2 increases,
more O2 combines with hemoglobin.
When the PO2 is between 60 and 100 mmHg,
hemoglobin is 90% or more saturated with O2
blood picks up a nearly full load of O2 from the lungs
even when the PO2 of alveolar air is as low as 60 mmHg.
The Hb–PO2 curve explains
why people can still perform well at high altitudes or when they have certain cardiac and pulmonary diseases, even though PO2 may drop as low as 60 mmHg.
Between 40 and 20 mmHg,
large amounts of O2 are released from hemoglobin in response to only small decreases in PO2.
In active tissues such as contracting muscles,
PO2 may drop well below 40 mmHg. Then, a large percentage of the O2 is released from hemoglobin, providing more O2 to metabolically active tissues.
Although PO2 is the most important factor that determines the percent O2 saturation of hemoglobin,
several other factors influence the tightness or affinity with which hemoglobin binds O2
The changing affinity of hemoglobin for O2 is another example of how
homeostatic mechanisms adjust body activities to cellular needs.
metabolically active tissue cells
need O2 and produce acids, CO2, and heat as wastes.
The following four factors affect the affinity of hemoglobin for O2:
acidity (pH)
Partial pressure of Carbon Dioxide
Temperature
2,3-bisphosphoglycerate (BPG)
As acidity increases (pH decreases), the affinity of hemoglobin for O2
decreases, and O2 dissociates more readily from hemoglobin
The main acids produced by metabolically active tissues are .
lactic acid and carbonic acid
When pH decreases, the entire oxygen–hemoglobin dissociation curve
shifts to the right; at any given PO2, Hb is less saturated with O2, a change termed the Bohr effect (BŌR).
The Bohr effect works both ways meaning:
An increase in H+ in blood causes O2 to unload from hemoglobin, and the binding of O2 to hemoglobin causes unloading of H+ from hemoglobin.
CO2 also can bind to hemoglobin, and the effect is
similar to that of H+ (shifting the curve to the right). As PCO2 rises, hemoglobin releases O2 more readily
PCO2 and pH are related factors because
low blood pH (acidity) results from high PCO2.
As CO2 enters the blood,
much of it is temporarily converted to carbonic acid (H2CO3), a reaction catalyzed by an enzyme in red blood cells called carbonic anhydrase
As the H+ concentration increases, pH decreases. Thus
, an increased PCO2 produces a more acidic environment, which helps release O2 from hemoglobin.
During exercise,
lactic acid—a by-product of anaerobic metabolism within muscles—also decreases blood pH.
Decreased PCO2 (and elevated pH)
shift the saturation curve to the left.
As pH decreases or PCO2 increases,
the affinity of hemoglobin for O2 declines, so less O2 combines with hemoglobin and more is available to tissues.
Within limits, as temperature increases,
so does the amount of O2 released from hemoglobin
Heat is a by-product of the metabolic reactions of all cells,
and the heat released by contracting muscle fibers tends to raise body temperature
Metabolically active cells require
more O2 and liberate more acids and heat. The acids and heat in turn promote release of O2 from oxyhemoglobin
In contrast, during hypothermia (lowered body temperature)
cellular metabolism slows, the need for O2 is reduced, and more O2 remains bound to hemoglobin (a shift to the left in the saturation curve)
A substance found in red blood cells called 2,3-bisphosphoglycerate (BPG) (bis′-fos-fō-GLIS-e-rāt), formerly called diphosphoglycerate (DPG),
decreases the affinity of hemoglobin for O2 and thus helps unload O2 from hemoglobin
BPG is formed
in red blood cells when they break down glucose to produce ATP in a process called glycolysis
When BPG combines with hemoglobin by binding to the terminal amino groups of the two beta globin chains,
the hemoglobin binds O2 less tightly at the heme group sites.
The greater the level of BPG,
the more O2 is unloaded from hemoglobin.
Certain hormones, such as ))________________ increase the formation of BPG.
thyroxine, human growth hormone, epinephrine, norepinephrine, and testosterone,
The level of BPG also is higher in people
living at higher altitudes.
Fetal hemoglobin (Hb-F) differs from adult hemoglobin (Hb-A) in
structure and in its affinity for O2
Hb-F has a higher affinity for O2 because
it binds BPG less strongly.
when PO2 is low,
Hb-F can carry up to 30% more O2 than maternal Hb-A
As the maternal blood enters the placenta, O2 is readily transferred to fetal blood. This is very important because
the O2 saturation in maternal blood in the placenta is quite low, and the fetus might suffer hypoxia were it not for the greater affinity of fetal hemoglobin for O2.
Carbon monoxide (CO) is
a colorless and odorless gas found in exhaust fumes from automobiles, gas furnaces and space heaters, and in tobacco smoke
Elevated blood levels of CO cause
carbon monoxide poisoning, which can cause the lips and oral mucosa to appear bright cherry-red (the color of hemoglobin with carbon monoxide bound to it).
Under normal resting conditions, each 100 mL of deoxygenated blood contains
the equivalent of 53 mL of gaseous CO2,
gaseous CO2 is transported in the blood in three main forms
Dissolved CO2
Carbamino compounds
Bicarbonate ions
The smallest percentage of gaseous CO2 —about 7%—is
dissolved in blood plasma. On reaching the lungs, it diffuses into alveolar air and is exhaled.
about 23% of CO2,
combines with the amino groups of amino acids and proteins in blood to form carbamino compounds
Because the most prevalent protein in blood is hemoglobin
(inside red blood cells), most of the CO2 transported as carbamino compounds is bound to hemoglobin.
The main CO2 binding sites are
the terminal amino acids in the two alpha and two beta globin chains.
Hemoglobin that has bound CO2 is termed
carbaminohemoglobin (Hb–CO2):
The formation of carbaminohemoglobin is greatly influenced by
PCO2.
in tissue capillaries PCO2 is relatively high,
which promotes formation of carbaminohemoglobin.
in pulmonary capillaries,
PCO2 is relatively low, and the CO2 readily splits apart from globin and enters the alveoli by diffusion.
The greatest percentage of CO2—about 70%—is transported in blood plasma as
bicarbonate ions
As CO2 diffuses into systemic capillaries and enters red blood cells,
it reacts with water in the presence of the enzyme carbonic anhydrase (CA) to form carbonic acid, which dissociates into H+ and HCO3−:
as blood picks up CO2,
HCO3− accumulates inside RBCs
Some HCO3− moves out into the blood plasma, down its concentration gradient. In exchange,
chloride ions (Cl−) move from blood plasma into the RBCs. This exchange of negative ions, which maintains the electrical balance between blood plasma and RBC cytosol, is known as the chloride shift The net effect of these reactions is that CO2 is removed from tissue cells and transported in blood plasma as HCO3−. As blood passes through pulmonary capillaries in the lungs, all of these reactions reverse and CO2 is exhaled.
The amount of CO2 that can be transported in the blood is influenced by
the percent saturation of hemoglobin with oxygen
The lower the amount of oxyhemoglobin (Hb–O2),
the higher the CO2-carrying capacity of the blood, a relationship known as the Haldane effect.
Two characteristics of deoxyhemoglobin give rise to the Haldane effect:
(1) Deoxyhemoglobin binds to and thus transports more CO2 than does Hb–O2. (2) Deoxyhemoglobin also buffers more H+ than does Hb–O2, thereby removing H+ from solution and promoting conversion of CO2 to HCO3− via the reaction catalyzed by carbonic anhydrase.
Deoxygenated blood returning to the pulmonary capillaries in the lungs (Figure 23.23a) contains
CO2 dissolved in blood plasma, CO2 combined with globin as carbaminohemoglobin (Hb–CO2), and CO2 incorporated into HCO3− within RBCs
The RBCs of deoxygenated blood returning to the pulmonary capillaries have also picked up
H+, some of which binds to and therefore is buffered by hemoglobin (Hb–H).
As blood passes through the pulmonary capillaries,
molecules of CO2 dissolved in blood plasma and CO2 that dissociates from the globin portion of hemoglobin diffuse into pulmonary alveolar air and are exhaled.
As CO2 is being exhaled, At the same time,
inhaled O2 is diffusing from pulmonary alveolar air into RBCs and is binding to hemoglobin to form oxyhemoglobin (Hb–O2). Carbon dioxide also is released from HCO3− when H+ combines with HCO3− inside RBCs.The H2CO3 formed from this reaction then splits into CO2, which is exhaled, and H2O.
As the concentration of HCO3− declines inside RBCs in pulmonary capillaries,
HCO3− diffuses in from the blood plasma, in exchange for Cl−.
In sum, oxygenated blood leaving the lungs
has increased O2 content and decreased amounts of CO2 and H+.
In systemic capillaries, as cells use O2 and produce CO2,
the chemical reactions reverse
Hemoglobin inside red blood cells transports
O2, CO2, and H+.
At rest, ____________ of O2 is used each minute by body cells.
about 200 mL
During strenuous exercise, O2 use
typically increases 15- to 20-fold in normal healthy adults, and as much as 30-fold in elite endurance-trained athletes.
The size of the thorax is altered by
the action of the breathing muscles, which contract as a result of nerve impulses transmitted from centers in the brain and relax in the absence of nerve impulses. These nerve impulses are sent from clusters of neurons located bilaterally in the brain stem. This widely dispersed group of neurons, collectively called the respiratory center,
the respiratory center, can be divided into two principal areas on the basis of location and function:
(1) the medullary respiratory center in the medulla oblongata and (2) the pontine respiratory group in the pons
The medullary respiratory center is made up of two collections of neurons called
the dorsal respiratory group (DRG), formerly called the inspiratory area, and the ventral respiratory group (VRG), formerly called the expiratory area.
During normal quiet breathing,
neurons of the DRG generate impulses to the diaphragm via the phrenic nerves and the external intercostal muscles via the intercostal nerves These impulses are released in bursts, which begin weakly, increase in strength for about two seconds, and then stop altogether.
When the nerve impulses reach the diaphragm and external intercostals, from the DRG
the muscles contract and inhalation occurs.
When the DRG becomes inactive after two seconds,
the diaphragm and external intercostals relax for about three seconds, allowing the passive recoil of the lungs and thoracic wall. Then, the cycle repeats itself.
The respiratory center is composed of
neurons in the medullary respiratory center in the medulla plus the pontine respiratory group in the pons.
Located in the VRG is a cluster of neurons called the pre-Bötzinger complex (BOT-zin-ger) that is believed to be important in
the generation of the rhythm of breathing
the pre-Bötzinger complex
analogous to the one in the heart, is composed of pacemaker cells that set the basic rhythm of breathing. The exact mechanism of these pacemaker cells is unknown and is the topic of much ongoing research.
it is thought that the pacemaker cells in the pre-Bötzinger complex
provide input to the DRG, driving the rate at which DRG neurons fire action potentials.
The remaining neurons of the VRG that are not in the pre-Bötzinger complex
do not participate in normal quiet breathing
The VRG becomes activated when
forceful breathing is required, such as during exercise, when playing a wind instrument, or at high altitudes.
During forceful inhalation (Figure 23.25b), nerve impulses from the DRG not only stimulate the diaphragm and external intercostal muscles to contract, they also activate
neurons of the VRG involved in forceful inhalation to send impulses to the accessory muscles of inhalation (sternocleidomastoid, scalenes, and pectoralis minor). Contraction of these muscles results in forceful inhalation.
During forceful exhalation
the DRG is inactive along with the neurons of the VRG that result in forceful inhalation.
during forceful exhalation those neurons of the VRG involved in forceful exhalation send nerve impulses to the accessory muscles of exhalation (internal intercostals, external abdominal oblique, internal abdominal oblique, transversus abdominis, and rectus abdominis).
The pontine respiratory group (PRG) (PON-tēn), formerly called the pneumotaxic area, is
a collection of neurons in the pons
The neurons in the PRG are active during
inhalation and exhalation.
The PRG
transmits nerve impulses to the DRG in the medulla
The PRG may play a role in both inhalation and exhalation by
modifying the basic rhythm of breathing generated by the VRG, as when exercising, speaking, or sleeping.
Activity of the respiratory center can be modified in response to
inputs from other brain regions, receptors in the peripheral nervous system, and other factors in order to maintain the homeostasis of breathing.
Since the cerebral cortex has connections with the respiratory center,
we can voluntarily alter our pattern of breathing.
Voluntary control is protective because
it enables us to prevent water or irritating gases from entering the lungs.
The ability to not breathe is limited by
the buildup of CO2 and H+ in the body.
When PCO2 and H+ concentrations increase to a certain level,
the DRG neurons of the medullary respiratory center are strongly stimulated, nerve impulses are sent along the phrenic and intercostal nerves to inspiratory muscles, and breathing resumes, whether the person wants it to or not.
Nerve impulses from the hypothalamus and limbic system also stimulate the respiratory center, allowing
emotional stimuli to alter breathing as, for example, in laughing and crying.
Certain chemical stimuli modulate
how quickly and how deeply we breathe.
The respiratory system functions to
maintain proper levels of CO2 and O2 and is very responsive to changes in the levels of these gases in body fluids.
Chemoreceptors in two locations of the respiratory system
monitor levels of CO2, H+, and O2 and provide input to the respiratory center
Central chemoreceptors are located
in or near the medulla oblongata in the central nervous system. They respond to changes in H+ concentration or PCO2, or both, in cerebrospinal fluid.
Peripheral chemoreceptors are located
in the aortic bodies, clusters of chemoreceptors located in the wall of the aortic arch, and in the carotid bodies, which are oval nodules in the wall of the left and right common carotid arteries where they divide into the internal and external carotid arteries.
peripheral chemoreceptors
are sensitive to changes in PO2, H+, and PCO2 in the blood.
Because CO2 is lipid-soluble,
it easily diffuses into cells where, in the presence of carbonic anhydrase, it combines with water (H2O) to form carbonic acid (H2CO3).
Carbonic acid quickly breaks down into H+ and HCO3−. Thus,
an increase in CO2 in the blood causes an increase in H+ inside cells, and a decrease in CO2 causes a decrease in H+.
Normally, the PCO2 in arterial blood
is 40 mmHg.
If even a slight increase in PCO2 occurs—
a condition called hypercapnia (hī′-per-KAP-nē-a) or hypercarbia—the central chemoreceptors are stimulated and respond vigorously to the resulting increase in H+ level.
The peripheral chemoreceptors also are stimulated by
both the high PCO2 and the rise in H+.
In addition, the peripheral chemoreceptors (but not the central chemoreceptors) respond to a deficiency of
O2. When PO2 in arterial blood falls from a normal level of 100 mmHg but is still above 50 mmHg, the peripheral chemoreceptors are stimulated.
Severe deficiency of O2
depresses activity of the central chemoreceptors and DRG, which then do not respond well to any inputs and send fewer impulses to the muscles of inhalation.
As the breathing rate decreases or breathing ceases altogether,
PO2 falls lower and lower, establishing a positive feedback cycle with a possibly fatal result.
The chemoreceptors participate in a negative feedback system that regulates
the levels of CO2, O2, and H+ in the blood
As a result of increased PCO2, decreased pH (increased H+), or decreased PO2,
input from the central and peripheral chemoreceptors causes the DRG to become highly active, and the rate and depth of breathing increase.
Rapid and deep breathing, called hyperventilation,
allows the inhalation of more O2 and exhalation of more CO2 until PCO2 and H+ are lowered to normal.
If arterial PCO2 is lower than 40 mmHg—
a condition called hypocapnia or hypocarbia—the central and peripheral chemoreceptors are not stimulated, and stimulatory impulses are not sent to the DRG. As a result, DRG neurons set their own moderate pace until CO2 accumulates and the PCO2 rises to 40 mmHg.
DRG neurons are more strongly stimulated when
PO2 is rising above normal than when PO2 is falling below normal.
Chemoreceptors are
sensory neurons that respond to changes in the levels of certain chemicals in the body.
An increase in arterial blood PCO2 stimulates
the dorsal respiratory group (DRG).
As soon as you start exercising,
your rate and depth of breathing increase, even before changes in PO2, PCO2, or H+ level occur. The main stimulus for these quick changes in respiratory effort is input from proprioceptors, which monitor movement of joints and muscles.
Nerve impulses from the proprioceptors
stimulate the DRG of the medulla. At the same time, axon collaterals (branches) of upper motor neurons that originate in the primary motor cortex (precentral gyrus) also feed excitatory impulses into the DRG.
Hypoxia (hī-POK-sē-a; hypo- = under) is
a deficiency of O2 at the tissue level. Based on the cause, we can classify hypoxia into four types,
Hypoxic hypoxia is caused by
a low PO2 in arterial blood as a result of high altitude, airway obstruction, or fluid in the lungs.
In anemic hypoxia,
too little functioning hemoglobin is present in the blood, which reduces O2 transport to tissue cells. Among the causes are hemorrhage, anemia, and failure of hemoglobin to carry its normal complement of O2, as in carbon monoxide poisoning.
In ischemic hypoxia (is-KĒ-mik),
blood flow to a tissue is so reduced that too little O2 is delivered to it, even though PO2 and oxyhemoglobin levels are normal.
In histotoxic hypoxia (his-tō-TOK-sik),
the blood delivers adequate O2 to tissues, but the tissues are unable to use it properly because of the action of some toxic agent. One cause is cyanide poisoning, in which cyanide blocks an enzyme required for the use of O2 during ATP synthesis.
Similar to those in the blood vessels, stretch-sensitive receptors called baroreceptors or stretch receptors are located in
the walls of bronchi and bronchioles.When these receptors become stretched during overinflation of the lungs, nerve impulses are sent along the vagus (X) nerves to the dorsal respiratory group (DRG) in the medullary respiratory center. In response, the DRG is inhibited and the diaphragm and external intercostals relax. As a result, further inhalation is stopped and exhalation begins.
As air leaves the lungs during exhalation,
the lungs deflate and the stretch receptors are no longer stimulated. Thus, the DRG is no longer inhibited, and a new inhalation begins. This reflex is referred to as the inflation reflex or Hering–Breuer reflex (HER-ing BROY-er).
In infants, the inflation reflex
appears to function in normal breathing.
In adults, the inflation reflex is not activated until
tidal volume (normally 500 mL) reaches more than 1500 mL. Therefore, the reflex in adults is a protective mechanism that prevents excessive inflation of the lungs, for example, during severe exercise, rather than a key component in the normal control of breathing.
What are some lesser factors that contribute to regulation of breathing
Limbic system stimulation
temperature
pain
stretching of the anal sphincter muscle
irritation of airways
blood pressure
How does limbic system stimulation contribute to the regulation of breathing
Anticipation of activity or emotional anxiety may stimulate the limbic system, which then sends excitatory input to the DRG, increasing the rate and depth of breathing.
How does temperature contribute to regulation of breathing
An increase in body temperature, as occurs during a fever or vigorous muscular exercise, increases the rate of breathing. A decrease in body temperature decreases breathing rate. A sudden cold stimulus (such as plunging into cold water) causes temporary apnea (AP-nē-a; a- = without; -pnea = breath), an absence of breathing.
How does pain contribute to the regulation of breathing
A sudden, severe pain brings about brief apnea, but a prolonged somatic pain increases breathing rate. Visceral pain may slow the rate of breathing.
How does stretching of the anal sphincter contribute to the regulation of breathing
This action increases the breathing rate and is sometimes used to stimulate respiration in a newborn baby or a person who has stopped breathing.
How does irritation of the airways contribute to the regulation of breathing
Physical or chemical irritation of the pharynx or larynx brings about an immediate cessation of breathing followed by coughing or sneezing.
how does blood pressure contribute to regulation of breathing
The carotid and aortic baroreceptors that detect changes in blood pressure have a small effect on breathing. A sudden rise in blood pressure decreases the rate of breathing, and a drop in blood pressure increases the breathing rate.
The respiratory and cardiovascular systems make adjustments in response to
both the intensity and duration of exercise.
as cardiac output rises,
the blood flow to the lungs, termed pulmonary perfusion, increases as well
the O2 diffusing capacity, a measure of the rate at which O2 can diffuse from alveolar air into the blood,
may increase threefold during maximal exercise because more pulmonary capillaries become maximally perfused.
During exercise
there is a greater surface area available for diffusion of O2 into pulmonary blood capillaries.
When muscles contract during exercise,
they consume large amounts of O2 and produce large amounts of CO2
During vigorous exercise,
O2 consumption and breathing both increase dramatically.
At the onset of exercise,
an abrupt increase in breathing is followed by a more gradual increase.
With moderate exercise, the increase is due mostly to an increase in
the depth of breathing rather than to increased breathing rate
When exercise is more strenuous,
the frequency of breathing also increases.
The abrupt increase in breathing at the start of exercise is due to
neural changes that send excitatory impulses to the dorsal respiratory group (DRG) of the medullary respiratory center in the medulla.
The abrupt increase in breathing at the start of exercise is due to neural changes that send excitatory impulses to the dorsal respiratory group (DRG) of the medullary respiratory center in the medulla. These changes include
(1) anticipation of the activity, which stimulates the limbic system; (2) sensory impulses from proprioceptors in muscles, tendons, and joints; and (3) motor impulses from the primary motor cortex (precentral gyrus).
The more gradual increase in breathing during moderate exercise is due to
chemical and physical changes in the bloodstream
The more gradual increase in breathing during moderate exercise is due to chemical and physical changes in the bloodstream, including
(1) slightly decreased PO2, due to increased O2 consumption; (2) slightly increased PCO2, due to increased CO2 production by contracting muscle fibers; and (3) increased temperature, due to liberation of more heat as more O2 is utilized.
During strenuous exercise,
HCO3− buffers H+ released by lactic acid in a reaction that liberates CO2, which further increases PCO2.
At the end of an exercise session,
an abrupt decrease in breathing is followed by a more gradual decline to the resting level.
At the end of an exercise session, an abrupt decrease in breathing is followed by a more gradual decline to the resting level. The initial decrease is due mainly to
changes in neural factors when movement stops or slows; the more gradual phase reflects the slower return of blood chemistry levels and temperature to the resting state.
effects of smoking on the respiratory system:
Nicotine constricts terminal bronchioles, which decreases airflow into and out of the lungs.
Carbon monoxide in smoke binds to hemoglobin and reduces its oxygen-carrying capability.
Irritants in smoke cause increased mucus secretion by the mucosa of the bronchial tree and swelling of the mucosal lining, both of which impede airflow into and out of the lungs.
Irritants in smoke also inhibit the movement of cilia and destroy cilia in the lining of the respiratory system. Thus, excess mucus and foreign debris are not easily removed, which further adds to the difficulty in breathing. This leads to a smoker’s cough and contributes to the tendency for smokers to be sick more often than non-smokers. The irritants can also convert the normal respiratory epithelium into stratified squamous epithelium, which lacks cilia and goblet cells.
With time, smoking leads to destruction of elastic fibers in the lungs and is the prime cause of emphysema. These changes cause collapse of small bronchioles and trapping of air in alveoli at the end of exhalation. The result is less efficient gas exchange.
At about 4 weeks of development,
the respiratory system begins as an outgrowth of the foregut (precursor of some digestive organs) just inferior to the pharynx. This outgrowth is called the respiratory bud
The endoderm lining the respiratory bud gives rise to
the epithelium and glands of the trachea, bronchi, and pulmonary alveoli.
Mesoderm surrounding the respiratory bud gives rise to
the connective tissue, cartilage, and smooth muscle of these structures.
The epithelial lining of the larynx develops from
the endoderm of the respiratory bud
the cartilages and muscles of the larynx originate from
the fourth and sixth pharyngeal arches, swellings on the surface of the embryo
As the respiratory bud elongates, its distal end enlarges to form
a globular laryngotracheal diverticulum, which gives rise to the trachea.
the tracheal bud divides into primary bronchial buds, which
branch repeatedly and develop into the bronchi. By 24 weeks, 17 orders of branches have formed and respiratory bronchioles have developed.
During weeks 6 to 16,
all major elements of the lungs have formed, except for those involved in gaseous exchange (respiratory bronchioles, alveolar ducts, and pulmonary alveoli).Since breathing is not possible at this stage, fetuses born during this time cannot survive.
During weeks 16 to 26,
lung tissue becomes highly vascular and respiratory bronchioles, alveolar ducts, and some primitive alveoli develop.
Although it is possible for a fetus born near 26 weeks to survive if given intensive care,
death frequently occurs due to the immaturity of the respiratory and other systems.
The respiratory system develops from
endoderm and mesoderm.
From 26 weeks to birth,
many more primitive pulmonary alveoli develop; they consist of pneumocytes type I (main sites of gaseous exchange) and pneumocytes type II that produce surfactant.Blood capillaries also establish close contact with the primitive pulmonary alveoli.
surfactant is necessary to
lower surface tension of alveolar fluid and thus reduce the tendency of pulmonary alveoli to collapse on exhalation
Although surfactant production begins by 20 weeks
, it is present in only small quantities. Amounts sufficient to permit survival of a premature (preterm) infant are not produced until 26 to 28 weeks’ gestation.
Infants born before 26 to 28 weeks are at high risk of
respiratory distress syndrome (RDS), in which the pulmonary alveoli collapse during exhalation and must be reinflated during inhalation
At about 30 weeks
, mature pulmonary alveoli develop.
it is estimated that only
about one-sixth of the full complement of pulmonary alveoli develop before birth; the remainder develop after birth during the first 8 years.
As the lungs develop,
they acquire their pleural sacs
The visceral pleura and the parietal pleura
develop from mesoderm. The space between the pleural layers is the pleural cavity.
During development, breathing movements of the fetus cause
the aspiration of fluid into the lungs This fluid is a mixture of amniotic fluid, mucus from bronchial glands, and surfactant.
At birth,
the lungs are about half-filled with fluid. When breathing begins at birth, most of the fluid is rapidly reabsorbed by blood and lymph capillaries and a small amount is expelled through the nose and mouth during delivery.
With advancing age,
the airways and tissues of the respiratory tract, including the pulmonary alveoli, become less elastic and more rigid; the chest wall becomes more rigid as well. The result is a decrease in lung capacity.
In fact, vital capacity (the maximum amount of air that can be exhaled after maximal inhalation)
can decrease as much as 35% by age 70.
with advancing age how is the respiratory system affected
A decrease in blood level of O2, decreased activity of alveolar macrophages, and diminished ciliary action of the epithelium lining the respiratory tract occur.
Because of age-related factors, elderly people
are more susceptible to pneumonia, bronchitis, emphysema, and other pulmonary disorders.
Age-related changes in the structure and functions of the lung can also contribute to
an older person’s reduced ability to perform vigorous exercises, such as running.
In the United States, lung cancer
is the leading cause of cancer death in both males and females, accounting for 160,000 deaths annually
The most common type of lung cancer,
bronchogenic carcinoma (brong′-kō-JEN-ik), starts in the epithelium of the bronchial tubes
Pneumonia (noo-MŌ-ne-a) is
an acute infection or inflammation of the pulmonary alveoli.
Chronic obstructive pulmonary disease (COPD) is
a type of respiratory disorder characterized by chronic and recurrent obstruction of airflow, which increases airway resistance
Emphysema (em-fi-SĒ-ma = blown up or full of air) is
a disorder characterized by destruction of the walls of the pulmonary alveoli, producing abnormally large air spaces that remain filled with air during exhalation.
Chronic bronchitis is
a disorder characterized by excessive secretion of bronchial mucus accompanied by a productive cough (sputum is raised) that lasts for at least 3 months of the year for two successive years.
Asthma (AZ-ma = panting) or bronchial asthma is
a disorder characterized by chronic airway inflammation, airway hypersensitivity to a variety of stimuli, and airway obstruction.
The bacterium Mycobacterium tuberculosis (mī′-kō-bak-TĒR-ē-um)
produces an infectious, communicable disease called tuberculosis (TB) that most often affects the lungs and the pleurae but may involve other parts of the body.
Pulmonary edema is
an abnormal accumulation of fluid in the interstitial spaces and pulmonary alveoli
Sudden infant death syndrome (SIDS) is
the sudden, unexpected death of an apparently healthy infant during sleep
Severe acute respiratory syndrome (SARS) is
an example of an emerging infectious disease, that is, a disease that is new or changing.
Malignant mesothelioma (mē-zō-thē-lē-OMA) is
a rare form of cancer that affects the mesothelium (simple squamous epithelium) of a serous membrane.
