Chapter 23: The Respiratory System

Question 1

define the steps that occur during respiration.

Answer 1

Respiration – the process of gas exchange in the body. 3 basic steps: pulmonary ventilation, external (pulmonary) respiration, and internal (tissue) respiration.

1. pulmonary ventilation – AKA breathing, the inhalation and exhalation of air and involves the exchange of air between the atmosphere and the alveoli of the lungs.
2. external (pulmonary) respiration – the exchange of gases between alveoli of the lungs and the blood in pulmonary capillaries across the pulmonary membrane. The pulmonary capillary gains O2 and loses Co2
3. internal (tissue) respiration – the exchange of gases between blood in systemic capillaries and tissue cells. Blood loses O2 and gains CO2. (Cellular respiration is the metabolic reactions within cells that consume O2 and give off CO2)

pulmonary ventilation or breathing

inhalation or inspiration – breathing in.

1. For air to enter the lungs, the pressure inside the alveoli must become lower than atmospheric pressure, achieved by increasing the size of the lungs.
2. First step in expanding the lungs during normal quiet inhalation is contraction of the diaphragm, with resistance from external intercostals. Responsible for about 75% of the air that enters lungs during quiet breathing.
3. The external intercostals contract, elevating the ribs, and is responsible for the remaining 25% of air entry.
4. Is an active process during quiet and forced breathing because it involves muscular contraction.

Boyle’s law – the inverse relationship between volume and pressure. The pressure of a gas in a closed container is inversely proportional to the volume of the container. Increase size of container, decrease pressure. describes the pressure changes that occur during pulmonary ventilation

intrapleural pressure – the pressure between the two pleural layers in the pleural cavity.

1. During quiet inhalations, is always sub-atmospheric.
2. Decreases with expansion of the thorax because the thoracic cavity size is increasing, increasing the pleural cavity size.

alveolar pressure or intrapulmonic pressure – the pressure inside the lungs. a. Inhalation occurs when alveolar pressure drops due to expansion of the thoracic cavity increasing overall size.

exhalation or expiration – breathing out.

1. Also due to a pressure gradient, but in the opposite direction.
2. Starts when the inspiratory muscles relax, decreasing the vertical, lateral, and anteroposterior diameters of the thoracic cavity, decreasing lung volume.
3. Is a passive process because no muscular contraction occurs, instead results from elastic recoil.
4. Is an active process only during forceful breathing.

elastic recoil – the chest wall and lungs have a natural tendency to spring back after having been stretched.

a. Two inwardly directed forces contribute to elastic recoil:

1. Recoil of elastic fibers that were stretched during inhalation
2. The inward pull of surface tension due to the film of alveolar fluid.

other factors affecting pulmonary ventilation

a. surface tension of alveolar fluid – thin layer of alveolar fluid coats the luminal surface of the alveoli and exerts surface tension.

1. 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.
2. When liquid surrounds a sphere of air, as in an alveolus or soap bubble, surface tension produces an inwardly directed force.
3. In the lungs, surface tension causes the alveolus to assume the smallest possible diameter.
4. During breathing, surface tension must be overcome to expand the lungs during each inhalation.
5. Surface tension also accounts for 2/3 of lung elastic recoil, which decreases the size of alveoli during exhalation.

b. Compliance – refers to how much effort is required to stretch the lungs and chest wall.

1. High compliance means that the lungs and chest wall expand easily. Low compliance means they resist expansion. Think thin vs thick balloon.
2. In the lungs, compliance is related to 2 main factors:
3. Elasticity and surface tension.
4. Elastic fibers are easily stretched and surfactant in alveolar fluid reduces surface tension.
5. Decreased compliance is a common feature in pulmonary conditions that 1. Scar lung tissue, 2. Cause lung tissue to be breathing patterns filled with fluid, 3. Produce a deficiency of surfactant, 4. Impede lung expansion in any way.

airway resistance – the walls of the airways, especially the bronchioles, offer some resistance to the normal flow of air into and out of the lungs.

1. Larger diameter airways have decreased resistance. During expansion of lungs, bronchioles enlarge due to walls pulling outward in all directions.
2. Airway diameter is also regulated by the degree of smooth muscle contraction or relaxation in the walls of the airways. Sympathetic signals from the ANS cause relaxation, which results in bronchodilation and decreased resistance.
3. Any condition that narrows or obstructs the airways increases resistance, so that more pressure is required to maintain the same airflow.
4. eupnea – the term for normal quiet breathing. Can consist of shallow or deep or both
5. costal breathing – a pattern of shallow (chest) breathing.
6. Consists of an upward and outward movement of the chest due to contraction of external intercostal muscles.

diaphragmatic breathing – a pattern of deep (abdominal) breathing

1. consists of the outward movement of the abdomen due to the contraction and descent of the diaphragm.

rythmicity center for respiration - medulla

Question 2

describe the anatomy and histology of the nose, pharynx, larynx, trachea, bronchi, and lungs.

Answer 2

respiratory system anatomy

upper respiratory system – nose, nasal cavity, pharynx, and associated structures

lower respiratory system – larynx, trachea, bronchi, lungs

conducting zone – series of interconnecting cavities and tubes both outside and within the lungs

ciliated pseudostratified columnar epithelium with goblet cells tissue that provides the functions of the inner layer of the conducting organs

a) Clean air of debris

b) Conduct air into the lungs

c) Add water to air

d) Warm air

nose

1. includes the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles
2. function to filter, warm, and moisten air and conduct it into the lungs

respiratory zone – consists of tubes and tissues within the lungs where gas exchange occurs

1. includes the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
2. function as main sites of gas exchange between air and blood.
3. external nares or nostrils – openings on the undersurface of the external nose
4. internal nares or choanae – the two openings posterior to the nasal cavities opening into the nasopharynx
5. nasal cavity – mucosa-lined cavity on either side of the nasal septum that opens onto the face at the external nares and into the nasopharynx at the internal nares.
6. Vestibule – the anterior portion of the nasal cavity, just inside the nostrils. It is surrounded by cartilage.
7. nasal septum – vertical partition composed of bone (perpendicular plate of the ethmoid and vomer) and cartilage, covered with a mucus membrane, separating the nasal cavity into left and right sides
8. superior, middle and inferior meatuses – series of groovelike air passageways that are formed by the nasal conchae

g. olfactory epithelium – the olfactory receptor cells, supporting cells, and basal cells that lie in the respiratory region near the superior nasal conchae and adjacent septum. Contains cilia but no goblet cells.

Pharynx – the throat, starts at internal nares and runs partway down the neck where it opens into the esophagus posteriorly and larynx anteriorly.

1. Nasopharynx – the superior portion of the pharynx. Lies posterior to the nasal cavity, extends to the soft palate.
2. soft palate – the posterior portion of the roof of the mouth, extends from palatine bones to the uvula, between nasopharynx and oropharynx. It is a muscular partition lined with mucus membrane.
3. eustachian tubes – the auditory (pharyngotympanic) tubes, open into the nasopharynx
4. pharyngeal tonsil – AKA adenoid. Located on posterior wall of nasopharynx
5. oropharynx – the intermediate portion of the pharynx. Posterior to the mouth and extending from the soft palate to the hyoid bone.
6. Has both respiratory and digestive functions.
7. Oropharynx is lined with nonkeratinized stratified squamous epithelium.
8. Fauces – the single opening from the mouth into the pharynx
9. palatine and lingual tonsils – two pairs of tonsils found in the oropharynx
10. laryngopharynx or hypopharynx – the inferior portion of the pharynx. Begins at the level of the hyoid bone, opens into esophagus and larynx inferiorly.
11. Both a respiratory and digestive pathway, lined by nonkeratinized stratified squamous epithelium.

Larynx – AKA voice box. A short passageway that connects the pharynx with the trachea. Lies in the midline of the neck, anterior to the esophagus and C4-C6 vertebrae. Consists of 9 pieces of cartilage:

1. thyroid cartilage (Adam’s apple) – the largest single cartilage of the larynx, consisting of 2 fused plates that form the anterior wall of the larynx.
2. Epiglottis – large, leaf-shaped piece of elastic cartilage that is covered with epithelium. The “stem” portion is the tapered inferior portion attached to the anterior rim of the thyroid cartilage. The “leaf” portion is the broad superior portion of the epiglottis that is unattached and free to move up and down like a trap door and closes the glottis during swallowing

Glottis – the vocal folds (true vocal cords) in the larynx plus the space between them called the rima glottides.

cricoid cartilage – a ring of hyaline cartilage that forms the inferior wall of the larynx. Attached to the first ring of cartilage of the trachea by the cricotracheal ligament. Connected to the thyroid cartilage by the cricothyroid ligament.

1. Is the landmark for making an emergency airway called tracheotomy.

arytenoid cartilages – paired triangular pieces of mostly hyaline cartilage, located at the posterior, superior border of the cricoid cartilage.

structures of voice production

1. vestibular folds or false vocal cords – superior pair of folds in the mucous membrane of the larynx.
2. vocal folds or true vocal cords – the inferior pair of folds in the mucous membrane of the larynx.

The principal structures of voice production.

1. Bands of elastic ligaments deep to the mucous membrane of the vocal folds are stretched between the rigid cartilages of the larynx.
2. Intrinsic laryngeal muscles attach to both the rigid cartilages and the vocal folds, contraction and relaxation varies the tension in the vocal folds.
3. Air passing through vibrates the folds and produces sounds by setting up sound waves in the column of air in the pharynx, nose, and mouth.
4. Variation in pitch is related to tension, loudness is related to pressure of air.

trachea (windpipe) – tubular passageway for air located anterior to the esophagus and extending from the larynx to the superior border of T5.

1. 4 layers of the tracheal wall, from deep to superficial are the mucosa, submucosa, hyaline cartilage, and adventitia
2. The mucosa consists of an epithelial layer of pseudostratified ciliated columnar epithelium and an underlying layer of lamina propria that contains elastic and reticular fibers.

c. The submucosa consists of areolar connective tissue that contains seromucous glands and their ducts

1. The hyaline cartilage are 16-20 incomplete rings that open posteriorly toward the esophagus.
2. The adventitia consists of areolar connective tissue that joins the trachea to surrounding tissues.

bronchus (plural is bronchi) – at the superior border of T5, the trachea divides into right main and left main bronchi

a. right and left primary bronchi – go into the right and left lungs.

1. Right is more vertical, shorter, and wider than the left.
2. Contain incomplete rings of cartilage and are lined by pseudostratified ciliated columnar epithelium.
3. Carina – internal ridge formed by a posterior and somewhat inferior projection of the last tracheal cartilage, at the point where the trachea divides into right and left main bronchi.
4. secondary bronchi or lobar bronchi – divisions of the main bronchi, one for each lobe of the lung, 3 on right, 2 on left.
5. tertiary bronchi or segmental bronchi – branches off the lobar bronchi, supplying specific bronchopulmonary segments within the lobes
6. 10 segmental bronchi in each lung.
7. bronchioles – branches off the tertiary or segmental bronchi which in turn branch repeatedly
8. terminal bronchioles – even smaller tubes that contain club (Clara) cells: columnar, non-ciliated cells interspersed among the epithelial cells.
9. Club cells may protect against inhaled toxins and carcinogens, produce surfactant, and function as stem cells giving rise to various cells of the epithelium.
10. The terminal bronchioles represent the END of the conducting zone of the respiratory system.

g. bronchial tree – the trachea, bronchi, and their branching structures up to and including the terminal bronchioles which resembles an upside down tree.
1. As the branching becomes more extensive in the bronchial tree, several structural changes may be

The mucous membrane in the bronchial tree changes from pseudostratified ciliated 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. Recall that ciliated epithelium of the respiratory membrane removes inhaled particles in two ways. Mucus produced by goblet cells traps the particles, and the cilia move the mucus and trapped particles toward the pharynx for removal. In regions where nonciliated simple cuboidal epithelium is present, inhaled particles are removed by macrophages.

1. Plates of cartilage gradually replace the incomplete rings of cartilage in main bronchi and finally disappear in the distal bronchioles.
2. As the amount of cartilage decreases, the amount of smooth muscle increases. Smooth muscle encircles the lumen in spiral bands and helps maintain patency. However, because there is no supporting cartilage, muscle spasms can close off the airways. This is what happens during an asthma attack, which can be a life-threatening situation.

Lungs – paired organs of respiration that lie on either side of the heart in the thoracic cavity. Separated from each other by the heart and other structures of the mediastinum which divides the thoracic cavity into two anatomically distinct chambers.

1. pleural membrane – double-layered serous membrane that encloses and protects each lung.
2. parietal pleura – the superficial layer, lines the wall of the thoracic cavity
3. visceral pleura – the deep layer, covers the lungs themselves.
4. pleural cavity – small space between the visceral and parietal pleurae that contains a small amount of lubricating fluid secreted by the membranes.
5. Pleural fluid reduces friction between the membranes, allowing them to slide over one another during breathing.
6. Also causes the two membranes to adhere to one another by surface tension.
7. base and apex of lung – base = broad inferior portion of the lung. Apex = narrow superior portion of the lung.
8. costal surface – the surface of the lung lying against the ribs
9. matches the round curvature of the ribs
10. mediastinal surface or medial surface – against the medial surface. Contains the hilum
11. hilum – region where bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit.
12. Root – pleura and connective tissue that hold together the structures of the hilum
13. cardiac notch – a concavity in the left lung in which the apex of the heart lies.
14. Fissures – a groove that divides each lung into lobes.
15. oblique fissure in both lungs – extends inferiorly and anteriorly. Divide each lung into superior and inferior lobes.
16. horizontal fissure in right lung – divides the right lung into middle and superior lobes. Forms a triangular shaped middle lobe with a medial base and a lateral point.
17. Lobes – 2 in left lung, 3 in right.
18. superior and inferior lobes in both lungs – see above notes.
19. middle lobe in right lung – see above notes.
20. bronchopulmonary segments – smaller divisions of a lobe of a lung supplied by its own branches of a bronchus. AKA the segment of lung tissue that each segmental bronchus supplies.
21. Lobules – many small compartments in each bronchopulmonary segment
22. Each lobule is wrapped in elastic connective tissue and contains a lymphatic vessel, an arteriole, a venule, and a branch from a terminal bronchiole
23. respiratory bronchioles – microscopic branches that are subdivided terminal bronchioles with alveoli budding from their walls
24. alveolar ducts – further subdivisions of respiratory bronchioles, 2-11 ducts per, which consist of simple squamous epithelium
25. alveolus (plural is alveoli) – cup-shaped outpouching lined by simple squamous epithelium and supported by a thin elastic basement membrane. AKA Air sac in the lung
26. alveolar sac – a cluster of alveoli that share a common opening
27. type I alveolar cells – more numerous type of cell in the walls of alveoli. Simple squamous epithelial cells that form a nearly continuous lining of the alveolar wall.
28. Main sites of gas exchange.

x. type II alveolar cells or septal cells – less common than Type 1, found between type 1 cells.
1. Rounded or cuboidal epithelial cells with free surfaces containing microvilli, that secrete alveolar fluid which keeps surfaces moist.
y. Surfactant – complex mixture of phospholipids and lipoproteins, produced by type 2 alveolar cells in the lungs, that decreases surface tension.
1. Reduces the tendency of alveoli to collapse and thus maintains their patency.
z. alveolar macrophages or dust cells – phagocytes that remove fine dust particles and other debris from the alveolar spaces.
aa. respiratory membrane – formed by the alveolar and capillary walls

1. the site for exchange of oxygen and CO2 between the air spaces in the lungs and the blood.
2. Very thin, 0.5 micrometers thick, allowing rapid diffusion of gases.
3. Consists of four layers, extending from alveolar air space to blood plasma:
4. A layer of type 1 and type 2 alveolar cells and associated alveolar macrophages that constitute the alveolar wall
5. An epithelial basement membrane underlying the alveolar wall
6. A capillary basement membrane that is often fused to the epithelial basement membrane
7. The capillary endothelium

bb. blood supply to lungs

1. lungs receive blood via two sets of arteries: pulmonary arteries and bronchial arteries.
2. Deoxygenated blood passes through the pulmonary trunk which divides into a left pulmonary artery and right pulmonary artery.
3. Return of oxygenated blood occurs by way of 4 pulmonary veins which empty into the left atrium.
4. Bronchial arteries which branch from the aorta, deliver oxygenated blood to the lungs. This blood perfuses the muscular walls of the bronchi and bronchioles.
5. Some blood drains into bronchial veins and returns to the heart by the superior vena cava but most blood returns to the heart via the pulmonary veins through connections between branches of the bronchial arteries and branches of the pulmonary arteries.

Question 3

explain the differences among tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.

Answer 3

lung volumes

tidal volume – the volume of one breath (VT)

1. varies a lot from one person to another, and in the same person at different times.
2. At rest, typically around 500mL
3. In a typical adult, about 70% of tidal volume (350mL) actually reaches the respiratory zone of the respiratory system. The other 30% remains in the conducting airways of the respiratory system.

minute ventilation – total volume of air inhaled and exhaled each minute. (MV)

a. equals resp rate multiplied by tidal volume.

spirometer or respirometer – the tool used to measure the volume of air exchanged during breathing and the respiratory rate. a. Recorded on a “spirogram”

anatomic (respiratory) dead space – the collective term for the conducting airways with air that does not undergo respiratory exchange.

alveolar ventilation rate – the volume of air per minute that actually reaches the respiratory zone.

inspiratory reserve volume – the additional inhaled air when taking a very deep breath.

a. About 3100mL in an average adult male, and 1900mL in an average adult female.

expiratory reserve volume – air forced out when you inhale normally and then exhale as forcibly as possible.

a. Extra 1200mL in males and 700mL in females.

residual volume – the amount of air that remains in the lungs even after expiratory reserve volume is forcibly exhaled.

1. Cannot be measured by spirometry.
2. Amounts to about 1200mL in males, 1100mL in females.

minimal volume – remaining air if the thoracic cavity is opened, the intrapleural pressure rises to equal the atmospheric pressure, and some of the residual air is forced out.

1. Provides a medical and legal tool for determining if a baby is stillborn or died after birth.
2. Fetal lungs contain no air, so if a piece of lung is placed in water and it floats, the infant died after birth.

Question 4

differentiate inspiratory capacity, functional residual capacity, vital capacity, and total lung capacity.

Answer 4

lung capacities – combinations of specific lung volumes.

inspiratory capacity – the sum of tidal volume and inspiratory reserve volume.

a. 500mL + 3100mL = 3600mL in males, and 500+1900=2400 in females

functional residual capacity – the sum of residual and expiratory reserve volume

a. 1200+1200= 2400mL in males, and 1100+700=1800mL in females

vital capacity – the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.

a. 4800mL in males, 3100mL in females

total lung capacity – sum of vital capacity and residual volume

a. 4800+1200= 6000mL in males, and 3100+1100=4200mL in females.

Question 5

explain Dalton’s law and Henry’s law.

Answer 5

exchange of oxygen and carbon dioxide – between alveolar air and pulmonary blood occurs via passive diffusion. Governed by 2 gas laws:

Dalton’s law – each gas in a mixture of gases exerts its own pressure as if no other gases were present.
partial pressure – the presence of a specific gas in a mixture.

1. The total pressure of the mixture is calculating by adding all the partial pressures.
2. Atmospheric pressure (760mmHg) = PN2 + PO2 + PAr + PH2O + PCO2 + Pother gases
3. To determine the partial pressure exerted by each component in the mixture, multiply the percentage of the gas in the mixture by the total pressure of the mixture. We know air is 78.6% nitrogen, 20.9% oxygen, and so on. So 0.786 x 760mmHg = 597.4 mmHg for PN2
4. These 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.
5. Each gas diffuses from an area where its partial pressure is greater to an area where its partial pressure is lower.

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.

1. The higher the partial pressure of a gas over a liquid, and the higher the solubility, the more gas will stay in solution.
2. An everyday example of Henry’s law: a bottle of pop has CO2 dissolved in it. When you open the bottle, it hisses and bubbles for some time. This is because the pop was bottled under high pressure and the CO2 bubbles out of the solution because the pressure decreases when you open the lid.
3. Henry’s law explains Nitrogen solubility in body fluids. respiratory system works with urinary system to regulate pH of body fluids

At normal air pressure, very little nitrogen dissolves because it has low solubility. But when scuba diving and breathing pressurized air, nitrogen is dissolved in plasma and interstitial fluid.

decompression sickness – when a diver ascends too rapidly and nitrogen that has dissolved cannot be eliminated by exhaling it.

1. Bubbles form in nervous tissue and symptoms can be mild to severe depending on the number of bubbles formed
2. Symptoms: joint pain, dizziness, SOB, extreme fatigue, paralysis, unconsciousness

Question 6

describe the exchange of oxygen and carbon dioxide in external and internal respiration.

Answer 6

external respiration or pulmonary gas exchange – the exchange of respiratory gases between the lungs and blood.

The diffusion of oxygen from air in the alveoli of the lungs to blood in pulmonary capillaries and diffusion of carbon dioxide in the opposite direction.

1. deoxygenated blood and oxygenated blood – external respiration converts deoxygenated blood coming from the right side of the heart to oxygenated blood returning to the left side of the heart.
2. internal respiration or systemic gas exchange – the exchange of respiratory gases between blood and body cells. AKA tissue respiration.

As oxygen leaves the bloodstream, oxygenated blood is converted to deoxygenated blood Internal respiration occurs in all body tissues.

rate of pulmonary and systemic gas exchange

a) Partial pressure difference of gases
b) surface are availability for gas exchange
c) Diffusion distance
d) Molecular weight and solubility of the gases

Question 7

describe how the blood transports oxygen and carbon dioxide.

Answer 7

transport of oxygen and carbon dioxide in the blood

oxygen transport – oxygen is transported by hemoglobin

a. oxygen is not easily dissolved in water so only 1.5% of inhaled O2 is dissolved in blood plasma. The other 98.5% is bound to hemoglobin in RBCs

oxyhemoglobin – hemoglobin combined with oxygen relationship between hemoglobin and oxygen partial pressure

1. most important factor that determines how much oxygen binds to hemoglobin is the partial pressure of oxygen PO2
2. the higher the PO2, the more O2 combines with Hb.
3. Hb can be partially saturated or fully saturated with O2.
4. Percent saturation of Hb expresses the average saturation of Hb with

oxygen. Ex. If each Hb is bound to 2 O2 molecules, the Hb is 50% saturated because it can hold 4 total.

oxygen hemoglobin dissociation curve – shows relationship between percent saturation of hemoglobin and PO2

1. when PO2 is high, Hb binds with large amts O2 and is almost 100% saturated.
2. When PO2 is low, Hb is only partially saturated.
3. Pulmonary capillaries – high PO2, a lot of O2 binds to Hb
4. Tissue capillaries – lower PO2, Hb holds less O2, dissolved O2 is unloaded via diffusion into tissue cells. 1. Note that Hb is still 75% saturated with O2 at a PO2 of 40mmHg, the average tissue cell PO2. This is why only 25% of available O2 unloads from Hb and is used by resting condition cells.

other factors affecting hemoglobin’s affinity for oxygen

a. acidity (Bohr effect) – as pH decreases, affinity of Hb for O2 decreases, and O2 dissociates more readily from Hb.

1. AKA increasing acidity enhances unloading of O2 from Hb
2. Bohr Effect – when pH decreases, the entire oxygen-Hb dissociation curve shifts to the right. At any given PO2, Hb is less saturated with O2.
3. Hb can act as a buffer for hydrogen ions, but when H+ ions bind to amino acids in Hb, they alter its structure slightly and decrease its oxygen carrying capacity.
4. By contrast, elevated pH increases affinity of Hb for O2 and shifts the curve to the left.

b. partial pressure of CO2 – CO2 can also bind to Hb, and the effect is similar to that of H+ (shifting the curve to the right)

1. as PCO2 rises, Hb releases O2 more readily.
2. PCO2 and pH are related because low blood pH results from high PCO2. Increased PCO2 produces a more acidic environment, which helps release O2 from Hb.

c. Temperature – within limits, as temp increases, so does the amount of O2 released from Hb.

1. Heat is a byproduct of metabolic reactions of all cells, and the heat released by contracting muscle fibers tends to raise body temp.
2. Metabolically active cells require more O2 and liberate more acids and heat. The acids and heat in turn promote release of O2 from oxyhemoglobin
3. In hypothermia, cellular metabolism slows, need for O2 is reduced, and more O2 remains bound to Hb.

d. BPG – substance found in RBCs called 2, 3,-biphosphoglycerate decreases the affinity of Hb for O2 and thus helps unload O2 from Hb.

1. Formed in RBCs when they break down glucose to produce ATP via glycolysis.
2. When BPG combines with Hb by binding to the terminal amino groups of the two beta globin chains, the Hb binds O2 less tightly at the heme group sites.
3. The greater the level of BPG, the more O2 is unloaded from Hb.
4. Certain hormones increases formation of BPG: thyroxine, hGH,

epinephrine, norepinephrine, testosterone.

1. BPG level is also higher in people living at higher altitudes.

carbon dioxide transport – transported in the blood in 3 main forms: dissolved CO2, carbamino compounds, bicarbonate ion (HCO3−)

1. dissolved CO2 – smallest %, about 7%, dissolved in blood plasma. On reaching the lungs, it diffuses into alveolar air and is exhaled
2. carbamino compounds – 23% combines with the amino groups of amino acids and proteins in blood to form carbamino compounds. The most prevalent protein in blood is Hb (inside RBCs), and most of the CO2 transported by carbamino compounds is bound to Hb.

carbaminohemoglobin (Hb-CO2) – hemoglobin that has bound CO2.

a. Formation is greatly influenced by PCO2.
1. In tissue capillaries, PCO2 is relatively high, which promotes formation of Hb-CO2. In pulmonary capillaries, PCO2 is relatively low, and the CO2 readily splits apart from globin and enters the alveoli by diffusion.

1. bicarbonate ion (HCO3−) – 70% of CO2 is transported in blood plasma as bicarbonate ions.
2. As CO2 diffuses into systemic capillaries and enters RBCs, it reacts with water in the presence of the enzyme carbonic anhydrase to form carbonic acid, which dissociates into the H+ and HCO3-
3. As blood picks up CO2, HCO3- accumulates inside RBCs. Some moves out into the blood plasma down its concentration gradient and Cl- ions move from plasma into the RBCs.
4. This exchange of negative ions maintains the electrical balance between blood plasma and RBC cytosol and is called the chloride shift.
5. As blood passes through pulmonary capillaries in the lungs, the reactions reverse and CO2 is exhaled.

Haldane effect – the lower the amount of oxyhemoglobin, the higher the CO2 carrying capacity of the blood

1. The amount of CO2 that can be transported in the blood is influenced by the percent saturation of Hb with O2.
2. Two characteristics of deoxyhemoglobin give rise to the Haldane effect:
3. Deoxyhemoglobin binds to and transports more CO2 than Hb- O2
4. Deoxyhemoglobin also buffers more H+ than Hb-O2, thereby removing H+ from solution and promoting conversion of CO2 to HCO3-

summary of gas exchange and transport in lungs and tissues

1. Deoxygenated blood returning to the pulmonary capillaries in the lungs contains CO2 dissolved in blood plasma, CO2combined with globin as carbaminohemoglobin (Hb–CO2), and CO2 incorporated into
   HCO3− within RBCs. The RBCs have also picked up H+, some of which binds to and therefore is buffered by hemoglobin (Hb–H).
2. 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 alveolar air and are exhaled. At the same time, inhaled O2 is diffusing from alveolar air into RBCs and is binding to hemoglobin to form oxyhemoglobin (Hb–O2).
3. Carbon dioxide also is released from HCO3− when H+ combines with HCO3− inside RBCs. The H2CO3formed from this reaction then splits into CO2, which is exhaled, and H2O.
4. 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+.
5. In systemic capillaries, as cells use O2 and produce CO2, the chemical reactions reverse.

Question 8

explain how the nervous system controls breathing.

Answer 8

control of respiration

respiratory centre – neurons in the pons and medulla oblongata of the brain stem that regulate breathing.

a. Divided into the medullary respiratory center and the pontine respiratory center.

medullary respiratory center – made up of two collections of neurons called the dorsal respiratory group and the ventral respiratory group.
dorsal respiratory group – formerly called the inspiratory area. Active in quiet breathing. Activates the ventral resp group during forceful breathing.

1. 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.
2. These impulses are released in bursts, which begin weakly, increases in strength for about 2 seconds, and then stop completely.

c. When the nerve impulses reach the muscles, they contract and inhalation occurs.
d. When the DRG becomes inactive after 2 seconds, the muscles relax for about 3 seconds and passive recoil of the lungs and thoracic wall occur. Then the cycle repeats itself.

ventral respiratory group – becomes activated when forceful breathing is required. Formerly called the expiratory area

1. Nerve impulses from the DRG stimulate the diaphragm and external intercostal muscles to contract but also activate neurons of the VRG involved in forceful inhalation to send impulses to the accessory muscles of inhalation (sternocleidomastoid, scalenes, and pectoralis minor)
2. Neurons of the VRG involved in forceful exhalation send nerve impulses to the accessory muscles of exhalation (internal intercostals, external oblique, internal oblique, transversus abdominis, rectus abdominis). The DRG and the neurons of the VRG that result in forceful inhalation are inactive during forceful exhalation.
3. There is a cluster of neurons in the VRG called the pre-Botzinger complex that is believed to be important in the generation of the rhythm of breathing.
4. Similar to the rhythm generator of the heart, it is composed of pacemaker cells that set the basic rhythm of breathing. Thought that the pacemaker cells provide input to the DRG, driving the rate at which DRG neurons fire action potentials.

pontine respiratory group – part of the respiratory center in the pons that continually sends inhibitory nerve impulses to the dorsal respiratory group, limiting inhalation and facilitating exhalation.

1. Formerly called the pneumotaxic area
2. These neurons are active during inhalation and exhalation.
3. The PRG transmits nerve impulses to the DRG in the medulla.
4. The PRG may play a role in both inhalation and exhalation by modifying the basic rhythm of breathing generated by the VRG

regulation of the respiratory centre

a. activity of the resp center can be modified in response to input from other brain regions, receptors in the peripheral nervous system, and other factors to maintain the homeostasis of breathing.

cortical influences

a. the cerebral cortex has connections with the respiratory center so we can voluntarily alter our pattern of breathing

• voluntary control enables us to prevent water or irritating gases from entering the lungs.
• The ability to not breathe is limited by the build up of CO2 and H+ in the body. When concentrations increase to a certain level, the DRG neurons of the medullary respiratory center are strongly stimulated and breathing resumes whether you want it or not.
• Nerve impulses from the hypothalamus and limbic system also stimulate the respiratory center, allowing emotional stimuli to alter breathing for example in laughing and crying.

chemoreceptor regulation – certain chemical stimuli modulate how quickly and how deeply we breathe.

a. central chemoreceptors – located in or near the medulla oblongata and in the central nervous system.
1. They respond to changes in H+ or PCO2 or both in CSF

1. peripheral chemoreceptors – located in the aortic bodies and in the carotid bodies and are part of the peripheral nervous system, responding to changes in PO2, H+, and PCO2 in the blood.
2. aortic bodies – clusters of chemoreceptors on or near the arch of the aorta.
3. Axons of sensory neurons from the aortic bodies are part of the vagus (X) nerve

carotid bodies – clusters of chemoreceptors on or near the carotid sinus; oval nodules in the wall of the left and right common carotid arteries where they divide into the internal and external carotid arteries.

1. Axons of sensory neurons from the carotid bodies are part of the right and left glossopharyngeal (IX) nerves

Hypercapnia – a slight increase in PCO2

1. The central chemoreceptors are stimulated and respond vigorously to the resulting increase in H+ level
2. The peripheral chemoreceptors are also stimulated by both the high PCO2 and rise in H+.
3. The peripheral (but not central) chemoreceptors also respond to a deficiency of O2

Hyperventilation – rapid and deep breathing that allows the inhalation of more O2 and exhalation of more CO2 until PCO2 and H+ are lowered to normal

Hypocapnia – if arterial PCO2 is lower than 40mmHg, the central and peripheral chemoreceptors are not stimulated and stimulatory impulses are not sent to the DRG.

1. Therefore DRG neurons set their own moderate pace until CO2 accumulates and the PCO2 rises to 40mmHg.

proprioceptor stimulation – monitor movement of joints and muscles and send impulses to the DRG of the medulla to alter rate and depth of breathing. At the same time, axon collaterals of upper motor neurons that originate in the primary motor cortex (precentral gyrus) also feed excitatory impulses to the DRG. inflation reflex

a. baroreceptors or stretch receptors – respond to over inflation of the lungs, sending nerve impulses along the vagus (X) nerves to the DRG, inhibiting it and allowing the diaphragm and external intercostals to relax.
1. inflation reflex or Hering Breuer reflex – As the lungs deflate, the stretch receptors are no longer stimulated, and the inhibitory impulses stop, therefore the DRG is not inhibited and a new inhalation can occur

Question 9

Other factors that control breathing?

Answer 9

other influences on breathing

Limbic system stimulation – anticipation of activity or emotional anxiety may stimulate the limbic system, which then sends excitatory input to the DRG, increases rate and depth of breathing

Temperature – increase in body temp increases rate of breathing. Decrease in body temp decreases rate of breathing.

Pain – sudden severe pain brings about brief apnea, but prolonged somatic pain increases breathing rate. Visceral pain may slow breathing rate.

Stretching the anal sphincter muscle – this action increases breathing rate and is sometimes used to stimulate respiration in a newborn baby or a person who has stopped breathing

Irritation of airways – physical or chemical irritation of the pharynx or larynx brings about an immediate cessation of breathing followed by coughing or sneezing
Blood pressure – the carotid and aortic baroreceptors that detect changes in BP have a small effect on breathing. A sudden rise in BP decreases breathing rate and a drop increases.

Apnea – absence of breathing

Question 10

Disorders

Answer 10

disorders

asthma – disorder characterized by chronic airway inflammation, airway hypersensitivity to a variety of stimuli, and airway obstruction

1. partially reversible, either spontaneously or with treatment
2. symptoms – difficult breathing, coughing, wheezing, chest tightness,

tachycardia, fatigue, moist skin, anxiety

1. treatment – acute attack is treated with an inhaled beta2-adrenergic

agonist (albuterol) to help relax smooth muscle in the bronchioles and open airways. Long term therapy aims to suppress the underlying inflammation, with anti-inflammatory drugs such as inhaled corticosteroids, cromolyn sodium, and leukotriene blockers.

chronic obstructive pulmonary disease (COPD) – type of respiratory disorder characterized by chronic and recurrent obstruction of airflow, which increases airway resistance.

1. Fourth leading cause of death behind heart disease, cancer, and cerebrovascular diseas
2. Principal types are emphysema and chronic bronchitis

Emphysema – disorder characterized by destruction of the walls of the alveoli, producing abnormally large airspaces that remain filled with air during exhalation.

1. With less surface area for gas exchange, O2 diffusion across the damaged respiratory membrane is reduced.
2. Blood O2 level is somewhat lowered and any activity that raises O2 requirements of cells leaves the patient breathless.

c. Elastic recoil decreases due to loss of elastic fibers and an increasing amount of air becomes trapped in the lungs at the end of exhalation.

1. Barrel chest results from several years of added exertion during inhalation increasing the size of the chest cage.
2. Generally caused by a long-term irritation: cigarette smoke, air pollution, and occupational exposure to industrial dust are the most common irritants.
3. Treatment – stop smoking, remove environmental irritants, exercise under medical supervision, breathing exercises, use of bronchodilators, and oxygen therapy.

chronic bronchitis – disorder characterized by excessive secretion of bronchial mucus accompanied by a productive cough that lasts for at least 3 months of the year for two successive years.

1. Leading cause is cigarette smoking. Inhaled irritants lead to chronic inflammation with an increase in the size and number of mucous glands and goblet cells in the airway epithelium. The thickened and excessive mucus produced narrows the airway and impairs ciliary function. Thus inhaled pathogens become embedded in airway secretions and multiply rapidly
2. Symptoms – productive cough, SOB, wheezing, cyanosis, pulmonary hypertension.
3. Treatment – similar to emphysema

lung cancer

1. at time of diagnosis, usually well advanced with distant metastases in 55% of patients and regional lymph node involvement in another 25%.
2. Overall survival rate is only 10-15%, most people die within 1 year of diagnosis
3. Causes- smoking is most common cause, second hand smoke, ionizing radiation, inhaled irritants such as asbestos and radon gas. Emphysema is a common precursor to developing lung cancer.
4. Symptoms – related to location of tumor. May include chronic cough, spitting blood, wheezing, SOB, chest pain, hoarseness, difficulty swallowing, weight loss, anorexia, fatigue, bone pain, contusion, balance problems, headache, anemia, thrombocytopenia, jaundice.
5. Treatment – partial or complete surgical removal of diseased lung, radiation therapy, chemotherapy.

Pneumonia – acute infection or inflammation of the alveoli.

a. The most common infectious cause of death

1. Most common cause of pneumonia is the pneumococcal bacterium streptococcus pneumoniae but other microbes can also cause it.
2. Most susceptible – elderly, infants, immunocompromised people, smokers, people with obstructive lung disease.
3. Most cases are preceded by an upper respiratory infection that is often viral, with individuals then developing fever, chills, productive or dry cough, malaise, chest pain, dyspnea, hemoptysis.
4. Treatment – antibiotics, bronchodilators, increased fluid intake, chest physiotherapy (percussion, vibration, postural drainage)

Tuberculosis – caused by bacterium mycobacterium tuberculosis

1. Produces an infectious, communicable disease called TB.
2. Most often affects the lungs and the pleurae but may involve other parts

of the body

1. Symptoms – fatigue, weight loss, lethargy, anorexia, low-grade fever,

night sweats, cough, dyspnea, chest pain, and hemoptysis, but often do

not develop until the disease is advanced

1. Treatment – medication called isoniazid

pulmonary edema – an abnormal accumulation of fluid in the interstitial spaces and alveoli of the lungs.

1. May arise from increased permeability of pulmonary capillaries (pulmonary origin) or increased pressure in the pulmonary capillaries (cardiac origin). The latter may coincide with CHF.
2. Most common symptom is dyspnea. Other symptoms incl wheezing, tachypnea, restlessness, feeling of suffocation, cyanosis, pallor, diaphoresis, pulmonary hypertension
3. Treatment – administering Oxygen, bronchodilators and meds to lower BP, diuretics, drugs to correct acid-base imbalance, suctioning of airways, mechanical ventilation.

sudden infant death syndrome (SIDS) – sudden, unexpected death of an apparently healthy infant during sleep.

1. Rarely occurs before 2 weeks or after 6 months of age, peak incidence between 2nd and 4th months
2. More common in premature infants, male babies, low-birth-weight babies, babies of drug users or smokers, babies that have stopped breathing and have had to be resuscitated, babies with upper respiratory tract infections, and babies who have had a sibling die of SIDS
3. African American and native American babies also at higher risk.
4. Exact cause unknown.
5. Recommended to sleep on back to decrease risk.

severe acute respiratory syndrome (SARS) – an example of an emerging infectious disease (a disease that is new or changing)

1. first appeared in southern china in 2002 and has spread worldwide.
2. Respiratory virus caused by a new variety of coronavirus
3. Symptoms – fever, malaise, muscle aches, dry cough, difficulty

breathing, chills, headache, diarrhea.

1. 10-20% of patients require mechanical ventilation and some die.
2. Spread primarily by person-to-person contact.
3. No effective treatment. Death rate is 5-10%, mostly elderly and people

with comorbidities.