Lab Exam 3

Question 1

Compare and contrast the structural organization and the functional organization of the respiratory
system

Answer 1

The respiratory system is organized structurally into two regions: an upper respiratory tract and a lower respiratory tract. The nose, nasal cavity, and pharynx form the upper respiratory tract. The larynx, trachea, bronchi, bronchioles (including terminal and respiratory bronchioles), alveolar ducts, and alveoli are the components of the lower respiratory tract.
The structures of the respiratory system are also categorized based on function. Pas­sageways that transport or conduct air are part of the conducting zone; these structures include the passageways from the nose to the end of the terminal bronchioles. Structures that participate in gas exchange with the blood—including the respiratory bronchioles, alveolar ducts, and alveoli—are part of the respiratory zone.

Question 2

Describe the structure of the mucosa that lines the respiratory tract and the structural changes
observed along its length

Answer 2

The respiratory passageway is exposed to the external environment and is lined internally by a mucosa, also called a mucous membrane. In general, the mucosa is composed of an epithelium resting upon a basement membrane, and an underlying lamina propria composed of areolar connective tissue. The epithelium is ciliated (having cilia) in most portions of the respiratory tract conducting zone.

Pseudostratified ciliated columnar epithelium lines the nasal cavity, paranasal sinuses, nasopharynx, trachea, inferior portion of larynx, main bronchi, and lobar bronchi.

Simple ciliated columnar epithelium lines the segmental bronchi, smaller bronchi, and large bronchioles.

Simple ciliated cuboidal epithelium lines the terminal and respiratory bronchioles (a progressive loss of cilia is observed).

Simple squamous epithelium forms both the alveolar ducts and alveoli.

Nonkeratinized stratified squamous epithelium lines regions of the respiratory tract subject to abrasion, including the oropharynx, laryngopharynx, the vocal cords and the superior portion of the larynx.

Question 3

Explain the function of mucus produced by the mucosa

Answer 3

The epithelium lining most of the respiratory tract contains goblet cells, and the underly­ing lamina propria houses both mucous and serous glands. Mucus is produced from the combined secretions of these cells and glands. Mucous secretions contain mucin, a protein that increases the viscosity of mucus to more effectively trap inhaled dust, dirt particles, microorganisms, and pollen. The secretions also contain specific substances to help defend the body against infectious agents, including lysozyme (an antibacterial enzyme), defensins (antimicrobial proteins), and immunoglobulin A (antibodies).
Both mucus and saliva entrap materials, which may be coughed up as a viscous substance called sputum.

Question 4

Describe the structure and function of the nose and nasal cavity

Answer 4

The nose is the first structure of the conducting passageway for inhaled air; it is formed by bone, hyaline cartilage, and dense irregular connective tissue covered with skin externally. Paired nasal bones form the bridge of the nose and support it superiorly. Anteroinferiorly from the bridge, there is one pair of lateral cartilages and there are two pairs of alar cartilages. The flared components of the nose are composed of dense irregular connective tissue. The paired nostrils, or nares are the anterior openings that lead into the nasal cavity.
The nasal cavity is oblong­shaped, and it extends from the nostrils to paired openings called choanae. The choanae are the “doorways” that lead from the nasal cavity into the pharynx. The floor of the nasal cavity is formed by the hard and soft palates, and the roof is composed of the nasal, frontal, eth­moid, and sphenoid bones, and some cartilage of the nose. The nasal septum divides the nasal cavity into left and right portions. The septum is formed anteriorly by the septal nasal cartilage and posteriorly by a thin, bony sheet com­ posed of the perpendicular plate of the ethmoid superiorly and the vomer bone inferiorly.
Three paired, bony projections are located along the lateral walls of the nasal cavity: the superior, middle, and inferior nasal conchae. Because the conchae help produce turbulence in the inhaled air, they are sometimes called the turbinate bones. The conchae partition the nasal cavity into sepa­rate air passages, each called a nasal meatus. A meatus is located immediately inferior to its corresponding nasal concha.

Question 5

Describe the structure and function of the nose and nasal cavity - 2

Answer 5

The nasal cavity is divided into three parts: the nasal vestibule, olfactory region, and respiratory region. The nasal vestibule is immediately internal to the nostrils and is lined by skin and coarse hairs called vibrissae to trap large particulates. This is the only normally visible portion of the nasal cavity.
The olfactory region is the superior portion of the nasal cavity. It contains the olfactory epithelium (which houses the olfactory receptors). Airborne molecules that dissolve in the mucus covering the olfactory epithelium stimulate olfactory receptors to detect differ­ent odors.
The respiratory region of the nasal cavity is lined by a mucosa composed of pseudostratified ciliated columnar epitheli­um. The lamina propria of this mucosal lining has an extensive vascular network. Nosebleeds (epistaxis) are especially common because of both the vast distribution of blood vessels and their superficial location (just deep to the epithelium), and they are more likely to occur during cold weather because the mucous membranes become dry and crack. Additionally, paired nasolacrimal ducts drain lacrimal secretions from the surface of each eye into the respiratory region of the nasal cavity.
A primary function of the nasal cavity is to condition the air as it enters the respiratory tract. The air is warmed to body temperature by the extensive array of blood vessels within the nasal cavity lin­ing. These vessels dilate in response to cold air, resulting in increased blood flow that helps to more effectively warm the inhaled air. The air is cleansed as inhaled microbes, dust, and other foreign material become trapped in the mucus covering the inner lining of the respiratory tract. Cilia then “sweep” the mucus and its trapped contents toward the pharynx to be swal­lowed. The air is also humidified as it passes through the moist environment of the nasal passageway. Conditioning of air is enhanced by conchae, which cause air turbulence that increases the amount of contact between the inhaled air and the mucosa.

Question 6

Identify the four paired paranasal sinuses and describe their functions

Answer 6

Thus, from a superior to inferior direction, they are the paired frontal, ethmoidal, and maxillary sinuses; the sphenoidal sinuses are located posterior to the ethmoidal sinuses. Ducts con­nect all paranasal sinuses to the nasal cavity. Both the paranasal sinuses and their ducts are lined by a pseudostratified ciliated columnar epithelium that is continuous with the mucosa of the nasal cavity. The mucus, with its trapped particulate matter, is swept by cilia from each paranasal sinus into the nasal cavity and then into the pharynx, where it is swallowed.

Question 7

Compare the three regions of the pharynx and identify and describe their associated structures

Answer 7

The pharynx, commonly called the throat, is a funnel­ shaped passageway. It is located posterior to the nasal cavity, oral cavity, and larynx. Air is conducted along its entire length, both air and food along its inferior portions. The lateral walls of the pharynx are composed of skeletal muscles that both contribute to distensibility (ability to stretch) needed to accommodate swallowed food and help force these materials into the esophagus. The pharynx is partitioned into three regions—from superior to inferior, they are the naso­pharynx, oropharynx, and laryngopharynx.

Question 8

Nasopharynx

Answer 8

The nasopharynx is the superior-most region of the pharynx. Located directly posterior to the nasal cavity and superior to the soft palate, the nasopharynx, like the nasal cavity, is lined by a pseudostratified ciliated columnar epithelium. Normally, only air passes through the nasopharynx. Material from both the oral cavity and the oropharynx typically is blocked from entering the nasophar­ynx by the soft palate, which elevates when we swallow. However, sometimes food or drink enters the nasopharynx and the nasal cavity, as when a person tries to swallow and then laughs at the same time. The soft palate cannot form a good seal for the nasopharynx, and the force from the laugh may propel some of the material into the nasal cavity. If the laugh is forceful enough, the material may come out the nostrils.
The nasopharynx lateral walls have paired openings into auditory tubes (eustachian tubes, or pharyngotympanic tubes) that connect the nasopharynx to the middle ear. These tubes equalize air pressure on either side of the tympanic membrane (eardrum) by allowing air to move between the nasopharynx and the middle ear. Infections within the pharynx can move through the auditory tube into the middle ear, result­ ing in a middle ear infection. A collection of lymphatic nodules, called the tubal tonsils, is located near the pharyngeal opening of these tubes. The posterior nasopharynx wall also houses a single pharyngeal tonsil. When this tonsil is enlarged, clinicians refer to it as the adenoids. Both the tubal and pharyngeal tonsils are composed of lymphatic tissue and help to prevent the spread of infections

Question 9

Oropharynx

Answer 9

The middle pharyngeal region, called the oropharynx, is immediately posterior to the oral cavity. The oropharynx extends from the level of the soft palate superiorly to the hyoid bone inferiorly. The palatine tonsils are located on lateral walls of the oro­pharynx, and the lingual tonsils are at the base of the tongue (and thus are in the anterior region of the oropharynx), providing defense against ingested or inhaled foreign materials

Question 10

Laryngopharynx

Answer 10

The inferior, narrowed region of the pharynx is the laryngopharynx, which is located directly posterior to the larynx. It extends from the level of the hyoid bone and is continuous on its inferior end with both the larynx anteriorly and the esophagus posteriorly. Both the oropharynx and laryngopharynx serve as a common passageway for food and air. They are lined by a nonkeratinized stratified squamous epithelium to protect these regions of the pharynx from abrasion associated with swallowing food

Question 11

Identify and describe the structure and general functions of the larynx

Answer 11

The larynx , also called the voice box, is continuous superiorly with the laryngophar­ynx and inferiorly with the trachea. The superior opening from the laryngopharynx into the larynx is called the laryngeal inlet, laryngeal aperture, or laryngeal aditus.
Functions of the Larynx
The larynx has several major functions:
∙ Serves as a passageway for air. The larynx is normally open to allow the passage of air.
∙ Prevents ingested materials from entering the respiratory tract. During swallowing, the laryngeal inlet is covered by the epiglottis to prevent ingested materials from entering the lower respiratory passageway.
∙ Produces sound for speech. Ligaments within the larynx, called vocal cords, vibrate as air is passed over them during an expiration.
∙ Assists in increasing pressure in the abdominal cavity. The epiglottis of the larynx closes over the laryngeal inlet so air cannot escape, and simultaneously abdominal muscles contract to increase abdominal pressure. This action is referred to as the Valsalva maneuver. You can experience the increase in abdominal pressure associated with the Valsalva maneuver by holding your breath while forcefully contracting your abdominal muscles.
∙ Participates in both a sneeze and cough reflex. Both a sneeze and a cough result in an explosive blast of exhaled air. This occurs when the abdominal muscles contract forcefully and the vocal cords are initially closed and then open abruptly as the pressure increases in the thoracic cavity. Sneezing is a reflex initiated by irritants in the nasal cavity, whereas coughing is initiated by irritants in the trachea and bronchi. Both help remove irritants from the respiratory tract.

Question 12

Larynx Anatomy - cartilages

Answer 12

The thyroid cartilage is the largest laryngeal cartilage. Shaped like a shield, it forms the anterior and lateral walls of the larynx. The almost V­shaped anterior projection of the thyroid cartilage is called the laryngeal prominence (commonly referred to as the Adam’s apple). This protuberance is generally larger in males because (1) the laryngeal inlet is narrower in males (90 degrees) than in females (120 degrees), and (2) it enlarges at puberty due to testosterone­induced growth.
The thyroid cartilage is attached to the lateral surface of the ring­ shaped cricoid cartilage located inferior to the thyroid cartilage. The large, spoon­ or leaf­shaped epiglottis is anchored to the inner aspect of the thyroid cartilage and projects posterosuperiorly into the pharynx. It closes over the laryngeal inlet during swallowing. The three smaller, paired cartilages, the arytenoid, corniculate, and cuneiform cartilages are located internally. All cartilages of the larynx, except the epiglottis, are composed of hyaline cartilage. The epiglottis, which opens and closes over the laryngeal inlet, is composed of the more flexible elastic cartilage

Question 13

Laryngeal ligaments

Answer 13

Extrinsic ligaments attach to the external surface of laryngeal cartilages and extend to other structures that include the superiorly located hyoid bone and inferiorly located trachea.
The intrinsic ligaments are located within the larynx and include both vocal ligaments and vestibular ligaments. The vocal ligaments are composed primarily of elastic connective tissue and extend anterior to posterior between the thyroid cartilage and the arytenoid cartilages. These ligaments are covered with a mucosa to form the vocal folds. Vocal folds also are called the true vocal cords because they produce sound when air passes between them. They are distinctive from the surrounding tissue because they are avascular and white. The opening between these folds is called the rima glottidis. Together the vocal folds and the rima glottidis form the glottis.
The vestibular ligaments form the other intrinsic ligaments. These extend between the thyroid cartilage to the arytenoid and corniculate cartilages. Together with the mucosa covering them, they form the vestibular folds located superior to the vocal folds. These folds also are called the false vocal cords because they have no function in sound production, but they protect the vocal folds. The opening between the vestibular folds is called the rima vestibuli.

Question 14

Identify and describe the structure and function of the trachea

Answer 14

The trachea is a flexible, slightly rigid, tubular organ. The anterior and lateral walls of the trachea are supported by 15 to 20 C­ shaped rings of hyaline cartilage called tracheal cartilages. The tracheal cartilages are connected superiorly and inferiorly with one another by elastic connective tissue sheets called anular ligaments.
Each C-­shaped tracheal cartilage is ensheathed in a perichondrium and a dense, fibrous membrane. The open ends of the cartilage rings are positioned posteriorly (adjacent to the esophagus) and are connected to each other by both the trachealis muscle and an elastic ligamentous membrane. The C­-shaped cartilage portion of each of these rings reinforces and provides structural support to the tracheal wall to ensure that the trachea remains open (patent) at all times. The more flexible trachealis muscle and ligamentous membrane on the posterior aspect of the trachea allow for distension during swallowing of food through the esophagus. The trachealis contracts during coughing to reduce the diameter of the tra­chea, thus facilitating the more rapid expulsion of air, helping to dislodge material from the air passageway.
An internal ridge of mucosa­ covered cartilage called the carina is located at the split of the trachea into the main bronchi. The carina has sensory receptors that are extremely sensitive and can induce a forceful cough when stimu­lated by irritants.

Question 15

Identify and describe the structural subdivisions of the bronchial tree

Answer 15

The bronchial tree is a highly branched system of air­conducting passages that originates at the main bronchi and progressively branches into narrower tubes that diverge throughout the lungs before ending in the alveoli

The trachea splits at the level of the sternal angle into the right and left main bronchi also known as primary bronchi. Each main bronchus projects inferiorly and later­ ally into a lung. The right main bronchus is shorter, wider, and more vertically oriented than the left main bronchus—thus, foreign particles are more likely to lodge in the right main bronchus. Both main bronchi, along with all associated pulmonary vessels, lymph vessels, and nerves, enter a lung on its medial surface.
Each main bronchus then branches into lobar bronchi (or secondary bronchi), which extend to each lobe of the lung. The right lung with three lobes has three lobar bronchi, and the left lung with two lobes has two lobar bronchi. Lobar bronchi are smaller in diameter than main bronchi. They further divide into segmental bronchi (or tertiary bronchi) that serve a division of the lung called a bronchopulmonary segment. The right lung is supplied with 10 segmental bronchi, and the left lung is supplied by 8 to 10 seg­mental bronchi. The bronchial tree continues to divide into more numerous and smaller bronchi and then bronchioles. There are approximately 9 to 12 different levels, or generations, of bronchial branch divisions; the main, lobar, and segmental bronchi are the first, second, and third generations of bronchi, respectively.
Bronchi lead into tubes that do not have cartilage in their walls called bronchioles. Terminal bronchioles are the last portion of the conducting pathway. They lead into respiratory bronchioles, the first segments of the respiratory zone

Question 16

Explain the processes of bronchoconstriction and bronchodilation.

Answer 16

Airflow is decreased when their smooth muscle is stimulated to contract, which narrows the diameter of the lumen (opening), causing bronchoconstriction. In contrast, airflow is increased when their smooth muscle relaxes, which widens the diameter of the lumen, causing bronchodilation. Note that broncho­ constriction lessens the amount of potentially harmful substances that may be inhaled into the alveoli, helping to protect the lungs, whereas bronchodilation maximizes the amount of air moved between the atmosphere and alveoli to increase the amount of oxygen that is delivered to the alveoli and the amount of carbon dioxide that is removed.

Question 17

Identify and describe the structure and function of the components of the respiratory zone

Answer 17

The respiratory zone is composed of respiratory bronchioles, alveolar ducts, and alveoli. These are all microscopic structures. The smallest respiratory bronchioles subdivide into thin airways called alveolar ducts that lead into alveolar sacs, which are composed of a cluster of alveoli. An alveolus is a small, saccular outpocketing (similar to a hollow grape).
Respiratory bronchioles typically are composed of a simple cuboidal epithelium, whereas both the alveolar ducts and alveoli are composed of a simple squamous epithelium. The epithelium within the respiratory zone is much thinner than in the conducting portion, thus facilitating gas diffusion between the respi­ratory zone and pulmonary capillaries.
The interalveolar septum contains elastic fibers that contribute to the ability of the lungs to stretch during inspiration and recoil during expiration.

Question 18

List three types of cells found in alveoli and describe the function of each

Answer 18

recoil during expiration.
Two cell types form the alveolar wall: alveolar type I cells and alveolar type II cells. Alveolar type I cells (or squamous alveolar cells) are the most common of the two types of cells. These simple squamous cells are the primary cells that form each alveolus. Alveolar type I cells collectively form the alveolar epithelium of the respiratory membrane. Alveolar type II cells (or septal cells), which are much less numer­ous, secrete an oily fluid called pulmonary surfactant. The function of surfactant is to prevent the collapse of alveoli.
A third type of cell that is part of the alveolus is the alveolar macrophage, also called a dust cell. This cell is a leukocyte that may be either fixed or free. Fixed alveolar macrophages remain within the connective tissue of the alveolar walls, whereas free alveolar macrophages are migratory cells that continually move across the alveolar surface within the alveoli. Both types of alveolar macrophages engulf microorganisms and particulate material that reaches the alveoli. The alveolar macrophages are able to leave the lungs either by entering the lymph vessels or by being coughed up in sputum and then expectorated from the mouth.

Question 19

Describe the structure and function of the respiratory membrane

Answer 19

The respiratory membrane is the thin barrier that oxygen and carbon dioxide dif­fuse across during gas exchange between the alveoli and the blood in the pulmonary capillaries. It consists of an alveolar type I cell, an individual endothelial cell of a capillary, and their fused base­ment membranes. Oxygen diffuses from the alveolus across the respiratory membrane into the pulmonary capillary, thereby allowing the erythrocytes in the blood to become oxygenated. Oxygen is then transported by the blood to systemic cells. Con­versely, carbon dioxide diffuses from the blood within the pulmo­nary capillary through the respiratory membrane to enter each alveolus. Once in the alveoli, carbon dioxide is expired from the respiratory system into the external environment.

Question 20

Identify and describe the general structure of the lungs

Answer 20

Each lung has a wide, concave base that rests infe­riorly upon the muscular diaphragm and an apex (or cupula) that is slightly superior and posterior to the clavicle. The lung surfaces are adjacent to the ribs, mediastinum, and diaphragm and are respec­ tively referred to as the costal surface, mediastinal surface, and diaphragmatic surface of the lungs.
Each lung has a conical shape with an indented region on its mediastinal surface called the hilum, through which pass the bron­chi, pulmonary vessels, lymph vessels, and autonomic nerves. Collectively, these structures that extend from the hilum are termed the root of the lung.

Question 21

Right and Left lung

Answer 21

The right and left lungs exhibit some obvious structural differ­ences. The right lung is larger and wider than the left lung, and is subdivided by two fissures into three lobes. The horizontal fissure separates the superior (upper) lobe from the middle lobe, whereas the oblique fissure separates the middle lobe from the inferior (lower) lobe. In contrast, the left lung—which is slightly smaller than the right lung because the heart projects into the left side of the tho­racic cavity—has only two lobes. The left lung has an oblique fissure that separates the superior lobe from the inferior lobe. The lingula of the left lung is a projection from the superior lobe that is homologous to the middle lobe of the right lung. The left lung also has two surface indentations to accommodate the heart: the cardiac impression on its medial surface and a cardiac notch on its anterior surface.
Each lung is partitioned into bronchopulmonary segments; there are 10 segments in the right lung and typically 8 to 10 in the left lung. Each bronchopulmonary seg­ment is an autonomous unit, encapsulated within connective tissue and supplied by its own segmental bronchus, a branch of both the pulmonary artery and vein, and lymph vessels.
Within each segment, the lung is organized into marble­sized lobules. Each lobule is surrounded by connective tissue and supplied by a terminal bronchiole, an arteriole, a venule, and a lymph vessel.

Question 22

Describe the innervation of the lungs by the two divisions of the autonomic nervous system

Answer 22

The smooth muscle and glands of the larynx, trachea, bronchial tree, and lungs are innervated by the lower motor neurons of the autonomic nervous system and controlled by autonomic nuclei within the brainstem. The bronchioles are dually innervated and, thus, are regulated by both the sym­pathetic and parasympathetic divisions. Sympathetic innervation to structures within the lungs originates generally from the T1–T5 seg­ments of the spinal cord. Stimulation of the bron­chioles by the sympathetic division relaxes smooth muscle within the bronchial walls, causing bronchodilation.
Parasympathetic innervation to structures within the lungs is from vagus nerves (CN X), and it stimulates smooth muscle contraction within the bronchial walls, causing bronchoconstriction. The vagus nerves are also the primary source of innervation to the larynx.

Question 22

Compare and contrast the two types of blood circulation through the lungs

Answer 22

Two types of blood circulation are associated with the lungs: the pulmonary circulation and the bronchial circulation. Pulmonary circulation delivers blood to the lungs for reoxygenation and removal of carbon dioxide.
In comparison, the bronchial circulation is a component of the systemic circulation and transports oxygenated blood to the tissues of the lungs. It consists of both small bronchial arter­ies and veins that supply the walls of bronchi and bronchioles. The cells of the smallest respiratory structures (such as alveoli and alveolar ducts) exchange their respiratory gases directly with the inhaled air. Approximately three or four bronchial arteries branch from the anterior wall of the descending thoracic aorta (or its branches). Thereafter, bronchial arteries divide to form capillary beds supplying structures in the bronchial tree. Bronchial veins collect venous blood from these capillary beds. Some of this deoxygenated blood drains into pulmonary veins, where it mixes with the freshly oxy­genated blood. Consequently, blood exiting the lungs within the pulmo­nary veins, which will be returned to the left side of the heart and circulated throughout the body, is slightly less oxygenated than the blood immediately leaving the pulmonary capillaries following gas exchange.

Question 23

Identify and describe the pleural membranes and the function of serous fluid within the pleural
cavity

Answer 23

The two pleural membranes include both the visceral pleura, which covers the outer surface of the lungs, and the parietal pleura, which lines the inner surface of the thoracic wall. Between the two pleural membranes is a potential space called the pleural cavity. Two pressures associated with the lungs are the intrapulmonary pressure (the pressure within the lungs) and the intrapleural pressure (pressure within the pleural cavity).
An oily serous fluid is produced by the serous membranes and released into the pleural cavity. Serous fluid acts as a lubricant, ensuring that the pleural surfaces slide by each other with minimal friction during breathing. Each pleural cavity normally contains less than 15 mL of serous fluid and is drained continuously by lymph vessels within the visceral pleura.

Question 24

Compare and contrast minute ventilation and alveolar ventilation and explain the significance of
each

Answer 24

The term pulmonary ventilation may also refer to the amount of air that is inhaled in 1 minute.
The amount of air that reaches the alveoli and is available for gas exchange per minute is termed alveolar ventilation. This volume is less than pulmonary ventilation because the volume of air in the anatomic dead space must be subtracted from the volume of air inhaled with each breath.

Question 25

Describe the relationship between anatomic dead space and physiologic dead space

Answer 25

When air is moved from the atmosphere into the respi­ratory tract, a portion of it remains in the conducting zone. This collec­tive space, where there is no exchange of respiratory gases, is referred to as the anatomic dead space, and it has an average volume of approximately 150 mL. The amount of air that reaches the alveoli and is available for gas exchange per minute is termed alveolar ventilation. This volume is less than pulmonary ventilation because the volume of air in the anatomic dead space must be subtracted from the volume of air inhaled with each breath.

Some respiratory disorders result in a decreased number of alveoli participating in gas exchange. This decrease can be due either to damage to the alveoli or to a change in the respiratory membrane, such as when fluid accumulates in the lungs with pneumonia. The difference in volume of air available for gas exchange is accounted for by the more inclusive term physiologic dead space, which is the normal anatomic dead space plus any loss of alveoli. The anatomic dead space is equivalent to the physiologic dead space in a healthy individual, because the loss of alveoli should be minimal.

Question 26

Define the four different respiratory volumes and explain how the four respiratory capacities are
calculated from the volume measurements

Answer 26

Tidal volume (TV) is the amount of air inhaled or exhaled per breath during quiet breathing. Inspiratory reserve volume (IRV) is the amount of air that can be forcibly inhaled beyond the tidal volume (after a normal inspiration). IRV is a measure of lung compliance. Expiratory reserve volume (ERV) is the amount that can be forcibly exhaled beyond the tidal volume (after a normal expiration). ERV is a measure of lung and chest wall elasticity. Finally, residual volume (RV) is the amount of air left in the lungs even after the most forceful expiration.

Inspiratory capacity = TV + IRV
Total ability to inspire

Functional residual capacity = ERV + RV
Amount of air normally left (residual) in lungs after you expire quietly

Vital capacity = TV + IRV + ERV
Measure of the amount of air the lungs are capable of holding

Total lung capacity = TV + IRV + ERV + RV
Total amount of air that can be in lung

Question 27

Define forced expiratory volume (FEV) and its clinical significance

Answer 27

Forced expiratory volume (FEV) is the percentage of the vital capacity that can be expelled in a specific period of time. For example, FEV1 is the vital capacity percentage that is expired in 1 second. This value is obtained by inspiring as much air as possible and then expelling the air from the lungs as quickly as possible. A healthy person should be able to expel 75–85% of the vital capacity in 1 second. Individuals with decreased ability to expire (individuals with emphysema) typically exhibit decreased FEV values.

Question 28

List the organs that make up the gastrointestinal (GI) tract

Answer 28

The GI tract organs essentially form a continuous tube that includes the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestine, and large intestine. It ends at the anus.

Question 29

List the accessory digestive organs and structures involved in the digestive process

Answer 29

Accessory digestive glands produce secretions that empty into the lumen of the GI tract and include the salivary glands, liver, and pancreas. Other accessory digestive organs are not glands. They include the teeth and tongue, which participate in the chewing and swallowing of food, and the gallbladder, which concentrates and stores the secretions of the liver.

Question 30

List and describe the four tunics (layers) that make up the gastrointestinal wall

Answer 30

From inner-most (adjacent to the lumen) to outermost, the four general tunics are the mucosa, submucosa, muscularis, and adventitia or serosa.

Question 31

Mucosa

Answer 31

The mucosa is the inner-lining mucous membrane. It typically consists of an epithelium, an underlying layer called the lamina propria, and a thin layer of muscularis mucosae.
The epithelium is in contact with the contents within the lumen. It is a simple columnar epithelium for most of the GI tract (stomach, small intestine, large intestine). The portions of the GI tract that must withstand abrasion (such as the esophagus) are lined by a nonkeratinized, stratified squamous epithelium.
The underlying lamina propria consists of areolar connective tissue that contains small blood and lymph vessels and fine, small branches of nerves. Absorption occurs when substances are moved through the simple columnar epithelial cells that line the GI tract wall and are absorbed into blood or lymphatic capillaries located within the lamina propria.
The muscularis mucosae is the deepest layer of the mucosa and is composed of a thin layer of smooth muscle. Con- tractions of this smooth muscle layer cause slight movements in the mucosa to gently “shake things up,” which (1) facilitates the release of secretions from the mucosa into the lumen and (2) increases contact of materials in the lumen with the epithelial layer of the mucosa for more efficient absorption.

Question 32

Submucosa

Answer 32

The submucosa is composed of areolar and dense irregular connective tissue, the relative amounts of each vary depending upon the specific region of the GI tract. Many large blood vessels, lymph vessels, nerves, and glands are within the submucosa. Fine branches of the nerves extend into the mucosa and, along with their associated autonomic ganglia, are collectively referred to as the submucosal nerve plexus, or Meissner plexus. These nerves innervate both the smooth muscle and glands of the mucosa and submucosa.
The areolar connective tissue of both the lamina propria of the mucosa and the submucosa house mucosa-associated lymphatic tissue (MALT). In the small intestine (and especially in its last portion, the ileum), larger aggregates of lymphatic nodules in the submucosa are called Peyer patches. The presence of MALT protects us from potentially harmful agents by preventing ingested microbes from crossing the GI tract wall and entering the body

Question 33

Muscularis

Answer 33

The muscularis is located deep to the submucosa and is composed of smooth muscle. The smooth muscle cells are arranged in an inner circular layer, which contains muscle cells oriented circumferentially within the GI tract wall, and an outer longitudinal layer, which is composed of muscle cells oriented lengthwise within the GI tract wall. Fine branches of nerves and their associated autonomic ganglia are located between these two layers of smooth muscle; these nerve branches control contractions of the muscularis and are collectively referred to as the myenteric nerve plexus, or Auerbach plexus.
The function of the muscularis is motility. If you think of the GI tract as a hollow tube, then contractions of the circular layer constrict the lumen of the tube, whereas contractions of the longitudinal layer shorten the tube. The collective contractions of these smooth muscle layers are associated with two primary types of motility: mixing and propulsion.

Question 34

Adventitia or Serosa

Answer 34

The outermost tunic may be either an adventitia or a serosa. An adventitia is composed of areolar connective tissue with dispersed collagen and elastic fibers. A serosa adventitia, but it is completely covered by a serous membrane called the visceral peritoneum. Only GI structures that are intraperitoneal organs have a serosa as their outermost tunic.

Question 35

Explain the function of the mesentery and describe the five individual mesenteries of the
abdominopelvic cavity

Answer 35

The general term mesentery refers to the double layer of peritoneum that supports, suspends, and stabilizes the intraperitoneal GI tract organs. Blood vessels, lymph vessels, and nerves that supply the GI tract are sandwiched between the two folds. Several terms are used to identify the individual mesenteries associated with specific organs:
∙ The greater omentum extends inferiorly like an apron from the inferolateral surface of the stomach (greater curvature) and covers most of the abdominal organs. It often accumulates large amounts of adipose connective tissue; thus, it is referred to as the “fatty apron” and insulates the abdominal organs and stores fat.
∙ The lesser omentum connects the superomedial surface of the stomach (lesser curvature) and the proximal end of the duodenum to the liver.
∙ The falciform ligament is a flat, thin, crescent-shaped peritoneal fold that attaches the liver to the internal surface of the anterior abdominal wall.
∙ The mesentery proper, which is sometimes referred to as the mesentery, is a fan-shaped fold of peritoneum that suspends most of the small intestine (the jejunum and the ileum) from the internal surface of the posterior abdominal wall.
∙ The mesocolon is a fold of the peritoneum that attaches the large intestine to the posterior abdominal wall. The mesocolon has several distinct sections, each named for the portion of the colon it suspends. For example, transverse mesocolon is associated with the transverse colon, whereas sigmoid mesocolon is associated with the sigmoid colon.

Question 36

Identify and describe the anatomic structures of the oral cavity

Answer 36

The oral cavity has two distinct spatial regions: (1) the vestibule (or buccal cavity), which is the space between the gums, lips, and cheeks; and (2) the oral cavity proper, which lies central to the teeth. The oral cavity is bounded laterally by the cheeks and anteriorly by the teeth and lips, and it leads posteriorly into the oropharynx.

The cheeks terminate at the fleshy lips (or labia) that are formed primarily by the orbicularis oris muscle. Lips have a reddish hue because of their abundant supply of superficial blood vessels and the reduced amount of keratin within their outer skin. The internal surfaces of both the superior and inferior lips each are attached to the gingivae (gums) by a thin mucosa fold in the midline, called the labial frenulum.
The palate forms the superior boundary of the oral cavity and acts as a barrier to separate it from the nasal cavity. The anterior two-thirds of the palate is hard and bony (called the hard palate), whereas the posterior one-third is soft and muscular (called the soft palate). The hard palate is formed by fusion of the two palatine processes of the maxillae and the horizontal plates of the two palatine bones. Failure of these bones to fuse results in a cleft palate, which is associated with swallowing issues. Prominent transverse palatine folds, or friction ridges, on the anterior hard palate assist the tongue in manipulating ingested materials prior to swallowing. Extending inferiorly from the posterior part of the soft palate is a cone-shaped medial projection called the uvula. When you swallow, the soft palate and the uvula elevate to close off the posterior entrance into the nasopharynx and prevent ingested materials from entering the nasal region.
The fauces represent the opening between the oral cavity and the oropharynx. The fauces are bounded by paired muscular folds or arches: the anterior palatoglossal arch. The name of each of these folds reflects its proximity to the tongue and pharynx, respectively. The palatine tonsils are housed between the arches.
The inferior surface, or floor, of the oral cavity houses the tongue. The tongue is formed primarily from skeletal muscle. Both extrinsic and intrinsic muscles move the tongue. Numerous small projections called papillae cover the superior (dorsal) surface of the tongue and are involved in the sense of taste. The posteroinferior region of the tongue also contains clusters of lymphatic tissue called the lingual tonsils. The inferior surface of the tongue attaches to the floor of the oral cavity by a thin vertical mucous membrane, the lingual frenulum. The tongue manipulates and mixes ingested materials during chewing and helps compress the partially digested materials against the palate to assist in mechanical digestion.

The epithelial lining of the oral cavity is a stratified squamous epithelium that protects against the abrasive activities associated with chewing. The nonkeratinized type of epithelium lines most of the oral cavity; the keratinized type lines the lips, portions of the tongue, and a small region of the hard palate.

Question 37

Describe the location of three pairs of salivary glands

Answer 37

Intrinsic salivary glands are unicellular glands that continuously release relatively small amounts of secretions independent of the presence of food.

Most saliva, however, is produced from multicellular exocrine glands outside the oral cavity called extrinsic salivary glands.

The parotid salivary glands are the largest salivary glands. Each parotid gland is located anterior and inferior to the ear, partially overlying the masseter muscle.

The submandibular salivary glands are both inferior to the floor of the oral cavity and medial to the body of the mandible.

The sublingual salivary glands are inferior to the tongue, and medial and anterior to the submandibular salivary glands.

Question 38

Define mastication

Answer 38

Mechanical digestion in the oral cavity is called mastication or chewing. It requires the coordinated activities of teeth, skeletal muscles in lips, tongue, cheeks, and jaws that are controlled by nuclei within the medulla oblongata and pons, collectively called the mastication center.

Answer 39

It has both a larger, convex inferolateral surface called the greater curvature and a smaller, concave superomedial surface called the lesser curvature. This organ is composed of four regions:
∙ The cardia is a small, narrow, superior entryway into the stomach lumen from the esophagus. The internal opening where the cardia meets the esophagus is called the cardiac orifice, which is the location of the inferior esophageal sphincter.
∙ The fundus is the dome-shaped region lateral and superior to the esophageal connection with the stomach. Its superior surface contacts the inferior surface of the thoracic diaphragm. The fundus has both weaker muscular contractions and a higher pH in its lumen area than other regions of the stomach.
∙ The body is the largest region of the stomach; it is inferior to the cardiac orifice and the fundus and extends to the pylorus.
∙ The pylorus is the narrow, funnel-shaped terminal region of the stomach. Its opening into the duodenum of the small intestine is called the pyloric orifice. Surrounding this pyloric orifice is a thick ring of circular smooth muscle called the pyloric sphincter. The pyloric sphincter regulates the movement of material from the stomach into the small intestine.
The internal stomach lining is composed of numerous gastric folds, or rugae.

The mucosa of the stomach has three significant features:
∙ It is lined by a simple columnar epithelium supported by lamina propria. The transition from stratified squamous in the esophagus to simple columnar epithelium in the stomach is abrupt. The simple columnar epithelial cells are replaced often (usually within a week) because of the harsh acidic environment of the stomach contents.
∙ The lining is indented by numerous depressions called gastric pits.
∙ Several gastric glands extend deep into the mucosa from the
base of each gastric pit. The muscularis mucosae partially surrounds the gastric glands and helps expel gastric gland secretions when it contracts.
The muscularis of the stomach varies from the general GI tract pattern in that it is composed of three smooth muscle layers instead of two: an inner oblique layer, a middle circular layer, and an outer longitudinal layer. The presence of a third (oblique) layer of smooth muscle assists the continued churning and blending of the swallowed bolus to help mechanically digest the food. The muscularis becomes increasingly thicker (and stronger) as it progresses from the body to the pylorus.

Question 40

Describe the histology of the small intestine & the glands found in the small intestine and their secretions

Answer 40

A villus is a small, fingerlike projection of the simple columnar epithelium and lamina propria of the mucosa. They increase the surface area of the epithelial lining through which nutrients are absorbed. The epithelium and lamina propria of each villus appears analogous to a glove (epithelium) covering a finger (lamina propria). Each villus contains an arteriole, a rich blood capillary network, and a venule. Most nutrients are absorbed into these blood capillaries. A lacteal is a type of lymphatic capillary also within the villus. A lacteal is responsible for absorbing lipids and lipid-soluble vitamins that are too large to be absorbed by the blood capillaries.
Microvilli are microscopic extensions of the plasma membrane of the simple columnar epithelial cells lining the small intestine. Microvilli further increase the surface area of the small intestine. Embedded within this brush border are various enzymes that complete the chemical digestion of most nutrients immediately before absorption called brush border enzymes.

Three of these cell types produce intestinal juice. The fourth type of cell secretes hormones into the blood.
∙ Goblet cells produce mucin that when hydrated form mucus, which lubricates and protects the intestinal lining. These cells increase in number from the duodenum to the ileum, because more lubrication is needed as digested materials (and water)
are absorbed and undigested materials (and less water) remain in the lumen.
∙ Unicellular gland cells synthesize enteropeptidase.
∙ The enteroendocrine cells release hormones such as CCK and secretin into the blood. We have already discussed the stomach associated functions of these hormones.
Another type of gland housed within the submucosal layer and found only in the proximal duodenum is called a duodenal submucosal gland (or Brunner gland). This gland produces a viscous, alkaline mucus secretion that protects the duodenum from the acidic chyme entering the duodenum from the stomach.

Question 41

List the accessory digestive organs associated with releasing secretions into the duodenum and describe the ducts that deliver these secretions

Answer 41

These ducts include the biliary apparatus from the liver and gallbladder, and the pancreatic ducts from the pancreas.
1. Right and left hepatic ducts merge to form a common hepatic duct.
2. Common hepatic and cystic ducts merge to form a common bile duct.
3. Main pancreatic duct merges with common bile duct at the hepatopancreatic ampulla, which extends into the duodenum.
4. Bile and pancreatic juices enter duodenum at the major duodenal papilla.

Question 42

Describe the histology of liver

Answer 42

The liver’s connective tissue capsule branches throughout the organ and forms septa that partition the liver into thousands of microscopic polyhedral hepatic lobules, which are the structural and functional units of the liver. Within hepatic lobules are liver cells called hepatocytes. At the periphery of each lobule are several portal triads, composed of a bile ductule, and microscopic branches of both the hepatic portal vein and the hepatic artery. At the center of each lobule is a central vein that drains the blood flow from the lobule. Central veins collect the blood and merge throughout the liver to form numerous hepatic veins that eventually empty into the inferior vena cava.

In cross section, a hepatic lobule looks like a side view of a bicycle wheel. The central vein is like the hub of the wheel. At the circumference of the wheel (where the tire would be) are the portal triads that are usually equidistant apart. Cords of hepatocytes make up the numerous spokes of the wheel, and they are bordered by hepatic sinusoids, which transport blood

Question 43

How does blood flow through the liver

Answer 43

The hepatic artery is a branch of the celiac trunk that extends off of the descending abdominal aorta and transports oxygenated blood to the liver. The hepatic portal vein is part of the hepatic portal system and transports deoxygenated and nutrient-rich blood from the capillary beds of the GI tract, spleen, and pancreas. The hepatic portal vein delivers approximately 75% of the blood volume to the liver (the hepatic artery brings the other 25%). The oxygenated blood from the hepatic artery branch (within the portal triad) and the deoxygenated blood of the hepatic portal vein branch (within the portal triad) both enter a sinusoid where the blood is “processed.”

Blood then drains into the central vein of the lobule. Central veins collect the blood from each lobule and merge throughout the liver to ultimately form several hepatic veins that empty into the inferior vena cava.

Question 44

How does bile flow through the liver

Answer 44

Bile is released from hepatocytes into bile canaliculi. These small channels transport bile to bile ductules of portal triads. (Observe that bile flow, which is away from the central vein to the portal triad, is in the opposite direction of blood flow, which moves from the portal triad to the central vein.) Bile within the bile ductules flows into progressively larger bile ducts until reaching either the right or left hepatic duct. The accessory digestive organ ducts transport the bile to the duodenum.

Question 45

Identify and describe the three major regions of the large intestine and four segments of the colon
of the large intestine

Answer 45

The cecum is a blind sac. It is the first portion of the large intestine and located in the right lower abdominal quadrant. This pouch extends inferiorly from the ileocecal valve. Chyme enters the cecum from the ileum. Projecting inferiorly from the posteromedial region of the cecum is the vermiform appendix, a thin, fingerlike sac lined by lymphocyte-filled lymphatic nodules. Both the cecum and the vermiform appendix are intraperitoneal organs. Research studies suggest that the appendix may harbor bacteria that are beneficial to the function of the colon.

At the level of the ileocecal valve, the second region of the large intestine, the colon, begins and forms an inverted U-shaped arch. The colon is partitioned into four segments: the ascending colon, transverse colon, descending colon, and sigmoid colon.

The ascending colon originates at the ileocecal valve and extends superiorly from the superior edge of the cecum along the right lateral border of the abdominal cavity. The ascending colon is retroperitoneal, since its posterior wall directly adheres to the posterior abdominal wall, and only its anterior surface is covered with peritoneum. This bend in the colon is called the right colic flexure, or the hepatic flexure.

The transverse colon originates at the right colic flexure and curves slightly anteriorly as it projects horizontally to the left across the anterior region of the abdominal cavity. The transverse colon is intraperitoneal. As the transverse colon approaches the spleen in the left upper quadrant of the abdomen, it makes a 90-degree turn inferiorly and posteriorly. The resulting bend in the colon is called the left colic flexure, or the splenic flexure.

The descending colon is retroperitoneal and located along the left side of the abdominal cavity and slightly posterior. It originates at the left colic flexure and descends vertically to the sigmoid colon.

The sigmoid colon originates at the sigmoid flexure and turns inferomedially into the pelvic cavity.
The sigmoid colon, like the transverse colon, is intraperitoneal. The sigmoid colon terminates at the rectum. The mesocolon, attaches each section of the colon to the posterior abdominal wall, with the mesocolon of each region specifically named (e.g., ascending mesocolon, transverse mesocolon).