Module 13: The Respiratory System

Lesson 4: Respiratory Physiology: Gas Exchange

Sinh Lý Hệ Hô Hấp: Trao Đổi Khí

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Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module The Respiratory System.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Respiratory System

acclimatization
process of adjustment that the respiratory system makes due to chronic exposure to high altitudes
acute mountain sickness (AMS)
condition that occurs a result of acute exposure to high altitude due to a low partial pressure of oxygen
ala
(plural = alae) small, flaring structure of a nostril that forms the lateral side of the nares
alar cartilage
cartilage that supports the apex of the nose and helps shape the nares; it is connected to the septal cartilage and connective tissue of the alae
alveolar dead space
air space within alveoli that are unable to participate in gas exchange
alveolar duct
small tube that leads from the terminal bronchiole to the respiratory bronchiole and is the point of attachment for alveoli
alveolar macrophage
immune system cell of the alveolus that removes debris and pathogens
alveolar pore
opening that allows airflow between neighboring alveoli
alveolar sac
cluster of alveoli
alveolus
small, grape-like sac that performs gas exchange in the lungs
anatomical dead space
air space present in the airway that never reaches the alveoli and therefore never participates in gas exchange
apex
tip of the external nose
apneustic center
network of neurons within the pons that stimulate the neurons in the dorsal respiratory group; controls the depth of inspiration
atmospheric pressure
amount of force that is exerted by gases in the air surrounding any given surface
Bohr effect
relationship between blood pH and oxygen dissociation from hemoglobin
Boyle’s law
relationship between volume and pressure as described by the formula: P1V1 = P2V2
bridge
portion of the external nose that lies in the area of the nasal bones
bronchial bud
structure in the developing embryo that forms when the laryngotracheal bud extends and branches to form two bulbous structures
bronchial tree
collective name for the multiple branches of the bronchi and bronchioles of the respiratory system
bronchiole
branch of bronchi that are 1 mm or less in diameter and terminate at alveolar sacs
bronchoconstriction
decrease in the size of the bronchiole due to relaxation of the muscular wall
bronchodilation
increase in the size of the bronchiole due to contraction of the muscular wall
bronchus
tube connected to the trachea that branches into many subsidiaries and provides a passageway for air to enter and leave the lungs
carbaminohemoglobin
bound form of hemoglobin and carbon dioxide
carbonic anhydrase (CA)
enzyme that catalyzes the reaction that causes carbon dioxide and water to form carbonic acid
cardiac notch
indentation on the surface of the left lung that allows space for the heart
central chemoreceptor
one of the specialized receptors that are located in the brain that sense changes in hydrogen ion, oxygen, or carbon dioxide concentrations in the brain
chloride shift
facilitated diffusion that exchanges bicarbonate (HCO3–) with chloride (Cl–) ions
conducting zone
region of the respiratory system that includes the organs and structures that provide passageways for air and are not directly involved in gas exchange
cricoid cartilage
portion of the larynx composed of a ring of cartilage with a wide posterior region and a thinner anterior region; attached to the esophagus
Dalton’s law
statement of the principle that a specific gas type in a mixture exerts its own pressure, as if that specific gas type was not part of a mixture of gases
dorsal respiratory group (DRG)
region of the medulla oblongata that stimulates the contraction of the diaphragm and intercostal muscles to induce inspiration
dorsum nasi
intermediate portion of the external nose that connects the bridge to the apex and is supported by the nasal bone
epiglottis
leaf-shaped piece of elastic cartilage that is a portion of the larynx that swings to close the trachea during swallowing
expiration
(also, exhalation) process that causes the air to leave the lungs
expiratory reserve volume (ERV)
amount of air that can be forcefully exhaled after a normal tidal exhalation
external nose
region of the nose that is easily visible to others
external respiration
gas exchange that occurs in the alveoli
fauces
portion of the posterior oral cavity that connects the oral cavity to the oropharynx
fibroelastic membrane
specialized membrane that connects the ends of the C-shape cartilage in the trachea; contains smooth muscle fibers
forced breathing
(also, hyperpnea) mode of breathing that occurs during exercise or by active thought that requires muscle contraction for both inspiration and expiration
foregut
endoderm of the embryo towards the head region
functional residual capacity (FRC)
sum of ERV and RV, which is the amount of air that remains in the lungs after a tidal expiration
glottis
opening between the vocal folds through which air passes when producing speech
Haldane effect
relationship between the partial pressure of oxygen and the affinity of hemoglobin for carbon dioxide
Henry’s law
statement of the principle that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas
hilum
concave structure on the mediastinal surface of the lungs where blood vessels, lymphatic vessels, nerves, and a bronchus enter the lung
hyperpnea
increased rate and depth of ventilation due to an increase in oxygen demand that does not significantly alter blood oxygen or carbon dioxide levels
hyperventilation
increased ventilation rate that leads to abnormally low blood carbon dioxide levels and high (alkaline) blood pH
inspiration
(also, inhalation) process that causes air to enter the lungs
inspiratory capacity (IC)
sum of the TV and IRV, which is the amount of air that can maximally be inhaled past a tidal expiration
inspiratory reserve volume (IRV)
amount of air that enters the lungs due to deep inhalation past the tidal volume
internal respiration
gas exchange that occurs at the level of body tissues
intra-alveolar pressure
(intrapulmonary pressure) pressure of the air within the alveoli
intrapleural pressure
pressure of the air within the pleural cavity
laryngeal prominence
region where the two lamine of the thyroid cartilage join, forming a protrusion known as “Adam’s apple”
laryngopharynx
portion of the pharynx bordered by the oropharynx superiorly and esophagus and trachea inferiorly; serves as a route for both air and food
laryngotracheal
bud forms from the lung bud, has a tracheal end and bulbous bronchial buds at the distal end
larynx
cartilaginous structure that produces the voice, prevents food and beverages from entering the trachea, and regulates the volume of air that enters and leaves the lungs
lingual tonsil
lymphoid tissue located at the base of the tongue
lung
organ of the respiratory system that performs gas exchange
lung bud
median dome that forms from the endoderm of the foregut
meatus
one of three recesses (superior, middle, and inferior) in the nasal cavity attached to the conchae that increase the surface area of the nasal cavity
naris
(plural = nares) opening of the nostrils
nasal bone
bone of the skull that lies under the root and bridge of the nose and is connected to the frontal and maxillary bones
nasal septum
wall composed of bone and cartilage that separates the left and right nasal cavities
nasopharynx
portion of the pharynx flanked by the conchae and oropharynx that serves as an airway
olfactory pit
invaginated ectodermal tissue in the anterior portion of the head region of an embryo that will form the nasal cavity
oropharynx
portion of the pharynx flanked by the nasopharynx, oral cavity, and laryngopharynx that is a passageway for both air and food
oxygen–hemoglobin dissociation curve
graph that describes the relationship of partial pressure to the binding and disassociation of oxygen to and from heme
oxyhemoglobin
(Hb–O2) bound form of hemoglobin and oxygen
palatine tonsil
one of the paired structures composed of lymphoid tissue located anterior to the uvula at the roof of isthmus of the fauces
paranasal sinus
one of the cavities within the skull that is connected to the conchae that serve to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consists of frontal, maxillary, sphenoidal, and ethmoidal sinuses
parietal pleura
outermost layer of the pleura that connects to the thoracic wall, mediastinum, and diaphragm
partial pressure
force exerted by each gas in a mixture of gases
peripheral chemoreceptor
one of the specialized receptors located in the aortic arch and carotid arteries that sense changes in pH, carbon dioxide, or oxygen blood levels
pharyngeal tonsil
structure composed of lymphoid tissue located in the nasopharynx
pharynx
region of the conducting zone that forms a tube of skeletal muscle lined with respiratory epithelium; located between the nasal conchae and the esophagus and trachea
philtrum
concave surface of the face that connects the apex of the nose to the top lip
pleural cavity
space between the visceral and parietal pleurae
pleural fluid
substance that acts as a lubricant for the visceral and parietal layers of the pleura during the movement of breathing
pneumotaxic center
network of neurons within the pons that inhibit the activity of the neurons in the dorsal respiratory group; controls rate of breathing
pulmonary artery
artery that arises from the pulmonary trunk and carries deoxygenated, arterial blood to the alveoli
pulmonary plexus
network of autonomic nervous system fibers found near the hilum of the lung
pulmonary surfactant
substance composed of phospholipids and proteins that reduces the surface tension of the alveoli; made by type II alveolar cells
pulmonary ventilation
exchange of gases between the lungs and the atmosphere; breathing
quiet breathing
(also, eupnea) mode of breathing that occurs at rest and does not require the cognitive thought of the individual
residual volume (RV)
amount of air that remains in the lungs after maximum exhalation
respiratory bronchiole
specific type of bronchiole that leads to alveolar sacs
respiratory cycle
one sequence of inspiration and expiration
respiratory epithelium
ciliated lining of much of the conducting zone that is specialized to remove debris and pathogens, and produce mucus
respiratory membrane
alveolar and capillary wall together, which form an air-blood barrier that facilitates the simple diffusion of gases
respiratory rate
total number of breaths taken each minute
respiratory volume
varying amounts of air within the lung at a given time
respiratory zone
includes structures of the respiratory system that are directly involved in gas exchange
root
region of the external nose between the eyebrows
thoracic wall compliance
ability of the thoracic wall to stretch while under pressure
thyroid cartilage
largest piece of cartilage that makes up the larynx and consists of two lamine
tidal volume (TV)
amount of air that normally enters the lungs during quiet breathing
total dead space
sum of the anatomical dead space and alveolar dead space
total lung capacity (TLC)
total amount of air that can be held in the lungs; sum of TV, ERV, IRV, and RV
total pressure
sum of all the partial pressures of a gaseous mixture
trachea
tube composed of cartilaginous rings and supporting tissue that connects the lung bronchi and the larynx; provides a route for air to enter and exit the lung
trachealis muscle
smooth muscle located in the fibroelastic membrane of the trachea
transpulmonary pressure
pressure difference between the intrapleural and intra-alveolar pressures
true vocal cord
one of the pair of folded, white membranes that have a free inner edge that oscillates as air passes through to produce sound
type I alveolar cell
squamous epithelial cells that are the major cell type in the alveolar wall; highly permeable to gases
type II alveolar cell
cuboidal epithelial cells that are the minor cell type in the alveolar wall; secrete pulmonary surfactant
ventilation
movement of air into and out of the lungs; consists of inspiration and expiration
ventral respiratory group (VRG)
region of the medulla oblongata that stimulates the contraction of the accessory muscles involved in respiration to induce forced inspiration and expiration
vestibular fold
part of the folded region of the glottis composed of mucous membrane; supports the epiglottis during swallowing
visceral pleura
innermost layer of the pleura that is superficial to the lungs and extends into the lung fissures
vital capacity (VC)
sum of TV, ERV, and IRV, which is all the volumes that participate in gas exchange
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
The purpose of the respiratory system is to perform gas exchange. Pulmonary ventilation provides air to the alveoli for this gas exchange process. At the respiratory membrane, where the alveolar and capillary walls meet, gases move across the membranes, with oxygen entering the bloodstream and carbon dioxide exiting. It is through this mechanism that blood is oxygenated and carbon dioxide, the waste product of cellular respiration, is removed from the body.
In order to understand the mechanisms of gas exchange in the lung, it is important to understand the underlying principles of gases and their behavior. In addition to Boyle’s law, several other gas laws help to describe the behavior of gases.

A. Gas Laws and Air Composition

Gas molecules exert force on the surfaces with which they are in contact; this force is called pressure. In natural systems, gases are normally present as a mixture of different types of molecules. For example, the atmosphere consists of oxygen, nitrogen, carbon dioxide, and other gaseous molecules, and this gaseous mixture exerts a certain pressure referred to as atmospheric pressure (Table 1). Partial pressure (Px) is the pressure of a single type of gas in a mixture of gases. For example, in the atmosphere, oxygen exerts a partial pressure, and nitrogen exerts another partial pressure, independent of the partial pressure of oxygen (Figure 1). Total pressure is the sum of all the partial pressures of a gaseous mixture. Dalton’s law describes the behavior of nonreactive gases in a gaseous mixture and states that a specific gas type in a mixture exerts its own pressure; thus, the total pressure exerted by a mixture of gases is the sum of the partial pressures of the gases in the mixture.

Partial pressure is extremely important in predicting the movement of gases. Recall that gases tend to equalize their pressure in two regions that are connected. A gas will move from an area where its partial pressure is higher to an area where its partial pressure is lower. In addition, the greater the partial pressure difference between the two areas, the more rapid is the movement of gases.

B. Solubility of Gases in Liquids

Henry’s law describes the behavior of gases when they come into contact with a liquid, such as blood. Henry’s law states that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas. The greater the partial pressure of the gas, the greater the number of gas molecules that will dissolve in the liquid. The concentration of the gas in a liquid is also dependent on the solubility of the gas in the liquid. For example, although nitrogen is present in the atmosphere, very little nitrogen dissolves into the blood, because the solubility of nitrogen in blood is very low. The exception to this occurs in scuba divers; the composition of the compressed air that divers breathe causes nitrogen to have a higher partial pressure than normal, causing it to dissolve in the blood in greater amounts than normal. Too much nitrogen in the bloodstream results in a serious condition that can be fatal if not corrected. Gas molecules establish an equilibrium between those molecules dissolved in liquid and those in air.

The composition of air in the atmosphere and in the alveoli differs. In both cases, the relative concentration of gases is nitrogen > oxygen > water vapor > carbon dioxide. The amount of water vapor present in alveolar air is greater than that in atmospheric air (Table 2). Recall that the respiratory system works to humidify incoming air, thereby causing the air present in the alveoli to have a greater amount of water vapor than atmospheric air. In addition, alveolar air contains a greater amount of carbon dioxide and less oxygen than atmospheric air. This is no surprise, as gas exchange removes oxygen from and adds carbon dioxide to alveolar air. Both deep and forced breathing cause the alveolar air composition to be changed more rapidly than during quiet breathing. As a result, the partial pressures of oxygen and carbon dioxide change, affecting the diffusion process that moves these materials across the membrane. This will cause oxygen to enter and carbon dioxide to leave the blood more quickly.

C. Ventilation and Perfusion

Two important aspects of gas exchange in the lung are ventilation and perfusion. Ventilation is the movement of air into and out of the lungs, and perfusion is the flow of blood in the pulmonary capillaries. For gas exchange to be efficient, the volumes involved in ventilation and perfusion should be compatible. However, factors such as regional gravity effects on blood, blocked alveolar ducts, or disease can cause ventilation and perfusion to be imbalanced.

The partial pressure of oxygen in alveolar air is about 104 mm Hg, whereas the partial pressure of oxygenated blood in pulmonary veins is about 100 mm Hg. When ventilation is sufficient, oxygen enters the alveoli at a high rate, and the partial pressure of oxygen in the alveoli remains high. In contrast, when ventilation is insufficient, the partial pressure of oxygen in the alveoli drops. Without the large difference in partial pressure between the alveoli and the blood, oxygen does not diffuse efficiently across the respiratory membrane. The body has mechanisms that counteract this problem. In cases when ventilation is not sufficient for an alveolus, the body redirects blood flow to alveoli that are receiving sufficient ventilation. This is achieved by constricting the pulmonary arterioles that serves the dysfunctional alveolus, which redirects blood to other alveoli that have sufficient ventilation. At the same time, the pulmonary arterioles that serve alveoli receiving sufficient ventilation vasodilate, which brings in greater blood flow. Factors such as carbon dioxide, oxygen, and pH levels can all serve as stimuli for adjusting blood flow in the capillary networks associated with the alveoli.

Ventilation is regulated by the diameter of the airways, whereas perfusion is regulated by the diameter of the blood vessels. The diameter of the bronchioles is sensitive to the partial pressure of carbon dioxide in the alveoli. A greater partial pressure of carbon dioxide in the alveoli causes the bronchioles to increase their diameter, as does a decreased level of oxygen in the blood supply, allowing carbon dioxide to be exhaled from the body at a greater rate. As mentioned above, a greater partial pressure of oxygen in the alveoli causes the pulmonary arterioles to dilate, increasing blood flow.
Gas exchange occurs at two sites in the body: in the lungs, where oxygen is picked up and carbon dioxide is released at the respiratory membrane, and at the tissues, where oxygen is released and carbon dioxide is picked up. External respiration is the exchange of gases with the external environment, and occurs in the alveoli of the lungs. Internal respiration is the exchange of gases with the internal environment, and occurs in the tissues. The actual exchange of gases occurs due to simple diffusion. Energy is not required to move oxygen or carbon dioxide across membranes. Instead, these gases follow pressure gradients that allow them to diffuse. The anatomy of the lung maximizes the diffusion of gases: The respiratory membrane is highly permeable to gases; the respiratory and blood capillary membranes are very thin; and there is a large surface area throughout the lungs.

A. External Respiration

The pulmonary artery carries deoxygenated blood into the lungs from the heart, where it branches and eventually becomes the capillary network composed of pulmonary capillaries. These pulmonary capillaries create the respiratory membrane with the alveoli (Figure 2). As the blood is pumped through this capillary network, gas exchange occurs. Although a small amount of the oxygen is able to dissolve directly into plasma from the alveoli, most of the oxygen is picked up by erythrocytes (red blood cells) and binds to a protein called hemoglobin, a process described later in this chapter. Oxygenated hemoglobin is red, causing the overall appearance of bright red oxygenated blood, which returns to the heart through the pulmonary veins. Carbon dioxide is released in the opposite direction of oxygen, from the blood to the alveoli. Some of the carbon dioxide is returned on hemoglobin, but can also be dissolved in plasma or is present as a converted form.

External respiration occurs as a function of partial pressure differences in oxygen and carbon dioxide between the alveoli and the blood in the pulmonary capillaries.

Although the solubility of oxygen in blood is not high, there is a drastic difference in the partial pressure of oxygen in the alveoli versus in the blood of the pulmonary capillaries. This difference is about 64 mm Hg: The partial pressure of oxygen in the alveoli is about 104 mm Hg, whereas its partial pressure in the blood of the capillary is about 40 mm Hg. This large difference in partial pressure creates a very strong pressure gradient that causes oxygen to rapidly cross the respiratory membrane from the alveoli into the blood.

The partial pressure of carbon dioxide is also different between the alveolar air and the blood of the capillary. However, the partial pressure difference is less than that of oxygen, about 5 mm Hg. The partial pressure of carbon dioxide in the blood of the capillary is about 45 mm Hg, whereas its partial pressure in the alveoli is about 40 mm Hg. However, the solubility of carbon dioxide is much greater than that of oxygen—by a factor of about 20—in both blood and alveolar fluids. As a result, the relative concentrations of oxygen and carbon dioxide that diffuse across the respiratory membrane are similar.

B. Internal Respiration

Internal respiration is gas exchange that occurs at the level of body tissues (Figure 3). Similar to external respiration, internal respiration also occurs as simple diffusion due to a partial pressure gradient. However, the partial pressure gradients are opposite of those present at the respiratory membrane. The partial pressure of oxygen in tissues is low, about 40 mm Hg, because oxygen is continuously used for cellular respiration. In contrast, the partial pressure of oxygen in the blood is about 100 mm Hg. This creates a pressure gradient that causes oxygen to dissociate from hemoglobin, diffuse out of the blood, cross the interstitial space, and enter the tissue. Hemoglobin that has little oxygen bound to it loses much of its brightness, so that blood returning to the heart is more burgundy in color.

Considering that cellular respiration continuously produces carbon dioxide, the partial pressure of carbon dioxide is lower in the blood than it is in the tissue, causing carbon dioxide to diffuse out of the tissue, cross the interstitial fluid, and enter the blood. It is then carried back to the lungs either bound to hemoglobin, dissolved in plasma, or in a converted form. By the time blood returns to the heart, the partial pressure of oxygen has returned to about 40 mm Hg, and the partial pressure of carbon dioxide has returned to about 45 mm Hg. The blood is then pumped back to the lungs to be oxygenated once again during external respiration.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

GasPercent of total compositionPartial pressure
(mm Hg)
Nitrogen (N2)78.6597.4
Oxygen (O2)20.9158.8
Water (H2O)0.43.0
Carbon dioxide (CO2)0.040.3
Others0.060.5
Total composition/total atmospheric pressure100%760.0

Partial pressure is the force exerted by a gas. The sum of the partial pressures of all the gases in a mixture equals the total pressure.

GasPercent of total compositionPartial pressure
(mm Hg)
Nitrogen (N2)74.9569
Oxygen (O2)13.7104
Water (H2O)6.240
Carbon dioxide (CO2)5.247
Total composition/total alveolar pressure100%760.0

In external respiration, oxygen diffuses across the respiratory membrane from the alveolus to the capillary, whereas carbon dioxide diffuses out of the capillary into the alveolus.

Oxygen diffuses out of the capillary and into cells, whereas carbon dioxide diffuses out of cells and into the capillary.

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Script:
  1. The behavior of gases can be explained by the principles of Dalton’s law and Henry’s law, both of which describe aspects of gas exchange.
  2. Dalton’s law states that each specific gas in a mixture of gases exerts force independently of the other gases in the mixture.
  3. This force is also called partial pressure.
  4. Henry’s law states that the amount of a specific gas that dissolves in a liquid is a function of its partial pressure.
  5. The greater the partial pressure of a gas, the more of that gas will dissolve in a liquid, as the gas moves toward equilibrium.
  6. Gas molecules move down a pressure gradient.
  7. In other words, gas moves from a region of high pressure to a region of low pressure.
  8. External respiration refers to gas exchange that occurs in the alveoli, whereas internal respiration refers to gas exchange that occurs in the tissue.
  9. Both involves the exchange of gases through simple diffusion driven by partial pressure gradients opposite to those at the respiratory membrane.
  10. In terms of external respiration, the partial pressure of oxygen is high in the alveoli and low in the blood of the pulmonary capillaries.
  11. As a result, oxygen diffuses across the respiratory membrane from the alveoli into the blood.
  12. In contrast, the partial pressure of carbon dioxide is high in the pulmonary capillaries and low in the alveoli.
  13. Therefore, carbon dioxide diffuses across the respiratory membrane from the blood into the alveoli.
  14. The amount of oxygen and carbon dioxide that diffuses across the respiratory membrane is similar.
  15. On the other hand, in internal respiration, the oxygen is utilized for cellular respiration.
  16. For that reason, its partial pressure in tissues is low, about 40 mm Hg.
  17. This prompts the oxygen release from hemoglobin, diffusion into tissues, and subsequent use.
  18. Conversely, the partial pressure of carbon dioxide is higher in tissues, leading to its diffusion into the bloodstream for transport back to the lungs.
  19. Upon returning to the heart, oxygen and carbon dioxide levels normalize, preparing the blood for reoxygenation during external respiration.
  20. Ventilation is the process that moves air into and out of the alveoli, and perfusion affects the flow of blood in the capillaries.
  21. Both are important in gas exchange, as ventilation must be sufficient to create a high partial pressure of oxygen in the alveoli.
  22. If ventilation is insufficient and the partial pressure of oxygen drops in the alveolar air, the capillary is constricted and blood flow is redirected to alveoli with sufficient ventilation.
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