Respiratory System - MCAT Biological and Biochemical Foundations of Living Systems
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The carbonic anhydrase reaction is shown below.
Which of the following outcomes seems the most reasonable for someone who has an increase in blood CO2 levels during exercise?
The carbonic anhydrase reaction is shown below.
Which of the following outcomes seems the most reasonable for someone who has an increase in blood CO2 levels during exercise?
The individual's blood pH level will decrease (become more acidic). The increase in CO2 will cause the carbonic anhydrase reaction to shift to the right, increasing the concentration of protons (H+) in the blood. The individual can raise their pH level back to normal by breathing out all of the excess CO2. This accounts, in part, for increased respiration rates during exercise (along with the increased demand for oxygen).
The individual's blood pH level will decrease (become more acidic). The increase in CO2 will cause the carbonic anhydrase reaction to shift to the right, increasing the concentration of protons (H+) in the blood. The individual can raise their pH level back to normal by breathing out all of the excess CO2. This accounts, in part, for increased respiration rates during exercise (along with the increased demand for oxygen).
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Whales are active at great, underwater depths for extended periods of time. Which of the following would LEAST contribute to such an ability?
Whales are active at great, underwater depths for extended periods of time. Which of the following would LEAST contribute to such an ability?
When whales dive to great depths, they are unable to replenish oxygen from the water's surface. Several adaptive characteristics allow for the whales to maintain adequate oxygen supply to their tissues: large lung capacity (to absorb a greater amount of oxygen when breathing), selective arterial constriction (to restrict blood flow to non-essential tissues and thus prevent inefficient oxygen consumption), high cellular tolerance for carbon dioxide (CO₂ will build up over time without gas exchange), and large muscle myoglobin concentrations (to replenish oxygen supply to muscles as necessary).
A high basal metabolic rate, however, would increase the demand for oxygen and thus would not be an adaptive characteristic for whales in order to maintain themselves at great, watery depths without an external supply of oxygen.
When whales dive to great depths, they are unable to replenish oxygen from the water's surface. Several adaptive characteristics allow for the whales to maintain adequate oxygen supply to their tissues: large lung capacity (to absorb a greater amount of oxygen when breathing), selective arterial constriction (to restrict blood flow to non-essential tissues and thus prevent inefficient oxygen consumption), high cellular tolerance for carbon dioxide (CO₂ will build up over time without gas exchange), and large muscle myoglobin concentrations (to replenish oxygen supply to muscles as necessary).
A high basal metabolic rate, however, would increase the demand for oxygen and thus would not be an adaptive characteristic for whales in order to maintain themselves at great, watery depths without an external supply of oxygen.
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Which of the following is a physiological consequence of breathing air with a slightly increased partial pressure of carbon dioxide?
Which of the following is a physiological consequence of breathing air with a slightly increased partial pressure of carbon dioxide?
Slightly increased levels, or partial pressures, of carbon dioxide (CO2) would signal for an increase in breathing rate. As CO2 levels in the blood rise due to the breathing of such air as described in the passage, a breathing mechanism in the brain is triggered to increase ventilation (hyperventilation) to remove as much CO2 through the lungs as possible. A decrease in breathing rate would build up CO2 to even higher levels, causing respiratory acidosis. There would be no changes to blood pressure because slight increases of CO2 has no significant effect on this property.
Slightly increased levels, or partial pressures, of carbon dioxide (CO2) would signal for an increase in breathing rate. As CO2 levels in the blood rise due to the breathing of such air as described in the passage, a breathing mechanism in the brain is triggered to increase ventilation (hyperventilation) to remove as much CO2 through the lungs as possible. A decrease in breathing rate would build up CO2 to even higher levels, causing respiratory acidosis. There would be no changes to blood pressure because slight increases of CO2 has no significant effect on this property.
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Where in the brain is respiration rate regulated?
Where in the brain is respiration rate regulated?
It is important to know that the medulla oblongata in the brainstem is the site of breathing rate control. pH receptors at the medulla sense the hydrogen concentration in the blood, and increase or decrease the rate of breathing to alter bicarbonate levels in the blood, maintaining healthy pH levels.
The cerebellum is involved in balance and coordination, while the frontal cortex and occipital lobe are both regions of the cerebrum, involved in higher thinking, processing, and voluntary actions.
It is important to know that the medulla oblongata in the brainstem is the site of breathing rate control. pH receptors at the medulla sense the hydrogen concentration in the blood, and increase or decrease the rate of breathing to alter bicarbonate levels in the blood, maintaining healthy pH levels.
The cerebellum is involved in balance and coordination, while the frontal cortex and occipital lobe are both regions of the cerebrum, involved in higher thinking, processing, and voluntary actions.
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Give the equation for total lung capacity.
Give the equation for total lung capacity.
The total lung capacity is the maximum amount of air that can fill the lungs.
The vital capacity is the amount of air that can be exhaled after fully inhaling.
The tidal volume is the amount of air inhaled during normal, relaxed breathing.
The expiratory reserve volume is the amount of air that can be forcibly exhaled after a normal exhalation.
The inspiratory reserve volume is the amount of air that can be forcibly inhaled after a normal inhalation.
The residual volume is the amount of air still remaining in the lungs after the expiratory reserve volume is exhaled.
By adding the residual volume and vital capacity, you can obtain a value for the total lung capacity.
The total lung capacity is the maximum amount of air that can fill the lungs.
The vital capacity is the amount of air that can be exhaled after fully inhaling.
The tidal volume is the amount of air inhaled during normal, relaxed breathing.
The expiratory reserve volume is the amount of air that can be forcibly exhaled after a normal exhalation.
The inspiratory reserve volume is the amount of air that can be forcibly inhaled after a normal inhalation.
The residual volume is the amount of air still remaining in the lungs after the expiratory reserve volume is exhaled.
By adding the residual volume and vital capacity, you can obtain a value for the total lung capacity.
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Both the sympathetic and the parasympathetic nervous systems are essential for homeostasis and for survival. For example, when we are trying to run away from a threat, the sympathetic nervous system is in full effect to allow us to escape from danger. However, when there is no obvious threat, the parasympathetic nervous system tends to be more in control.
There are similarities and differences between the sympathetic and the parasympathetic nervous systems. In preganglionic nerve fibers, both the sympathetic and the parasympathetic nervous system utilize the neurotransmitter acetylcholine. Closer to the target organ, the parasympathetic nervous system remains dependent on acetylcholine whereas norepinephrine and epinephrine are the predominant neurotransmitters utilized by the sympathetic nervous system.
When norepinephrine and epinephrine bind to their receptors, different effects are carried out based on the type of receptor, affinity, and location of the receptor. For example, epinephrine has a higher affinity for the beta-2 receptor. When epinephrine binds to the beta-2 receptor, common effects include vasodilation and bronchodilation. Norepinephrine has a stronger affinity for the alpha-1, alpha-2 and beta-1 receptors. When norepinephrine binds to its receptor, common effects on the body include vasoconstriction (alpha-1), increased heart rate (beta-1) and uterine contraction (alpha-1).
When a patient has a severe allergic reaction, a common prescribed drug is epinephrine. Which of the follow best explains the effects of epinephrine on a patient experiencing a severe allergic reaction?
Both the sympathetic and the parasympathetic nervous systems are essential for homeostasis and for survival. For example, when we are trying to run away from a threat, the sympathetic nervous system is in full effect to allow us to escape from danger. However, when there is no obvious threat, the parasympathetic nervous system tends to be more in control.
There are similarities and differences between the sympathetic and the parasympathetic nervous systems. In preganglionic nerve fibers, both the sympathetic and the parasympathetic nervous system utilize the neurotransmitter acetylcholine. Closer to the target organ, the parasympathetic nervous system remains dependent on acetylcholine whereas norepinephrine and epinephrine are the predominant neurotransmitters utilized by the sympathetic nervous system.
When norepinephrine and epinephrine bind to their receptors, different effects are carried out based on the type of receptor, affinity, and location of the receptor. For example, epinephrine has a higher affinity for the beta-2 receptor. When epinephrine binds to the beta-2 receptor, common effects include vasodilation and bronchodilation. Norepinephrine has a stronger affinity for the alpha-1, alpha-2 and beta-1 receptors. When norepinephrine binds to its receptor, common effects on the body include vasoconstriction (alpha-1), increased heart rate (beta-1) and uterine contraction (alpha-1).
When a patient has a severe allergic reaction, a common prescribed drug is epinephrine. Which of the follow best explains the effects of epinephrine on a patient experiencing a severe allergic reaction?
Epinephrine binds to the beta-2 receptor. The binding of epinephrine to the beta-2 receptor causes bronchodilation by relaxing the smooth muscles surrounding the airway. The relaxation of the smooth muscles around the airway increases the airway diameter and therefore allows the patient to breathe easier.
Epinephrine binds to the beta-2 receptor. The binding of epinephrine to the beta-2 receptor causes bronchodilation by relaxing the smooth muscles surrounding the airway. The relaxation of the smooth muscles around the airway increases the airway diameter and therefore allows the patient to breathe easier.
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Which two muscles do humans use primarily for inhalation?
Which two muscles do humans use primarily for inhalation?
The two muscles that help with breathing are the diaphragm and the external intercostal muscles. The diaphragm pulls the thoracic cavity downward and the external intercostal muscles expand the cavity outward. This expansion of the thoracic cavity leads to a decrease in pressure and allows air to be drawn into the lungs.
The two muscles that help with breathing are the diaphragm and the external intercostal muscles. The diaphragm pulls the thoracic cavity downward and the external intercostal muscles expand the cavity outward. This expansion of the thoracic cavity leads to a decrease in pressure and allows air to be drawn into the lungs.
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Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.
In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.
Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.
Duchenne Muscular Dystrophy is usually fatal by age 30. Which of the following is the most likely cause of death for these patients?
Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.
In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.
Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.
Duchenne Muscular Dystrophy is usually fatal by age 30. Which of the following is the most likely cause of death for these patients?
Duchenne Muscular Dystrophy is a muscular disorder, so cause of death will be related to muscle weakening. Two main muscles are essential to maintaining the body: the heart and the diaphragm. As the disease progresses to these muscles, causing weakening of the heart and diaphragm, the body begins to deteriorate and cause of death is usually heart failure or respiratory failure when these muscles give out.
Contraction of the diaphragm allows air to enter the lungs. A weaker contraction means less air flow, and eventually leads to respiratory failure.
Duchenne Muscular Dystrophy is a muscular disorder, so cause of death will be related to muscle weakening. Two main muscles are essential to maintaining the body: the heart and the diaphragm. As the disease progresses to these muscles, causing weakening of the heart and diaphragm, the body begins to deteriorate and cause of death is usually heart failure or respiratory failure when these muscles give out.
Contraction of the diaphragm allows air to enter the lungs. A weaker contraction means less air flow, and eventually leads to respiratory failure.
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Which of the following is NOT a function of the upper respiratory system?
I. Inspired air is saturated with water.
II. Inspired air is filtered for particulates such as pollen.
III. Inspired air is brought to body temperature.
IV. Secretory immunoglobulins (IgA) bind certain antigens.
V. All of these are normal functions of the upper respiratory system.
Which of the following is NOT a function of the upper respiratory system?
I. Inspired air is saturated with water.
II. Inspired air is filtered for particulates such as pollen.
III. Inspired air is brought to body temperature.
IV. Secretory immunoglobulins (IgA) bind certain antigens.
V. All of these are normal functions of the upper respiratory system.
By its argumentative phrasing, the question invites the respondent to "bite" on the least commonly discussed function of the respiratory system. Three possible responses are pretty obviously correct, but the statement about immunoglobulins is also true. Recall that IgA is present in secretions such as tears, saliva, and mucous fluids, and it indeed constitutes an important barrier to infectious agents. Some pathogens are capable of destroying this protein, facilitating their attachment to mucosal cells or biofilms.
By its argumentative phrasing, the question invites the respondent to "bite" on the least commonly discussed function of the respiratory system. Three possible responses are pretty obviously correct, but the statement about immunoglobulins is also true. Recall that IgA is present in secretions such as tears, saliva, and mucous fluids, and it indeed constitutes an important barrier to infectious agents. Some pathogens are capable of destroying this protein, facilitating their attachment to mucosal cells or biofilms.
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Which of the following represents the pathway of the respiratory system?
Which of the following represents the pathway of the respiratory system?
The respiratory system begins in the nasal cavity and proceeds into the pharynx followed by the larynx and trachea. The trachea then branches into left and right primary bronchi, which continue to branch into secondary and tertiary bronchi. The tertiary bronchi contain all smooth muscle and continue to branch into bronchioles. The bronchioles are then divided into terminal bronchioles followed by respiratory bronchioles, which are then attached to the alveolar ducts containing the alveolar sac.
The respiratory system begins in the nasal cavity and proceeds into the pharynx followed by the larynx and trachea. The trachea then branches into left and right primary bronchi, which continue to branch into secondary and tertiary bronchi. The tertiary bronchi contain all smooth muscle and continue to branch into bronchioles. The bronchioles are then divided into terminal bronchioles followed by respiratory bronchioles, which are then attached to the alveolar ducts containing the alveolar sac.
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Which fact about respiration and gas exchange is false?
Which fact about respiration and gas exchange is false?
When the diaphragm contracts, the thoracic cavity actually expands, lowering the pressure in the thoracic cavity below atmospheric pressure. Air is drawn from high to low pressure ("negative-pressure breathing"). So, the statement about diaphragmatic contraction is false. All other choices are true.
When the diaphragm contracts, the thoracic cavity actually expands, lowering the pressure in the thoracic cavity below atmospheric pressure. Air is drawn from high to low pressure ("negative-pressure breathing"). So, the statement about diaphragmatic contraction is false. All other choices are true.
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What is the correct path of air flow during inspiration?
What is the correct path of air flow during inspiration?
Air travels through the nose and mouth through the pharynx. It then flows through the larynx and the trachea before entering the bronchi. The bronchi branch into the bronchioles and finally terminate into the alveoli, where gas exchange can take place between the lungs and the blood stream.
Air travels through the nose and mouth through the pharynx. It then flows through the larynx and the trachea before entering the bronchi. The bronchi branch into the bronchioles and finally terminate into the alveoli, where gas exchange can take place between the lungs and the blood stream.
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What important detergent lines the alveoli in the lungs and keeps the alveoli expanded?
What important detergent lines the alveoli in the lungs and keeps the alveoli expanded?
Surfactant is a vital detergent needed for gas exchange between the lungs and the blood stream. Its role is to lower the surface tension on the interior of the alveolar sac. Without surfactant, alveoli would collapse and gas exchange would be inhibited.
Surfactant is a vital detergent needed for gas exchange between the lungs and the blood stream. Its role is to lower the surface tension on the interior of the alveolar sac. Without surfactant, alveoli would collapse and gas exchange would be inhibited.
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Pleural membranes surround the lungs. These membranes serve as the glue between the lungs and the thoracic cavity. Which of the following statements is correct about these structures?
Pleural membranes surround the lungs. These membranes serve as the glue between the lungs and the thoracic cavity. Which of the following statements is correct about these structures?
The visceral pleura lines the outside of the lungs, the parietal pleura lines the thoracic cavity, and the intrapleural space seals the two layers together. These three components are all necessary for normal inhalation. When the layers are broken, lungs are at risk for collapsing.
The visceral pleura lines the outside of the lungs, the parietal pleura lines the thoracic cavity, and the intrapleural space seals the two layers together. These three components are all necessary for normal inhalation. When the layers are broken, lungs are at risk for collapsing.
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Recall from your studies of the human lungs that total lung capacity (TLC) is given by the sum of residual volume (RV) and vital capacity (VC).
Which of the following correctly represents the lung's vital capacity (VC)?
Recall from your studies of the human lungs that total lung capacity (TLC) is given by the sum of residual volume (RV) and vital capacity (VC).
Which of the following correctly represents the lung's vital capacity (VC)?
Vital capacity refers to the total volume of the lung through which air can be passed during respiration. Tidal volume is the average normal amount of air in a given breath. Expiratory reserve volume is the maximum volume of air that can be forcefully exhaled (minus the tidal volume), while inspiratory reserve volume is the volume of air that can be forcefully inhaled (minus the tidal volume). The total volume of the lung through which air can be passed is thus given by the sum of the normal volume (TV), forceful expiration (ERV), and forceful inspiration (IRV).
VC = TV + ERV+ IRV
Residual volume (RV) refers to the latent space in the lungs that cannot be compressed or expanded. Air cannot be fully dispelled from the lungs, or they would collapse; the remaining air volume after forceful expiration is the residual volume.
So TV + ERV + IRV + residual volume (RV) = total lung capacity (TLC).
Vital capacity refers to the total volume of the lung through which air can be passed during respiration. Tidal volume is the average normal amount of air in a given breath. Expiratory reserve volume is the maximum volume of air that can be forcefully exhaled (minus the tidal volume), while inspiratory reserve volume is the volume of air that can be forcefully inhaled (minus the tidal volume). The total volume of the lung through which air can be passed is thus given by the sum of the normal volume (TV), forceful expiration (ERV), and forceful inspiration (IRV).
VC = TV + ERV+ IRV
Residual volume (RV) refers to the latent space in the lungs that cannot be compressed or expanded. Air cannot be fully dispelled from the lungs, or they would collapse; the remaining air volume after forceful expiration is the residual volume.
So TV + ERV + IRV + residual volume (RV) = total lung capacity (TLC).
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In cases of severe asthma, a patient's bronchioles can become chronically inflamed and obstructed, increasing the necessary effort to inflate the lungs with air. Which of the following might be a symptom of severe asthma?
In cases of severe asthma, a patient's bronchioles can become chronically inflamed and obstructed, increasing the necessary effort to inflate the lungs with air. Which of the following might be a symptom of severe asthma?
More effort is necessary to inflate the lungs in severe asthma, so processes that enhance this activity will be increased to compensate. Inflation is an active process that is carried out by contractions of the diaphragm and chest accessory muscles (e.g. the external intercostals). These muscles will have to work harder if inspiration is inhibited, and thus grow larger, or hypertrophy, over time.
The size of the diaphragm does not reduce if it works harder over time. Increased difficulty in breathing would lead to higher levels of carbon dioxide in the blood and lower levels of oxygen in the blood. Higher levels of carbon dioxide would increase its partial pressure in the blood.
More effort is necessary to inflate the lungs in severe asthma, so processes that enhance this activity will be increased to compensate. Inflation is an active process that is carried out by contractions of the diaphragm and chest accessory muscles (e.g. the external intercostals). These muscles will have to work harder if inspiration is inhibited, and thus grow larger, or hypertrophy, over time.
The size of the diaphragm does not reduce if it works harder over time. Increased difficulty in breathing would lead to higher levels of carbon dioxide in the blood and lower levels of oxygen in the blood. Higher levels of carbon dioxide would increase its partial pressure in the blood.
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Which statement about the respiratory system is false?
Which statement about the respiratory system is false?
The epiglottis closes to prevent food from entering the trachea, not the esophagus. We want the food to enter the digestive tract while avoiding the respiratory system.
All of the other answer choices are correct statements. High partial pressure of oxygen in the alveoli forces oxygen across the capillary epithelium and into the blood. Contraction of the diaphragm increases the size of the thoracic cavity; increasing the volume decreases the pressure and pulls in air from the environment. When the diaphragm relaxes, passive exhalation occurs.
The epiglottis closes to prevent food from entering the trachea, not the esophagus. We want the food to enter the digestive tract while avoiding the respiratory system.
All of the other answer choices are correct statements. High partial pressure of oxygen in the alveoli forces oxygen across the capillary epithelium and into the blood. Contraction of the diaphragm increases the size of the thoracic cavity; increasing the volume decreases the pressure and pulls in air from the environment. When the diaphragm relaxes, passive exhalation occurs.
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Which of the following is true of the respiratory processes?
Which of the following is true of the respiratory processes?
The diaphragm contracts during inspiration and relaxes during expiration. External intercostals are used for inspiration, and internal intercostals are used for expiration only if it is forced expiration. Usually expiration is a passive process, unless someone is forcefully exhaling, such as during strenuous exercise.
Contraction of the diaphragm increases the volume of the thoracic cavity, decreasing the pressure. When the pressure in the lungs is less than the atmospheric pressure, air will be drawn into the lungs. When the diaphragm relaxes (passively), the thoracic cavity shrinks and air is expelled.
The diaphragm contracts during inspiration and relaxes during expiration. External intercostals are used for inspiration, and internal intercostals are used for expiration only if it is forced expiration. Usually expiration is a passive process, unless someone is forcefully exhaling, such as during strenuous exercise.
Contraction of the diaphragm increases the volume of the thoracic cavity, decreasing the pressure. When the pressure in the lungs is less than the atmospheric pressure, air will be drawn into the lungs. When the diaphragm relaxes (passively), the thoracic cavity shrinks and air is expelled.
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Which of the following processes is not involved in inhalation?
Which of the following processes is not involved in inhalation?
The process of inhalation involves a coordinated series of steps beginning with the contraction and flattening of the diaphragm. This serves to decrease the pressure in the thoracic space, pulling the lung with it to expand the lung volume. By the ideal gas law, we know that when the volume is increased at a fixed temperature, the pressure decreases. The low intra-lung pressure pulls air in from outside, completing the inspiratory process.
To promote forceful inhalation, the exterior intercostals can contract. These muscle are located on the outside of the ribs and help to further expand the thoracic cavity when contracted. In contrast, the interior intercostal muscles are located on the inside of the ribs and help to shrink the thoracic cavity during contraction, aiding in forceful exhalation. The interior intercostals are not involved in inhalation.
The process of inhalation involves a coordinated series of steps beginning with the contraction and flattening of the diaphragm. This serves to decrease the pressure in the thoracic space, pulling the lung with it to expand the lung volume. By the ideal gas law, we know that when the volume is increased at a fixed temperature, the pressure decreases. The low intra-lung pressure pulls air in from outside, completing the inspiratory process.
To promote forceful inhalation, the exterior intercostals can contract. These muscle are located on the outside of the ribs and help to further expand the thoracic cavity when contracted. In contrast, the interior intercostal muscles are located on the inside of the ribs and help to shrink the thoracic cavity during contraction, aiding in forceful exhalation. The interior intercostals are not involved in inhalation.
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Which of the following cases best represents exhalation?
Which of the following cases best represents exhalation?
The diaphragm is a dome-shaped muscle at the base of the thoracic cavity. When contracted the diaphragm pulls downward, expanding the volume of the thoracic cavity and reducing the pressure. This negative pressure pulls air into the lungs, allowing inspiration. The external intercostal muscles are situated along the outside of the rib cage, and can help expand the ribs when contracted to cause forced inhalation.
When the diaphragm relaxes, the thoracic cavity shrinks to its normal size and releases the air from the lungs. Exhalation is mostly passive, however contraction of the internal intercostals can increase the pressure in the thoracic cavity. The internal intercostals are arranged on the interior of the rib cage, and can effectively pull the ribs closer together. This further decreases the space available to the lungs, causing forced expiration.
The diaphragm is a dome-shaped muscle at the base of the thoracic cavity. When contracted the diaphragm pulls downward, expanding the volume of the thoracic cavity and reducing the pressure. This negative pressure pulls air into the lungs, allowing inspiration. The external intercostal muscles are situated along the outside of the rib cage, and can help expand the ribs when contracted to cause forced inhalation.
When the diaphragm relaxes, the thoracic cavity shrinks to its normal size and releases the air from the lungs. Exhalation is mostly passive, however contraction of the internal intercostals can increase the pressure in the thoracic cavity. The internal intercostals are arranged on the interior of the rib cage, and can effectively pull the ribs closer together. This further decreases the space available to the lungs, causing forced expiration.
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