MCAT Biology : Other Respiratory Physiology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #24 : Respiratory System

Whales are active at great, underwater depths for extended periods of time. Which of the following would LEAST contribute to such an ability?

Possible Answers:

Selective arterial constriction

High basal metabolic rate

Large lung capacity

Large muscle myoglobin concentrations

High cellular tolerance for carbon dioxide

Correct answer:

High basal metabolic rate

Explanation:

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.

Example Question #2 : Other Respiratory Physiology

The carbonic anhydrase reaction is shown below.

Which of the following outcomes seems the most reasonable for someone who has an increase in blood COlevels during exercise?

Possible Answers:

The increase in blood COwill cause an increase in blood H2O

Their blood pH will increase

The increase in CO2 will not affect the individual in any of these ways

Their blood pH will decrease

Correct answer:

Their blood pH will decrease

Explanation:

The individual's blood pH level will decrease (become more acidic). The increase in COwill 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).

Example Question #25 : Respiratory System

Which of the following is a physiological consequence of breathing air with a slightly increased partial pressure of carbon dioxide?

Possible Answers:

Increased breathing rate

Decreased blood pressure

Decreased breathing rate

Increased blood pressure

No change in breathing rate

Correct answer:

Increased breathing rate

Explanation:

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.

Example Question #26 : Respiratory System

Where in the brain is respiration rate regulated?

Possible Answers:

Medulla oblongata

Frontal cortex

Occipital lobe

Cerebellum

Correct answer:

Medulla oblongata

Explanation:

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.

Example Question #27 : Respiratory System

Give the equation for total lung capacity.

Possible Answers:

Total lung capacity = expiratory reserve volume + inspiratory reserve volume

Total lung capacity = tidal volume + expiratory reserve volume

Total lung capacity = tidal volume + residual volume

Total lung capacity = vital capacity + residual volume

Total lung capacity = inspiratory reserve volume + vital capacity

Correct answer:

Total lung capacity = vital capacity + residual volume

Explanation:

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.

Example Question #1 : Other Respiratory Physiology

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? 

Possible Answers:

Epinephrine binds to the alpha-1 receptor. Activating the alpha-1 receptor causes vasodilation and bronchodilation. Bronchodilation allows the patient to breath by relaxing the smooth muscle that is constricting the airway.  

Epinephrine binds to the beta-1 receptor.  Activating the beta-1 receptor causes vasodilation and bronchoconstriction. Bronchoconstriction allows the patient to breath by relaxing the smooth muscle that is constricting the airway.  

Epinephrine binds to the beta-2 receptor. Activating the beta-2 receptor causes vasodilation and bronchodilation. Bronchodilation allows the patient to breath easier by relaxing the smooth muscle that is constricting the airway.

Epinephrine binds to the beta-2 receptor. Activating the beta-2 receptor causes vasodilation and bronchoconstriction. Bronchoconstriction allows the patient to breath by relaxing the smooth muscle that is constricting the airway.  

Epinephrine binds to the beta-1 receptor. Activating the beta-1 receptor causes vasodilation and bronchodilation. Bronchodilation allows the patient to breath by relaxing the smooth muscle that is constricting the airway.  

Correct answer:

Epinephrine binds to the beta-2 receptor. Activating the beta-2 receptor causes vasodilation and bronchodilation. Bronchodilation allows the patient to breath easier by relaxing the smooth muscle that is constricting the airway.

Explanation:

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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