MCAT Biology : Respiratory Structures and Lung Mechanics

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Respiratory Structures And Lung Mechanics

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.

Possible Answers:

V

II

III

I

IV

Correct answer:

V

Explanation:

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.

Example Question #2 : Respiratory Structures And Lung Mechanics

Which of the following represents the pathway of the respiratory system?

Possible Answers:

Nasal cavity, pharynx, larynx, trachea, bronchioles, primary bronchi, secondary bronchi, tertiary bronchi, respiratory bronchioles, alveolar duct, alveolar sac

Nasal cavity, larynx, pharynx, trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar duct, alveolar sac

Nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar duct, alveolar sac

Nasal cavity, trachea, pharynx, larynx, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar duct, alveolar sac

Nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, tertiary bronchi, respiratory bronchioles, terminal bronchioles, bronchioles, alveolar duct, alveolar sac

Correct answer:

Nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar duct, alveolar sac

Explanation:

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.

Example Question #1 : Respiratory Structures And Lung Mechanics

What is the correct path of air flow during inspiration?

Possible Answers:

Nose and mouth -> larynx -> pharynx -> trachea -> bronchi -> bronchioles -> alveoli

Nose and mouth -> pharynx -> larynx -> trachea -> bronchioles -> bronchi -> alveoli

Nose and mouth -> pharynx -> larynx -> trachea -> bronchi -> bronchioles -> alveoli

Nose and mouth -> larynx -> pharynx -> trachea -> alveoli -> bronchi -> bronchioles

Correct answer:

Nose and mouth -> pharynx -> larynx -> trachea -> bronchi -> bronchioles -> alveoli

Explanation:

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.

Example Question #2 : Respiratory Structures And Lung Mechanics

What important detergent lines the alveoli in the lungs and keeps the alveoli expanded?

Possible Answers:

Surfactant

None of the other answers

Plasma

Mucous

Correct answer:

Surfactant

Explanation:

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.

Example Question #4 : Respiratory Structures And Lung Mechanics

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?

Possible Answers:

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

The thoracic cavity and lungs are only only connected by the parietal pleura

The thoracic cavity and lungs are only only connected by the visceral pleura

The parietal pleura lines the outside of the lungs, the visceral pleura lines the thoracic cavity, and the intrapleural space seals the two layers together

Correct answer:

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

Explanation:

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. 

Example Question #5 : Respiratory Structures And Lung Mechanics

Which two muscles do humans use primarily for inhalation?

Possible Answers:

Visceral and parietal pleurae

 

Diaphragm and teres minor

Diaphragm and external intercostal muscles

Internal and external intercostal muscles

 

Correct answer:

Diaphragm and external intercostal muscles

Explanation:

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.

Example Question #6 : Respiratory Structures And Lung Mechanics

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)?

Possible Answers:

The sum of tidal volume (TV) and expiratory reserve volume (ERV)

 

The sum of expiratory reserve volume (ERV) and inspiratory reserve volume (IRV)

 

Vital capacity (VC) and tidal volume (TV) are the same value

The sum of tidal volume (TV), expiratory reserve volume (ERV), and inspiratory reserve volume (IRV)

Correct answer:

The sum of tidal volume (TV), expiratory reserve volume (ERV), and inspiratory reserve volume (IRV)

Explanation:

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).

Example Question #7 : Respiratory Structures And Lung Mechanics

Which statement about the respiratory system is false?

Possible Answers:

Expiration of air is considered to be a passive process

The  in the alveoli is higher than the  in the blood that travels to the lungs for oxygenation

When we are eating, the epiglottis closes to prevent food from entering the esophagus

When the diaphragm contracts, pressure in the lungs decreases compared to atmospheric pressure

Correct answer:

When we are eating, the epiglottis closes to prevent food from entering the esophagus

Explanation:

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.

Example Question #8 : Respiratory Structures And Lung Mechanics

Which fact about respiration and gas exchange is false?

Possible Answers:

A molecule of hemoglobin is composed of four subunits; a molecule of myoglobin has only one

Both the aorta and the pulmonary veins carry oxygenated blood

Vital capacity (VC) + residual volume (RV) = total lung capacity (TLC)

When the diaphragm contracts, air is expelled from the lungs into the outside environment

Fetal hemoglobin is able to bind oxygen more tightly than maternal hemoglobin

Correct answer:

When the diaphragm contracts, air is expelled from the lungs into the outside environment

Explanation:

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.

Example Question #2 : Respiratory Structures And Lung Mechanics

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?

Possible Answers:

High oxygen levels in the blood

Low carbon dioxide levels in the blood

Decrease in the partial pressure of carbon dioxide in the blood

Reduction in the size of the diaphragm

Hypertrophy of the chest accessory muscles

Correct answer:

Hypertrophy of the chest accessory muscles

Explanation:

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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