Respiratory System — MCQs

Respiratory System Indian Medical PG Practice Questions and MCQs

Question 831: Which of the following best describes hypoxic pulmonary vasoconstriction?

A. Reversible pulmonary vasoconstriction due to hypoxia (Correct Answer)
B. Irreversible pulmonary vasoconstriction due to hypoxia
C. Redirects blood to well-ventilated areas
D. Occurs immediately in response to hypoxia

Explanation: ***Reversible pulmonary vasoconstriction due to hypoxia*** - Hypoxic pulmonary vasoconstriction (HPV) is a physiological response in which **pulmonary arterioles constrict** in areas of the lung with low oxygen levels. - This mechanism is **reversible**, meaning that when oxygen levels improve, the constricted vessels will dilate again. - The underlying mechanism involves hypoxia-induced inhibition of voltage-gated K⁺ channels in pulmonary arterial smooth muscle, leading to membrane depolarization, Ca²⁺ influx, and smooth muscle contraction. *Irreversible pulmonary vasoconstriction due to hypoxia* - This statement is incorrect because HPV is fundamentally a **reversible process**, designed to adapt to transient changes in alveolar oxygen. - Irreversible vasoconstriction typically occurs in chronic hypoxia, leading to **pulmonary hypertension** and structural remodeling (vascular remodeling with medial hypertrophy), which is a pathological state rather than the acute physiological response of HPV. *Redirects blood to well-ventilated areas* - While this is the **physiological purpose** and overall effect of hypoxic pulmonary vasoconstriction, it describes the functional outcome rather than what HPV fundamentally is. - The redirection of blood flow is the **consequence** of vasoconstriction in hypoxic areas, which optimizes ventilation-perfusion matching. *Occurs immediately in response to hypoxia* - While HPV does begin rapidly in response to hypoxia (within seconds to minutes), this describes the **timing characteristic** rather than what HPV is. - This statement is also somewhat imprecise, as the response involves intracellular signaling pathways that take time to manifest fully, though the onset is relatively quick compared to other vascular responses.

Question 832: Which equation is used to calculate physiological dead space?

A. Dalton's law
B. Bohr equation (Correct Answer)
C. Charles's law
D. Boyle's law

Explanation: ***Bohr equation*** - The Bohr equation is used to calculate **physiological dead space**, which is the sum of anatomical dead space and alveolar dead space. - It relates the partial pressure of carbon dioxide in arterial blood to the partial pressure of carbon dioxide in expired air, along with **tidal volume** and expired volume. *Dalton's law* - Dalton's law states that the **total pressure** exerted by a mixture of non-reactive gases is equal to the **sum of the partial pressures** of individual gases. - It is used to calculate partial pressures of gases in a mixture, not dead space. *Charles's law* - Charles's law describes the relationship between the **volume and temperature** of a gas at constant pressure. - It states that the volume of a given mass of gas is directly proportional to its absolute temperature. *Boyle's law* - Boyle's law describes the inverse relationship between the **pressure and volume** of a gas at constant temperature. - It is fundamental to understanding mechanics of breathing, but not dead space calculation.

Question 833: Which of the following is used for the diagnosis of asthma?

A. Measurement of tidal volume
B. End expiratory flow rate
C. Total lung capacity
D. FEV1 (Correct Answer)

Explanation: ***FEV1*** - **Forced expiratory volume in 1 second (FEV1)** is the gold standard spirometric parameter for asthma diagnosis - Key diagnostic criteria include: - Reduced **FEV1/FVC ratio** (<0.70 or <0.75-0.80 in adults) - **Bronchodilator reversibility**: ≥12% and ≥200 mL increase in FEV1 after inhaled short-acting β2-agonist - This reversibility distinguishes asthma from fixed obstructive diseases like COPD - Serial **peak expiratory flow (PEF)** monitoring can also demonstrate variability characteristic of asthma *Measurement of tidal volume* - **Tidal volume** measures the amount of air inhaled or exhaled during normal breathing (typically ~500 mL at rest) - Not a diagnostic parameter for asthma as it doesn't assess **airway obstruction** or **hyperresponsiveness** - May be reduced during acute exacerbations but lacks specificity for asthma diagnosis *End expiratory flow rate* - Not a standard diagnostic parameter for asthma - While **mid-expiratory flow rates** (FEF25-75%) and **peak expiratory flow (PEF)** are assessed, **FEV1** remains the primary diagnostic measure - FEV1 provides better reproducibility and standardization for diagnosis *Total lung capacity* - **Total lung capacity (TLC)** represents total lung volume after maximal inhalation - May be normal or increased in asthma due to **air trapping** and hyperinflation - Not used as a primary diagnostic criterion as asthma diagnosis focuses on demonstrating **reversible airflow limitation**, not lung volumes

Question 834: Where are glomus cells primarily located?

A. Bladder
B. Brain
C. Kidney
D. Carotid and aortic bodies (Correct Answer)

Explanation: ***Carotid and aortic bodies*** - **Glomus cells**, also known as **chemoreceptors**, are primarily located in the **carotid bodies** at the bifurcation of the common carotid artery and in the **aortic bodies** near the aortic arch. - These cells are crucial for monitoring blood oxygen, carbon dioxide, and pH levels, playing a vital role in the body's **respiratory and cardiovascular regulation**. *Bladder* - The bladder’s primary function is to store urine, and it contains specialized cells for distension and contraction, but not **glomus cells** involved in chemoreception. - While the bladder does have nerve endings, they are mainly concerned with detecting stretch and facilitating micturition, not monitoring blood gas levels. *Brain* - The brain contains various specialized cells, including neurons and glial cells, which are responsible for its complex functions. - Although the brain has centers that respond to blood gas changes (e.g., in the medulla), the primary **peripheral chemoreceptors (glomus cells)** are not located within the brain tissue itself. *Kidney* - The kidneys are involved in filtering blood, regulating blood pressure, and producing hormones, containing specialized cells like **juxtaglomerular cells** and podocytes. - However, they do not contain **glomus cells** as a primary site for sensing blood gas levels.

Question 835: Which of the following statements about lung compliance is NOT true?

A. Measured by intrapleural pressure at different lung volumes. (Correct Answer)
B. Decreased at the height of inspiration.
C. Increased in emphysema.
D. Increased by surfactant.

Explanation: ***Measured by intrapleural pressure at different lung volumes.*** - Lung compliance is measured by the **change in lung volume (ΔV)** divided by the **change in transpulmonary pressure (ΔP)**, which is the difference between alveolar and intrapleural pressure. - While intrapleural pressure is a component of transpulmonary pressure, compliance is not measured solely by intrapleural pressure at different lung volumes. *Increased in emphysema.* - This statement is **true**. Emphysema involves the destruction of **elastic fibers** in the lung tissue. - Loss of elastic recoil leads to an **increase in compliance**, meaning the lungs are easier to distend but collapse more readily. *Decreased at the height of inspiration.* - This statement is **true**. At high lung volumes (height of inspiration), the **elastic limit** of the lung tissue is approached. - The lungs become **stiffer** and less compliant, requiring a greater pressure change for a given volume change. *Increased by surfactant.* - This statement is **true**. Surfactant reduces **surface tension** in the alveoli. - By lowering surface tension, surfactant prevents alveolar collapse and **increases overall lung compliance**, making it easier to inflate the lungs.

Question 836: Gas exchange in tissues takes place at?

A. Artery
B. Capillary (Correct Answer)
C. Vein
D. Venules

Explanation: ***Capillary*** - **Capillaries** are the smallest and most numerous blood vessels, with very thin walls (only one cell thick), which facilitates the efficient exchange of gases, nutrients, and waste products between blood and tissues. - Their extensive network ensures close proximity to nearly every cell in the body, maximizing the surface area and minimizing the diffusion distance for **gas exchange**. *Artery* - Arteries carry **oxygenated blood** away from the heart to the tissues but have thick, muscular walls designed for high pressure and transport, not for direct exchange with tissues. - They branch into smaller arterioles, which then lead to capillaries, making them a conduit rather than an exchange site. *Vein* - Veins carry **deoxygenated blood** back to the heart from the tissues and have relatively thin walls compared to arteries but are still too thick for efficient gas exchange. - They primarily serve as blood return vessels and reservoirs. *Venules* - Venules are small blood vessels that merge from capillaries and eventually combine to form veins; they primarily function in collecting blood from capillary beds. - While slightly more permeable than larger veins, their main role is still collection and transport, not the extensive gas exchange facilitated by capillaries.

Question 837: Which of the following contains the PRIMARY central chemoreceptors responsible for detecting CO2 and pH changes in cerebrospinal fluid?

A. Medulla (Correct Answer)
B. Baroreceptors in carotid sinus
C. Peripheral chemoreceptors in carotid bodies
D. All of the above

Explanation: ***Medulla*** - The **medulla oblongata** in the brainstem houses the primary central chemoreceptors. - These chemoreceptors are located on the **ventral surface of the medulla** and are highly sensitive to changes in the **pH of the cerebrospinal fluid (CSF)**, which is indirectly affected by the partial pressure of carbon dioxide (PCO2) in arterial blood. - CO2 diffuses across the blood-brain barrier, combines with water to form H+ ions, which directly stimulate these central chemoreceptors. *Baroreceptors in carotid sinus* - **Baroreceptors** primarily detect changes in **arterial blood pressure**, not CO2 or pH levels. - They are located in the carotid sinus and aortic arch and are involved in cardiovascular reflexes, not direct chemoreception for respiratory drive. *Peripheral chemoreceptors in carotid bodies* - **Peripheral chemoreceptors** in the carotid bodies (and aortic bodies) detect changes in **arterial blood O2, CO2, and pH**. - However, they are **peripheral**, not central chemoreceptors, and are the primary detectors of **hypoxemia**. - They contribute to respiratory drive but are secondary to central chemoreceptors for CO2 detection. *All of the above* - This option is incorrect because only the **medulla** contains the primary central chemoreceptors for CO2 and pH detection in CSF. - Baroreceptors detect blood pressure, and peripheral chemoreceptors are not central chemoreceptors.

Question 838: What is the Bohr effect in relation to hemoglobin's affinity for oxygen?

A. Decrease in CO2 affinity of hemoglobin when the pH of blood falls
B. Decrease in O2 affinity of hemoglobin when the pH of blood rises
C. Decrease in O2 affinity of hemoglobin when the pH of blood falls (Correct Answer)
D. Decrease in CO2 affinity of hemoglobin when the pH of blood rises

Explanation: ***Decrease in O2 affinity of hemoglobin when the pH of blood falls*** - The **Bohr effect** describes how **hemoglobin's affinity for oxygen decreases** in acidic environments (lower pH), leading to increased oxygen release to tissues. - This physiological response is crucial in active tissues, where increased metabolism produces more **carbon dioxide** and **lactic acid**, lowering the local pH. *Decrease in CO2 affinity of hemoglobin when the pH of blood falls* - This statement incorrectly relates the Bohr effect to **CO2 affinity** and its change with pH in this manner. - The Bohr effect primarily concerns oxygen affinity, not CO2 affinity; CO2 and H+ directly influence oxygen binding. *Decrease in O2 affinity of hemoglobin when the pH of blood rises* - An **increase in pH** (alkaline environment) would, in fact, **increase hemoglobin's affinity for oxygen**, promoting oxygen uptake in the lungs. - This describes the opposite of the Bohr effect, which is about oxygen release in acidic conditions. *Decrease in CO2 affinity of hemoglobin when the pH of blood rises* - While pH changes do affect CO2 transport, this statement does not accurately describe the Bohr effect. - The **Haldane effect** is more relevant to the relationship between oxygenation status and hemoglobin's CO2 affinity.

Question 839: Transpulmonary pressure is the difference between:

A. Pressure in alveoli and intrapleural pressure (Correct Answer)
B. The pressure in the bronchus and atmospheric pressure
C. The difference between atmospheric pressure and intrapleural pressure
D. The difference between atmospheric pressure and intraalveolar pressure

Explanation: ***Pressure in alveoli and intrapleural pressure*** - Transpulmonary pressure is the **pressure gradient** across the lung wall, which is essential for maintaining alveolar inflation. - It is calculated as the **alveolar pressure minus the intrapleural pressure**. *The pressure in the bronchus and atmospheric pressure* - This difference would represent the pressure driving airflow through the **bronchial tree**, not the pressure across the lung wall itself. - It's a measure relevant to **airway resistance**, not lung distension. *The difference between atmospheric pressure and intrapleural pressure* - This difference is related to the **intrathoracic pressure**, which influences venous return and cardiac function, but not directly the distension of the lungs. - It does not account for the **alveolar pressure**, which is the primary internal pressure expanding the lung. *The difference between atmospheric pressure and intraalveolar pressure* - This difference is the **driving pressure for airflow** into or out of the lungs. - It represents the pressure gradient that causes air to move between the **atmosphere and the alveoli** during inspiration and expiration.

Question 840: What does the Hering-Breuer reflex decrease during respiration?

A. Duration of inspiration (Correct Answer)
B. Depth of inspiration
C. Depth of expiration
D. Duration of expiration

Explanation: ***Duration of inspiration*** - The **Hering-Breuer reflex** is a protective reflex that prevents overinflation of the lungs by inhibiting further inspiration once the lungs are adequately stretched. - Activation of **stretch receptors** in the bronchial walls sends signals via the vagus nerve to the brainstem, which then inhibits the inspiratory neurons, thus **shortening the inspiratory phase**. *Duration of expiration* - The Hering-Breuer reflex primarily affects inspiration and does not directly shorten the duration of expiration. - Expiration is typically a passive process at rest, driven by the elastic recoil of the lungs, and its duration is not the main target of this reflex. *Depth of inspiration* - While the reflex ultimately limits the **volume of inspired air**, its primary action is to *terminate* inspiration, thus affecting its duration rather than directly reducing the force or 'depth' of each breath. - The **depth of inspiration** is more related to the strength of inspiratory muscle contraction and central respiratory drive. *Depth of expiration* - The Hering-Breuer reflex does not influence the depth of expiration. - Expiration is largely passive, and the depth of expiration is typically not regulated by this reflex unless breathing becomes forced.

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