Respiratory System Practice Questions

Q: Functional residual capacity in normal adult is?

2400 ml. ***2400 ml*** - **Functional residual capacity (FRC)** is the volume of air remaining in the lungs after a normal passive exhalation. - In a healthy adult, the average FRC is approximately **2400 mL**, or 2.4 liters. *500 ml* - This volume typically represents the **tidal volume (TV)**, which is the amount of air exchanged during normal, quiet breathing. - Tidal volume is a much smaller component of lung capacity compared to FRC. *1200 ml* - This value is close to the **residual volume (RV)**, which is the amount of air remaining in the lungs after a maximal forceful exhalation. - FRC is the sum of expiratory reserve volume and residual volume, thus larger than RV alone. *3200 ml* - This value is closer to the **inspiratory capacity (IC)**, which is the maximum volume of air that can be inspired after a normal expiration. - Alternatively, it could be closer to the **vital capacity (VC)**, which is typically around 4500-5000 mL in healthy adults, making 3200 mL still too low for VC and too high for FRC.

Q: Distending capacity of lung (maximum change in volume during inspiration) is maximum at?

Base of the lung. ***Base of the lung*** - Due to **gravitational forces**, the negative intrapleural pressure is less negative at the base compared to the apex, meaning the alveoli at the base are less stretched at rest. - This **lesser distension at rest** allows the alveoli at the base to have a greater capacity to expand and distend during inspiration, leading to better ventilation. *Apex of the lung* - The **more negative intrapleural pressure** at the apex causes alveoli to be more distended (larger) at functional residual capacity (FRC). - These already stretched alveoli have **less capacity to further distend** during inspiration, leading to less ventilation compared to the base. *Mid region of the lung* - The distending capacity in the mid-region is **intermediate** between the apex and the base. - It is **not the maximum** because the gravitational gradient of intrapleural pressure still allows the base to have a greater change in volume. *Lower lobe of the lung* - While the base of the lung is part of the lower lobe, referring specifically to the "lower lobe" is still **less precise** than the "base." - The specific term "base" refers to the region with the **largest distending capacity** due to the physiological pressure gradient.

Q: Diffusion related to O2 transport across respiratory membrane is an example of?

Simple diffusion. ***Simple diffusion*** - Oxygen crosses the **respiratory membrane** (alveolar and capillary walls) directly through the lipid bilayer, driven by its **partial pressure gradient**. - This process does not require protein carriers or metabolic energy, fitting the definition of **simple diffusion**. *Facilitated diffusion* - This type of diffusion requires a **specific protein carrier** to transport molecules across the membrane. - While it does not require metabolic energy, oxygen transport across the respiratory membrane is efficient enough via simple diffusion due to its small size and lipid solubility. *Active diffusion* - This term is a **misnomer**; diffusion is by definition a passive process. - **Active transport** involves moving molecules against their concentration gradient, which requires metabolic energy (ATP). *Osmotic diffusion* - **Osmosis** specifically refers to the diffusion of **water** across a selectively permeable membrane. - It does not describe the movement of gases like oxygen.

Q: Which of the following is a feature of pulmonary oxygen toxicity?

All of the options. ***All of the options*** - All three listed features are well-established manifestations of **pulmonary oxygen toxicity** - **Oxygen free radicals** generated during prolonged exposure to high O₂ concentrations cause synergistic damage affecting multiple cellular and physiological processes - The combination of these effects leads to significant **lung injury** and respiratory dysfunction **Why each option is correct:** **Increased capillary endothelial permeability:** - Oxygen free radicals directly damage endothelial cells, disrupting tight junctions - Results in **pulmonary edema** and impaired gas exchange - One of the earliest manifestations of O₂ toxicity **Decreased mucociliary transport in airways:** - High O₂ concentrations impair ciliated epithelial cell function - Alters mucus viscosity and composition - Reduces clearance of inhaled particles and pathogens, increasing risk of **respiratory infections** **Inhibition of phagocytosis function of alveolar macrophages:** - Alveolar macrophages are highly susceptible to oxidative stress - Impaired ability to phagocytose pathogens and cellular debris - Compromises the **lung's immune defense** and promotes inflammation

Q: Which of the following does not stimulate central chemoreceptors?

Hypoxia. ***Hypoxia*** - Central chemoreceptors are primarily sensitive to **PCO2** and **hydrogen ion concentration** in the CSF and are not significantly stimulated by hypoxia. - Peripheral chemoreceptors (located in the carotid and aortic bodies) are the main sensors for **hypoxia**. *Increased PCO2* - An increase in **PCO2** in the arterial blood readily diffuses across the blood-brain barrier into the **cerebrospinal fluid (CSF)**. - In the CSF, CO2 is converted to **carbonic acid**, which dissociates into hydrogen ions, directly stimulating central chemoreceptors. *Hydrogen ion concentration in CSF* - Central chemoreceptors are directly stimulated by an increase in the **hydrogen ion concentration** in the CSF. - This increased acidity is typically a result of elevated CO2 levels diffusing into the CSF. *None of the options stimulate* - This option is incorrect because both **increased PCO2** and **hydrogen ion concentration in the CSF** are potent stimulators of central chemoreceptors. - Central chemoreceptors are crucial for regulating ventilation in response to changes in blood gases.

Q: Which of the following statements is true about the Bohr effect?

Decrease affinity of O2 by increase PCO2. ***Decrease affinity of O2 by increase PCO2*** - The **Bohr effect** describes how an increase in **PCO2** (carbon dioxide partial pressure) or a decrease in pH (more acidic environment) reduces hemoglobin's affinity for oxygen. - This is the most complete statement, as increased PCO2 leads to increased H+ (via CO2 + H2O → H2CO3 → H+ + HCO3-), which binds to hemoglobin and reduces oxygen affinity. - This facilitates oxygen release to metabolically active tissues producing more CO2 and H+. - Causes a **right shift** of the oxygen-hemoglobin dissociation curve. *Left shift of Hb-O2 dissociation curve* - A **left shift** indicates *increased* affinity of hemoglobin for oxygen (seen with decreased PCO2, increased pH, decreased temperature, or decreased 2,3-BPG). - The Bohr effect causes a **right shift**, not a left shift, signifying *decreased* oxygen affinity and promoting oxygen release to tissues. - This option is the opposite of what occurs in the Bohr effect. *It is due to H+.* - While **H+ ions** are indeed the molecular mechanism of the Bohr effect (H+ binds to histidine residues on hemoglobin, stabilizing the deoxygenated T-state), this statement alone is incomplete. - It doesn't mention the physiological trigger (increased PCO2) or the functional consequence (decreased O2 affinity). - The first option is more comprehensive and better describes the complete Bohr effect phenomenon. *All are true* - This is incorrect because the statement about a **left shift** is definitively false. - The Bohr effect produces a *right shift*, not a left shift, of the Hb-O2 dissociation curve.

Q: Which of the following factors can cause an increase in pulmonary arterial pressure?

Hypoxia. ***Hypoxia*** - Hypoxia causes **pulmonary vasoconstriction**, which is a unique response of the pulmonary circulation compared to systemic circulation. - This vasoconstriction increases **pulmonary vascular resistance**, directly leading to an elevation in pulmonary arterial pressure. - This phenomenon is known as **hypoxic pulmonary vasoconstriction (HPV)**, an important physiological mechanism. *Histamine* - In the pulmonary vasculature, histamine primarily causes **vasodilation**, which would *decrease* pulmonary arterial pressure. - While it can cause bronchoconstriction, its direct effect on pulmonary arterial pressure is not an increase. *ANP* - **Atrial natriuretic peptide (ANP)** primarily causes **vasodilation** and diuresis. - This effect would lead to a *reduction* in blood volume and systemic vascular resistance, thereby *decreasing* pulmonary arterial pressure. *PGI2* - **Prostacyclin (PGI2)** is a potent **vasodilator** and **platelet aggregation inhibitor**. - Its vasodilatory action would lead to a *decrease* in pulmonary vascular resistance and thus *lower* pulmonary arterial pressure.

Q: Closing volume is related to which of the following?

Residual volume. ***Residual volume*** - **Closing volume (CV)** is the lung volume at which the smallest airways in dependent lung regions begin to close during expiration. - CV is measured as the volume of gas expired from the beginning of airway closure (phase IV of the single-breath nitrogen test) down to **residual volume (RV)**. - **Closing Capacity (CC) = Closing Volume (CV) + Residual Volume (RV)**, demonstrating their direct mathematical relationship. - When CC exceeds FRC (functional residual capacity), airways close during normal tidal breathing, leading to gas trapping and V/Q mismatch. - CV increases with age, smoking, and obstructive lung diseases, encroaching on the expiratory reserve volume and eventually affecting tidal breathing. *Tidal volume* - **Tidal volume (TV)** is the volume of air inhaled or exhaled during normal, quiet breathing (approximately 500 mL in adults). - TV is not used in the measurement or definition of closing volume. - While increased CV can cause airway closure *during* tidal breathing (when CC > FRC), TV itself is not mathematically or definitionally related to CV. *Vital capacity* - **Vital capacity (VC)** is the maximum volume of air that can be exhaled after maximal inspiration (VC = IRV + TV + ERV). - VC is a measure of overall ventilatory capacity but does not specifically relate to the point at which airways begin to close. - CV represents a small fraction of the total lung volumes and is specifically about airway mechanics, not maximal breathing capacity. *None of the options* - This is incorrect because **residual volume** has a direct mathematical relationship with closing volume through the equation CC = CV + RV.

Q: What is the primary function of the human respiratory system?

Gas exchange. ***Gas exchange*** - The primary function of the respiratory system is to facilitate the exchange of gases (oxygen and carbon dioxide) between the air and the blood. - This process occurs mainly in the alveoli of the lungs, where oxygen diffuses into the bloodstream and carbon dioxide diffuses out. *Nutrient absorption* - Nutrient absorption is the primary function of the digestive system, not the respiratory system. - The digestive system breaks down food into molecules that can be absorbed into the bloodstream. *Hormone regulation* - Hormone regulation is primarily controlled by the endocrine system, which produces and secretes hormones to regulate various bodily functions. - While some hormones can affect respiratory rate, hormone regulation is not the respiratory system's primary function. *Waste elimination* - The primary organ for waste elimination from the blood is the kidney, as part of the urinary system, which excretes metabolic waste products. - The respiratory system eliminates carbon dioxide (a metabolic waste product), but this is considered part of gas exchange rather than general waste elimination.

Question 1

Functional residual capacity in normal adult is?

Accepted Answer

2400 ml

Answer

500 ml

Answer

1200 ml

Answer

3200 ml

Question 2

Distending capacity of lung (maximum change in volume during inspiration) is maximum at?

Accepted Answer

Base of the lung

Answer

Apex of the lung

Answer

Mid region of the lung

Answer

Lower lobe of the lung

Question 3

Diffusion related to O2 transport across respiratory membrane is an example of?

Accepted Answer

Simple diffusion

Answer

Facilitated diffusion

Answer

Active diffusion

Answer

Osmotic diffusion

Question 4

Which of the following is a feature of pulmonary oxygen toxicity?

Accepted Answer

All of the options

Answer

Decreased mucociliary transport in airways

Answer

Increased capillary endothelial permeability

Answer

Inhibition of phagocytosis function of alveolar macrophages

Question 5

What is the maximum voluntary ventilation (MVV) and how does it relate to respiratory function?

Accepted Answer

Maximum amount of air that can be inspired and expired in one minute

Answer

Amount of air expired in one minute at rest

Answer

Maximum amount of air that can be inspired per breath

Answer

Maximum amount of air remaining in lung after forced expiration

Question 6

Which of the following does not stimulate central chemoreceptors?

Accepted Answer

Hypoxia

Answer

None of the options stimulate

Answer

Increased PCO2

Answer

Hydrogen ion concentration in CSF

Question 7

Which of the following statements is true about the Bohr effect?

Accepted Answer

Decrease affinity of O2 by increase PCO2

Answer

All are true

Answer

Left shift of Hb-02 dissociation curve

Answer

It is due to H+.

Question 8

Which of the following factors can cause an increase in pulmonary arterial pressure?

Accepted Answer

Hypoxia

Answer

Histamine

Answer

ANP

Answer

PGI2

Question 9

Closing volume is related to which of the following?

Accepted Answer

Residual volume

Answer

Tidal volume

Answer

Vital capacity

Answer

None of the options

Question 10

What is the primary function of the human respiratory system?

Accepted Answer

Gas exchange

Answer

Nutrient absorption

Answer

Hormone regulation

Answer

Waste elimination

Respiratory System — MCQs

Respiratory System — MCQs

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