Respiratory System Practice Questions

Q: Which of the following statements about the O2-Hb dissociation curve is correct?

It demonstrates cooperative binding.. ***It demonstrates cooperative binding.*** - **Cooperative binding** describes how the binding of one oxygen molecule to hemoglobin increases the affinity of the remaining binding sites for oxygen. - This property gives the O2-Hb dissociation curve its characteristic **sigmoid (S-shaped)** appearance, allowing for efficient oxygen loading in the lungs and unloading in the tissues. *The curve is a straight line.* - The O2-Hb dissociation curve is **sigmoid or S-shaped**, not a straight line, due to the phenomenon of cooperative binding. - A straight line would imply a constant affinity of hemoglobin for oxygen, which is not the case. *It is 100% saturated at a PO2 of 100 mmHg.* - Hemoglobin is typically around **97-98% saturated** at a PO2 of 100 mmHg (arterial blood). - Complete 100% saturation is rarely achieved under physiological conditions. *A hemoglobin molecule can carry 4 molecules of O2.* - While this statement is factually true (one hemoglobin molecule has **four heme groups** and can bind up to **four molecules of oxygen**), it describes the structure and oxygen-carrying capacity of hemoglobin rather than a characteristic of the dissociation **curve itself**. - The question asks about features of the O2-Hb dissociation curve, and cooperative binding is the key property that defines the curve's behavior and sigmoid shape.

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 factor increases the affinity of hemoglobin for O2?

High pH. ***High pH*** - A **high pH** (alkalosis) increases hemoglobin's affinity for oxygen, shifting the **oxygen dissociation curve to the left**. - This is known as the **Bohr effect**, where an increase in pH (i.e., decreased H+ concentration) enhances oxygen binding. *Acidosis* - **Acidosis** (low pH) decreases hemoglobin's affinity for oxygen, promoting oxygen release to tissues. - This effect, part of the **Bohr effect**, shifts the **oxygen dissociation curve to the right**. *Hyperthermia* - **Increased body temperature** (hyperthermia) reduces hemoglobin's affinity for oxygen. - This causes the **oxygen dissociation curve to shift to the right**, facilitating oxygen delivery to metabolically active, warm tissues. *High PCO2* - An **elevated partial pressure of carbon dioxide (PCO2)** decreases hemoglobin's affinity for oxygen. - This is also part of the **Bohr effect**, as high PCO2 leads to increased H+ concentration (lower pH), shifting the **oxygen dissociation curve to the right**.

Q: Which of the following statements about carboxyhemoglobin is true?

Causes a left shift of the Hb-O2 dissociation curve. ***Correct: Causes a left shift of the Hb-O2 dissociation curve*** - Carbon monoxide (CO) binds to hemoglobin with an affinity **210-250 times greater** than oxygen, forming carboxyhemoglobin (COHb). - When CO occupies some heme sites, it causes **allosteric conformational changes** in the hemoglobin molecule, increasing the oxygen affinity of the remaining unoccupied heme sites. - This results in a **left shift of the oxygen-hemoglobin dissociation curve**, meaning hemoglobin holds oxygen more tightly and releases it less readily to tissues. - This combination of **reduced oxygen-carrying capacity** (functional anemia) and **impaired oxygen release** (left shift) makes CO poisoning particularly dangerous. *Incorrect: Takes up oxygen very quickly* - This is false; COHb does **not** take up oxygen. - CO occupies the heme binding sites, **preventing** oxygen from binding. - CO's high affinity for hemoglobin means it displaces and blocks oxygen binding, reducing the blood's oxygen-carrying capacity. *Incorrect: Causes histotoxic hypoxia in tissues* - This is incorrect; CO poisoning causes **hypoxic hypoxia** (inadequate oxygen delivery), not histotoxic hypoxia. - **Histotoxic hypoxia** is caused by agents like **cyanide**, which inhibit cellular enzymes (cytochrome oxidase) and prevent tissues from utilizing oxygen. - COHb reduces oxygen delivery but does not impair cellular oxygen utilization mechanisms. *Incorrect: None of the options* - This is incorrect because the statement about the left shift of the Hb-O2 dissociation curve is physiologically accurate and well-established in medical literature.

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: 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: 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.

Question 1

Which of the following statements about the O2-Hb dissociation curve is correct?

Accepted Answer

It demonstrates cooperative binding.

Answer

The curve is a straight line.

Answer

It is 100% saturated at a PO2 of 100 mmHg.

Answer

A hemoglobin molecule can carry 4 molecules of O2.

Question 2

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 3

Which factor increases the affinity of hemoglobin for O2?

Accepted Answer

High pH

Answer

Acidosis

Answer

Hyperthermia

Answer

High PCO2

Question 4

What is the primary graphical difference between the Hb-O2 dissociation curve and the Hb-CO curve?

Accepted Answer

The Hb-CO curve is shifted to the left compared to the Hb-O2 curve.

Answer

CO has a higher affinity for hemoglobin than oxygen.

Answer

None of the options.

Answer

CO binding prevents normal oxygen release despite high oxygen saturation

Question 5

Which of the following statements about carboxyhemoglobin is true?

Accepted Answer

Causes a left shift of the Hb-O2 dissociation curve

Answer

None of the options

Answer

Takes up oxygen very quickly

Answer

Causes histotoxic hypoxia in tissues

Question 6

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 7

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 8

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 9

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 10

Functional residual capacity in normal adult is?

Accepted Answer

2400 ml

Answer

500 ml

Answer

1200 ml

Answer

3200 ml

Respiratory System — MCQs

Respiratory System — MCQs

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