Respiratory System Practice Questions

Q: Where does the respiratory exchange of gases begin?

Bronchiole. ***Correct: Bronchiole (Respiratory Bronchioles)*** - The **respiratory zone** where gas exchange begins starts at the **respiratory bronchioles** - Respiratory bronchioles have **occasional alveoli** budding from their walls, marking the first site where oxygen and carbon dioxide exchange occurs - This represents the **transition** from the conducting zone (which only transports air) to the respiratory zone (where gas exchange happens) - According to standard respiratory physiology, the respiratory zone includes: respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli *Incorrect: Alveoli* - While **alveoli** are the **primary and most efficient** site of gas exchange due to their enormous surface area (~70 m²) and thin walls - They are NOT where gas exchange "begins" - gas exchange has already started in the respiratory bronchioles - Alveoli represent the terminal and most developed part of the respiratory zone where the majority of gas exchange occurs *Incorrect: Bronchi* - **Bronchi** are part of the **conducting zone** of the respiratory system - Their walls are too thick and they lack alveoli, so **no gas exchange** occurs here - Their function is to conduct air to and from the lungs, with mucus and cilia helping to filter particles *Incorrect: Tissue level* - **Tissue level** gas exchange refers to **internal/systemic respiration** - the exchange of gases between blood and body tissues - This occurs in systemic capillaries throughout the body, NOT in the lungs - The question asks about where respiratory exchange begins in the lungs (external respiration), not tissue-level gas exchange

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 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: 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: 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: How does myoglobin respond to the Bohr effect compared to hemoglobin?

No effect on oxygen affinity. **No effect on oxygen affinity (Correct)** - Myoglobin has only one heme group, thus it **does not exhibit cooperativity** or allosteric regulation, unlike hemoglobin - The **Bohr effect**, which describes the pH and CO2-dependent changes in oxygen affinity, primarily applies to **hemoglobin's tetrameric structure** - Myoglobin's oxygen affinity **remains constant** regardless of pH or CO2 levels *Increased affinity for oxygen (Incorrect)* - This statement is incorrect because myoglobin's oxygen affinity is **already very high** and largely unaffected by the conditions that trigger the Bohr effect - The Bohr effect causes hemoglobin's affinity to *decrease* in acidic or high CO2 environments, facilitating oxygen release - Myoglobin does not exhibit this pH-dependent shift *Decreased affinity for oxygen (Incorrect)* - This would imply that myoglobin is sensitive to pH and CO2 levels in a way that promotes oxygen release, which is **not the case** - Myoglobin functions to **store oxygen** in muscles and release it only at very low partial pressures, independent of pH changes - Only hemoglobin shows decreased affinity under Bohr effect conditions *Same affinity for oxygen (Incorrect)* - This is incorrect because it suggests both molecules maintain the same affinity under varying conditions, which misunderstands the question - Hemoglobin's oxygen affinity **changes significantly** due to the Bohr effect (decreases with lower pH), whereas myoglobin's remains constant - The key distinction is that myoglobin has **no response** to Bohr effect conditions, not that it maintains the "same" affinity as hemoglobin

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

Question 1

Where does the respiratory exchange of gases begin?

Accepted Answer

Bronchiole

Answer

Bronchi

Answer

Alveoli

Answer

Tissue level

Question 2

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 3

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 4

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

Accepted Answer

Hypoxia

Answer

Histamine

Answer

ANP

Answer

PGI2

Question 5

Which factor increases the affinity of hemoglobin for O2?

Accepted Answer

High pH

Answer

Acidosis

Answer

Hyperthermia

Answer

High PCO2

Question 6

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 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

How does myoglobin respond to the Bohr effect compared to hemoglobin?

Accepted Answer

No effect on oxygen affinity

Answer

Increased affinity for oxygen

Answer

Decreased affinity for oxygen

Answer

Same affinity for oxygen

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

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

Respiratory System — MCQs

Respiratory System — MCQs

On this page

Practice by Chapter

Want unlimited practice?