Respiratory System Practice Questions

Q: Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

An increase in arterial carbon dioxide tension. ***An increase in arterial carbon dioxide tension*** - An increase in **arterial PCO2** (hypercapnia) leads to a rapid decrease in the **pH of the cerebrospinal fluid (CSF)**, which strongly stimulates **central chemoreceptors** in the medulla. - While overwhelmingly driven by central chemoreceptors, a significant increase in **arterial PCO2** also causes a slight decrease in **arterial pH**, which can additionally stimulate **peripheral chemoreceptors** in the carotid and aortic bodies, leading to increased ventilation. *A decrease in arterial oxygen content* - A decrease in **arterial oxygen content** (e.g., due to anemia or carbon monoxide poisoning) without a significant drop in **arterial PO2** primarily affects oxygen delivery to tissues. - It does not directly stimulate peripheral chemoreceptors, which are sensitive to **PO2**, not content, nor does it affect central chemoreceptors directly to increase ventilation in this manner. *A decrease in arterial blood pressure* - A decrease in **arterial blood pressure** is sensed by **baroreceptors** and primarily triggers cardiovascular reflexes (e.g., increased heart rate and vasoconstriction) to restore blood pressure. - It does not directly stimulate peripheral or central chemoreceptors to significantly increase ventilation unless severe hypoperfusion leads to significant changes in arterial blood gases. *A decrease in arterial oxygen tension* - A decrease in **arterial oxygen tension (PO2)**, especially when it falls below approximately 60 mmHg, acts as a potent stimulus for **peripheral chemoreceptors**. - However, **central chemoreceptors** are primarily sensitive to **PCO2** and CSF pH, and a decrease in **arterial PO2** alone has little direct effect on their activity.

Q: Transpulmonary pressure is the difference between:

Pressure in alveoli and intrapleural pressure. ***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.

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

Medulla. ***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.

Q: Which of the following defines vital capacity?

Maximum air that can be expirated after maximum inspiration. ***Maximum air that can be expirated after maximum inspiration*** - **Vital capacity (VC)** is the maximum volume of air that can be exhaled after a maximal inspiration. - It represents the sum of **tidal volume (TV)**, **inspiratory reserve volume (IRV)**, and **expiratory reserve volume (ERV)**. - VC = TV + IRV + ERV *Air in lung after normal expiration* - This describes the **functional residual capacity (FRC)**, which is the volume of air remaining in the lungs after a normal passive exhalation. - FRC = ERV + RV (expiratory reserve volume + residual volume). *Maximum air that can be expirated after normal expiration* - This refers to the **expiratory reserve volume (ERV)**, the additional amount of air that can be exhaled forcibly after a normal passive exhalation. - It is the extra air expelled beyond tidal volume during forced expiration. *Maximum air in lung after end of maximal inspiration* - This definition corresponds to **total lung capacity (TLC)**, which is the maximum volume of air the lungs can hold after a maximal inspiration. - TLC = VC + RV (vital capacity + residual volume).

Q: What is the primary physiological effect of increased 2,3-DPG on hemoglobin?

Decreased affinity of hemoglobin to oxygen. ***Decreased affinity of hemoglobin to oxygen*** - **2,3-Diphosphoglycerate (2,3-DPG)** binds to the beta subunits of deoxyhemoglobin, stabilizing the **deoxygenated state** and thus **reducing hemoglobin's affinity for oxygen**. - This is the **primary molecular mechanism** by which 2,3-DPG exerts its effect, facilitating **oxygen unloading** in peripheral tissues. - This decreased affinity manifests graphically as a **right shift** in the oxygen-hemoglobin dissociation curve. *Increased affinity of hemoglobin to oxygen* - This is incorrect because 2,3-DPG specifically works to **decrease hemoglobin's affinity** for oxygen, promoting oxygen release. - Increased affinity would mean oxygen is held more tightly, which is counterproductive for **oxygen delivery** to tissues. *Left shift of oxygen-hemoglobin dissociation curve* - A **left shift** indicates **increased affinity** of hemoglobin for oxygen, meaning oxygen is held more tightly. - Since 2,3-DPG decreases affinity, it causes a **right shift**, not a left shift. *Right shift of oxygen-hemoglobin dissociation curve* - While this is the **graphical representation** of 2,3-DPG's effect, it is a **consequence** of the primary molecular mechanism (decreased affinity). - A right shift signifies that for any given partial pressure of oxygen, hemoglobin is **less saturated** with oxygen, reflecting the decreased affinity caused by 2,3-DPG binding.

Q: What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

50 ml/min. ***50 ml/min*** - The body typically consumes about **250 ml/min of oxygen** at rest and produces approximately **200 ml/min of carbon dioxide**. - The difference between oxygen consumed and carbon dioxide produced is therefore **50 ml/min** (250 - 200 = 50). - This difference exists because the **respiratory quotient (RQ)** is approximately **0.8** (200/250), meaning less CO2 is produced than O2 consumed on a molar basis. *20 ml/min* - This value is **too low** and underestimates the physiological difference between oxygen consumption and carbon dioxide production. - With typical O2 consumption of 250 ml/min and RQ of 0.8, the difference cannot be this small. *75 ml/min* - This value represents an **overestimation** of the difference between oxygen consumption and carbon dioxide production under normal resting conditions. - This would imply an RQ of approximately 0.7, which is lower than the typical mixed diet RQ of 0.8. *100 ml/min* - This value is a significant **overestimation** of the physiological difference. - This would suggest an RQ of 0.6, which is not physiologically normal for resting conditions on a mixed diet.

Q: What is the estimated PaO2 after giving FiO2 at 0.5 in a normal person?

> 200 mmHg. ***> 200 mmHg*** - In a **normal healthy person** breathing FiO2 of 0.5 (50% oxygen), the expected **PaO2** is typically **250-300 mmHg**. - Using the **alveolar gas equation**: PAO2 = FiO2(PB - PH2O) - PaCO2/RQ = 0.5(760 - 47) - 40/0.8 ≈ **306 mmHg** - The normal **A-a gradient** is 5-15 mmHg, so PaO2 = 306 - 10 ≈ **296 mmHg** - **Clinical rule of thumb**: PaO2 ≈ 5 × FiO2% = 5 × 50 = **250 mmHg** (approximation accounting for physiological shunt) - Therefore, the expected range is clearly **> 200 mmHg** in a normal individual *150–200 mmHg* - This range would indicate **mild oxygenation impairment** or increased shunt fraction - While adequate for tissue oxygenation, this is **lower than expected** for a normal person on 50% oxygen - May suggest underlying **mild V/Q mismatch** or early pulmonary dysfunction *100–150 mmHg* - This represents **moderate impairment** in oxygen transfer - Indicates significant **pulmonary pathology** such as pneumonia, ARDS, or substantial shunt - Not consistent with normal lung function on FiO2 0.5 *< 100 mmHg* - This represents **severe hypoxemia** despite supplemental oxygen - Indicates **critical pulmonary dysfunction** with large shunt or severe V/Q mismatch - Requires immediate intervention and is never expected in a healthy individual on 50% oxygen

Q: True about normal expiration is:

Chest wall has a tendency to move outward which is balanced by inward recoil of alveoli. ***Chest wall has a tendency to move outward which is balanced by inward recoil of alveoli*** - At **Functional Residual Capacity (FRC)**, the outward recoil of the **chest wall** balances the inward elastic recoil of the **lungs**, resulting in no net force and a stable lung volume. - This equilibrium point represents the resting volume of the respiratory system when respiratory muscles are relaxed during **normal expiration**. - This statement directly describes the **mechanism** of normal expiration—the passive process driven by balanced recoil forces. *At the end of normal expiration, the air in the lung is FRC* - While **technically true** that FRC is the volume remaining after normal expiration, this option describes the **endpoint volume** rather than the process of normal expiration itself. - The question asks what is true **about normal expiration** (the process), not what is true **at the end** of expiration (the outcome). - The correct answer better addresses the mechanism and forces involved during the expiratory process. *In expiration pleural pressure is equal to alveolar pressure* - **INCORRECT**: Pleural pressure is **always negative** relative to alveolar pressure (typically -5 to -8 cm H₂O at FRC). - During **normal expiration**, pleural pressure becomes *less negative* as lung volume decreases, but **never equals** alveolar pressure. - If pleural pressure equaled alveolar pressure, the lungs would collapse (pneumothorax). *Muscles that elevate the chest cage are classified as muscles of expiration* - **INCORRECT**: Muscles that **elevate the chest cage**, such as the **external intercostals** and **diaphragm**, are primarily involved in **inspiration**. - **Normal expiration** is a *passive process* driven by the elastic recoil of the lungs and chest wall, **not requiring muscle contraction**.

Question 1

Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

Accepted Answer

An increase in arterial carbon dioxide tension

Answer

A decrease in arterial oxygen content

Answer

A decrease in arterial blood pressure

Answer

A decrease in arterial oxygen tension

Question 2

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

Accepted Answer

Decrease in O2 affinity of hemoglobin when the pH of blood falls

Answer

Decrease in CO2 affinity of hemoglobin when the pH of blood falls

Answer

Decrease in O2 affinity of hemoglobin when the pH of blood rises

Answer

Decrease in CO2 affinity of hemoglobin when the pH of blood rises

Question 3

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

Accepted Answer

Measured by intrapleural pressure at different lung volumes.

Answer

Decreased at the height of inspiration.

Answer

Increased in emphysema.

Answer

Increased by surfactant.

Question 4

Transpulmonary pressure is the difference between:

Accepted Answer

Pressure in alveoli and intrapleural pressure

Answer

The pressure in the bronchus and atmospheric pressure

Answer

The difference between atmospheric pressure and intrapleural pressure

Answer

The difference between atmospheric pressure and intraalveolar pressure

Question 5

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

Accepted Answer

Medulla

Answer

Baroreceptors in carotid sinus

Answer

Peripheral chemoreceptors in carotid bodies

Answer

All of the above

Question 6

Which of the following defines vital capacity?

Accepted Answer

Maximum air that can be expirated after maximum inspiration

Answer

Air in lung after normal expiration

Answer

Maximum air in lung after end of maximal inspiration

Answer

Maximum air that can be expirated after normal expiration

Question 7

What is the primary physiological effect of increased 2,3-DPG on hemoglobin?

Accepted Answer

Decreased affinity of hemoglobin to oxygen

Answer

Increased affinity of hemoglobin to oxygen

Answer

Left shift of oxygen-hemoglobin dissociation curve

Answer

Right shift of oxygen-hemoglobin dissociation curve

Question 8

What is the difference between the amount of Oxygen consumed and Carbon Dioxide produced per minute at rest?

Accepted Answer

50 ml/min

Answer

20 ml/min

Answer

75 ml/min

Answer

100 ml/min

Question 9

What is the estimated PaO2 after giving FiO2 at 0.5 in a normal person?

Accepted Answer

> 200 mmHg

Answer

< 100 mmHg

Answer

150–200 mmHg

Answer

100–150 mmHg

Question 10

True about normal expiration is:

Accepted Answer

Chest wall has a tendency to move outward which is balanced by inward recoil of alveoli

Answer

In expiration pleural pressure is equal to alveolar pressure

Answer

Muscles that elevate the chest cage are classified as muscles of expiration

Answer

At the end of normal expiration, the air in the lung is FRC

Respiratory System — MCQs

Respiratory System — MCQs

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