Respiratory System Practice Questions

Q: In forceful expiration, which of the following neurons gets fired?

VRG. ***VRG*** - The **ventral respiratory group (VRG)** contains both inspiratory and expiratory neurons, and it is primarily involved in controlling the muscles necessary for **forceful breathing**. - During forceful expiration, the expiratory neurons in the VRG become active, stimulating accessory muscles of expiration like the **internal intercostals** and **abdominal muscles**. *DRG* - The **dorsal respiratory group (DRG)** primarily contains inspiratory neurons and is fundamental for **normal, quiet breathing**. - Its activity leads to contraction of the diaphragm and external intercostals, and it is largely inactive during quiet expiration, which is a passive process. *Pneumotaxic centre* - The **pneumotaxic center** (or pontine respiratory group) helps to fine-tune breathing patterns by **inhibiting inspiration**, thereby limiting the duration of inhalation. - It influences the rate and depth of breathing but does not directly activate muscles for forceful expiration. *Chemoreceptors* - **Chemoreceptors** (central and peripheral) monitor blood levels of **carbon dioxide (PCO2)**, **oxygen (PO2)**, and **pH**, and they send signals to the respiratory centers to adjust breathing accordingly. - While they regulate the overall respiratory drive, they do not directly fire to initiate forceful expiration; rather, they modulate the activity of the respiratory groups in the brainstem.

Q: Functional residual capacity (FRC) is defined as the volume of air remaining in the lungs at which specific moment in the respiratory cycle?

After normal expiration. ***After normal expiration*** - **Functional residual capacity (FRC)** is the volume of air remaining in the lungs at the end of a **normal, passive expiration**. - It represents the sum of the **expiratory reserve volume (ERV)** and the **residual volume (RV)**. *During active expiration* - **Active expiration** involves the use of accessory muscles to force more air out of the lungs than during normal expiration. - This process would result in a lung volume less than FRC, closer to the **residual volume**. *At peak inspiration* - **Peak inspiration** represents the total lung capacity (TLC), which is the maximum volume of air the lungs can hold after a maximal inspiratory effort. - This is the largest lung volume, significantly greater than FRC. *During active inspiration* - **Active inspiration** is the process of inhaling air, which increases lung volume. - FRC is a static volume measured at the end of expiration, not during the dynamic process of inhaling.

Q: What happens to gas exchange when the Va/Q ratio approaches infinity?

No exchange of O2 and CO2 occurs.. ***No exchange of O2 and CO2 occurs.*** - When the **Va/Q ratio approaches infinity**, it signifies a scenario of **ventilation without perfusion** (Q approaches zero). - This represents **alveolar dead space** - despite adequate ventilation, there is **no blood flow** to participate in gas exchange. - Therefore, **no O2 enters the blood** and **no CO2 leaves the blood**, making this the most accurate description of what happens to gas exchange. *Partial pressure of O2 becomes negligible.* - This statement is incorrect because with **no blood flow** (Q = 0), the alveolar air retains high O2 partial pressure. - O2 is being delivered via ventilation but not removed by blood, so **alveolar PO2** would approach that of **inspired air (~150 mmHg)**, not become negligible. *Partial pressure of CO2 becomes negligible.* - While this statement is technically true (alveolar PCO2 would approach zero/inspired air levels), it doesn't directly answer what happens to **gas exchange**. - With no blood flowing through the alveolus, no **CO2 from venous blood** can reach the alveolus to be excreted. - However, the question asks about **gas exchange** itself, not just partial pressures, making the first option more comprehensive. *Partial pressures of both CO2 and O2 remain normal.* - This statement is incorrect as the **Va/Q mismatch** significantly alters the partial pressures of both gases. - In infinite Va/Q scenario (dead space ventilation), **alveolar PO2 would be high** (approaching inspired air ~150 mmHg) and **alveolar PCO2 would be low** (approaching zero).

Q: With increase in age, which of the following statements about lung function is true?

Pulmonary compliance increases. ***Pulmonary compliance increases*** - With **increasing age**, there is a loss of **elastic recoil** in the lungs due to changes in elastin and collagen fibers, leading to an increase in **pulmonary compliance**. - This increased compliance means the lungs become less stiff and easier to inflate, but also less able to recoil and expel air effectively. - The **net effect** of aging is increased compliance, as the loss of elastic fibers is the predominant change in normal aging. *Residual volume decreases* - **Residual volume (RV)** actually **increases** with age. This is because the loss of elastic recoil makes it harder to fully exhale, causing more air to remain in the lungs after a maximal exhalation. - An increased residual volume contributes to an overall rise in **functional residual capacity** and total lung capacity in older adults. *Mucociliary clearance increases* - **Mucociliary clearance** generally **decreases** with age. This is due to a reduction in the number and function of cilia, as well as changes in mucus quality. - Impaired mucociliary clearance makes older individuals more susceptible to respiratory infections and difficulties in clearing secretions. *Fibrosis of the interstitium decreases* - The **fibrosis of the interstitium** can **increase** with age in some individuals. However, in normal aging (without pathological conditions), the predominant change is loss of elastic recoil rather than significant fibrotic changes. - When present, increased interstitial fibrosis would make the lungs stiffer, but this is not the primary age-related change in healthy individuals.

Q: What is the partial pressure for oxygen in the inspired air?

158 mm Hg. ***158 mm Hg*** - The partial pressure of oxygen in inspired air (PIO2) is calculated by multiplying the **fraction of inspired oxygen (FiO2)** by the total atmospheric pressure. - At sea level, atmospheric pressure is approximately **760 mm Hg** and FiO2 is 21% (0.21), so 0.21 × 760 mm Hg = **159.6 mm Hg**, which rounds to 158 mm Hg. - This represents **dry atmospheric air** before it enters the respiratory tract. *116 mm Hg* - This value does not correspond to a standard physiological measurement in respiratory physiology. - It is lower than inspired air PO2 but higher than alveolar PO2, making it an intermediate value used as a distractor. - **Humidified tracheal air** has PO2 of approximately 150 mm Hg: (760-47) × 0.21 = 149.7 mm Hg, where 47 mm Hg is water vapor pressure. *0.3 mm Hg* - This value is extremely low and represents the approximate **partial pressure of oxygen in mixed venous blood**, not inspired air. - Such a low value in inspired air would indicate **severe hypoxia** incompatible with life. - This is used as an unrealistic distractor. *100 mm Hg* - This value represents the approximate **partial pressure of oxygen in alveolar air (PAO2) and arterial blood (PaO2)**. - It is lower than inspired air due to humidification, mixing with residual air, and continuous oxygen uptake by blood. - It does not represent the partial pressure of oxygen in the inspired atmospheric air.

Q: What is the Haldane Effect?

CO2 delivery by increased O2. ***CO2 delivery by increased O2*** - The **Haldane effect** describes how **oxygenation of hemoglobin** decreases its affinity for **carbon dioxide (CO2)**, leading to the release of CO2 from the blood. - This is crucial in the lungs, where high oxygen levels promote CO2 unloading for exhalation. *O2 delivery by increased CO2* - This describes the **Bohr effect**, where an increase in **carbon dioxide (CO2)** or acidity in the tissues causes hemoglobin to release **oxygen (O2)**. - The Haldane effect is the converse, relating oxygen binding to CO2 release, not the other way around. *CO2 delivery by increased CO2* - This statement is inherently circular and does not describe a physiological effect. - It confuses the mechanism with the substance being transported. *O2 delivery by increased CO* - **Carbon monoxide (CO)** has a much higher affinity for hemoglobin than oxygen, forming **carboxyhemoglobin** and impairing oxygen delivery. - This is related to **carbon monoxide poisoning**, not a physiological regulatory effect like the Haldane or Bohr effects.

Q: Damage to pneumotaxic center along with vagus nerve causes which type of respiration?

Apneustic breathing. ***Apneustic breathing*** - Damage to the **pneumotaxic center** prevents the normal inhibition of inspiration, leading to **prolonged inspiratory gasps**. - **Vagal nerve damage** further removes the inhibitory feedback from the lungs, exacerbating the inspiratory "holds" characteristic of apneustic breathing. *Cheyne-Stokes breathing* - This pattern is characterized by a **crescendo-decrescendo pattern** of breathing, interspersed with periods of **apnea**. - It is often associated with conditions like **heart failure**, stroke, or severe neurological damage, not specifically the pneumotaxic center and vagus nerve. *Deep and slow breathing* - This pattern can be seen in conditions like **Kussmaul breathing** (due to metabolic acidosis) or as a compensatory mechanism. - It does not directly result from the combined damage of the **pneumotaxic center** and the **vagus nerve**. *Shallow and rapid breathing* - This pattern is commonly seen in restrictive lung diseases, anxiety, or pain, where tidal volume is decreased and respiratory rate increased. - It does not reflect the **prolonged inspiration** that would result from a compromised pneumotaxic center and vagal input.

Q: Which of the following parameters indicates the elimination of CO2 from the lungs?

PaCO2. ***PaCO2*** - **Partial pressure of carbon dioxide in arterial blood (PaCO2)** directly reflects the efficiency of **alveolar ventilation**, which is the process of eliminating CO2 from the lungs. - When CO2 elimination is adequate, PaCO2 remains within the normal range (35-45 mmHg); higher or lower values indicate ventilatory impairment or hyperventilation, respectively. *PaO2* - **PaO2** measures the partial pressure of **oxygen in arterial blood** and indicates oxygenation, not the efficiency of carbon dioxide elimination. - While CO2 elimination and oxygenation are interdependent, **PaO2** primarily reflects how well oxygen is being transported from the lungs to the blood. *pH* - **pH** indicates the **acidity or alkalinity of the blood**, which is influenced by both respiratory (CO2) and metabolic (bicarbonate) components. - Although CO2 elimination affects pH through the carbonic acid-bicarbonate buffer system, pH itself is an overall measure of acid-base balance, not a direct indicator of CO2 elimination. *HCO3 level* - **Bicarbonate (HCO3-)** is a **metabolic component** of the acid-base balance, primarily regulated by the kidneys. - While it helps buffer CO2-induced acid changes, HCO3 level alone does not directly reflect the efficiency of CO2 elimination from the lungs.

Q: In zero gravity, the V/Q ratio is?

1. ***Correct: 1*** - In **zero gravity**, the normal physiological effects of gravity on both ventilation and perfusion are eliminated, leading to a more uniform distribution. - Without gravity, blood flow and gas distribution become more even throughout the lungs, resulting in a V/Q ratio that approaches **unity (1)** across all lung regions. - This represents the ideal physiological state where ventilation perfectly matches perfusion. *Incorrect: 0.8* - A V/Q ratio of **0.8** represents the **average normal V/Q ratio** in an upright individual on Earth, where gravity creates disparities in ventilation and perfusion. - This value is an average, with regional variations (apex ~3.3, base ~0.6) in the lungs; it does not reflect the uniform conditions of zero gravity. *Incorrect: 2* - A V/Q ratio of **2** would indicate a significant **ventilation-perfusion mismatch** where ventilation greatly exceeds perfusion. - This scenario suggests substantial **dead space ventilation**, which is not the expected outcome in a zero-gravity environment where distribution is balanced. *Incorrect: 3* - A V/Q ratio of **3** represents an even more extreme case of **ventilation exceeding perfusion**, indicating severe physiologic dead space. - Such a high V/Q ratio would signify a major functional impairment, which is contrary to the more ideal and uniform distribution expected in zero gravity.

Q: What is the respiratory quotient?

CO2 released to O2 consumed. **CO2 released to O2 consumed** - The **respiratory quotient (RQ)** is a ratio used in metabolism to describe the proportion of **carbon dioxide (CO2) produced** by the body relative to the **oxygen (O2) consumed**. - It is calculated as the **volume of CO2 released** divided by the **volume of O2 consumed** over a specific period. - RQ = VCO2/VO2, where VCO2 is CO2 production and VO2 is O2 consumption. *CO2 consumed to O2 released* - This option is incorrect as it reverses the correct order and refers to **CO2 consumption and O2 release**, which are not the standard components of the RQ calculation. - The body primarily **releases CO2** and **consumes O2** during cellular respiration. *O2 released to CO2 consumed* - This option is also incorrect because it inverts both the gases and the direction of their metabolic flow (release vs. consumption). - Metabolic processes involve **O2 consumption** and **CO2 release**, not the other way around. *O2 consumed to CO2 released* - This option incorrectly reverses the numerator and denominator in the RQ formula. - The standard definition places **CO2 production** in the numerator and **O2 consumption** in the denominator.

Question 1

In forceful expiration, which of the following neurons gets fired?

Accepted Answer

VRG

Answer

DRG

Answer

Pneumotaxic centre

Answer

Chemoreceptors

Question 2

Functional residual capacity (FRC) is defined as the volume of air remaining in the lungs at which specific moment in the respiratory cycle?

Accepted Answer

After normal expiration

Answer

During active expiration

Answer

At peak inspiration

Answer

During active inspiration

Question 3

What happens to gas exchange when the Va/Q ratio approaches infinity?

Accepted Answer

No exchange of O2 and CO2 occurs.

Answer

Partial pressure of O2 becomes negligible.

Answer

Partial pressure of CO2 becomes negligible.

Answer

Partial pressures of both CO2 and O2 remain normal.

Question 4

With increase in age, which of the following statements about lung function is true?

Accepted Answer

Pulmonary compliance increases

Answer

Fibrosis of the interstitium decreases

Answer

Residual volume decreases

Answer

Mucociliary clearance increases

Question 5

What is the partial pressure for oxygen in the inspired air?

Accepted Answer

158 mm Hg

Answer

116 mm Hg

Answer

0.3 mm Hg

Answer

100 mm Hg

Question 6

What is the Haldane Effect?

Accepted Answer

CO2 delivery by increased O2

Answer

O2 delivery by increased CO2

Answer

CO2 delivery by increased CO2

Answer

O2 delivery by increased CO

Question 7

Damage to pneumotaxic center along with vagus nerve causes which type of respiration?

Accepted Answer

Apneustic breathing

Answer

Cheyne-Stokes breathing

Answer

Deep and slow breathing

Answer

Shallow and rapid breathing

Question 8

Which of the following parameters indicates the elimination of CO2 from the lungs?

Accepted Answer

PaCO2

Answer

pH

Answer

PaO2

Answer

HCO3 level

Question 9

In zero gravity, the V/Q ratio is?

Accepted Answer

1

Answer

0.8

Answer

2

Answer

3

Question 10

What is the respiratory quotient?

Accepted Answer

CO2 released to O2 consumed

Answer

CO2 consumed to O2 released

Answer

O2 released to CO2 consumed

Answer

O2 consumed to CO2 released

Respiratory System — MCQs

Respiratory System — MCQs

On this page

Practice by Chapter

Want unlimited practice?