Respiratory System Practice Questions

Q: What is characteristic of the base of the lung compared to the apex of the lung?

Higher ventilation/perfusion ratio. **Explanation:** In the upright position, both ventilation (V) and perfusion (Q) increase from the apex to the base of the lung due to the effects of gravity. However, **perfusion increases much more steeply than ventilation** as we move downwards. 1. **Why Option C is Correct:** The Ventilation/Perfusion (V/Q) ratio is determined by the relative rates of these two parameters. At the **apex**, ventilation is higher than perfusion, resulting in a high V/Q ratio (approx. 3.3). At the **base**, perfusion is significantly higher than ventilation, leading to a **lower V/Q ratio (approx. 0.6)**. Therefore, the apex has a higher V/Q ratio compared to the base. 2. **Why Other Options are Incorrect:** * **Option A & B:** Because the apex has a high V/Q ratio (over-ventilated relative to blood flow), the alveolar $P_{O2}$ is higher and $P_{CO2}$ is lower at the apex. Conversely, the base has a lower $P_{O2}$ and higher $P_{CO2}$ in the capillary blood leaving the alveoli. * **Option D:** V/Q ratios are never uniform across the lung in a vertical position due to the uneven distribution of blood flow (West Zones). **High-Yield Clinical Pearls for NEET-PG:** * **Zone of West:** The lung is divided into three zones. Zone 1 (Apex) has the highest V/Q ratio; Zone 3 (Base) has the lowest. * **Tuberculosis:** *M. tuberculosis* prefers the **apex** of the lung because the high V/Q ratio there provides a high-oxygen environment favorable for its growth. * **Compliance:** Alveoli at the **base** are more compliant and expand more during inspiration compared to the already "stretched" alveoli at the apex.

Q: Increased ventilation at the start of exercise is primarily due to which of the following?

Proprioceptors. **Explanation:** The control of ventilation during exercise occurs in three distinct phases. The **immediate increase** in ventilation at the very onset of exercise (Phase I) occurs before any metabolic changes can be detected in the blood. **Why Proprioceptors are correct:** This rapid initial rise is mediated by **neural mechanisms** rather than chemical ones. As muscles begin to contract and joints move, **proprioceptors** (mechanoreceptors in joints and muscles) send excitatory impulses to the respiratory center in the medulla. Simultaneously, the "central command" from the motor cortex stimulates both the muscles and the respiratory centers. This anticipatory response ensures that oxygen delivery and CO₂ removal increase the moment physical activity begins. **Analysis of Incorrect Options:** * **A. Stretch Receptors:** These are involved in the Hering-Breuer reflex, which prevents over-inflation of the lungs by inhibiting inspiration; they do not initiate the exercise response. * **C. Pain Receptors:** While pain can increase respiratory rate (hyperpnea), it is not the physiological trigger for the coordinated ventilatory increase seen at the start of exercise. * **D. Arterial PCO₂:** This is the most potent stimulus for respiration at **rest**. However, during exercise, arterial PCO₂ actually tends to remain constant or even slightly decrease due to alveolar hyperventilation. It is responsible for the gradual adjustment (Phase II), not the immediate start. **High-Yield NEET-PG Pearls:** * **Phase I (Start):** Neural (Proprioceptors + Central Command). * **Phase II (During):** Humoral/Chemical factors (though PaO₂ and PaCO₂ remain remarkably stable in healthy individuals). * **Phase III (Recovery):** Gradual decline as neural stimulus ceases and "oxygen debt" is repaid. * **Key Fact:** The primary driver for increased ventilation during exercise is **not** hypoxia or hypercapnia, but neural feed-forward mechanisms.

Q: Ventilation-perfusion ratio is least at which part of the lung?

Base. **Explanation:** The Ventilation-Perfusion ratio (V/Q) is determined by the relationship between alveolar ventilation (V) and pulmonary blood flow (Q). In a standing individual, both ventilation and perfusion increase from the apex to the base due to the effects of gravity. However, **perfusion (Q) increases much more steeply than ventilation (V)** as we move down the lung. 1. **Why the Base is Correct:** At the base, the increase in blood flow is disproportionately higher than the increase in ventilation. Because the denominator (Q) is significantly larger, the **V/Q ratio is lowest at the base** (approximately **0.6**). 2. **Why the Apex is Incorrect:** At the apex, both V and Q are lower than at the base, but blood flow is particularly low due to gravity. Since the denominator (Q) is very small, the **V/Q ratio is highest at the apex** (approximately **3.0**). 3. **Why the Middle Lobe is Incorrect:** The middle lobe represents a transitional zone where the V/Q ratio is intermediate (closer to the ideal 0.8–1.0) compared to the extremes of the apex and base. **High-Yield NEET-PG Pearls:** * **V/Q Ratio Values:** Apex ≈ 3.0 (High); Base ≈ 0.6 (Low). * **Gas Exchange:** Because the V/Q is highest at the apex, $P_AO_2$ is highest and $P_ACO_2$ is lowest there. * **Clinical Correlation:** *Mycobacterium tuberculosis* prefers the apex because the high V/Q ratio results in a high oxygen tension ($P_AO_2$), which favors the growth of this aerobe. * **Zone 3 of West:** Located at the base, where both arterial and venous pressures exceed alveolar pressure ($Pa > Pv > PA$), leading to maximum perfusion.

Q: Surfactant contains?

DPCC. **Explanation:** **1. Why DPCC is Correct:** Pulmonary surfactant is a complex mixture of lipids and proteins secreted by **Type II alveolar epithelial cells**. Its primary component (approx. 90%) is phospholipids, the most abundant and functionally significant being **Dipalmitoylphosphatidylcholine (DPPC)**, also known as **Lecithin**. * **Mechanism:** DPPC is an amphipathic molecule that reduces **surface tension** at the air-liquid interface of the alveoli. By lowering surface tension, it prevents alveolar collapse (atelectasis) during expiration and increases lung compliance, thereby reducing the work of breathing. **2. Why Incorrect Options are Wrong:** * **B. Nitrous oxide:** This is an inorganic gas used primarily as an anesthetic and analgesic agent; it is not a structural component of the lung or surfactant. * **C. Angiotensin:** While the lungs are the primary site for the conversion of Angiotensin I to Angiotensin II (via ACE located in the pulmonary capillary endothelium), Angiotensin itself is a hormone involved in blood pressure regulation, not a component of surfactant. * **D. VIP (Vasoactive Intestinal Peptide):** This is a neuropeptide that acts as a bronchodilator and vasodilator in the lungs, but it is not a constituent of the surfactant complex. **3. High-Yield Clinical Pearls for NEET-PG:** * **L/S Ratio:** A Lecithin/Sphingomyelin ratio **> 2.0** in amniotic fluid indicates fetal lung maturity. * **Surfactant Proteins:** Contains four proteins: **SP-A and SP-D** (innate immunity/opsonization) and **SP-B and SP-C** (surface activity). **SP-B** is the most critical for surfactant function. * **Clinical Correlation:** Deficiency of surfactant in premature infants leads to **Infant Respiratory Distress Syndrome (IRDS)** or Hyaline Membrane Disease. * **Stimulus for Secretion:** Alveolar expansion (deep breathing/stretching) is the most important physiological stimulus for surfactant release.

Q: Why do males have deeper voices compared to females?

Longer vocal cords. **Explanation:** The pitch of the human voice is primarily determined by the **length, tension, and mass** of the vocal cords. During puberty, the surge of testosterone in males leads to significant anatomical changes in the larynx. **1. Why "Longer vocal cords" is correct:** In males, the vocal cords grow significantly longer (approx. 17–25 mm) compared to females (approx. 12–17 mm). According to the principles of acoustics, longer and thicker vocal cords vibrate at a **lower frequency**. This lower fundamental frequency results in a deeper, more resonant voice. **2. Analysis of Incorrect Options:** * **B. Increased vibration due to testosterone:** This is physiologically incorrect. Testosterone causes the cords to become thicker and longer, which actually leads to a **decrease** in the frequency of vibration (slower vibration), resulting in a lower pitch. * **C. Infrathyroid position of the larynx:** The larynx is located anterior to the pharynx; "infrathyroid" is not a standard anatomical term describing laryngeal position in relation to gender-based pitch. * **D. Thickened arytenoids:** While the laryngeal cartilages enlarge, the pitch is specifically determined by the vocal folds (cords) themselves, not the thickness of the arytenoid cartilages. **Clinical Pearls for NEET-PG:** * **The "Adam’s Apple":** The male larynx grows larger and tilts anteriorly, creating the laryngeal prominence (thyroid cartilage). * **Hormonal Influence:** Voice deepening is a **secondary sexual characteristic**. If prepubertal castration occurs (historical "Castrati"), the larynx does not enlarge, and the high-pitched prepubescent voice is maintained. * **Pitch vs. Intensity:** Pitch is determined by frequency (vocal cord length/tension), while intensity (loudness) is determined by the amplitude of vibration and subglottic air pressure.

Q: Which of the following is required for pulmonary maturation during gestation?

Surfactant. **Explanation:** The correct answer is **Surfactant**. Pulmonary maturation is defined by the lung's ability to maintain alveolar stability and facilitate gas exchange after birth. The most critical factor for this process is the production of pulmonary surfactant by **Type II pneumocytes**. **Why Surfactant is Correct:** Surfactant is a lipoprotein complex (primarily Dipalmitoylphosphatidylcholine - DPPC) that reduces **surface tension** at the air-liquid interface of the alveoli. According to the Law of Laplace ($P = 2T/r$), smaller alveoli have a higher collapsing pressure. Surfactant prevents this collapse (atelectasis) during expiration, increases lung compliance, and reduces the work of breathing. Its production begins around 24–28 weeks of gestation and reaches maturity by 35 weeks. **Analysis of Incorrect Options:** * **A. Cortisol:** While cortisol is the most important *hormonal stimulus* that triggers surfactant synthesis, it is not the substance that provides maturation itself. It is a catalyst, not the functional end-product. * **C. Amniotic Fluid:** Though the fetus "breathes" amniotic fluid to help expand the lungs structurally, it does not contribute to biochemical maturation or surface tension reduction. * **D. Acetylcholine:** This is a neurotransmitter involved in parasympathetic signaling and has no direct role in the structural or biochemical maturation of the fetal lung. **High-Yield NEET-PG Pearls:** * **L/S Ratio:** A Lecithin/Sphingomyelin ratio **>2.0** in amniotic fluid indicates fetal lung maturity. * **Glucocorticoids:** Betamethasone or Dexamethasone is administered to mothers in preterm labor (before 34 weeks) to accelerate surfactant production. * **NRDS:** Deficiency of surfactant leads to Neonatal Respiratory Distress Syndrome (Hyaline Membrane Disease), characterized by widespread atelectasis and ground-glass appearance on X-ray.

Question 1

What is the functional residual capacity?

Accepted Answer

The amount of air that can be forcibly exhaled from the lungs after normal exhalation.

Answer

The amount of air remaining in the lungs after a normal exhalation.

Answer

The maximum amount of air that can be forcibly exhaled from the lungs after maximum inhalation.

Answer

The total amount of air in the lungs after maximum inhalation.

Question 2

What is characteristic of the base of the lung compared to the apex of the lung?

Accepted Answer

Higher ventilation/perfusion ratio

Answer

Higher pulmonary arterial oxygen pressure

Answer

Higher pulmonary arterial carbon dioxide pressure

Answer

Same ventilation/perfusion ratio

Question 3

Increased ventilation at the start of exercise is primarily due to which of the following?

Accepted Answer

Proprioceptors

Answer

Stretch receptors

Answer

Pain receptors

Answer

Arterial PCO2

Question 4

Ventilation-perfusion ratio is least at which part of the lung?

Accepted Answer

Base

Answer

Apex

Answer

Middle lobe

Answer

None

Question 5

Surfactant contains?

Accepted Answer

DPCC

Answer

Nitrous oxide

Answer

Angiotensin

Answer

VIP

Question 6

Why do males have deeper voices compared to females?

Accepted Answer

Longer vocal cords

Answer

Increased vibration due to testosterone

Answer

Infrathyroid position of the larynx

Answer

Thickened arytenoids

Question 7

Which of the following is required for pulmonary maturation during gestation?

Accepted Answer

Surfactant

Answer

Cortisol

Answer

Amniotic fluid

Answer

Acetylcholine

Question 8

Toxic effects of high oxygen tension include all of the following except?

Accepted Answer

Decreased cerebral blood flow

Answer

Pulmonary edema

Answer

Retinal damage

Answer

CNS excitation and convulsion

Question 9

Holding one's breath after hyperventilating for some time is dangerous because:

Accepted Answer

Alkalosis can lead to tetany.

Answer

It can lead to CO2 necrosis.

Answer

Lack of CO2 stimulation can lead to dangerous levels of anoxia.

Answer

Decreased CO2 shifts the oxygen dissociation curve to the left.

Question 10

If the concentration of inhaled O2 is doubled in a normal person, what will be the resultant effect?

Accepted Answer

O2 dissolved in plasma increases, but O2 bound to Hb remains relatively constant

Answer

O2 dissolved in plasma increases, but O2 bound to Hb decreases

Answer

O2 dissolved in plasma remains constant, but O2 bound to Hb increases

Answer

O2 dissolved in plasma remains constant, but O2 bound to Hb remains constant

Respiratory System — MCQs

Respiratory System — MCQs

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