Respiratory System Practice Questions

Q: The afferent (sensory) endings for the Hering-Breuer reflex are mechanoreceptors located in which part of the respiratory system?

Bronchi and bronchioles. **Explanation** The **Hering-Breuer Inflation Reflex** is a protective mechanism that prevents over-inflation of the lungs. The reflex is initiated when the tidal volume exceeds a certain threshold (typically >1.5 liters in adults). **1. Why Bronchi and Bronchioles are correct:** The afferent receptors for this reflex are **slowly adapting stretch receptors (mechanoreceptors)** located within the smooth muscle walls of the **bronchi and bronchioles**. When the lungs inflate, these receptors are stretched, sending inhibitory impulses via the **Vagus nerve (CN X)** to the inspiratory center (dorsal respiratory group) in the medulla. This terminates inspiration and initiates expiration, effectively regulating the depth of breathing. **2. Why other options are incorrect:** * **Carotid arteries:** These contain peripheral chemoreceptors (Carotid bodies) that sense changes in $PaO_2$, $PaCO_2$, and pH, not lung stretch. * **Alveoli:** While gas exchange occurs here, the primary stretch receptors for the Hering-Breuer reflex are located in the conducting airways (bronchi/bronchioles), not the alveolar walls. (Note: J-receptors are located near alveolar capillaries but respond to congestion/edema). * **Diaphragm:** This is an effector muscle. It contains muscle spindles, but they are not the primary mediators of the Hering-Breuer reflex. **High-Yield Clinical Pearls for NEET-PG:** * **Afferent Pathway:** Vagus Nerve (CN X). * **Effect:** It increases the respiratory rate by shortening the duration of inspiration (it is a "self-terminating" mechanism). * **Infants:** This reflex is much more active and physiologically significant in neonates than in healthy adults. * **Hering-Breuer Deflation Reflex:** A separate reflex where lung deflation triggers an increase in inspiratory effort (to prevent lung collapse).

Q: The surfactant is secreted by which type of cell in the alveoli?

Type 2 Pneumocyte. **Explanation:** **Correct Option: B. Type 2 Pneumocyte** Surfactant is a surface-active lipoprotein complex (primarily consisting of **Dipalmitoylphosphatidylcholine - DPPC**) secreted by **Type 2 Pneumocytes** (also known as granular pneumocytes). These cells are cuboidal in shape and contain characteristic secretory organelles called **Lamellar bodies**. The primary function of surfactant is to reduce surface tension at the air-liquid interface of the alveoli, preventing alveolar collapse (atelectasis) during expiration and increasing lung compliance. **Analysis of Incorrect Options:** * **A. Type 1 Pneumocyte:** These are thin, squamous cells covering ~95% of the alveolar surface area. Their primary role is providing a thin barrier for efficient **gas exchange**, not secretion. * **C. Alveolar Epithelial cells:** This is a general term encompassing both Type 1 and Type 2 pneumocytes. While technically correct in a broad sense, "Type 2 Pneumocyte" is the specific and most accurate answer required for medical examinations. * **D. Alveolar Macrophage:** Also known as **Dust cells**, these are mononuclear phagocytes that scavenge inhaled particulates and pathogens. They do not produce surfactant; however, they play a role in its degradation/clearance. **High-Yield Clinical Pearls for NEET-PG:** * **Development:** Surfactant production begins around **24–28 weeks** of gestation, but adequate levels are often not reached until **35 weeks**. * **Clinical Correlation:** Deficiency of surfactant in premature infants leads to **Infant Respiratory Distress Syndrome (IRDS)** or Hyaline Membrane Disease. * **L/S Ratio:** A Lecithin/Sphingomyelin ratio of **>2:1** in amniotic fluid indicates fetal lung maturity. * **Glucocorticoids:** These are administered to mothers in preterm labor to accelerate surfactant synthesis by stimulating Type 2 pneumocytes.

Q: Hypoxic hypoxia is seen in which of the following conditions?

Arteriovenous shunt. **Explanation:** Hypoxia is defined as a deficiency in the amount of oxygen reaching the tissues. It is classified into four types: Hypoxic, Anemic, Stagnant, and Histotoxic. **1. Why Arteriovenous (AV) Shunt is Correct:** **Hypoxic hypoxia** is characterized by a low partial pressure of arterial oxygen (**PaO₂**). In an **Arteriovenous shunt** (specifically right-to-left shunts), deoxygenated venous blood bypasses the ventilated alveoli and mixes directly with oxygenated arterial blood. This "venous admixture" dilutes the oxygen content and significantly lowers the PaO₂, leading to hypoxic hypoxia. **2. Analysis of Incorrect Options:** * **Carbon Monoxide (CO) Poisoning:** This causes **Anemic Hypoxia**. CO competes with oxygen for binding sites on hemoglobin. While the PaO₂ remains normal, the oxygen-carrying capacity of the blood is severely reduced. * **Ischemia:** This leads to **Stagnant (Ischemic) Hypoxia**. Here, PaO₂ and oxygen content are normal, but blood flow to the tissues is inadequate due to heart failure or local vessel obstruction. * **Hydrogen Cyanide Poisoning:** This causes **Histotoxic Hypoxia**. The oxygen delivery to tissues is normal, but the cells cannot utilize it because cyanide inhibits the cytochrome oxidase enzyme in the electron transport chain. **High-Yield NEET-PG Pearls:** * **Hypoxic Hypoxia** is the only type where **PaO₂ is decreased**. Causes include high altitude, hypoventilation, and V/Q mismatch. * In **Anemic Hypoxia**, the oxygen dissociation curve (ODC) shifts to the **left** (in CO poisoning), but the hallmark is reduced oxygen content with normal PaO₂. * **Cyanosis** is typically absent in Histotoxic and Anemic hypoxia but is a common feature of Hypoxic and Stagnant hypoxia.

Q: Which of the following assists in the unloading of oxygen to tissue cells by oxyhemoglobin?

All of the above. The unloading of oxygen from hemoglobin to tissues is governed by the **Oxygen-Hemoglobin Dissociation Curve (OHDC)**. Factors that shift this curve to the **right** decrease hemoglobin's affinity for oxygen, thereby facilitating oxygen delivery to metabolically active cells. ### **Explanation of Options:** * **Bohr Effect:** This describes the phenomenon where an increase in $CO_2$ concentration or a decrease in $pH$ (acidity) leads to a rightward shift of the OHDC. In tissues, $CO_2$ reacts with water to form carbonic acid, lowering the $pH$ and causing hemoglobin to release $O_2$. * **2,3-Diphosphoglycerate (2,3-DPG):** This byproduct of glycolysis in RBCs binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state. This reduces oxygen affinity and promotes unloading. Levels increase during chronic hypoxia (e.g., high altitude, anemia). * **Low $PO_2$ and High $PCO_2$:** Tissues consume $O_2$ and produce $CO_2$. A low $PO_2$ creates a partial pressure gradient that pulls $O_2$ off hemoglobin, while high $PCO_2$ triggers the Bohr effect. Since all these factors independently and synergistically promote oxygen release, **Option D** is the correct answer. ### **High-Yield NEET-PG Pearls:** * **Mnemonic for Right Shift (CADET, face Right!):** **C**O2 increase, **A**cidosis, **D**PG (2,3-DPG), **E**xercise, **T**emperature increase. * **Haldane Effect:** The opposite of the Bohr effect; it describes how oxygenation of hemoglobin in the lungs promotes the unloading of $CO_2$. * **Fetal Hemoglobin (HbF):** Has a **left** shift compared to adult HbA because it does not bind 2,3-DPG effectively, allowing it to "pick up" $O_2$ from maternal blood.

Q: What substance is produced by lung tissue for use within the lungs?

Surfactant. **Explanation:** The correct answer is **Surfactant**. This question tests the distinction between substances produced by the lungs for local function versus those involved in systemic endocrine pathways. **1. Why Surfactant is Correct:** Surfactant is a surface-active lipoprotein complex (primarily Dipalmitoylphosphatidylcholine or DPPC) produced by **Type II Alveolar cells (Pneumocytes)**. Its primary role is to reduce surface tension at the air-liquid interface of the alveoli. This prevents alveolar collapse (atelectasis) during expiration and increases lung compliance. Crucially, surfactant is produced *within* the lung tissue for *local* use within the alveoli. **2. Why the Other Options are Incorrect:** * **Angiotensin I:** This is produced in the plasma when Renin acts on Angiotensinogen (secreted by the liver). It is not produced by lung tissue. * **Renin:** This enzyme is synthesized, stored, and secreted by the **Juxtaglomerular (JG) cells** of the kidneys in response to low blood pressure. * **Angiotensin II:** While the lungs are the primary site for the conversion of Angiotensin I to Angiotensin II (via **Angiotensin-Converting Enzyme (ACE)** located on the pulmonary capillary endothelium), Angiotensin II is a systemic hormone. It is released into the circulation to act on the adrenal cortex and peripheral vasculature; it is not produced for "use within the lungs." **High-Yield Clinical Pearls for NEET-PG:** * **L/S Ratio:** A Lecithin/Sphingomyelin ratio > 2.0 in amniotic fluid indicates fetal lung maturity. * **NRDS:** Deficiency of surfactant in premature infants leads to Neonatal Respiratory Distress Syndrome (Hyaline Membrane Disease). * **Glucocorticoids:** These are administered antenatally to accelerate surfactant production in cases of threatened preterm delivery. * **Amiodarone:** Can cause pulmonary toxicity by interfering with surfactant metabolism in Type II pneumocytes.

Q: Stimulation of the apneustic center causes which of the following?

Marked increase in inspiratory activity. ### Explanation The respiratory center in the brainstem consists of several groups of neurons that regulate the rate and depth of breathing. The **Apneustic Center**, located in the lower pons, plays a stimulatory role in inspiration. **Why Option B is Correct:** The primary function of the apneustic center is to send stimulatory signals to the **Dorsal Respiratory Group (DRG)** in the medulla. This stimulation prevents the "switch-off" of the inspiratory ramp signal, leading to prolonged inspiratory gasps (apneustic breathing). Therefore, its stimulation results in a **marked increase in inspiratory activity** and depth. **Analysis of Incorrect Options:** * **Option A:** Stimulation of the apneustic center actually **delays** the inhibitory signal. It is the pneumotaxic center that increases the inhibitory signal to shorten inspiration. * **Option C:** The pneumotaxic center and apneustic center act antagonistically. The pneumotaxic center (upper pons) inhibits the apneustic center to limit the duration of inspiration. * **Option D:** Cessation of respiration (apnea) occurs with bilateral destruction of the medullary centers or severe brainstem depression, not by stimulating a center that promotes inspiration. **High-Yield Facts for NEET-PG:** * **Pneumotaxic Center (Nucleus Parabrachialis):** Acts as the "off-switch" for inspiration. It increases the respiratory rate by shortening the inspiratory phase. * **Apneustic Breathing:** Characterized by long, gasping inspirations with a pause at full inspiration. It is clinically seen in lesions of the upper pons (where the pneumotaxic center is located, leaving the apneustic center unopposed). * **Hering-Breuer Reflex:** A protective mechanism where stretch receptors in the lungs signal the DRG via the Vagus nerve to stop inspiration, preventing over-inflation.

Question 1

Which of the following conditions is NOT associated with a decrease in pO2?

Accepted Answer

Interstitial fibrosing alveolitis

Answer

COPD

Answer

CHF

Answer

Bronchiectasis

Question 2

The afferent (sensory) endings for the Hering-Breuer reflex are mechanoreceptors located in which part of the respiratory system?

Accepted Answer

Bronchi and bronchioles

Answer

Carotid arteries

Answer

Alveoli

Answer

Diaphragm

Question 3

The surfactant is secreted by which type of cell in the alveoli?

Accepted Answer

Type 2 Pneumocyte

Answer

Type 1 Pneumocyte

Answer

Alveolar Epithelial cells

Answer

Alveolar Macrophage

Question 4

All of the following statements about the V/Q ratio are true EXCEPT:

Accepted Answer

Low PACO2 is found at the base of the lung.

Answer

At the apex of the lung, there is a high ventilation-perfusion ratio.

Answer

There is no change in the V/Q ratio due to postural changes.

Answer

High PAO2 is found at the apex of the lung.

Question 5

Hypoxic hypoxia is seen in which of the following conditions?

Accepted Answer

Arteriovenous shunt

Answer

Carbon monoxide poisoning

Answer

Hydrogen cyanide poisoning

Answer

Ischemia

Question 6

Which of the following assists in the unloading of oxygen to tissue cells by oxyhemoglobin?

Accepted Answer

All of the above

Answer

Bohr effect

Answer

2,3-diphosphoglycerate

Answer

Low partial pressure of oxygen and high partial pressure of carbon dioxide in tissues

Question 7

What substance is produced by lung tissue for use within the lungs?

Accepted Answer

Surfactant

Answer

Angiotensin I

Answer

Renin

Answer

Angiotensin II

Question 8

Stimulation of the apneustic center causes which of the following?

Accepted Answer

Marked increase in inspiratory activity

Answer

Decrease in the inhibitory ramp signal

Answer

Stimulation of the pneumotaxic center

Answer

Cessation of spontaneous respiration

Question 9

The major sign of hypoventilation is:

Accepted Answer

Hypercapnia

Answer

Cyanosis

Answer

Dyspnoea

Answer

Hypoxia

Question 10

Which of the following statements regarding zones of blood flow in the lung is true?

Accepted Answer

In mitral stenosis, the apex of the lung may be converted to zone III.

Answer

When changing from a standing to a supine position, the entire lung exhibits zone II blood flow.

Answer

During intermittent positive pressure ventilation (IPPV), the entire lung is converted to zone III.

Answer

In an upright posture, zone III is absent throughout the lung.

Respiratory System — MCQs

Respiratory System — MCQs

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