NEET-PG 2015 - Physiology Practice Questions

Q: Which of the following structures contains baroreceptors that detect changes in blood pressure?

Carotid sinus. ***Carotid sinus*** - The **carotid sinus** is a dilation at the bifurcation of the common carotid artery, containing **baroreceptors** sensitive to changes in blood pressure [1]. - These baroreceptors are **mechanoreceptors** that respond to the stretching of the vessel wall due to increased arterial pressure, sending signals to the brainstem to regulate blood pressure. *Carotid body* - The **carotid body** is a chemoreceptor that primarily detects changes in **blood oxygen, carbon dioxide, and pH** levels, not blood pressure [2]. - It plays a crucial role in regulating **respiration** in response to hypoxemia. *Aortic body* - The **aortic body** is a **chemoreceptor** located near the aortic arch that primarily monitors **blood oxygen, carbon dioxide, and pH levels**. - Note: While the aortic body itself is a chemoreceptor, the **aortic arch** (a different structure) does contain baroreceptors [1]. However, this option specifically refers to the aortic body, which is not a baroreceptor. - The aortic body contributes to the regulation of **respiration** in response to hypoxemia, not directly blood pressure. *None of the options* - This option is incorrect because the **carotid sinus** is a well-known site for baroreceptors involved in blood pressure regulation.

Q: Which of the following is the MOST important factor determining whether a substance can be filtered at the glomerulus?

Molecular weight of the substance. ***Molecular weight of the substance*** - The **glomerular filtration barrier** acts as a size-selective filter, generally permeable to substances with a molecular weight less than 5,000-10,000 Daltons - Larger molecules are typically restricted from filtration due to the **size exclusion** property of the glomerular basement membrane and podocyte slit diaphragms - This is the **primary determinant** of whether a substance can be filtered at all, making it the most important factor among the given options *Lipid solubility of the substance* - **Lipid solubility** is more relevant for reabsorption and secretion in the renal tubules, particularly for passive diffusion across tubular cell membranes - It has minimal direct influence on the initial filtration process at the glomerulus, which is primarily a **pressure-driven, size- and charge-selective ultrafiltration** process - The glomerular capillary wall is not a lipid membrane barrier for the filtration process *Binding capacity to albumin* - Substances bound to **large plasma proteins** like albumin (molecular weight ~67,000 Daltons) cannot pass through the glomerular filtration barrier - While important for determining the *free, filterable fraction* of a substance in plasma, the binding itself is secondary to the fundamental molecular weight/size restriction - Only the **free (unbound) fraction** of a substance is available for filtration, and whether it filters depends primarily on its molecular weight *None of the options* - This option is incorrect because **molecular weight** is indeed the most critical factor among the given options for determining whether a substance can be filtered at the glomerulus

Q: Mechanism of secretion of ammonia in distal tubule is?

Passive diffusion. ***Passive diffusion*** - Ammonia (NH3) is a **lipid-soluble molecule** that can readily cross cell membranes, including those of the distal tubule and collecting duct, down its **concentration gradient**. - This process is crucial for regulating **acid-base balance**, as NH3 traps H+ ions to form NH4+, which is then excreted. *Primary active transport* - This mechanism involves the direct use of **ATP hydrolysis** to move ions against their concentration gradient, which is not the primary way ammonia is secreted in the distal tubule. - While NH4+ can be secreted via active transport in some segments (e.g., substituting for K+ on the Na-K-2Cl cotransporter in the thick ascending limb), free ammonia diffusion is distinct. *Symport* - **Symport** involves the co-transport of two or more different molecules or ions in the same direction across a cell membrane, powered by an electrochemical gradient. - This mechanism is not typically involved in the secretion of uncharged, lipid-soluble ammonia. *Antiport* - **Antiport** is a type of coupled transport where two different ions or molecules move in opposite directions across a membrane. - While antiport systems are essential for various renal functions (e.g., Na+/H+ exchanger), they are not the primary mechanism for the secretion of free ammonia in the distal tubule.

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: Vital capacity is measured by:

Spirometer. ***Spirometer*** - A **spirometer** is a device used to measure lung volumes and capacities, including **vital capacity**. - It measures the volume of air inspired and expired by evaluating mechanical changes in the volume of air in the lungs. *Plethysmography* - **Plethysmography** is primarily used to measure **residual volume** and **total lung capacity**, not vital capacity directly. - This method measures changes in body volume to infer changes in lung volume. *Gas-dilution method* - The **gas-dilution method**, typically using helium, is used to measure the **functional residual capacity (FRC)** and subsequently calculate residual volume and total lung capacity. - It involves rebreathing a known concentration of gas to determine the volume of gas already in the lungs. *Nitrogen washout technique* - The **nitrogen washout technique** is also used to measure **functional residual capacity (FRC)** and detect uneven ventilation. - It involves breathing 100% oxygen to wash out all nitrogen from the lungs, allowing for calculation of lung volumes.

Q: Which part of the sympathetic nervous system is responsible for secreting catecholamines?

Adrenal medulla. ***Adrenal medulla*** - The adrenal medulla acts as a modified **sympathetic ganglion**, directly innervated by **preganglionic sympathetic fibers**. - Upon stimulation, it releases a high concentration of **epinephrine** (adrenaline) and a smaller amount of **norepinephrine** (noradrenaline) into the bloodstream, acting as hormones. *Cardiac ganglion* - **Cardiac ganglia** are parasympathetic ganglia located in the heart, involved in regulating heart rate and contractility via acetylcholine release. - They do not secrete **catecholamines** but rather act as relay stations for parasympathetic innervation. *Cervical sympathetic chain* - The **cervical sympathetic chain** primarily innervates structures in the head, neck, and upper limbs, influencing functions like pupils, salivary glands, and sweat glands. - While it contains sympathetic neurons, its primary role is not the systemic release of **catecholamines** into the bloodstream. *Thoracic sympathetic chain* - The **thoracic sympathetic chain** provides sympathetic innervation to organs in the thoracic and abdominal cavities, influencing heart rate, bronchodilation, and visceral blood flow. - Like other sympathetic ganglia, it releases norepinephrine at target organ synapses, but it does not serve as a major endocrine gland for systemic catecholamine release.

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: Isocapnic buffering is?

Normal pCO2 with increased CO2. ***Normal pCO2 with increased CO2*** - Isocapnic buffering refers to the process where the body buffers an **increase in lactic acid** or other metabolic acids without a significant change (maintaining it within a normal range) in **arterial partial pressure of carbon dioxide (pCO2)**. - This is achieved by an increase in **ventilation** stimulated by the acid, which expels more CO2 to compensate for the additional CO2 produced from the buffering reaction, thereby keeping pCO2 stable. *Increased pCO2 with increased CO2* - This scenario would indicate **hypoventilation** or a failure of the respiratory compensation mechanism to maintain pCO2 within normal limits during an increased metabolic CO2 load. - **Increased pCO2** would signify a state of **respiratory acidosis** or inadequate respiratory compensation, not isocapnic buffering. *Increased pCO2 with decreased CO2* - This statement is inherently contradictory; it is not possible to have an **increased pCO2** simultaneously with **decreased CO2** in the context of buffering. - **pCO2** is a measure of the partial pressure of carbon dioxide, directly related to the amount of CO2 present and dissolved in the blood. *None of the options* - This option is incorrect because "Normal pCO2 with increased CO2" accurately describes the physiological phenomenon of **isocapnic buffering**.

Question 1

Which of the following structures contains baroreceptors that detect changes in blood pressure?

Accepted Answer

Carotid sinus

Answer

Carotid body

Answer

Aortic body

Answer

None of the options

Question 2

Which of the following is the MOST important factor determining whether a substance can be filtered at the glomerulus?

Accepted Answer

Molecular weight of the substance

Answer

Lipid solubility of the substance

Answer

Binding capacity to albumin

Answer

None of the options

Question 3

Mechanism of secretion of ammonia in distal tubule is?

Accepted Answer

Passive diffusion

Answer

Primary active transport

Answer

Symport

Answer

Antiport

Question 4

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 5

What is the PRIMARY mechanism by which the Na+-Ca2+ exchanger functions in cardiac muscle cells?

Accepted Answer

Na+-Ca2+ exchanger acts to remove Ca2+ from heart muscle cells

Answer

Na+-Ca2+ exchanger requires ATP directly

Answer

The Na+-Ca2+ exchanger operates in reverse mode during normal cardiac contraction

Answer

The Na+-Ca2+ exchanger primarily moves Ca2+ into cardiac muscle cells during systole

Question 6

What does the ST Segment of an ECG correspond to?

Accepted Answer

Plateau phase between ventricular depolarization and repolarization

Answer

Ventricular depolarization

Answer

Atrial depolarization

Answer

AV Conduction

Question 7

Vital capacity is measured by:

Accepted Answer

Spirometer

Answer

Plethysmography

Answer

Nitrogen washout technique

Answer

Gas-dilution method

Question 8

Which part of the sympathetic nervous system is responsible for secreting catecholamines?

Accepted Answer

Adrenal medulla

Answer

Cardiac ganglion

Answer

Cervical sympathetic chain

Answer

Thoracic sympathetic chain

Question 9

In zero gravity, the V/Q ratio is?

Accepted Answer

1

Answer

0.8

Answer

2

Answer

3

Question 10

Isocapnic buffering is?

Accepted Answer

Normal pCO2 with increased CO2

Answer

None of the options

Answer

Increased pCO2 with increased CO2

Answer

Increased pCO2 with decreased CO2

NEET-PG 2015 — Physiology