NEET-PG 2012 - Physiology Practice Questions

Q: What is the normal range of interstitial pressure?

-5 to 0 mmHg. ***-5 to 0 mmHg*** - The interstitial fluid is normally under a **slight negative pressure**, typically ranging from **-5 to 0 mmHg** - This negative pressure helps pull fluid from the capillaries into the interstitial space and facilitates **lymphatic drainage** - Maintained by continuous drainage of fluid and proteins by the **lymphatic system** - This range is the commonly accepted value in standard physiology references for Indian medical exams *-3 to 0 mmHg* - While this range acknowledges the typically **negative nature** of interstitial pressure, it represents a slightly narrower range - Some sources cite this as the average range, but **-5 to 0 mmHg** is the more commonly accepted standard range - Not the most precise or widely cited range for exam purposes *0 to 5 mmHg* - This range suggests a **positive interstitial pressure**, which is generally **abnormal** - Indicates **edema formation** due to excess fluid accumulation in the interstitial space - Positive pressure impairs fluid reabsorption and lymphatic drainage - Represents pathological fluid dynamics *5 to 10 mmHg* - Represents significant **positive interstitial pressure** leading to severe **interstitial edema** - Markedly impairs tissue function and fluid exchange - Indicates pathological conditions where capillary filtration far exceeds lymphatic drainage capacity - Associated with severe edematous states

Q: ANP acts at which site?

Collecting duct. ***Collecting duct*** - Atrial Natriuretic Peptide (**ANP**) exerts its primary effect on the **collecting duct** by inhibiting sodium reabsorption, leading to increased sodium and water excretion (natriuresis and diuresis). - This action helps to reduce blood volume and blood pressure in conditions like **hypervolemia**. *Glomerulus* - While ANP does cause **afferent arteriolar dilation** and **efferent arteriolar constriction**, increasing **glomerular filtration rate** (GFR), its direct tubular action is most prominent in the collecting duct. - The primary function of the glomerulus is **filtration**, influenced by many factors including pressure, but it is not the main site of ANP's direct tubular reabsorptive effects. *Loop of Henle* - The loop of Henle is responsible for establishing the **medullary osmotic gradient** and reabsorbing a significant amount of sodium and water. - ANP has minor effects on the loop of Henle, but its most impactful reabsorptive modulation occurs downstream in the collecting duct. *PCT* - The **proximal convoluted tubule (PCT)** is where the bulk of reabsorption of filtered substances (e.g., glucose, amino acids, most sodium and water) occurs. - ANP has very little direct influence on the reabsorptive processes of the PCT.

Q: Which of the following is most important in sodium and water retention ?

Renin angiotensin system. ***Renin angiotensin system*** - The **renin-angiotensin-aldosterone system (RAAS)** is the most important mechanism for **both sodium AND water retention**, which is what the question specifically asks about. - **Aldosterone** directly promotes **sodium reabsorption** in the principal cells of the collecting duct by increasing apical ENaC channels and basolateral Na-K-ATPase pumps. - **Angiotensin II** stimulates sodium reabsorption in the proximal tubule and also stimulates ADH release, contributing to water retention. - When sodium is retained, **water follows passively** due to the osmotic gradient, resulting in effective volume expansion. - RAAS is the primary system activated in states of volume depletion and is most important for combined sodium and water retention. *Vasopressin* - **Vasopressin (ADH)** primarily controls **water retention only** by increasing aquaporin-2 channels in the collecting duct. - While crucial for water balance, it has minimal direct effect on sodium reabsorption. - It causes retention of **free water**, which can actually dilute plasma sodium concentration. - ADH is the answer if the question asked about water retention alone, but not for combined sodium and water retention. *ANP* - **Atrial natriuretic peptide (ANP)** promotes **sodium and water excretion** (natriuresis and diuresis). - Released in response to atrial stretch from volume expansion. - Acts to *oppose* retention mechanisms, making it incorrect for this question. *BNP* - **Brain natriuretic peptide (BNP)** similarly promotes **natriuresis and diuresis**. - Released from ventricular myocytes in response to volume overload. - Like ANP, it acts to *excrete* sodium and water, not retain them.

Q: What is the effect of acetylcholine on the Lower Esophageal Sphincter (LES)?

Causes contraction. ***Correct Option: Causes contraction*** - Acetylcholine acts on **M3 muscarinic receptors** on LES smooth muscle cells to cause **contraction** - This is part of the **excitatory cholinergic pathway** that maintains LES tone and prevents gastroesophageal reflux - Acetylcholine is released from **excitatory motor neurons** in the myenteric plexus *Incorrect: Causes relaxation* - LES relaxation during swallowing is mediated by **nitric oxide (NO)** and **vasoactive intestinal peptide (VIP)**, NOT acetylcholine - These inhibitory neurotransmitters are released from separate **inhibitory motor neurons** - The relaxation response during swallowing is due to activation of the inhibitory pathway, which suppresses cholinergic tone *Incorrect: No effect on LES* - Acetylcholine has a significant effect on the LES - It is one of the key neurotransmitters maintaining basal LES tone - Loss of cholinergic input can lead to decreased LES pressure *Incorrect: Contraction followed by relaxation* - Acetylcholine itself causes only contraction - The swallowing reflex involves coordinated activation of inhibitory (NO/VIP) and suppression of excitatory (acetylcholine) pathways - The sequence of events is neural, not a biphasic response to acetylcholine alone

Q: Diurnal variation of ACTH depends on ?

Suprachiasmatic nucleus. ***Suprachiasmatic nucleus*** - The **suprachiasmatic nucleus (SCN)** acts as the body's **master circadian clock**, synchronizing various physiological rhythms, including the **diurnal variation of ACTH** secretion. - It receives light input from the **retina** and projects to other brain regions to regulate the timing of hormone release. *Supraoptic nucleus* - The **supraoptic nucleus (SON)** is primarily involved in the production of **vasopressin (ADH)** and **oxytocin**, which are released by the posterior pituitary. - It does not directly control the diurnal rhythm of ACTH. *Ventrolateral nucleus* - The **ventrolateral preoptic area (VLPO)** is a key region for **sleep regulation**, promoting sleep by inhibiting wake-promoting neurotransmitters. - While it contributes to sleep-wake cycles, it is not the primary regulator of ACTH's diurnal variation. *Thalamus* - The **thalamus** is a major relay center for sensory information and plays a role in consciousness, sleep, and alertness. - It does not directly control the **circadian rhythm of ACTH secretion**.

Q: Nonshivering thermogenesis in adults is due to:

Brown fat between the shoulders. ***Brown fat between the shoulders*** - In adults, the primary **effector tissue** for **non-shivering thermogenesis** is **brown adipose tissue (BAT)**, with major depots located between the shoulders, around the neck, and along the spine. - **BAT** contains specialized mitochondria with **uncoupling protein 1 (UCP1)** that uncouples oxidative phosphorylation, generating heat instead of ATP. - This is the tissue where non-shivering thermogenesis actually occurs, making it the direct answer to what non-shivering thermogenesis is "due to." *Noradrenaline* - **Noradrenaline** is the key neurotransmitter that **activates brown fat** via **β3-adrenergic receptors** to initiate non-shivering thermogenesis. - While noradrenaline is the **trigger/stimulus**, the actual heat production occurs in brown adipose tissue. - Noradrenaline itself does not produce heat directly; it acts as the signal that activates the thermogenic machinery in BAT. *Thyroid hormone* - **Thyroid hormone** increases **basal metabolic rate** and can potentiate the thermogenic response by upregulating UCP1 expression in brown fat. - Its role is **permissive and long-term** rather than being the immediate effector of acute non-shivering thermogenesis. - It modulates overall cellular metabolism but is not the primary mechanism for rapid heat generation in cold exposure. *Muscle metabolism* - **Muscle contraction** during shivering generates heat through increased ATP hydrolysis, which is **shivering thermogenesis**. - **Non-shivering thermogenesis** specifically refers to heat production **without muscle contraction**, making muscle metabolism the mechanism for shivering, not non-shivering, thermogenesis.

Q: Which of the following is NOT a location where multi-unit smooth muscle is present?

Gut. ***Gut*** - The gut primarily contains **unitary (single-unit) smooth muscle**, characterized by cells connected by **gap junctions** that allow for synchronized contractions (e.g., peristalsis). - This type of smooth muscle exhibits **spontaneous rhythmic contractions** due to pacemaker cells, and its activity is modulated by neural and hormonal inputs rather than requiring individual innervation of each cell. - Multi-unit smooth muscle is **NOT present** in the gut. *Blood vessels* - Many larger blood vessels (e.g., large arteries) contain **multi-unit smooth muscle**, which allows for **fine, graded control** over vascular tone and blood flow. - Each muscle cell is typically **innervated individually**, enabling precise regulation of contraction strength. *Iris* - The iris contains **multi-unit smooth muscle** (e.g., sphincter pupillae and dilator pupillae muscles) which control pupil size. - These muscles require **individual innervation** to allow for very fine and precise movements in response to light intensity changes. *Ciliary muscle* - The ciliary muscle of the eye contains **multi-unit smooth muscle**, which controls the shape of the lens for accommodation (focusing). - These muscle fibers are **individually innervated** to allow precise control of lens curvature for near and far vision.

Q: What happens to the pressure in the calf compartment during the heel touch phase of walking?

Increases compared to resting pressure. ***Increases compared to resting pressure*** - During **heel strike (initial contact)**, the calf muscles (**gastrocnemius and soleus**) contract eccentrically to control ankle dorsiflexion and decelerate the foot - Simultaneous **weight bearing** and **muscle contraction** within the confined fascial compartment lead to increased intramuscular pressure - This is a well-documented phenomenon in gait biomechanics and exercise physiology *Decreases compared to resting pressure* - Incorrect: Muscle activation and weight bearing during initial contact inherently increase compartment pressure - Pressure decrease occurs during swing phase when the limb is unloaded and muscles are relaxed *First increases and then decreases* - While pressure varies throughout the complete gait cycle, the **heel touch phase specifically** is characterized by an initial pressure increase - The brief duration of heel strike does not typically show a biphasic pressure pattern within this single phase *Remains the same as resting pressure* - Incorrect: Active weight bearing and eccentric muscle contraction during heel strike necessarily elevate intramuscular pressure above resting levels - Resting pressure only occurs when the limb is unloaded and muscles are inactive

Q: Which of the following statements about volume receptors is NOT true?

They are located in carotid sinus. ***They are located in carotid sinus*** - Volume receptors, primarily **atrial stretch receptors** and receptors in the **pulmonary vessels**, are located in the low-pressure areas of the circulation, not the carotid sinus. - The carotid sinus primarily contains **baroreceptors** which detect changes in arterial pressure, not blood volume. *They are low pressure receptors* - This statement is true; volume receptors are indeed **low-pressure receptors** found in the atria and great veins. - They primarily monitor **extracellular fluid volume** and central venous pressure. *They provide afferents for thirst control* - This statement is true; when blood volume decreases, the firing rate of these receptors decreases, signaling the **central nervous system** to stimulate thirst. - This is an important mechanism for regulating **fluid intake** and maintaining hydration. *They mediate vasopressin release* - This statement is true; a decrease in blood volume reduces the afferent signaling from volume receptors, which consequently stimulates the release of **vasopressin (ADH)**. - Vasopressin then increases **water reabsorption** in the kidneys to conserve fluid.

Question 1

What is the normal range of interstitial pressure?

Accepted Answer

-5 to 0 mmHg

Answer

-3 to 0 mmHg

Answer

0 to 5 mmHg

Answer

5 to 10 mmHg

Question 2

ANP acts at which site?

Accepted Answer

Collecting duct

Answer

Glomerulus

Answer

Loop of Henle

Answer

PCT

Question 3

Which of the following is most important in sodium and water retention ?

Accepted Answer

Renin angiotensin system

Answer

ANP

Answer

BNP

Answer

Vasopressin

Question 4

What is the effect of acetylcholine on the Lower Esophageal Sphincter (LES)?

Accepted Answer

Causes contraction

Answer

Causes relaxation

Answer

No effect on LES

Answer

Contraction followed by relaxation

Question 5

Diurnal variation of ACTH depends on ?

Accepted Answer

Suprachiasmatic nucleus

Answer

Supraoptic nucleus

Answer

Ventrolateral nucleus

Answer

Thalamus

Question 6

Nonshivering thermogenesis in adults is due to:

Accepted Answer

Brown fat between the shoulders

Answer

Muscle metabolism

Answer

Thyroid hormone

Answer

Noradrenaline

Question 7

Which of the following is NOT a location where multi-unit smooth muscle is present?

Accepted Answer

Gut

Answer

Blood vessels

Answer

Iris

Answer

Ciliary muscle

Question 8

What happens to the pressure in the calf compartment during the heel touch phase of walking?

Accepted Answer

Increases compared to resting pressure

Answer

Decreases compared to resting pressure

Answer

First increases and then decreases

Answer

Remains the same as resting pressure

Question 9

Which one of the following is the CORRECT statement regarding coronary blood flow?

Accepted Answer

Coronary blood flow is directly related to perfusion pressure and inversely related to resistance

Answer

Coronary blood flow is inversely related to perfusion pressure and directly related to resistance

Answer

Coronary blood flow is directly related to perfusion pressure and also to resistance

Answer

Coronary blood flow is inversely related to both pressure and resistance

Question 10

Which of the following statements about volume receptors is NOT true?

Accepted Answer

They are located in carotid sinus

Answer

They are low pressure receptors

Answer

They mediate vasopressin release

Answer

They provide afferents for thirst control

NEET-PG 2012 — Physiology