NEET-PG 2012 - Physiology Practice Questions

Q: What happens to the concentration of inulin as fluid passes through the Proximal Convoluted Tubule (PCT)?

Concentration of inulin increases. ***Concentration of inulin increases*** - Inulin is **freely filtered** at the glomerulus and is neither reabsorbed nor secreted along the renal tubule, making it an excellent marker for **glomerular filtration rate (GFR)**. - As water is reabsorbed from the PCT, the volume of tubular fluid decreases, causing the concentration of **unreabsorbed solutes**, like inulin, to increase. *Concentration of urea remains constant* - Urea is **reabsorbed** along the tubule, though passively; its concentration typically **increases** initially in the PCT due to water reabsorption, but then decreases as some is reabsorbed. - The statement is incorrect because urea concentration changes significantly throughout the nephron, particularly increasing as water is reabsorbed and then decreasing with some reabsorption. *Concentration of HCO3- increases* - The majority (approximately 80-90%) of **bicarbonate (HCO3-)** is reabsorbed in the PCT, primarily through its conversion to CO2 within the tubular lumen and then back to HCO3- intracellularly. - Therefore, the concentration of HCO3- in the tubular fluid actually **decreases** significantly as fluid passes through the PCT. *Concentration of Na+ decreases* - **Sodium (Na+)** is actively reabsorbed along the entire nephron, with about 65-70% reabsorbed in the PCT. - While Na+ is reabsorbed, water follows passively, so its concentration in the tubular fluid remains relatively **iso-osmotic** with plasma, meaning its concentration does not significantly decrease as fluid passes through the PCT, remaining fairly constant.

Q: Gastric secretions are essential for absorption of -

Cobalamin. ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].

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: Which of the following hormones does not mediate its action through cAMP?

Estrogen. ***Estrogen*** - **Estrogen** is a **steroid hormone** that mediates its action by binding to intracellular receptors, forming a complex that directly influences gene transcription. - Steroid hormones, due to their **lipophilicity**, can cross the cell membrane and do not typically rely on cell surface receptors or second messengers like cAMP. *Glucagon* - **Glucagon** acts on a **G protein-coupled receptor (GPCR)**, specifically a Gs-coupled receptor, leading to the activation of adenylyl cyclase. - This activation increases the intracellular concentration of **cAMP**, which then activates protein kinase A to mediate its effects, primarily on glucose metabolism. *Follicle stimulating hormone* - **FSH** binds to a **GPCR** on target cells, activating the Gs protein pathway. - This activation stimulates **adenylyl cyclase** and increases intracellular **cAMP** levels, which are critical for its role in gamete development. *Luteinizing hormone* - **LH**, like FSH, binds to a cell surface **GPCR** that activates the Gs protein. - This leads to the stimulation of **adenylyl cyclase** and an increase in **cAMP**, mediating its effects on steroidogenesis and ovulation.

Q: What is the fixed length of a myosin filament?

1.6 micrometers. ***1.6 micrometers*** - Myosin filaments, also known as **thick filaments**, are integral components of muscle contraction and have a characteristic fixed length. This length is precisely **1.6 micrometers** in mammalian skeletal muscle. - This consistent length is crucial for the **sliding filament model** of muscle contraction, ensuring proper overlap with actin filaments and efficient force generation. *0.16 nm* - This value is significantly too small; **nanometers (nm)** are typically used for atomic or molecular distances, not for entire protein filaments like myosin. - A myosin filament is composed of hundreds of myosin molecules, making its overall length much larger than a fraction of a nanometer. *16 nm* - While nanometers are used for molecular structures, 16 nm is still too small for a myosin filament. The entire filament is roughly **100 times larger** than this value. - This dimension might be more appropriate for the diameter of a single myosin molecule's head region, but not the entire filament's length. *1.6 mm* - This value is significantly too large; **millimeters (mm)** are visible to the naked eye and represent macroscopic objects. - Muscle filaments are microscopic structures, and a length of 1.6 mm would imply they are many times longer than an entire muscle cell.

Q: In which condition is venous blood most commonly observed to have a high hematocrit in routine clinical practice?

Dehydration. Dehydration - In **dehydration**, the total body water is reduced, leading to a decrease in plasma volume [1, 5]. This concentrates the red blood cells, resulting in a relatively **high hematocrit**. [3] - This is a common finding as the body attempts to conserve fluid, making it a primary cause of **elevated hematocrit** in clinical practice. *Anemia* - **Anemia** is characterized by a decrease in the number of red blood cells or a reduced hemoglobin concentration, which would lead to a **low hematocrit**, not a high one [2]. - This condition involves insufficient oxygen-carrying capacity due to a deficiency in red blood cells or hemoglobin [2]. *Hypervolemia* - **Hypervolemia** describes an excess of fluid in the blood, which would dilute the blood components, leading to a relatively **low hematocrit** [1]. - This condition is often associated with conditions like heart failure or kidney disease, where fluid retention is common. *Acute blood loss* - In **acute blood loss**, the loss of whole blood immediately after the event would initially reduce both red blood cells and plasma proportionally, not immediately raising hematocrit [2]. - As the body attempts to compensate by shifting extravascular fluid into the circulation, this would further dilute the blood, eventually leading to a **decreased hematocrit** [2].

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: During acclimatization to hot environments, increased sweating efficiency is primarily due to enhanced sensitivity of which receptors?

Cholinergic receptors. ***Cholinergic receptors*** - **Sweat glands** are innervated by **sympathetic postganglionic fibers** that release **acetylcholine**, acting on **muscarinic cholinergic receptors** to stimulate sweating. - During **acclimatization**, the sweat glands become more sensitive to acetylcholine, resulting in **increased sweating efficiency** and a lower threshold temperature for sweating. *Adrenergic receptors* - Adrenergic receptors are primarily involved in the sympathetic nervous system's response to **norepinephrine** and **epinephrine**, mediating effects like **vasoconstriction** and **bronchodilation**. - They are not the primary receptors responsible for stimulating **eccrine sweat gland** secretion in response to heat. *Noradrenergic receptors* - **Noradrenergic receptors** are a type of adrenergic receptor that respond to **norepinephrine** (noradrenaline). - While sympathetic activity increases in hot environments, the primary stimulation of **sweat glands** is via **acetylcholine** acting on cholinergic receptors, not noradrenergic receptors. *Dopaminergic receptors* - **Dopaminergic receptors** respond to **dopamine** and are involved in various functions including **motor control**, **reward**, and **neuroendocrine regulation**. - These receptors are not directly involved in the physiological regulation of **sweating efficiency** during heat acclimatization.

Question 1

What happens to the concentration of inulin as fluid passes through the Proximal Convoluted Tubule (PCT)?

Accepted Answer

Concentration of inulin increases

Answer

Concentration of urea remains constant

Answer

Concentration of HCO3- increases

Answer

Concentration of Na+ decreases

Question 2

Gastric secretions are essential for absorption of -

Accepted Answer

Cobalamin

Answer

Fat

Answer

Thiamine

Answer

Folic acid

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

Which of the following hormones does not mediate its action through cAMP?

Accepted Answer

Estrogen

Answer

Glucagon

Answer

Follicle stimulating hormone

Answer

Luteinizing hormone

Question 5

What is the fixed length of a myosin filament?

Accepted Answer

1.6 micrometers

Answer

0.16 nm

Answer

16 nm

Answer

1.6 mm

Question 6

Which of the following statements about lung compliance is NOT true?

Accepted Answer

Measured by intrapleural pressure at different lung volumes.

Answer

Decreased at the height of inspiration.

Answer

Increased in emphysema.

Answer

Increased by surfactant.

Question 7

In which condition is venous blood most commonly observed to have a high hematocrit in routine clinical practice?

Accepted Answer

Dehydration

Answer

Anemia

Answer

Hypervolemia

Answer

Acute blood loss

Question 8

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 9

ANP acts at which site?

Accepted Answer

Collecting duct

Answer

Glomerulus

Answer

Loop of Henle

Answer

PCT

Question 10

During acclimatization to hot environments, increased sweating efficiency is primarily due to enhanced sensitivity of which receptors?

Accepted Answer

Cholinergic receptors

Answer

Adrenergic receptors

Answer

Noradrenergic receptors

Answer

Dopaminergic receptors

NEET-PG 2012 — Physiology