NEET-PG 2015 Practice Questions

Q: Chymotrypsinogen is activated into chymotrypsin by:

Trypsin. ***Activation of Chymotrypsinogen by Trypsin*** - **Trypsin** is the primary enzyme responsible for the activation of **chymotrypsinogen** into its active form, **chymotrypsin**, by cleaving a specific peptide bond. - This activation is part of a cascade of proteolytic enzyme activations in the **pancreatic juice**, crucial for protein digestion in the small intestine. *Pepsin* - **Pepsin** is a protease active in the **stomach**, requiring an acidic environment for its activity, and is involved in the initial breakdown of proteins. - It does not play a role in the activation of pancreatic zymogens like chymotrypsinogen; its primary function is protein digestion in the gastric lumen. *Renin* - **Renin** is an enzyme primarily involved in the **renin-angiotensin-aldosterone system** (RAAS), which regulates blood pressure and fluid balance. - Its action involves cleaving **angiotensinogen** to form angiotensin I, and it has no role in the activation of digestive enzymes like chymotrypsinogen. *HCl* - **Hydrochloric acid (HCl)** is produced in the stomach and is essential for providing the acidic environment required for **pepsin's activity** and for denaturing proteins. - While HCl is crucial for digestion, it does not directly activate chymotrypsinogen; this activation is an enzymatic process carried out by another protease.

Q: Which of the following is an example of an exopeptidase?

Carboxypeptidases. ***Carboxypeptidases*** - **Carboxypeptidases** are enzymes that cleave the **C-terminal** (carboxyl end) amino acid from a polypeptide chain, making them a type of exopeptidase. - They are crucial in protein digestion, releasing individual amino acids from the end of protein chains. *Trypsin* - **Trypsin** is an **endopeptidase** that cleaves peptide bonds within protein chains, specifically at the carboxyl side of **lysine** or **arginine** residues. - It does not cleave amino acids from the ends of polypeptide chains. *Chymotrypsin* - **Chymotrypsin** is an **endopeptidase** that cleaves peptide bonds within a polypeptide chain, primarily at the carboxyl side of **tyrosine**, **tryptophan**, or **phenylalanine**. - Its action is internal to the protein sequence, not at the termini. *Elastase* - **Elastase** is also an **endopeptidase** that cleaves peptide bonds internally, specifically targeting small, uncharged amino acid residues like **alanine**, **glycine**, and **valine**. - Its primary role is to break down elastin, an elastic protein in connective tissues, but it does so by internal cleavage.

Q: A substance has a clearance similar to inulin clearance. How is this substance primarily excreted in urine?

Glomerular filtration. ***Glomerular filtration*** - **Inulin** is a gold standard for measuring **glomerular filtration rate** (GFR) because it is freely filtered by the glomeruli and is neither reabsorbed nor secreted by the renal tubules. - Therefore, a substance with clearance similar to inulin is primarily excreted via **glomerular filtration**. *Tubular Secretion* - If a substance were primarily excreted by tubular secretion, its clearance would be **higher than the GFR**, as secretion adds more of the substance to the urine than filtration alone. - This mechanism is characteristic of substances like **para-aminohippurate (PAH)**, which is used to measure renal plasma flow. *Vascular leakage* - **Vascular leakage** is not a normal mechanism of substance excretion in the urine. - It refers to the abnormal passage of fluid and macromolecules from blood vessels into tissues, often seen in conditions like inflammation or sepsis, and does not directly contribute to renal clearance. *Both tubular secretion and glomerular filtration* - If a substance were excreted by both **tubular secretion and glomerular filtration**, its clearance would also be **higher than the GFR**, similar to substances that undergo significant tubular secretion. - The fact that its clearance is *similar* to inulin specifically points to filtration as the predominant and almost exclusive mechanism.

Q: What is the normal range of urinary pH?

6.0 - 6.5. ***6.0 - 6.5*** - This represents the **average normal urinary pH range** in healthy individuals. - While the kidney can produce urine with pH ranging from 4.5 to 8.0 (the full physiological range), the **typical urinary pH** in most healthy people is around 6.0, making this the most representative normal range. - This slightly acidic pH reflects normal renal handling of dietary acids and metabolic processes. *4.5 - 5.0* - This represents the **lower acidic end** of the physiological range. - While kidneys can produce urine this acidic in response to acid loads, this is **not the average normal range**. - Persistently low pH may indicate **metabolic acidosis**, high protein diet, or conditions like diabetic ketoacidosis. *5.0 - 5.5* - This range is **more acidic than average** but still within physiological limits. - This may be seen with high protein intake or mild acid loading, but it's not the most representative of typical normal urinary pH. *7.0 - 7.5* - This represents a **more alkaline urine**, which is at the upper end of the physiological range. - While healthy kidneys can produce alkaline urine (especially with alkaline diets), persistently elevated pH may indicate **urinary tract infections** with urea-splitting bacteria (Proteus species), renal tubular acidosis, or alkaline diet.

Q: Increased aldosterone and ADH secretion following major trauma results in all the following except?

Increased water excretion. ***Increased water excretion*** - **ADH (antidiuretic hormone)** increases water reabsorption in the collecting ducts, leading to a *decrease* in water excretion, not an increase. - Increased aldosterone and ADH would promote fluid retention to maintain blood volume following trauma, thus reducing water loss via urine. *Decreased Na+ excretion in urine* - **Aldosterone** acts on the renal tubules to increase **sodium reabsorption** and potassium excretion. - This response is crucial in **conserving sodium** and thereby maintaining extracellular fluid volume after trauma. *Increased K+ excretion in urine* - **Aldosterone** directly stimulates **potassium secretion** into the urine in the principal cells of the collecting ducts. - This is a normal physiological consequence of increased aldosterone levels. *Increased osmolarity of urine* - **ADH** increases the permeability of the collecting ducts to water, leading to **more water reabsorption** back into the bloodstream. - This removal of water from the urine concentrates the solutes, resulting in a **more concentrated (higher osmolarity)** urine.

Q: Which carrier pump is responsible for transporting solutes in the thick ascending limb of the loop of Henle?

Sodium-potassium-chloride cotransporter. * **Sodium-potassium-chloride cotransporter.** * This transporter, specifically the **Na+-K+-2Cl- cotransporter (NKCC2)**, is highly expressed in the apical membrane of the thick ascending limb. * It actively reabsorbs **sodium, potassium, and chloride ions** from the filtrate, contributing significantly to the medullary interstitial osmotic gradient. * *NaCl- cotransporter* * The **NaCl cotransporter (NCC)** is primarily found in the **distal convoluted tubule**, not the thick ascending limb. * It reabsorbs sodium and chloride in a 1:1 ratio and is the target of thiazide diuretics. * *Na+-H+ exchanger* * The **Na+-H+ exchanger (NHE3)** is predominantly located in the **proximal tubule** where it plays a crucial role in bicarbonate reabsorption and acid-base balance. * While some NHE activity exists in other nephron segments, it is not the primary carrier in the thick ascending limb. * *Na+-K+ exchanger* * The **Na+-K+ exchanger** or **Na+/K+-ATPase pump** is located on the basolateral membrane of most renal tubular cells, including the thick ascending limb. * Its main function is to maintain the electrochemical gradient by pumping **sodium out of the cell** and potassium into the cell, which indirectly drives other transporters but is not the apical cotransporter responsible for initial solute reabsorption in the thick ascending limb.

Q: Which part of the stomach is primarily responsible for receiving and storing ingested food?

Body. ***Body*** - The **body (corpus)** is the largest part of the stomach, situated between the fundus and the antrum [1]. - This region is **primarily responsible for receiving and storing ingested food** as the main reservoir [2]. - It also produces **gastric acid and enzymes** (like pepsinogen) for the initial digestion of food [1]. - The body serves as the **principal storage chamber** where food accumulates after passing through the cardia [2]. *Fundus* - The **fundus** is the dome-shaped upper part of the stomach, located superior to the cardia. - While it can temporarily hold food and gas, it is **not the primary storage site** [2]. - Its main role is to serve as a **pressure buffer** and accumulation site for gases during digestion [2]. *Antrum* - The **antrum** is the lower, narrower part of the stomach, located before the pylorus. - It plays a crucial role in **mixing and grinding food with gastric juices** and propelling chyme towards the pylorus [1], [2]. - This is the **grinding chamber**, not a storage area [2]. *Pylorus* - The **pylorus** is the opening that connects the stomach to the duodenum, controlled by the pyloric sphincter. - Its main function is to **regulate the emptying of chyme** into the small intestine, not to store food [3].

Q: What is the primary function of the myenteric plexus?

Regulating motility. ***Regulating motility*** - The myenteric plexus, also known as **Auerbach's plexus**, is primarily responsible for coordinating the **rhythmic contractions** and **relaxation of the gastrointestinal (GI) smooth muscle**. - Its strategic location between the **longitudinal and circular muscle layers** allows it to directly influence the strength and frequency of peristalsis, thus regulating the movement of food through the digestive tract. *Regulating GI secretion* - While it has some indirect influence, the **submucosal plexus** (Meissner's plexus) is the primary neural network regulating **secretory functions** of the GI tract. - The myenteric plexus's main role is more directly related to muscle contraction and relaxation rather than glandular secretion. *Regulating local blood flow* - Local blood flow in the GI tract is primarily regulated by the **sympathetic and parasympathetic nervous systems**, along with local metabolic factors and hormones. - The myenteric plexus has a minimal direct role in the control of **GI blood vessel smooth muscle**. *Regulating absorption* - Absorption is primarily a function of the **intestinal epithelial cells** and is regulated by various transport mechanisms, hormones, and local factors. - While the enteric nervous system influences mucosal function indirectly, the myenteric plexus's primary role is **motor control** rather than directly regulating nutrient absorption processes.

Q: Secretion of bile out of hepatocytes occurs via?

Active transport. ***Active transport*** - Bile secretion by hepatocytes is an **energy-dependent process** against concentration gradients, requiring specific transporter proteins. - This active mechanism ensures efficient bile flow and prevents reflux, crucial for processes like **fat digestion and absorption**. *Passive diffusion* - **Passive diffusion** involves substances moving down their concentration gradient without energy expenditure. - Bile components, like bile salts, are highly concentrated within hepatocytes and need to be moved against this gradient. *Facilitated diffusion* - This type of diffusion utilizes **transmembrane proteins** to move substances down their concentration gradient, but still does not directly consume ATP. - Bile components are often transported against their concentration gradient, which is not facilitated diffusion. *Osmosis* - **Osmosis** specifically refers to the movement of water across a semipermeable membrane from a region of higher water concentration to a region of lower water concentration. - While water is a component of bile, the primary mechanism of moving bile solutes out of the hepatocyte is not osmosis.

Q: Intestinal absorption of calcium is mainly increased by?

Calcitriol. ***Calcitriol*** - **Calcitriol** (1,25-dihydroxyvitamin D3) is the hormonally active form of vitamin D, which is essential for increasing **calcium absorption** from the intestines. - It stimulates the synthesis of **calcium-binding proteins** in intestinal epithelial cells, facilitating active transport of calcium. *Parathormone* - **Parathormone (PTH)** primarily regulates calcium by increasing its reabsorption in the **kidneys** and stimulating its release from **bones**. - While it indirectly promotes calcitriol synthesis, its *direct* effect on intestinal calcium absorption is minimal compared to calcitriol. *Glucocorticoids* - **Glucocorticoids** generally have an *inhibitory* effect on calcium absorption in the intestine and can also increase renal excretion of calcium. - Prolonged use can lead to **osteoporosis** due to their negative impact on bone formation and calcium balance. *ACTH* - **ACTH (adrenocorticotropic hormone)** primarily stimulates the adrenal cortex to produce **cortisol** and other glucocorticoids. - It has **no direct role** in regulating calcium absorption from the intestines.

Question 1

Chymotrypsinogen is activated into chymotrypsin by:

Accepted Answer

Trypsin

Answer

Pepsin

Answer

Renin

Answer

HCl

Question 2

Which of the following is an example of an exopeptidase?

Accepted Answer

Carboxypeptidases

Answer

Trypsin

Answer

Chymotrypsin

Answer

Elastase

Question 3

A substance has a clearance similar to inulin clearance. How is this substance primarily excreted in urine?

Accepted Answer

Glomerular filtration

Answer

Tubular Secretion

Answer

Vascular leakage

Answer

Both tubular secretion and glomerular filtration

Question 4

What is the normal range of urinary pH?

Accepted Answer

6.0 - 6.5

Answer

4.5 - 5.0

Answer

5.0 - 5.5

Answer

7.0 - 7.5

Question 5

Increased aldosterone and ADH secretion following major trauma results in all the following except?

Accepted Answer

Increased water excretion

Answer

Increased osmolarity of urine

Answer

Increased K+ excretion in urine

Answer

Decreased Na+ excretion in urine

Question 6

Which carrier pump is responsible for transporting solutes in the thick ascending limb of the loop of Henle?

Accepted Answer

Sodium-potassium-chloride cotransporter

Answer

NaCl cotransporter

Answer

Na+-H+ exchanger

Answer

Na+-K+ exchanger

Question 7

Which part of the stomach is primarily responsible for receiving and storing ingested food?

Accepted Answer

Body

Answer

Antrum

Answer

Pylorus

Answer

Fundus

Question 8

What is the primary function of the myenteric plexus?

Accepted Answer

Regulating motility

Answer

Regulating GI secretion

Answer

Regulating local blood flow

Answer

Regulating absorption

Question 9

Secretion of bile out of hepatocytes occurs via?

Accepted Answer

Active transport

Answer

Passive diffusion

Answer

Facilitated diffusion

Answer

Osmosis

Question 10

Intestinal absorption of calcium is mainly increased by?

Accepted Answer

Calcitriol

Answer

Parathormone

Answer

Glucocorticoids

Answer

ACTH

NEET-PG 2015

Biochemistry

Physiology