NEET-PG 2015 Practice Questions

Q: Sertoli cells are derived from -

Coelomic epithelium. Sertoli cells are derived from the **coelomic epithelium** (surface epithelium) of the urogenital ridge during gonadal development. - The coelomic epithelium proliferates to form the **primitive sex cords** (medullary cords in males), and cells within these cords differentiate into Sertoli cells. - These cells are essential for **spermatogenesis**, providing structural support and nutrition to developing germ cells, and producing **anti-Müllerian hormone (AMH)** which causes regression of Müllerian ducts in male development [1]. *Germinal epithelium* - This is an **outdated term** previously used for the surface epithelium of the gonad, based on the misconception that it gave rise to germ cells. - Modern embryology uses the term **coelomic epithelium** or surface epithelium instead. - While historically used, this terminology is no longer preferred in current medical literature. *Genital swelling* - **Genital swellings** (labioscrotal swellings) are external mesodermal structures that develop into the **scrotum** in males or **labia majora** in females. - These are external genitalia components and are not the source of internal testicular cells like Sertoli cells. *Primordial germ cells* - **Primordial germ cells (PGCs)** originate from the epiblast, migrate via the hindgut to the developing gonads, and differentiate into **spermatogonia** (males) or **oogonia** (females) [1]. - They form the **germ cell lineage** (gametes), not somatic support cells like Sertoli cells, which are of coelomic epithelial origin.

Q: Which of the following is not a substrate for gluconeogenesis?

Leucine. ***Leucine*** - **Leucine** is an exclusively **ketogenic amino acid**, meaning its breakdown products can only be converted into **ketone bodies** or fatty acids, not glucose. - It does not have a carbon skeleton that can be directly converted into **pyruvate** or **oxaloacetate**, which are key intermediates in gluconeogenesis. *Lactate* - **Lactate** is a major substrate for gluconeogenesis, particularly during exercise or fasting. - It is converted to **pyruvate** by **lactate dehydrogenase**, and pyruvate can then enter the gluconeogenic pathway. *Propionate* - **Propionate** is a fatty acid with an odd number of carbon atoms, primarily derived from the catabolism of odd-chain fatty acids or from bacterial fermentation in the colon. - It can be converted into **succinyl CoA**, an intermediate of the citric acid cycle, which can then be used for gluconeogenesis. *Glycerol* - **Glycerol**, released during the breakdown of triglycerides, is an important substrate for gluconeogenesis. - It is phosphorylated to **glycerol-3-phosphate**, which is then oxidized to **dihydroxyacetone phosphate (DHAP)**, an intermediate in glycolysis and gluconeogenesis.

Q: Which of the following processes primarily utilizes lactate produced anaerobically?

Cori cycle. ***Cori cycle*** - The **Cori cycle** (lactic acid cycle) involves the transport of **lactate** produced during anaerobic metabolism in muscles to the liver. - In the **liver**, this lactate is then converted back to **glucose** via gluconeogenesis, which can be returned to the muscles. *Gluconeogenesis* - **Gluconeogenesis** is the synthesis of glucose from non-carbohydrate precursors, one of which is lactate. - While it uses lactate, it is only one component of the broader **Cori cycle**, which describes the inter-organ cooperation. *Glycolysis* - **Glycolysis** is the metabolic pathway that breaks down glucose into pyruvate, which can then be converted to lactate under anaerobic conditions. - This process *produces* lactate but does not *utilize* it, acting upstream of lactate production. *TCA cycle* - The **TCA cycle** (Krebs cycle) is a central part of aerobic respiration that oxidizes acetyl-CoA to produce ATP, NADH, and FADH2. - It does not directly utilize lactate; instead, lactate is typically converted to pyruvate before potentially entering the TCA cycle under aerobic conditions.

Q: Citrate synthase is inhibited by -

ATP. ***ATP*** - **Citrate synthase**, a key enzyme in the Krebs cycle, is inhibited by **high levels of ATP**, indicating a high energy state in the cell. - This allosteric inhibition helps regulate the metabolic flux through the cycle, slowing it down when energy is abundant. *ADP* - **ADP** typically signifies a low energy state and would generally act as an **activator** rather than an inhibitor for metabolic pathways that produce ATP. - In this context, ADP would promote the activity of enzymes involved in energy generation, including those in the Krebs cycle. *Insulin* - **Insulin** is a hormone that promotes fuel storage and utilization, generally **activating** metabolic pathways rather than directly inhibiting enzymes like citrate synthase. - Its primary role is to regulate blood glucose levels and promote glucose uptake and utilization. *Glucagon* - **Glucagon** is a hormone that mobilizes fuel from storage and is typically associated with **catabolic processes**, often increasing metabolic activity in response to low blood glucose. - It does not directly inhibit citrate synthase; its main actions are on glucoregulation.

Q: Fumarate is formed from which amino acid?

Tyrosine. ***Tyrosine*** - **Tyrosine** is a **glucogenic and ketogenic amino acid** that is catabolized to acetoacetate and fumarate. - **Fumarate** then enters the **citric acid cycle (Krebs cycle)**, whereas acetoacetate is a ketone body. *Methionine* - **Methionine** is an **essential amino acid** and a precursor for **S-adenosylmethionine (SAM)**, a methyl donor in many reactions. - Its catabolism produces **succinyl CoA**, not fumarate, through a series of steps via propionyl CoA. *Valine* - **Valine** is a **branched-chain amino acid (BCAA)** that is exclusively **glucogenic**. - Its catabolism ultimately leads to the formation of **succinyl CoA**, which can enter the citric acid cycle. *Histidine* - **Histidine** is an **essential amino acid** that is catabolized to **formiminoglutamate (FIGLU)**. - FIGLU is then converted to **glutamate**, which can eventually be deaminated to α-ketoglutarate, a citric acid cycle intermediate, but not directly fumarate.

Q: Most important carbohydrate store for maintaining blood glucose homeostasis -

Hepatic glycogen. ***Hepatic glycogen*** - The liver contains **100-120g of glycogen**, which is the most crucial carbohydrate store for **maintaining blood glucose homeostasis**. - **Hepatic glycogen** can be mobilized and released as glucose into the bloodstream to supply all body tissues, especially during fasting. - Although muscle glycogen is quantitatively larger (~400-500g), it cannot contribute to blood glucose as muscle lacks glucose-6-phosphatase. - The liver's unique ability to release free glucose makes hepatic glycogen the **most metabolically important** carbohydrate store. *Blood glucose* - **Blood glucose** (~5g total in circulation) represents carbohydrates available for immediate energy, not a storage form. - This is far too small to be considered a major carbohydrate reserve. *Glycogen in adipose tissue* - **Adipose tissue** primarily stores **fat (triglycerides)**, with negligible glycogen content. - Adipose tissue plays virtually no role in carbohydrate storage. *None of the options* - This is incorrect because **hepatic glycogen** is indeed the most important carbohydrate store for glucose homeostasis.

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: 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: 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.

Question 1

Sertoli cells are derived from -

Accepted Answer

Coelomic epithelium

Answer

Genital swelling

Answer

Primordial germ cells

Answer

Germinal epithelium

Question 2

Which of the following is not a substrate for gluconeogenesis?

Accepted Answer

Leucine

Answer

Lactate

Answer

Propionate

Answer

Glycerol

Question 3

Which of the following processes primarily utilizes lactate produced anaerobically?

Accepted Answer

Cori cycle

Answer

Gluconeogenesis

Answer

TCA cycle

Answer

Glycolysis

Question 4

Citrate synthase is inhibited by -

Accepted Answer

ATP

Answer

Insulin

Answer

Glucagon

Answer

ADP

Question 5

Fumarate is formed from which amino acid?

Accepted Answer

Tyrosine

Answer

Methionine

Answer

Valine

Answer

Histidine

Question 6

Most important carbohydrate store for maintaining blood glucose homeostasis -

Accepted Answer

Hepatic glycogen

Answer

Blood glucose

Answer

Glycogen in adipose tissue

Answer

None of the options

Question 7

Which statement best describes first-order kinetics in pharmacokinetics?

Accepted Answer

Elimination of the drug is proportional to the serum concentration

Answer

Absorption of the drug is independent of the serum concentration

Answer

Absorption of the drug is proportional to the serum concentration

Answer

Elimination of the drug is independent of the serum concentration

Question 8

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 9

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 10

Mechanism of secretion of ammonia in distal tubule is?

Accepted Answer

Passive diffusion

Answer

Primary active transport

Answer

Symport

Answer

Antiport

NEET-PG 2015

Anatomy

Biochemistry

Pharmacology

Physiology