NEET-PG 2012 Practice Questions

Q: Which of the following is NOT a branch of 1st part of maxillary artery?

Greater palatine artery. ***Greater palatine artery*** - This artery is a branch of the **third part** of the maxillary artery, which supplies the palate. - The third part of the maxillary artery (also known as the pterygopalatine part) gives off branches that pass through the pterygopalatine fossa. *Middle meningeal artery* - This is a significant branch of the **first part** of the maxillary artery, entering the cranial cavity via the **foramen spinosum** to supply the dura mater. - It is often injured in head trauma, leading to an **epidural hematoma**. *Accessory meningeal artery* - This artery also arises from the **first part** of the maxillary artery and enters the skull through the **foramen ovale** to supply the dura mater. - It is a smaller branch compared to the middle meningeal artery. *Inferior alveolar artery* - It is a branch of the **first part** of the maxillary artery, descending to enter the mandible via the **mandibular foramen** to supply the teeth and bone of the mandible. - It gives off the **mylohyoid branch** before entering the mandibular foramen.

Q: Which of the following metabolites is involved in glycogenolysis, glycolysis and gluconeogenesis ?

Glucose-6-phosphate. ***Glucose-6-phosphate*** - In **glycogenolysis**, **glycogen phosphorylase** breaks down glycogen into **glucose-1-phosphate**, which is then converted into **glucose-6-phosphate** by **phosphoglucomutase**. - In **glycolysis**, **glucose-6-phosphate** is isomerized to **fructose-6-phosphate** by **phosphoglucose isomerase**, committing it to the glycolytic pathway. - In **gluconeogenesis**, **glucose-6-phosphate** is the final product formed from other precursors; it can then be dephosphorylated to free glucose by **glucose-6-phosphatase**. *Galactose-1-phosphate* - This is an intermediate specifically in **galactose metabolism**, not directly involved in the central common pathways of glycogenolysis, glycolysis, or gluconeogenesis. - It is converted to **glucose-1-phosphate** via the **Leloir pathway** (involving **galactose-1-phosphate uridylyltransferase**), which can then enter glycogen metabolism. *Uridine diphosphoglucose* - **UDP-glucose** is crucial for **glycogen synthesis** (**glycogenesis**), serving as the activated glucose donor. - It is not directly a metabolite in the catabolic process of glycogenolysis, nor is it a direct intermediate in glycolysis or gluconeogenesis. *Fructose-6-phosphate* - **Fructose-6-phosphate** is a key intermediate in **glycolysis** and **gluconeogenesis**, specifically downstream from **glucose-6-phosphate**. - However, it is not directly produced from glycogenolysis; **glucose-6-phosphate** is the direct link between glycogenolysis and glycolysis.

Q: What is the rate-controlling enzyme of fatty acid synthesis?

Acetyl-CoA carboxylase. ***Acetyl-CoA carboxylase*** - **Acetyl-CoA carboxylase (ACC)** catalyzes the committed step in fatty acid synthesis, converting **acetyl-CoA** to **malonyl-CoA**. - This enzyme is subject to both allosteric regulation (e.g., activation by **citrate** and inhibition by **long-chain fatty acyl-CoA**) and hormonal regulation (e.g., phosphorylation by glucagon and dephosphorylation by insulin). *Thioesterase* - **Thioesterase** is the enzyme responsible for releasing the completed fatty acid chain from the **fatty acid synthase complex**. - While essential for the termination of synthesis, it does not regulate the initiation or overall rate of the pathway. *Transacetylase* - **Transacetylase** (specifically, acetyl-CoA-ACP transacetylase and malonyl-CoA-ACP transacetylase) is involved in transferring acetyl and malonyl groups to the **acyl carrier protein (ACP)** within the fatty acid synthesis complex. - This is an intermediary step, but not the primary **rate-controlling** or committed step. *Ketoacyl synthase* - **Ketoacyl synthase (or β-ketoacyl-ACP synthase)** is responsible for condensing the growing acyl chain with malonyl-ACP, leading to the formation of a **β-ketoacyl-ACP**. - This is a crucial chain elongation step within the fatty acid synthase complex, but not the enzyme that controls the overall commitment to fatty acid synthesis.

Q: Which hormone is known to repress the biosynthesis of the enzyme pyruvate carboxylase?

Insulin. ***Insulin*** - **Insulin** is an anabolic hormone that promotes glucose utilization and opposes **gluconeogenesis**. - While insulin does inhibit hepatic glucose production, it primarily acts by **repressing PEPCK (phosphoenolpyruvate carboxykinase)**, the rate-limiting enzyme of gluconeogenesis, rather than directly repressing pyruvate carboxylase biosynthesis. - **Note:** Modern biochemistry emphasizes that insulin's main transcriptional target in gluconeogenesis is **PEPCK**, not pyruvate carboxylase. However, this was the expected answer for **NEET-2012**, reflecting the understanding at that time. - Insulin also promotes dephosphorylation and inactivation of gluconeogenic enzymes and enhances glucose uptake and glycolysis. *Glucagon* - **Glucagon** is a catabolic hormone that **activates** enzymes involved in **gluconeogenesis** and glycogenolysis to raise blood glucose levels. - It would **increase**, not repress, the biosynthesis and activity of gluconeogenic enzymes including **pyruvate carboxylase**. *Cortisol* - **Cortisol** is a glucocorticoid hormone that **stimulates gluconeogenesis** in the liver as part of the stress response. - It typically **upregulates** the synthesis and activity of gluconeogenic enzymes like **pyruvate carboxylase** and **PEPCK**. *Growth hormone* - **Growth hormone** generally **increases insulin resistance** and can have a **diabetogenic effect**, promoting glucose production rather than repressing gluconeogenic enzymes. - It does not directly repress gluconeogenic enzyme biosynthesis; its metabolic effects favor lipolysis and protein synthesis.

Q: Which of the following is the most characteristic symptom of obstruction of the inferior vena cava?

Paraumblical dilatation. ***Paraumbilical dilatation*** - Obstruction of the **inferior vena cava (IVC)** leads to collateral circulation through superficial veins, especially around the umbilicus, causing **paraumbilical dilatation** (caput medusae). - This collateral flow bypasses the obstructed IVC to return blood to the superior vena cava system. *Thoraco-epigastric dilatation* - This pattern of collateral circulation is more characteristic of **superior vena cava (SVC) obstruction**, where blood from the upper body needs to bypass the SVC. - The dilated veins would typically be seen on the chest and upper abdomen, draining towards the femoral veins. *Oesophageal varices* - **Oesophageal varices** are typically caused by **portal hypertension** [1], often secondary to liver cirrhosis, not directly by IVC obstruction. - They represent portosystemic collateral veins, diverging from the portal system to the systemic circulation [1]. *Haemorrhoids* - **Haemorrhoids** are dilated veins in the anal canal, most commonly caused by **straining** during defecation or conditions that increase intra-abdominal pressure [2]. - While they can be a sign of portal hypertension [1], **IVC obstruction** is not their primary or most characteristic cause.

Q: Which of the following conditions can lead to pulmonary infarction?

Blockage of 2nd and 3rd generation end arteries. ***Blockage of 2nd and 3rd generation end arteries*** - These are **true end arteries** beyond the reach of **bronchial collateral circulation**, making pulmonary infarction more likely when blocked. - The **dual blood supply** (pulmonary and bronchial arteries) is compromised at this level, leading to tissue necrosis and infarction. *Saddle embolus at bifurcation* - A **saddle embolus** typically causes **sudden death** or **acute cor pulmonale** rather than pulmonary infarction. - The **main pulmonary artery bifurcation** is proximal enough that **bronchial collateral circulation** can still maintain tissue viability. *Arterioles being blocked* - **Arterioles** are small vessels that can be compensated by the **dual blood supply** from both pulmonary and bronchial circulations. - The **bronchial artery collaterals** can provide adequate perfusion to prevent infarction at this level. *None of the above* - This option is incorrect as **blockage of 2nd and 3rd generation end arteries** does cause pulmonary infarction. - The lung's **dual circulation** protects against infarction except when **true end arteries** are involved.

Q: What is the average daily volume of pancreatic secretion in humans?

1.5 L. ***1.5 L*** - The **pancreas** produces approximately **1.5 liters (1200-1500 mL) of pancreatic juice** daily in humans. - This secretion is rich in **digestive enzymes** (amylase, lipase, proteases) and **bicarbonate** for neutralization of gastric acid in the duodenum. - This is the standard value cited in **major physiology textbooks** (Ganong, Guyton & Hall). *2.5 L* - **2.5 liters** overestimates the typical daily pancreatic secretion volume. - This value may represent **combined secretions** from multiple sources or confuse pancreatic output with total upper GI secretions. - Normal pancreatic secretion ranges from **1-2 liters**, making 2.5 L above the physiological range. *5.0 L* - **5.0 liters** represents an abnormally high volume for daily pancreatic secretion alone. - This volume is closer to the **total daily secretions** from stomach, pancreas, and bile combined. - Not consistent with **normal pancreatic physiology**. *10 L* - **10 liters** is grossly excessive for pancreatic secretion and represents approximately the **total volume of all gastrointestinal secretions** (saliva, gastric, pancreatic, bile, intestinal) combined daily. - This is **not physiologically realistic** for pancreatic output alone.

Q: What is the normal range for the CSF/plasma glucose ratio?

0.6 - 0.8. ***Correct: 0.6 - 0.8*** - This ratio indicates that cerebrospinal fluid (CSF) glucose concentration is typically 60-80% of plasma glucose concentration - This range is crucial for identifying metabolic or infectious pathologies affecting the central nervous system - Normal CSF glucose is approximately 50-80 mg/dL when plasma glucose is 70-120 mg/dL *Incorrect: 0.2 - 0.4* - A ratio in this range indicates significantly low CSF glucose, suggesting conditions like bacterial meningitis or hypoglycorrhachia - This is well below the normal physiological proportion of glucose in the CSF relative to plasma - Seen in bacterial/tuberculous meningitis, fungal infections, or malignancy *Incorrect: 1.0 - 1.2* - A CSF/plasma glucose ratio close to or above 1.0 would imply that CSF glucose levels are equal to or higher than plasma levels, which is physiologically impossible under normal conditions - Glucose transport into the CSF is regulated by GLUT-1 transporters and typically results in lower concentrations than in plasma - The blood-brain barrier maintains this gradient *Incorrect: 1.2 - 1.6* - This range is even more exaggerated and physiologically impossible, as CSF glucose cannot exceed plasma glucose in a healthy individual - Such a high ratio would contradict the mechanisms of glucose transport across the blood-brain barrier - Would suggest laboratory error if observed

Q: Which hormone primarily inhibits gastric acid secretion in response to acidic chyme?

Somatostatin. ***Somatostatin*** - **Somatostatin** is the **primary hormone** that inhibits gastric acid secretion in response to acidic chyme. - Released by D cells in the stomach and duodenum when pH drops below 3.0. - **Direct inhibitory effects:** Inhibits parietal cells directly, suppresses gastrin release from G cells, and blocks histamine release from ECL cells. - Acts as the main **negative feedback mechanism** to prevent excessive gastric acidification. *Secretin* - **Secretin** is released by S cells in the duodenum in response to acidic chyme (pH < 4.5). - Its **primary function** is to stimulate pancreatic bicarbonate secretion to neutralize duodenal acid. - While it does have a **secondary effect** of inhibiting gastric acid secretion, this is not its primary role. *Gastrin* - **Gastrin** is a hormone that **stimulates** gastric acid secretion, not inhibits it. - Released by G cells in the gastric antrum in response to peptides, amino acids, and gastric distension. - Promotes acid secretion by stimulating parietal cells and ECL cells (which release histamine). *Insulin* - **Insulin** is a pancreatic hormone primarily involved in **glucose metabolism** and cellular glucose uptake. - It has **no significant role** in the regulation of gastric acid secretion.

Question 1

Which of the following is NOT a branch of 1st part of maxillary artery?

Accepted Answer

Greater palatine artery

Answer

Accessory meningeal artery

Answer

Inferior alveolar artery

Answer

Middle meningeal artery

Question 2

Which of the following metabolites is involved in glycogenolysis, glycolysis and gluconeogenesis ?

Accepted Answer

Glucose-6-phosphate

Answer

Uridine diphosphoglucose

Answer

Fructose-6-phosphate

Answer

Galactose-1-phosphate

Question 3

Which of the following best describes the difference between glucokinase and hexokinase?

Accepted Answer

Glucokinase has higher Km for glucose compared to hexokinase.

Answer

Glucokinase is not inhibited by glucose-6-phosphate unlike hexokinase.

Answer

Glucokinase has a low affinity for glucose.

Answer

Glucokinase activity increases with glucose concentration while hexokinase remains saturated.

Question 4

What is the rate-controlling enzyme of fatty acid synthesis?

Accepted Answer

Acetyl-CoA carboxylase

Answer

Thioesterase

Answer

Transacetylase

Answer

Ketoacyl synthase

Question 5

Which hormone is known to repress the biosynthesis of the enzyme pyruvate carboxylase?

Accepted Answer

Insulin

Answer

Cortisol

Answer

Glucagon

Answer

Growth hormone

Question 6

Which of the following is the most characteristic symptom of obstruction of the inferior vena cava?

Accepted Answer

Paraumblical dilatation

Answer

Thoraco-epigastric dilatation

Answer

Haemorrhoides

Answer

Oesophageal varices

Question 7

Which of the following conditions can lead to pulmonary infarction?

Accepted Answer

Blockage of 2nd and 3rd generation end arteries

Answer

Saddle embolus at bifurcation

Answer

Arterioles being blocked

Answer

None of the above.

Question 8

What is the average daily volume of pancreatic secretion in humans?

Accepted Answer

1.5 L

Answer

5.0 L

Answer

10 L

Answer

2.5 L

Question 9

What is the normal range for the CSF/plasma glucose ratio?

Accepted Answer

0.6 - 0.8

Answer

1.2 - 1.6

Answer

0.2 - 0.4

Answer

1.0 - 1.2

Question 10

Which hormone primarily inhibits gastric acid secretion in response to acidic chyme?

Accepted Answer

Somatostatin

Answer

Secretin

Answer

Insulin

Answer

Gastrin

NEET-PG 2012

Anatomy

Biochemistry

Internal Medicine

Pathology

Physiology