NEET-PG 2013 Practice Questions

Q: How many ossification centers develop at the distal end of the humerus?

3. ***3*** - The distal end of the humerus develops **three primary ossification centers**: the capitellum, trochlea, and medial epicondyle [1]. - These centers appear sequentially and their ossification pattern is important for assessing **skeletal maturity** in children using the CRITOE mnemonic [1]. - The capitellum appears at 1 year, medial epicondyle at 5 years, and trochlea at 9 years. *2* - This number is too low and only accounts for the **capitellum and medial epicondyle**, missing the trochlea. - While these are the first two to appear, there is an additional primary ossification center (trochlea) that develops later. *5* - This number is incorrect; there are only **three primary ossification centers** at the distal humerus, not five. - This may cause confusion with other joints or by counting secondary ossification centers. *4* - This number is incorrect; while the lateral epicondyle does ossify, it is not consistently counted as a **primary ossification center**. - The standard anatomical teaching recognizes **three primary centers**: capitellum, trochlea, and medial epicondyle.

Q: Type of collagen found in space of Disse in liver is -

Collagen III & IV. ***Collagen III & IV*** - The **space of Disse** in the liver contains a delicate extracellular matrix predominantly composed of **collagen type III (reticular fibers)**, which provides structural support, and **collagen type IV**, a major component of basement membranes. - This specific collagen composition is crucial for regulating the exchange of solutes between **sinusoidal blood** and **hepatocytes**, as well as for the functional integrity of the liver [1]. *Collagen I & II* - **Collagen type I** is the most abundant collagen in the human body, found in connective tissues like **bone, skin, tendons, and ligaments**, but is not primary in the space of Disse. - **Collagen type II** is characteristic of **hyaline cartilage** and vitreous humor, and is not a significant component of the liver's extracellular matrix in the space of Disse. *Collagen II* - As mentioned, **collagen type II** is primarily found in **cartilage** and vitreous humor, which are distinct from the architectural requirements of the liver sinusoidal space. - Its presence in the space of Disse would not provide the necessary structural flexibility and support for the metabolic functions of the liver. *Collagen II & V* - While **collagen type V** is a minor fibrillar collagen that associates with collagen type I in many tissues, it is not a primary component of the space of Disse. - **Collagen type II** is, again, largely confined to cartilaginous structures, making this an unlikely combination for the liver microenvironment.

Q: Interosseous membrane of forearm is pierced by?

Anterior interosseous artery. ***Anterior interosseous artery*** - The **anterior interosseous artery** pierces the **interosseous membrane** in the **distal forearm** (approximately 5 cm above the wrist) to anastomose with the **posterior interosseous artery** and contribute to the **palmar carpal arch**. - This artery arises from the **common interosseous artery**, a branch of the **ulnar artery**. - This is the **classically taught structure** that pierces the interosseous membrane and is the standard answer in examination contexts. *Brachial artery* - The **brachial artery** is the main artery of the arm and terminates in the **cubital fossa** by dividing into the **radial** and **ulnar arteries**. - It does not pierce the **interosseous membrane** of the forearm as it is located in the arm, not the forearm. *Posterior interosseous artery* - The **posterior interosseous artery** arises from the **common interosseous artery** and passes **posteriorly between the oblique cord and the upper border of the interosseous membrane** to enter the posterior compartment of the forearm. - While it may pierce the membrane distally to anastomose anteriorly, the **anterior interosseous artery** is the structure **classically described** as piercing the membrane in standard anatomical teaching and examination contexts. *Ulnar recurrent artery* - The **ulnar recurrent arteries** (anterior and posterior branches) arise from the **ulnar artery** near the **cubital fossa** and ascend to participate in the **anastomosis around the elbow joint**. - These arteries do not pierce the **interosseous membrane** of the forearm.

Q: The energy for glycogenesis is provided by -

UTP. ***UTP*** - **Uridine triphosphate (UTP)** is essential for **glycogenesis** as it activates glucose by forming **UDP-glucose** from glucose-1-phosphate. - The reaction (Glucose-1-P + UTP → UDP-glucose + PPi) creates a **high-energy intermediate** that drives glycogen synthesis. - The subsequent hydrolysis of pyrophosphate (PPi) makes this activation step **irreversible**, and the energy stored in UDP-glucose is used for **glycosidic bond formation** when glucose is added to the growing glycogen chain. *GTP* - **Guanosine triphosphate (GTP)** is primarily involved in **protein synthesis**, G-protein signaling, and the citric acid cycle. - It is not used for glucose activation in glycogenesis; that role is specific to **UTP**. *GDP* - **Guanosine diphosphate (GDP)** is a product of GTP hydrolysis and functions in regulatory processes. - It does not serve as an energy donor for glycogen synthesis. *AMP* - **Adenosine monophosphate (AMP)** is a low-energy signal molecule that indicates cellular energy depletion. - High AMP levels **inhibit glycogenesis** and activate glycogenolysis through allosteric regulation of key enzymes. - It does not provide energy for anabolic pathways like glycogen synthesis.

Q: Rate limiting step in pyrimidine synthesis?

Carbamoyl phosphate synthase-II. ***Carbamoyl phosphate synthetase II (CPS-II)*** - **CPS-II** is the **committed and rate-limiting enzyme** in **de novo pyrimidine synthesis** in **mammals (including humans)** - It catalyzes the formation of **carbamoyl phosphate** from glutamine, CO₂, and 2 ATP in the **cytoplasm** - This is the **first committed step** and the main **regulatory checkpoint**, inhibited by UTP (feedback inhibition) and activated by PRPP and ATP - CPS-II is part of the **CAD complex** (carbamoyl phosphate synthetase, aspartate transcarbamoylase, dihydroorotase) in mammals *Aspartate transcarbamoylase (ATCase)* - ATCase catalyzes the **second step**: condensation of carbamoyl phosphate with aspartate to form carbamoyl aspartate - While ATCase is the **rate-limiting step in bacteria** (E. coli), in **mammals** it is part of the CAD complex and **not the primary regulatory step** - This option is incorrect for human/mammalian biochemistry tested in NEET PG *Dihydro-orotase* - The **third enzyme** in the pathway, converting carbamoyl aspartate to dihydroorotate - Part of the CAD complex in mammals but **not the rate-limiting step** *Dihydroorotate dehydrogenase* - Catalyzes the **fourth step**: oxidation of dihydroorotate to orotate - Located on the **outer surface of the inner mitochondrial membrane** (only mitochondrial enzyme in the pathway) - Important enzyme but **not rate-limiting**

Q: Which of the following is the major glycosaminoglycan of synovial fluid?

Hyaluronic acid. ***Hyaluronic acid*** - **Hyaluronic acid** is the primary glycosaminoglycan in **synovial fluid**, providing its characteristic **viscosity** and **lubricating properties**. - It plays a crucial role in maintaining **joint health** by reducing friction and acting as a shock absorber. *Chondroitin sulfate* - **Chondroitin sulfate** is abundant in **cartilage**, contributing to its **compressive strength**. - While present in connective tissues, it is not the major glycosaminoglycan of synovial fluid. *Dermatan sulfate* - **Dermatan sulfate** is primarily found in **skin**, **blood vessels**, and **heart valves**. - Its main roles involve tissue structure and repair, not lubrication of synovial fluid. *Heparan sulfate* - **Heparan sulfate** is found on **cell surfaces** and in the **extracellular matrix**, especially in the **basement membranes**. - It regulates cell growth, adhesion, and signaling, and is not a major component of synovial fluid viscosity.

Q: Reducing equivalents produced in glycolysis are transported from cytosol to mitochondria by ?

Malate-aspartate shuttle. ***Malate shuttle*** - The **malate-aspartate shuttle** is a primary mechanism for transporting **NADH reducing equivalents** from the cytosol to the mitochondrial matrix for **oxidative phosphorylation**. - It involves a series of **enzymes and transporters** that indirectly move electrons from NADH by converting **oxaloacetate to malate** in the cytosol, which then enters the mitochondria. *Carnitine* - **Carnitine** is primarily involved in the transport of **long-chain fatty acids** into the mitochondrial matrix for **beta-oxidation**. - It is not directly involved in the shuttle of NADH reducing equivalents generated during glycolysis. *Creatine* - **Creatine** and its phosphorylated form, **phosphocreatine**, are crucial for **energy buffering and transport** in tissues with high and fluctuating energy demands, like muscle and brain. - The creatine-phosphocreatine shuttle facilitates the rapid regeneration of ATP, but it is not involved in transporting glycolytic reducing equivalents. *Glutamate shuttle* - While glutamate and aspartate are components of the **malate-aspartate shuttle**, there isn't a standalone "glutamate shuttle" for transporting glycolytic reducing equivalents. - The **glutamate-aspartate transaminase** is an enzyme within the malate-aspartate shuttle, converting oxaloacetate to aspartate and alpha-ketoglutarate to glutamate from the matrix to the cytosol.

Q: Which of the following statements about hypercalcemia in sarcoidosis is false?

Parathormone level is increased. ***Parathormone level is increased*** - In **sarcoidosis-associated hypercalcemia**, the parathormone (PTH) level is typically **low or suppressed**. [1] - This is because the hypercalcemia is due to **extra-renal 1-$\alpha$ hydroxylation** of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol) by macrophages in granulomas, not primary hyperparathyroidism. [1] *PTHrP level is increased* - This statement is **false** for sarcoidosis. Elevated **parathyroid hormone-related peptide (PTHrP)** is a common cause of hypercalcemia in **malignancy**, particularly squamous cell carcinomas, but not in sarcoidosis. - Hypercalcemia in sarcoidosis is **PTH-independent** and not mediated by PTHrP. [1] *Oral steroids are useful* - This statement is **true**. **Corticosteroids** (like oral prednisone) are effective in treating hypercalcemia in sarcoidosis. - They work by **inhibiting the activity of 1-$\alpha$ hydroxylase** in alveolar macrophages and reducing intestinal calcium absorption. *Calcitriol level is increased* - This statement is **true**. In sarcoidosis, activated **macrophages within granulomas** aberrantly express **1-$\alpha$ hydroxylase**. [1] - This leads to the **extra-renal synthesis of calcitriol** (1,25-dihydroxyvitamin D), which increases intestinal calcium absorption and bone resorption, causing hypercalcemia. [1]

Q: Which of the following statements is false regarding hereditary spherocytosis?

Decreased MCHC. ***Decreased MCHC*** - Hereditary spherocytosis typically presents with an **increased MCHC** due to the spherocytes being more concentrated. - MCHC is a measure of the hemoglobin concentration in red blood cells, and in spherocytosis, this value is often elevated rather than decreased. *Defect in ankyrin* - This is a true statement; hereditary spherocytosis is associated with a defect in **ankyrin**, a protein that helps maintain the cell's membrane structure [2]. - Mutations in ankyrin lead to instability of the red blood cell membrane, resulting in spherocyte formation [2]. *Decreased MCV* - In hereditary spherocytosis, MCV is often **normal or slightly increased**, as it reflects the volume of red blood cells, which can be misinterpreted due to the presence of spherocytes. - Spherocytes are smaller cells, which can mistakenly suggest a falsely decreased MCV if not properly interpreted [1]. *Reticulocytosis* - This condition typically presents with **reticulocytosis** as a response to hemolysis, indicating the bone marrow is producing more red blood cells to compensate [1]. - The presence of reticulocytosis is a common finding in hereditary spherocytosis due to increased destruction of spherocytes. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 597-598. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 640-641.

Q: What physiological mechanism leads to an increase in cardiac output?

Increased myocardial contractility. ***Increased myocardial contractility*** - **Increased myocardial contractility** directly leads to a greater **stroke volume** (the amount of blood pumped with each beat), thus increasing cardiac output (Cardiac Output = Stroke Volume × Heart Rate). - This can be stimulated by factors such as **sympathetic nervous system activation** or positive inotropic agents. *Inhalation* - While inhalation can temporarily affect venous return and intrathoracic pressure, it does not directly or consistently lead to a sustained increase in **cardiac output**. - Its primary effect is on **respiration**, not cardiac performance. *Increased parasympathetic activity* - Increased parasympathetic activity, primarily via the **vagus nerve**, acts to **decrease heart rate** and myocardial contractility. - This effect would typically **reduce cardiac output**, not increase it. *Transitioning from a supine to a standing position* - Transitioning to a standing position usually causes a **temporary decrease in venous return** and a brief drop in cardiac output as blood pools in the lower extremities. - The body then compensates by increasing heart rate and peripheral vascular resistance to maintain blood pressure, but the initial effect on cardiac output is generally a transient decrease.

Question 1

How many ossification centers develop at the distal end of the humerus?

Accepted Answer

3

Answer

2

Answer

5

Answer

4

Question 2

Type of collagen found in space of Disse in liver is -

Accepted Answer

Collagen III & IV

Answer

Collagen I & II

Answer

Collagen II

Answer

Collagen II & V

Question 3

Interosseous membrane of forearm is pierced by?

Accepted Answer

Anterior interosseous artery

Answer

Brachial artery

Answer

Posterior interosseous artery

Answer

Ulnar recurrent artery

Question 4

The energy for glycogenesis is provided by -

Accepted Answer

UTP

Answer

GTP

Answer

GDP

Answer

AMP

Question 5

Rate limiting step in pyrimidine synthesis?

Accepted Answer

Carbamoyl phosphate synthase-II

Answer

Aspartate transcarbamoylase (ATCase)

Answer

Dihydroorotate dehydrogenase

Answer

Dihydro-orotase

Question 6

Which of the following is the major glycosaminoglycan of synovial fluid?

Accepted Answer

Hyaluronic acid

Answer

Chondroitin sulfate

Answer

Dermatan sulfate

Answer

Heparan sulfate

Question 7

Reducing equivalents produced in glycolysis are transported from cytosol to mitochondria by ?

Accepted Answer

Malate-aspartate shuttle

Answer

Carnitine

Answer

Creatine

Answer

Glutamate shuttle

Question 8

Which of the following statements about hypercalcemia in sarcoidosis is false?

Accepted Answer

Parathormone level is increased

Answer

PTHrP level is increased

Answer

Oral steroids are useful

Answer

Calcitriol level is increased

Question 9

Which of the following statements is false regarding hereditary spherocytosis?

Accepted Answer

Decreased MCHC

Answer

Defect in ankyrin

Answer

Reticulocytosis

Answer

Normal to increased MCV

Question 10

What physiological mechanism leads to an increase in cardiac output?

Accepted Answer

Increased myocardial contractility

Answer

Inhalation

Answer

Increased parasympathetic activity

Answer

Transitioning from a supine to a standing position

NEET-PG 2013

Anatomy

Biochemistry

Internal Medicine

Pathology

Physiology