NEET-PG 2013 Practice Questions

Q: Which chamber of the heart forms the posterior surface?

Left Atrium (LA). ***Left Atrium (LA)*** - The **left atrium** forms the posterior surface of the heart, lying in front of the esophagus and thoracic aorta [1]. - Its posterior position makes it susceptible to enlargement, which can compress the **esophagus** and cause dysphagia [1]. *Right Atrium (RA)* - The **right atrium** primarily forms the right border of the heart and receives deoxygenated blood from the systemic circulation. - It lies anteriorly and to the right, behind the sternum and costal cartilages. *Left Ventricle (LV)* - The **left ventricle** forms the apex of the heart and part of the left border. - It is positioned *inferiorly* and *anteriorly*, contributing significantly to the *diaphragmatic surface* of the heart. *Right Ventricle (RV)* - The **right ventricle** forms the majority of the anterior surface of the heart, directly behind the sternum. - It also contributes to the *inferior surface* of the heart, resting on the diaphragm.

Q: All are infraclavicular branches of brachial plexus except ?

Long thoracic nerve. Long thoracic nerve - The long thoracic nerve originates directly from the roots (C5, C6, C7) of the brachial plexus, making it a supraclavicular branch. - It does not arise from the cords of the brachial plexus, which are located infraclavicularly. Ulnar nerve - The ulnar nerve arises from the medial cord of the brachial plexus, which is an infraclavicular structure. - It supplies many intrinsic hand muscles and the ulnar half of the flexor digitorum profundus. Axillary nerve - The axillary nerve is a branch of the posterior cord of the brachial plexus, classifying it as an infraclavicular branch. - It innervates the deltoid and teres minor muscles. Thoracodorsal nerve - The thoracodorsal nerve also originates from the posterior cord of the brachial plexus, making it an infraclavicular branch [1]. - It provides motor innervation to the latissimus dorsi muscle [1].

Q: What is the most dependent part of the peritoneal cavity in a female in the standing position?

Pouch of Douglas. ***Pouch of Douglas*** - The **rectouterine pouch** (Pouch of Douglas) is the most dependent part of the peritoneal cavity in females when standing. - It lies between the **rectum posteriorly** and the **uterus anteriorly**, extending down to the posterior fornix of the vagina [1]. - Due to gravity, any free fluid in the peritoneal cavity (blood, pus, ascitic fluid) collects here in the upright position. - **Clinical significance:** This is why culdocentesis (needle aspiration through the posterior vaginal fornix) can detect intraperitoneal fluid [1]. *Vesicouterine pouch* - Located between the **uterus posteriorly** and the **bladder anteriorly** [1]. - It is **superior** to the Pouch of Douglas and therefore not the most dependent part. - Fluid would collect in the Pouch of Douglas before reaching this pouch in a standing position. *Paracolic gutter* - The **paracolic gutters** are peritoneal recesses lateral to the ascending and descending colon. - While they can collect fluid, they are **not the lowest point** in the peritoneal cavity in an upright position. - The right paracolic gutter can serve as a pathway for fluid to spread between the pelvis and subphrenic spaces. *None of the options* - This is incorrect as the **Pouch of Douglas** is definitively the most dependent part of the peritoneal cavity in females in the standing position. - It is a well-established anatomical fact taught in all standard anatomy textbooks.

Q: Which of the following lipoproteins is most strongly associated with an increased risk of cardiovascular diseases and is commonly referred to as "bad cholesterol"?

LDL. ***LDL*** - **Low-density lipoprotein (LDL)** is commonly referred to as "bad" cholesterol because elevated levels are the **primary driver** of atherosclerotic plaque buildup in arterial walls. - LDL particles transport cholesterol from the liver to peripheral tissues; when present in excess, they infiltrate the arterial intima and undergo oxidative modification, triggering inflammatory responses that lead to atherosclerosis. - **Clinical significance:** LDL cholesterol is the primary target of lipid-lowering therapy in cardiovascular disease prevention. *VLDL* - **Very low-density lipoprotein (VLDL)** primarily transports endogenously synthesized **triglycerides** from the liver to peripheral tissues. - While elevated VLDL levels do contribute to cardiovascular risk (particularly through conversion to small, dense LDL particles), it is not the primary lipoprotein targeted in cardiovascular risk assessment. *Chylomicron* - **Chylomicrons** transport **dietary lipids** (triglycerides and cholesterol) from the intestines to tissues after meals. - They are rapidly cleared from circulation (half-life of 5-10 minutes) and are typically not present during fasting, making their contribution to chronic atherosclerotic plaque formation minimal. *Lp(a)* - **Lipoprotein(a) [Lp(a)]** is structurally similar to LDL but contains an additional apolipoprotein(a) molecule, which has homology to plasminogen and may interfere with fibrinolysis. - While Lp(a) is an independent cardiovascular risk factor, it is less commonly measured in routine clinical practice, and **LDL remains the cornerstone lipoprotein** for cardiovascular risk stratification and management.

Q: Which of the following statements about vitamin E is false?

Water soluble vitamin. ***Water soluble vitamin*** - This statement is false because **vitamin E** is a **fat-soluble vitamin**, meaning it dissolves in lipids and is stored in the body's fatty tissues and liver. - Its absorption requires the presence of dietary fat and bile salts, unlike water-soluble vitamins. *Act as antioxidant* - **Vitamin E** is a powerful **lipid-soluble antioxidant**, protecting cell membranes from damage by scavenging **free radicals**. - It helps prevent **oxidative damage** to polyunsaturated fatty acids within cell membranes. *Chemically tocopherol* - The most biologically active form of **vitamin E** is **alpha-tocopherol**, although vitamin E encompasses a group of eight fat-soluble compounds, including tocopherols and tocotrienols. - This term correctly identifies the chemical nature of the prominent forms of vitamin E. *Prevent lipid peroxidation of cell membrane* - As an **antioxidant**, **vitamin E** specifically interferes with the **propagation of lipid peroxidation**, a chain reaction that damages cell membranes by oxidizing their lipid components. - It donates an electron to **free radicals**, thereby neutralizing them and protecting the integrity of the cell membrane.

Q: Which of the following is a natural uncoupler found in brown adipose tissue?

Thermogenin. ***Correct: Thermogenin*** - Also known as **uncoupling protein 1 (UCP1)**, it is a **mitochondrial inner membrane protein** naturally expressed in **brown adipose tissue** - Thermogenin creates a **proton leak** across the inner mitochondrial membrane, bypassing ATP synthase and dissipating the proton gradient as heat, thereby mediating **non-shivering thermogenesis** - This is the only natural uncoupler among the options listed *Incorrect: 2,4-Nitrophenol* - This compound is **not a naturally occurring uncoupler** in mammalian tissues - While it can act as a synthetic uncoupler in laboratory settings, it is not found in biological systems *Incorrect: 2,4-Dinitrophenol* - This is a well-known **synthetic chemical uncoupler** of oxidative phosphorylation, historically used as a weight-loss drug (now banned due to toxicity) - It works by carrying protons across the inner mitochondrial membrane, but it is **not a natural biological molecule** found in the body *Incorrect: Oligomycin* - Oligomycin is an **inhibitor of ATP synthase (Complex V)**, not an uncoupler - It binds to the F0 subunit of ATP synthase, blocking the flow of protons through the enzyme and thereby preventing ATP synthesis - This blocks both the proton gradient dissipation AND ATP production, which is mechanistically different from uncoupling

Q: Which of the following statements regarding collagen synthesis is incorrect?

Hydroxylation of proline occurs in Golgi apparatus. ***Hydroxylation of proline occurs in Golgi apparatus*** - This statement is incorrect because the **hydroxylation of proline** residues occurs in the **endoplasmic reticulum** (ER), not the Golgi apparatus. - This step is critical for forming stable **triple helix** structures of collagen and requires **vitamin C**. *Synthesized in ribosomes as preprocollagen* - This statement is correct. Collagen synthesis begins in the cytoplasm, where mRNA is translated by **ribosomes** into **preprocollagen**, which contains a signal peptide. - The signal peptide directs the nascent polypeptide chain into the lumen of the **endoplasmic reticulum**. *Hydroxylation of lysine occurs in ER* - This statement is correct. Following entry into the ER, specific **lysine** residues are hydroxylated by **lysyl hydroxylase** to form hydroxylysine. - This hydroxylation, along with that of proline, is crucial for **cross-linking** and stability of the collagen molecule. *Triple helix assembly occurs in ER* - This statement is correct. After hydroxylation and glycosylation of some residues, three procollagen alpha chains self-assemble to form a **triple helix** within the **endoplasmic reticulum**. - This assembly is stabilized by **disulfide bonds** at the C-terminal ends and molecular chaperones.

Q: What is the blood form of folic acid?

Methyltetrahydrofolate. ***Methyltetrahydrofolate*** - **5-methyltetrahydrofolate (5-MTHF)** is the **primary circulating form** of folate in the blood plasma and the most metabolically active form of folate. - It plays a crucial role in various metabolic pathways, especially in **one-carbon metabolism** for DNA synthesis and repair. *Folinic acid* - **Folinic acid** (leucovorin) is a **reduced form of folic acid** that does not require reduction by dihydrofolate reductase for activity. - It is often used as a therapeutic agent, particularly to **counteract the effects of methotrexate** toxicity, but it is not the main physiological circulating form. *Pteroglutamate* - **Pteroglutamate** is a generic term referring to compounds structurally related to folic acid, which is itself chemically known as pteroylglutamic acid. - While it describes the **general structure**, it is not the specific blood form of folic acid. *None of the options* - This option is incorrect because **methyltetrahydrofolate** is indeed the correct answer.

Q: Which type of muscle fibers has fewer mitochondria?

Type IIb fibers (Fast-twitch fibers). ***Type IIb fibers (Fast-twitch fibers)*** - These fibers rely primarily on **anaerobic glycolysis** for ATP production, which is a less efficient process than aerobic respiration and therefore requires fewer mitochondria. - Their primary function is rapid, powerful contractions over short durations, leading to quick fatigue. *Type IIa fibers* - These fibers are **fast-twitch oxidative-glycolytic** fibers, meaning they have a moderate number of mitochondria to support both aerobic and anaerobic metabolism. - They are capable of generating strong contractions and are more fatigue-resistant than Type IIb fibers but less so than Type I fibers. *Type I fibers (Red fibers)* - Known as **slow-twitch oxidative fibers**, they have a high density of mitochondria to support continuous **aerobic respiration** for sustained, low-intensity contractions. - Their rich blood supply and high myoglobin content give them their characteristic red color and make them highly fatigue-resistant. *Type IIx fibers (Intermediate fibers)* - These fibers are very similar to Type IIb fibers in their metabolic profile, often considered an intermediate or even functionally equivalent type depending on the species. - They also primarily utilize **anaerobic glycolysis** and have a relatively low mitochondrial content, making them prone to fatigue.

Q: How many transmembrane spanning domains does the Na+-K+-Cl- cotransporter contain?

12 transmembrane spanning domain. ***12 transmembrane spanning domain*** - The **Na+-K+-Cl- cotransporter (NKCC)**, specifically NKCC1 and NKCC2 isoforms, is a multipass transmembrane protein. - It is known to contain **12 transmembrane spanning domains**, which are α-helical regions that cross the cell membrane. *5 transmembrane spanning domain* - This number is **too low** for the complex structure of the NKCC cotransporter. - Proteins with 5 transmembrane domains typically have different functional roles and structural characteristics. *7 transmembrane spanning domain* - This number is characteristic of **G protein-coupled receptors (GPCRs)**, a distinct family of membrane proteins. - The NKCC cotransporter functions as an ion transporter and does not share the structural motif of GPCRs. *9 transmembrane spanning domain* - This number is also **insufficient** to describe the known topology of the NKCC cotransporter. - Ion transporters like NKCC generally require a higher number of transmembrane domains to form the necessary pore and binding sites.

Question 1

Which chamber of the heart forms the posterior surface?

Accepted Answer

Left Atrium (LA)

Answer

Right Atrium (RA)

Answer

Left Ventricle (LV)

Answer

Right Ventricle (RV)

Question 2

All are infraclavicular branches of brachial plexus except ?

Accepted Answer

Long thoracic nerve

Answer

Axillary nerve

Answer

Thoracodorsal nerve

Answer

Ulnar nerve

Question 3

What is the most dependent part of the peritoneal cavity in a female in the standing position?

Accepted Answer

Pouch of Douglas

Answer

Vesicouterine pouch

Answer

Paracolic gutter

Answer

None of the options

Question 4

Which of the following lipoproteins is most strongly associated with an increased risk of cardiovascular diseases and is commonly referred to as "bad cholesterol"?

Accepted Answer

LDL

Answer

VLDL

Answer

Chylomicron

Answer

Lp (a)

Question 5

Which of the following statements about vitamin E is false?

Accepted Answer

Water soluble vitamin

Answer

Act as antioxidant

Answer

Chemically tocopherol

Answer

Prevent lipid peroxidation of cell membrane

Question 6

Which of the following is a natural uncoupler found in brown adipose tissue?

Accepted Answer

Thermogenin

Answer

2,4-Nitrophenol

Answer

2,4-Dinitrophenol

Answer

Oligomycin

Question 7

Which of the following statements regarding collagen synthesis is incorrect?

Accepted Answer

Hydroxylation of proline occurs in Golgi apparatus

Answer

Hydroxylation of lysine occurs in ER

Answer

Synthesized in ribosomes as preprocollagen

Answer

Triple helix assembly occurs in ER

Question 8

What is the blood form of folic acid?

Accepted Answer

Methyltetrahydrofolate

Answer

Folinic acid

Answer

Pteroglutamate

Answer

None of the options

Question 9

Which type of muscle fibers has fewer mitochondria?

Accepted Answer

Type IIb fibers (Fast-twitch fibers)

Answer

Type I fibers (Red fibers)

Answer

Type IIa fibers

Answer

Type IIx fibers (Intermediate fibers)

Question 10

How many transmembrane spanning domains does the Na+-K+-Cl- cotransporter contain?

Accepted Answer

12 transmembrane spanning domain

Answer

5 transmembrane spanning domain

Answer

7 transmembrane spanning domain

Answer

9 transmembrane spanning domain

NEET-PG 2013

Anatomy

Biochemistry

Physiology