NEET-PG 2012 Practice Questions

Q: What is the lower limit of the retropharyngeal space?

Bifurcation of trachea. Bifurcation of trachea - The retropharyngeal space extends inferiorly to approximately the level of T4-T5 vertebrae, corresponding to the bifurcation of the trachea and the superior mediastinum. - This space lies between the buccopharyngeal fascia (posterior to pharynx) and the alar layer of prevertebral fascia. - Clinically, infections or abscesses in this space can descend into the posterior mediastinum, making knowledge of this inferior extent crucial for surgical management. - Note: Some anatomical texts describe the space ending at T1-T2, but for clinical and surgical purposes, the functional inferior limit extends to the bifurcation of the trachea. C7 - While some texts describe the retropharyngeal space as terminating around C7 (level of the lower border of cricoid cartilage), this represents the narrower definition. - The clinical and surgical definition extends the space further inferiorly to allow for tracking of infections into the chest. - C7 alone does not represent the accepted lower limit for examination purposes. 4th esophageal constriction - The fourth esophageal constriction is not a standard anatomical landmark (esophagus has 3-4 constrictions depending on classification). - Esophageal constrictions are luminal narrowings within the esophagus itself and do not define the boundaries of the retropharyngeal space, which is a fascial space posterior to both pharynx and esophagus. None of the options - This is incorrect because bifurcation of the trachea is the recognized lower limit of the retropharyngeal space for clinical and examination purposes. - Understanding this anatomical boundary is essential for predicting the spread of deep neck space infections.

Q: Where is the neurovascular plane located in the anterior abdominal wall?

Between internal oblique and transversus abdominis. ***Between internal oblique and transversus abdominis*** - This space, often referred to as the **transversus abdominis plane (TAP)**, contains the major neurovascular bundles supplying the anterior abdominal wall [1]. - The nerves here are the lower **thoracic (T7-T11)** and **iliohypogastric/ilioinguinal (L1) nerves**, along with accompanying blood vessels [1]. *Between external oblique and internal oblique* - This fascial plane primarily houses some superficial nerves and vessels but not the main neurovascular supply to the abdominal wall muscles. - The major neurovascular bundles for deeper muscle layers and skin are located deeper to the **internal oblique** [1]. *Below transversus abdominis* - Below the **transversus abdominis** muscle lies the **transversalis fascia**, an extraperitoneal fat layer, and then the **peritoneum**. - This deeper region primarily contains retroperitoneal structures and organs, not the main neurovascular plane for the abdominal wall. *Above external oblique* - The layer above the **external oblique** muscle is primarily subcutaneous tissue and skin. - While superficial nerves and vessels are present here, this is not the main neurovascular plane that supplies the muscles of the anterior abdominal wall.

Q: Blastocyst makes contact with endometrium on ?

5 - 7 days. ***5-7 days*** - The **blastocyst makes initial contact** (apposition) with the **endometrium** around **day 5-6 after fertilization**. - **Implantation**, which includes adhesion and invasion, typically begins around day 6 and is complete by day 10. - This timeframe allows the blastocyst to travel from the fallopian tube to the uterus and for the uterine lining to be optimally prepared. *< 3 days* - Within the first few days after fertilization, the zygote is still undergoing **cleavage** and development into a **morula**, then a young blastocyst, while traveling down the fallopian tube. - It has not yet reached the uterus or developed sufficiently to interact with the endometrium. *8-11 days* - By 8-11 days, the process of implantation is usually **well underway or completed**, with the blastocyst already invading the endometrial wall. - Initial contact and attachment occur prior to this period. *15-16 days* - This timeframe is well beyond the typical window for initial blastocyst contact and implantation. - By 15-16 days post-fertilization, the embryo would be undergoing **gastrulation** and early organogenesis, assuming successful implantation.

Q: From which ribs does the spleen extend?

9th to 11th rib. ***9th to 11th rib*** - The **spleen** is located in the **left upper quadrant** of the abdomen, deep to the 9th, 10th, and 11th ribs. - Its protected position beneath these ribs makes it vulnerable to injury from trauma to the left lower chest or upper abdomen. *5th to 9th rib* - This range primarily covers the location of the **heart** and the upper part of the **lungs**. - While the spleen is superior to other abdominal organs, it does not extend as high as the 5th rib. *2nd to 5th rib* - This region is mainly associated with the **upper lobes of the lungs** and the **superior mediastinum**. - The spleen is an abdominal organ and is situated much lower in the thoracic cavity. *11th to 12th rib* - This range is too low and posterior for the typical position of the spleen, especially for its superior border. - The 12th rib primarily overlies the **kidneys** and the more inferior aspects of the diaphragm.

Q: Fluoroacetate inhibits?

Aconitase. ***Aconitase*** - **Fluoroacetate** is metabolically converted to **fluorocitrate**, which is a potent competitive inhibitor of **aconitase**. - **Aconitase** is the enzyme responsible for converting **citrate to isocitrate** in the **Krebs cycle**, and its inhibition blocks the cycle. *Citrate synthase* - This enzyme is responsible for the formation of **citrate** from **acetyl-CoA** and **oxaloacetate**. - While fluoroacetate indirectly affects the cycle, it does not directly inhibit **citrate synthase**. *Succinate dehydrogenase* - This enzyme is part of the **Krebs cycle** and the **electron transport chain**, converting **succinate to fumarate**. - **Malonate** is a competitive inhibitor of succinate dehydrogenase, not **fluoroacetate**. *Alpha-ketoglutarate dehydrogenase* - This enzyme catalyzes the conversion of **alpha-ketoglutarate to succinyl-CoA** in the **Krebs cycle**. - Specific inhibitors of this enzyme include **arsenite** and **mercury compounds**, but not fluoroacetate.

Q: Why is oxidized LDL considered more atherogenic?

Is taken up by scavenger receptors. ***Is taken up by scavenger receptors*** - **Oxidized LDL (oxLDL)** is taken up by **scavenger receptors (CD36, SR-A)** on macrophages, which have **no feedback regulation**. - Unlike native LDL receptors that downregulate when cells have sufficient cholesterol, **scavenger receptors continue unlimited uptake**, leading to foam cell formation. - This **unregulated uptake mechanism** is the key reason why oxLDL is **more atherogenic** than native LDL. - The result is lipid-laden macrophages forming **fatty streaks**, the initial lesions of **atherosclerosis**. *Is not recognized by LDL receptors* - While true that oxLDL has **reduced affinity** for native LDL receptors due to oxidative modification, this alone doesn't explain increased atherogenicity. - The critical factor is what happens instead—its uptake via an **alternative, unregulated pathway**. *Accumulates in macrophages* - This is a **consequence** of scavenger receptor uptake, not the primary mechanism. - Foam cell formation occurs **because** of unregulated scavenger receptor uptake, making this a downstream effect. *Promotes inflammation in arterial walls* - OxLDL does promote inflammation through multiple mechanisms (cytokine release, endothelial dysfunction). - However, this is a **secondary effect** that occurs after uptake and accumulation—not the primary reason for atherogenicity.

Q: Major source of energy for brain in fasting/starvation?

Ketone bodies. ***Ketone bodies*** - During **prolonged fasting or starvation**, the body depletes its **glycogen stores** and begins to break down fatty acids. The liver converts these fatty acids into **ketone bodies**, such as **acetoacetate and beta-hydroxybutyrate**. - These **ketone bodies** can cross the **blood-brain barrier** and be used by the brain as an alternative energy source when glucose becomes scarce, preventing protein breakdown for gluconeogenesis. *Glucose* - While **glucose** is the primary and preferred energy source for the brain under normal physiological conditions, its availability significantly decreases during **prolonged fasting or starvation**. - The brain requires a continuous supply of glucose, but in states of severe caloric restriction, the body must conserve glucose for other critical functions and adapt by using alternative fuels. *Glycogen* - **Glycogen** is a stored form of glucose found predominantly in the **liver and muscles**. - The brain itself has minimal **glycogen stores**, which are rapidly depleted during fasting, and thus cannot be a major long-term energy source. *Fatty acids* - **Fatty acids** are a major energy source for many tissues in the body, especially during fasting, but they **cannot directly cross the blood-brain barrier** in significant amounts to fuel the brain. - Instead, **fatty acids** are metabolized into **ketone bodies** in the liver, which then serve as the brain's alternative fuel.

Q: What is the primary function of a primer in DNA replication?

Initiation of DNA replication. ***Initiation of DNA replication*** - DNA polymerase cannot synthesize new DNA strands de novo; it requires a pre-existing 3'-hydroxyl group to begin adding nucleotides. - The **primer**, a short RNA sequence, provides this necessary **3'-hydroxyl group**, allowing DNA polymerase to start synthesizing the new DNA strand. *Transcription* - This process involves synthesizing **RNA from a DNA template**, primarily carried out by **RNA polymerase**. - While primers are involved in DNA synthesis, they do not directly initiate the process of transcription. *Translation* - **Translation** is the process of synthesizing **proteins from mRNA templates** using ribosomes, tRNA, and amino acids. - This process is distinct from DNA synthesis and does not involve primers; its initiation involves start codons and ribosomal subunits. *Termination of DNA replication* - **Termination of DNA replication** occurs when replication forks meet or at specific termination sequences, often with the involvement of specialized proteins. - Primers are involved in the *start* of replication, not its conclusion.

Q: Enzyme deficient in Type I Hyperlipidemia?

Lipoprotein lipase. ***Lipoprotein lipase*** - **Type I hyperlipidemia**, also known as **familial hyperchylomicronemia**, is characterized by a deficiency in **lipoprotein lipase (LPL)**. - LPL is crucial for hydrolyzing triglycerides in **chylomicrons** and **VLDLs** into fatty acids and glycerol, allowing their uptake by tissues. *HMG CoA reductase* - This enzyme is involved in the **rate-limiting step of cholesterol synthesis** in the liver. - While it plays a role in lipid metabolism, its deficiency is not characteristic of **Type I hyperlipidemia**. *Peroxidase* - **Peroxidase** is an enzyme involved in various oxidative reactions, including the breakdown of **hydrogen peroxide**. - It is not directly involved in the metabolism of **chylomicrons** or **triglycerides**, and its deficiency is unrelated to hyperlipidemia. *Cholesterol acyl transferase* - This enzyme, often referring to **lecithin-cholesterol acyltransferase (LCAT)** or **acyl-CoA:cholesterol acyltransferase (ACAT)**, is involved in **cholesterol esterification**. - While important for cholesterol transport and storage, its deficiency is not the primary cause of **Type I hyperlipidemia**, which is marked by severe **chylomicronemia**.

Q: Which of the following is most important in sodium and water retention ?

Renin angiotensin system. ***Renin angiotensin system*** - The **renin-angiotensin-aldosterone system (RAAS)** is the most important mechanism for **both sodium AND water retention**, which is what the question specifically asks about. - **Aldosterone** directly promotes **sodium reabsorption** in the principal cells of the collecting duct by increasing apical ENaC channels and basolateral Na-K-ATPase pumps. - **Angiotensin II** stimulates sodium reabsorption in the proximal tubule and also stimulates ADH release, contributing to water retention. - When sodium is retained, **water follows passively** due to the osmotic gradient, resulting in effective volume expansion. - RAAS is the primary system activated in states of volume depletion and is most important for combined sodium and water retention. *Vasopressin* - **Vasopressin (ADH)** primarily controls **water retention only** by increasing aquaporin-2 channels in the collecting duct. - While crucial for water balance, it has minimal direct effect on sodium reabsorption. - It causes retention of **free water**, which can actually dilute plasma sodium concentration. - ADH is the answer if the question asked about water retention alone, but not for combined sodium and water retention. *ANP* - **Atrial natriuretic peptide (ANP)** promotes **sodium and water excretion** (natriuresis and diuresis). - Released in response to atrial stretch from volume expansion. - Acts to *oppose* retention mechanisms, making it incorrect for this question. *BNP* - **Brain natriuretic peptide (BNP)** similarly promotes **natriuresis and diuresis**. - Released from ventricular myocytes in response to volume overload. - Like ANP, it acts to *excrete* sodium and water, not retain them.

Question 1

What is the lower limit of the retropharyngeal space?

Accepted Answer

Bifurcation of trachea

Answer

4th esophageal constriction

Answer

C7

Answer

None of the options

Question 2

Where is the neurovascular plane located in the anterior abdominal wall?

Accepted Answer

Between internal oblique and transversus abdominis

Answer

Between external oblique and internal oblique

Answer

Below transversus abdominis

Answer

Above external oblique

Question 3

Blastocyst makes contact with endometrium on ?

Accepted Answer

5 - 7 days

Answer

< 3 days

Answer

8 - 11 days

Answer

15-16 days

Question 4

From which ribs does the spleen extend?

Accepted Answer

9th to 11th rib

Answer

5th to 9th rib

Answer

2nd to 5th rib

Answer

11th to 12th rib

Question 5

Fluoroacetate inhibits?

Accepted Answer

Aconitase

Answer

Citrate synthase

Answer

Succinate dehydrogenase

Answer

Alpha-ketoglutarate dehydrogenase

Question 6

Why is oxidized LDL considered more atherogenic?

Accepted Answer

Is taken up by scavenger receptors

Answer

Is not recognized by LDL receptors

Answer

Promotes inflammation in arterial walls

Answer

Accumulates in macrophages

Question 7

Major source of energy for brain in fasting/starvation?

Accepted Answer

Ketone bodies

Answer

Glucose

Answer

Glycogen

Answer

Fatty acids

Question 8

What is the primary function of a primer in DNA replication?

Accepted Answer

Initiation of DNA replication

Answer

Transcription

Answer

Translation

Answer

Termination of DNA replication

Question 9

Enzyme deficient in Type I Hyperlipidemia?

Accepted Answer

Lipoprotein lipase

Answer

HMG CoA reductase

Answer

Peroxidase

Answer

Cholesterol acyl transferase

Question 10

Which of the following is most important in sodium and water retention ?

Accepted Answer

Renin angiotensin system

Answer

ANP

Answer

BNP

Answer

Vasopressin

NEET-PG 2012

Anatomy

Biochemistry

Physiology