NEET-PG 2015 Practice Questions

Q: In the context of blood pressure regulation, where are baroreceptors primarily located?

Tunica adventitia. ***Tunica adventitia*** - **Baroreceptors** are specialized mechanoreceptive nerve endings that detect changes in blood pressure by sensing arterial wall stretch. - These sensory nerve endings are primarily located in the **tunica adventitia** (outermost layer) of the **carotid sinus** and **aortic arch** [1]. - The adventitia contains the **nerve fibers and endings** (including baroreceptors), as well as the vasa vasorum and connective tissue supporting the vessel wall [1]. - The nerve terminals extend from the adventitia toward the adventitial-medial border where they sense wall tension changes. *Tunica media* - The **tunica media** is the middle layer composed of **smooth muscle cells** and elastic fibers. - While this layer responds to stretch and changes thickness with blood pressure variations, it does **not contain nerve endings or baroreceptors** [1]. - The media is responsible for vasoconstriction and vasodilation but lacks the sensory innervation needed for baroreception. *Tunica intima* - The **tunica intima** is the innermost layer lined by **endothelial cells**. - Its primary functions include providing a smooth surface for blood flow and regulating vascular permeability. - This layer does not house baroreceptors or other mechanoreceptive nerve endings. *None of the options* - This option is incorrect because **tunica adventitia** is indeed the correct location of baroreceptors. - The adventitia contains the neural elements necessary for blood pressure sensing in these specialized arterial regions [1].

Q: Which of the following proteins is primarily responsible for marking other proteins for degradation?

Ubiquitin. **Ubiquitin** - **Ubiquitin** is a small regulatory protein that marks proteins for degradation by targeting them to the **proteasome**. - The ubiquitination process involves a cascade of enzymes (E1, E2, E3) that sequentially attach ubiquitin to the target protein, forming a **polyubiquitin chain**. *RNAse* - **RNAse** (Ribonuclease) is an enzyme that catalyzes the degradation of **RNA into smaller components**. - Its primary function is in **RNA processing** and turnover, not protein degradation. *Zymase* - **Zymase** is a complex of enzymes that catalyzes the **fermentation of sugar into ethanol and carbon dioxide**. - It is commonly found in yeast and is essential for **alcoholic fermentation**, with no role in protein degradation. *Chaperone* - **Chaperone proteins** assist in the **folding of newly synthesized proteins** and the refolding of misfolded or denatured proteins. - Their role is to ensure proper protein structure and function, preventing aggregation, rather than marking proteins for destruction.

Q: Apo B48 is synthesized in -

Intestine. ***Intestine*** - **Apo B48** is a truncated form of apolipoprotein B-100, uniquely synthesized in the **intestine** through RNA editing. - It is a crucial structural component of **chylomicrons**, which are lipoprotein particles responsible for transporting exogenous dietary lipids from the intestine to other tissues. *Liver* - The liver primarily synthesizes **Apo B100**, which is a full-length apolipoprotein B and a major component of VLDL, IDL, and LDL. - It does not produce Apo B48. *Kidney* - The kidneys are involved in filtering waste products and regulating fluid balance, but they do not play a role in the synthesis of apolipoproteins like Apo B48. - Kidney cells are not equipped with the specific machinery for Apo B mRNA editing. *RBCs* - Red blood cells (RBCs) are primarily responsible for oxygen transport and lack a nucleus and most organelles, including those required for protein synthesis. - Therefore, RBCs cannot synthesize proteins such as Apo B48.

Q: Bacteria most commonly involved in bowel decomposition after death is?

Clostridium perfringens. ***Clostridium perfringens*** - This bacterium is a ubiquitous **anaerobe** in the gut and is known for its rapid proliferation after death, producing gases that contribute to **bloating and decomposition**. - It is a primary cause of **gas gangrene** in living individuals, reflecting its tissue-destructive capabilities, which extend to post-mortem changes. - Produces large amounts of **hydrogen and CO2**, making it the most significant contributor to post-mortem gas formation and putrefaction. *Streptococcus pyogenes* - While a significant pathogen in life, causing conditions like **strep throat** and **necrotizing fasciitis**, it is not the primary agent of putrefaction. - Its role in post-mortem decomposition is generally less prominent compared to anaerobic gut flora. *Pseudomonas aeruginosa* - This bacterium is an opportunistic pathogen often associated with infections in immunocompromised individuals or in healthcare settings. - It is not typically identified as the most common or primary bacterium involved in the initial stages of post-mortem **bowel decomposition**, though it can be present in later stages. *Escherichia coli* - While *E. coli* is abundant in the bowel and participates in post-mortem decomposition, it is not the **most common** agent responsible for gas production and tissue decomposition. - *Clostridium perfringens* proliferates more rapidly and produces significantly more gas, making it the predominant bacterium in bowel putrefaction.

Q: Which of the following is an aromatase inhibitor?

Letrozole. ***Letrozole*** - **Letrozole** is a commonly used **aromatase inhibitor**, which works by blocking the enzyme **aromatase** that converts androgens into estrogens [1]. - This reduction in estrogen levels is crucial in treating **hormone-sensitive breast cancers** [1]. *Tamoxifen* - **Tamoxifen** is a **selective estrogen receptor modulator (SERM)**, not an aromatase inhibitor [2]. - It acts by blocking estrogen receptors in breast tissue while potentially stimulating them in other tissues like bone and uterus [2]. *Danazol* - **Danazol** is a synthetic androgen that suppresses the hypothalamic-pituitary-gonadal axis, leading to **decreased estrogen production**. - It works by inhibiting gonadotropin release and directly inhibiting ovarian steroidogenesis, rather than blocking the aromatase enzyme directly. *Taxane* - **Taxanes** are a class of **chemotherapy drugs** that interfere with cell division by stabilizing microtubules. - They are used to treat various cancers, including breast cancer, but do not act as aromatase inhibitors.

Q: Which of the following is NOT a side effect of atropine?

Diarrhoea. ***Diarrhoea*** - Atropine is a **muscarinic antagonist** that blocks the action of **acetylcholine** on muscarinic receptors in the gastrointestinal tract. - This leads to **decreased GI motility** and **decreased secretions**, typically causing **constipation**, NOT diarrhoea. - Diarrhoea would be associated with **cholinergic agonists** or anticholinesterases, which increase GI motility. *Blurring of vision* - Atropine causes **mydriasis** (pupil dilation) and **cycloplegia** (paralysis of the ciliary muscle). - **Cycloplegia** impairs accommodation for near vision, leading to **blurring of vision**. - This is a common anticholinergic side effect. *Urinary retention* - Atropine blocks **M3 receptors** on the **detrusor muscle**, causing bladder relaxation and reduced contractility. - This leads to **urinary retention**, especially in patients with pre-existing conditions like **prostatic hypertrophy**. *Confusion in elderly* - Atropine can cross the **blood-brain barrier** and cause **CNS effects** including confusion, agitation, and delirium. - Elderly patients are particularly susceptible to these **central anticholinergic effects**.

Q: Acetaminophen [Paracetamol] induced liver toxicity is due to which metabolite?

NAPQI. ***NAPQI*** - **N-acetyl-p-benzoquinone imine (NAPQI)** is a highly reactive and toxic metabolite produced during acetaminophen metabolism, especially in overdose situations [1, 3]. - When glutathione stores are depleted due to excessive NAPQI formation, this metabolite covalently binds to hepatic macromolecules, causing **hepatocellular damage and necrosis** [1, 3].*N-acetylcysteine* - **N-acetylcysteine (NAC)** is the antidote for acetaminophen overdose, not the toxic metabolite itself [2, 3]. - NAC works by replenishing hepatic **glutathione stores**, which helps detoxify NAPQI and prevent liver injury [2, 3].*Co-Q* - **Coenzyme Q10 (CoQ10)** is an endogenous antioxidant and electron carrier in the mitochondrial respiratory chain. - It is not a metabolite of acetaminophen and plays no direct role in acetaminophen-induced liver toxicity.*Cytochrome 'C'* - **Cytochrome c** is a protein involved in the electron transport chain in mitochondria and plays a critical role in apoptosis. - While cellular damage from NAPQI can eventually lead to cytochrome c release and apoptosis, cytochrome c itself is not a metabolite of acetaminophen or the direct cause of toxicity.

Q: Which carrier pump is responsible for transporting solutes in the thick ascending limb of the loop of Henle?

Sodium-potassium-chloride cotransporter. * **Sodium-potassium-chloride cotransporter.** * This transporter, specifically the **Na+-K+-2Cl- cotransporter (NKCC2)**, is highly expressed in the apical membrane of the thick ascending limb. * It actively reabsorbs **sodium, potassium, and chloride ions** from the filtrate, contributing significantly to the medullary interstitial osmotic gradient. * *NaCl- cotransporter* * The **NaCl cotransporter (NCC)** is primarily found in the **distal convoluted tubule**, not the thick ascending limb. * It reabsorbs sodium and chloride in a 1:1 ratio and is the target of thiazide diuretics. * *Na+-H+ exchanger* * The **Na+-H+ exchanger (NHE3)** is predominantly located in the **proximal tubule** where it plays a crucial role in bicarbonate reabsorption and acid-base balance. * While some NHE activity exists in other nephron segments, it is not the primary carrier in the thick ascending limb. * *Na+-K+ exchanger* * The **Na+-K+ exchanger** or **Na+/K+-ATPase pump** is located on the basolateral membrane of most renal tubular cells, including the thick ascending limb. * Its main function is to maintain the electrochemical gradient by pumping **sodium out of the cell** and potassium into the cell, which indirectly drives other transporters but is not the apical cotransporter responsible for initial solute reabsorption in the thick ascending limb.

Q: Which of the following is considered the most important intracellular buffer in human physiology?

Phosphate buffer. ***Phosphate buffer*** - The **phosphate buffer system (H₂PO₄⁻/HPO₄²⁻)** is the most important intracellular buffer due to relatively high concentrations of inorganic phosphates within cells - The pKa₂ of approximately **6.8 is close to intracellular pH** (~7.0-7.2), providing optimal buffering capacity - Plays a crucial role in buffering acids and bases generated by metabolic processes within cells and is also important in renal tubular buffering *Albumin protein* - **Proteins**, including albumin, are important **extracellular buffers** in plasma due to their abundant ionizable amino acid residues - While proteins do contribute to intracellular buffering (especially hemoglobin in RBCs), the **phosphate system is more significant** for general intracellular pH regulation *Ammonia buffer* - The **ammonia buffer system (NH₃/NH₄⁺)** is primarily a **renal buffer system** that plays a crucial role in acid excretion via urine - It is not considered the primary intracellular buffer for metabolic acid-base balance within cells *Bicarbonate buffer* - The **bicarbonate buffer system (HCO₃⁻/H₂CO₃)** is the **most important extracellular buffer system**, critical for maintaining blood pH - Although present intracellularly, its buffering capacity is less prominent than phosphate within cells due to lower intracellular bicarbonate concentration and its pKa of 6.1 being further from intracellular pH

Q: Amount of blood loss in Stage I of hemorrhagic shock is -

<15%. ***<15%*** - Stage I (Class I) hemorrhagic shock is characterized by **minimal blood loss of up to 15%** of total blood volume (up to 750 mL in a 70 kg adult). - This is the **universally accepted ATLS definition** for Class I hemorrhage. - At this level, compensatory mechanisms maintain normal vital signs with minimal clinical manifestations. - Patients typically show minimal or no symptoms, with possible mild tachycardia only. * 100 bpm), tachypnea, and decreased pulse pressure, but blood pressure remains normal. - This is too broad to specifically define Stage I. * 120 bpm), altered mental status, and decreased urine output. - This is far beyond the compensated Stage I definition.

Question 1

In the context of blood pressure regulation, where are baroreceptors primarily located?

Accepted Answer

Tunica adventitia

Answer

Tunica intima

Answer

None of the options

Answer

Tunica media

Question 2

Which of the following proteins is primarily responsible for marking other proteins for degradation?

Accepted Answer

Ubiquitin

Answer

RNAse

Answer

Zymase

Answer

Chaperone

Question 3

Apo B48 is synthesized in -

Accepted Answer

Intestine

Answer

Liver

Answer

Kidney

Answer

RBCs

Question 4

Bacteria most commonly involved in bowel decomposition after death is?

Accepted Answer

Clostridium perfringens

Answer

Streptococcus pyogenes

Answer

Pseudomonas aeruginosa

Answer

Escherichia coli

Question 5

Which of the following is an aromatase inhibitor?

Accepted Answer

Letrozole

Answer

Tamoxifen

Answer

Danazol

Answer

Taxane

Question 6

Which of the following is NOT a side effect of atropine?

Accepted Answer

Diarrhoea

Answer

Urinary retention

Answer

Confusion of elderly

Answer

Blurring of vision

Question 7

Acetaminophen [Paracetamol] induced liver toxicity is due to which metabolite?

Accepted Answer

NAPQI

Answer

Co-Q

Answer

Cytochrome 'C'

Answer

N-acetylcysteine

Question 8

Which carrier pump is responsible for transporting solutes in the thick ascending limb of the loop of Henle?

Accepted Answer

Sodium-potassium-chloride cotransporter

Answer

NaCl cotransporter

Answer

Na+-H+ exchanger

Answer

Na+-K+ exchanger

Question 9

Which of the following is considered the most important intracellular buffer in human physiology?

Accepted Answer

Phosphate buffer

Answer

Albumin protein

Answer

Ammonia buffer

Answer

Bicarbonate buffer

Question 10

Amount of blood loss in Stage I of hemorrhagic shock is -

Accepted Answer

<15%

Answer

<10%

Answer

<30%

Answer

<40%

NEET-PG 2015

Anatomy

Biochemistry

Forensic Medicine

Pharmacology

Physiology

Surgery