NEET-PG 2017 Practice Questions

Q: Which enzyme marked as $X$ is missing in synthesis of vitamin $D_{3}$ ?

17-alpha-hydroxylase. ***17-alpha-hydroxylase*** - The diagram illustrates the synthesis of **vitamin D3**, which involves hydroxylation steps at positions C-25 in the liver and C-1 in the kidneys. These are catalyzed by **25-hydroxylase** and **1-alpha-hydroxylase**, respectively. - **17-alpha-hydroxylase** is involved in the synthesis of steroid hormones (like cortisol, androgens, and estrogens) from cholesterol, not in the synthesis or metabolism of vitamin D3; therefore, its absence would not be relevant to vitamin D synthesis. *3-beta-hydroxylase* - **3-beta-hydroxysteroid dehydrogenase** is crucial for the synthesis of all steroid hormones, converting delta-5-3-hydroxysteroids to delta-4-3-ketosteroids. - Its presence is essential for **steroidogenesis**, but it does not play a direct role in the specific hydroxylation steps for vitamin D activation. *21-hydroxylase* - **21-hydroxylase** is an enzyme involved in the synthesis of steroid hormones such as cortisol and aldosterone from progesterone and 17-hydroxyprogesterone. - Deficiency of this enzyme leads to **congenital adrenal hyperplasia**, a condition unrelated to vitamin D metabolism. *24-hydroxylase* - **24-hydroxylase** is responsible for the inactivation of vitamin D metabolites by adding a hydroxyl group at position C-24, leading to degradation. - This enzyme is part of the **catabolic pathway** to regulate vitamin D levels, rather than being a missing enzyme in the primary synthesis of active vitamin D.

Q: The following reaction occurs in which part of kidney?

Proximal convoluted tubule. **Proximal convoluted tubule** - The image shows the conversion of 25-hydroxycholecalciferol to **1,25 (OH)₂-D₃**, also known as calcitriol, via the enzyme **1α-hydroxylase**. - This critical hydroxylation reaction, occurring primarily in the **proximal convoluted tubule** cells of the kidney, produces the biologically active form of vitamin D. *Distal convoluted tubule* - The distal convoluted tubule is primarily involved in **fine-tuning** water and electrolyte reabsorption, influenced by hormones like aldosterone and antidiuretic hormone. - It does not contain the necessary enzymes, specifically **1α-hydroxylase**, for the final activation step of vitamin D. *Loop of Henle* - The loop of Henle's main function is to create a **medullary osmotic gradient** through countercurrent multiplication, crucial for concentrating urine. - It plays no significant role in the **hydroxylation of vitamin D** precursors. *Collecting duct* - The collecting duct is responsible for final adjustments to urine volume and concentration, largely under the influence of **antidiuretic hormone**. - It lacks the **enzymatic machinery** (1α-hydroxylase) required for the activation of vitamin D.

Q: Name the antigen marked as X determining blood group A.

N-Acetyl-Galactosamine. ***N-Acetyl-Galactosamine*** - Blood group A antigens are formed by the addition of **N-acetylgalactosamine** to the H antigen precursor molecule on the surface of red blood cells. - This sugar modification is catalyzed by the **A transferase enzyme**, which is specific for N-acetylgalactosamine. *N-Acetyl-Glucosamine* - While N-acetylglucosamine is a component of many glycans, it is not the terminal sugar that defines the **blood group A antigen**. - **N-acetylglucosamine** is a key building block for the H antigen and other blood group precursors, but not the specific modifying sugar for A. *Dermatan sulphate* - **Dermatan sulfate** is a **glycosaminoglycan** primarily found in connective tissues, skin, and blood vessels. - It plays a role in wound healing and coagulation, but is not involved in **ABO blood group determination**. *Keratan sulfate* - **Keratan sulfate** is another **glycosaminoglycan** found in cartilage, cornea, and bone. - It contributes to tissue hydration and structural integrity, but it is not part of the **ABO blood group antigens**.

Q: Which of the following will occur on efferent arteriolar constriction?

Increased GFR. ***Increased GFR*** - **Efferent arteriolar constriction** increases resistance to blood flow out of the glomerulus, causing blood to 'back up' and increase the **glomerular hydrostatic pressure (PGC)** - Higher **glomerular hydrostatic pressure** leads to increased net filtration pressure, which directly results in **increased glomerular filtration rate (GFR)** - This is the **primary and most clinically significant effect** of efferent arteriolar constriction - The increased PGC helps maintain GFR even when renal blood flow decreases slightly *Decreased GFR* - This is incorrect because **efferent arteriolar constriction** increases glomerular hydrostatic pressure, thereby **increasing GFR**, not decreasing it - Only severe efferent constriction that critically reduces renal plasma flow would eventually decrease GFR - The immediate and primary effect is always an increase in GFR *Increase flow in vasa recta* - This is incorrect; **efferent arteriolar constriction** actually **decreases** flow to the vasa recta - The constriction reduces blood flow exiting the glomerulus, which means less blood reaches the downstream peritubular capillaries and vasa recta - This decreased perfusion of the vasa recta can enhance urine concentration by reducing washout of the medullary concentration gradient *Decreased flow in vasa recta* - While this is physiologically true (efferent constriction does reduce peritubular and vasa recta blood flow), it is **not the primary or most significant effect** being tested - In the context of efferent arteriolar constriction, the **increased GFR** is the dominant and most clinically relevant consequence - The question asks "which will occur" expecting the primary hemodynamic effect on glomerular function - Decreased vasa recta flow is a secondary consequence, whereas increased GFR is the direct and immediate result

Q: The A wave in His bundle electrogram shows presence of:

Atrial depolarization. ***Atrial depolarization*** - The **A wave** in a His bundle electrogram represents the electrical activity corresponding to **atrial depolarization**. This is the first electrical event recorded prior to ventricular activation. - It signifies the activation of the atria, preceding the impulse transmission through the AV node and His bundle. *Atrial repolarization* - **Atrial repolarization** is generally not clearly visible as a distinct wave in a His bundle electrogram, as its electrical signal is usually small and often obscured by the much larger QRS complex from ventricular depolarization. - The T-wave on a surface ECG corresponds to ventricular repolarization, and there isn't a directly analogous, easily identifiable wave for atrial repolarization in standard His bundle recordings. *AV node activation* - **AV node activation** itself is a slow electrical process that does not generate a distinct, sharply defined wave in the His bundle electrogram. - The time taken for conduction through the AV node is represented by the **AH interval**, which is the duration between the A wave (atrial activation) and the H wave (His bundle activation). *Atrial depolarization to AV node activation* - This option describes a **duration or interval**, specifically the **AH interval**, which reflects the time from the beginning of atrial activation (A wave) to the beginning of His bundle activation (H wave) and primarily represents AV nodal conduction. - The A wave itself signifies a specific electrical event (**atrial depolarization**), not the entire period from atrial depolarization up to AV node activation.

Q: Which of the following is correct about the pressure volume loop of left ventricle?

Aortic valve opens at 2. ***Aortic valve opens at 2*** - Point 2 marks the moment when **left ventricular pressure exceeds aortic pressure**, causing the aortic valve to open. - This is the transition point between **isovolumetric contraction** (1→2) and **ventricular ejection** (2→3). - From point 2 onwards, blood is actively ejected from the left ventricle into the aorta during **systole**. *1 to 2 indicates isovolumetric relaxation* - The phase from point 1 to point 2 shows an increase in **pressure at constant volume**, which represents **isovolumetric contraction**, not relaxation. - During **isovolumetric contraction**, both the mitral and aortic valves are closed, and the ventricle contracts without changing volume, building up pressure. - **Isovolumetric relaxation** occurs from point 3 to point 4, where pressure drops at constant volume after the aortic valve closes. *2 to 3 indicates ventricular diastole* - The period from point 2 to point 3 represents **ventricular ejection**, which is part of **ventricular systole**, not diastole. - During this phase, the aortic valve is open, and blood is being ejected from the left ventricle into the aorta while ventricular volume decreases. - **Ventricular diastole** includes isovolumetric relaxation (3→4) and ventricular filling (4→1). *Pulmonic valve opens at 3* - Point 3 represents the **closure of the aortic valve** at the end of ventricular ejection, not its opening. - The **pulmonic valve** is part of the right ventricular circuit, not the left ventricle; it opens during right ventricular ejection into the pulmonary artery. - This question specifically addresses the **left ventricular** pressure-volume loop.

Q: Which of the following is correct about the point marked $Z$ on the cardiac cycle?

Aortic valve opens. ***Aortic valve opens*** - At point Z, the **left ventricular pressure (LVP)** curve (solid red line) intersects and surpasses the **aortic pressure (AP)** curve (dashed line), marking the moment the **aortic valve opens** and blood begins to be ejected into the aorta. - This event signifies the transition from **isovolumetric contraction** to rapid **ventricular ejection phase** during systole. *Mitral valve opens* - The **mitral valve opens** during diastole, when the **left ventricular pressure (LVP)** falls below the **left atrial pressure (LAP)**, allowing ventricular filling. - This event would typically occur much later in the cardiac cycle, around point 5 or 6, after the aortic valve closes. *Tricuspid valve opens* - The **tricuspid valve opens** during diastole when the right ventricular pressure falls below the right atrial pressure. This event is not directly depicted for the left side of the heart in this Wigger's diagram. - It plays a role in right heart filling and is not related to the events occurring at point Z in the left heart cycle. *Mid systolic click* - A **mid-systolic click** is typically associated with **mitral valve prolapse**, occurring during mid-systole as the mitral leaflets prolapse into the left atrium. - Point Z represents the beginning of ejection, not a valvular abnormality.

Q: The pressure-volume loop of left ventricle tracing of the patient indicates:

Diastolic dysfunction. ***Diastolic dysfunction*** - The pressure-volume loop for the patient is shifted to the **left and upward** relative to the control loop, indicating higher left ventricular pressure for a given volume during diastole. - The **end-diastolic pressure-volume relationship (EDPVR)**, shown by the lower right curve, is steeper for the patient, meaning the ventricle is **stiffer or less compliant** during filling. *Systolic dysfunction* - Systolic dysfunction would be characterized by a **reduced stroke volume** (narrower loop horizontally) and a **lower ejection fraction**, often accompanied by a shift to the right due to increased end-diastolic volume. - The **end-systolic pressure-volume relationship (ESPVR)**, which represents contractility, would be shifted downwards and to the right in systolic dysfunction, indicating impaired contractility. *Decreased atrial compliance* - Decreased atrial compliance would primarily affect **atrial pressures** and the force of atrial contraction, which might indirectly impact ventricular filling, but is not directly represented by the ventricular pressure-volume loop's morphology in this manner. - The primary indicator of atrial compliance is often via atrial pressure-volume relationships or specific atrial function studies, not the ventricular loop's overall shift. *Increased atrial compliance* - Increased atrial compliance would allow the atria to accommodate more volume at lower pressures, potentially *improving* ventricular filling if the ventricle itself is compliant, but it would not explain the **elevated ventricular diastolic pressures** seen in the patient's tracing. - This condition would typically lead to lower atrial pressures, which is the opposite of what would contribute to the observed ventricular diastolic dysfunction.

Q: Which of the following dissociation curve mentioned is for myoglobin?

Green. ***Green*** - The **green curve** represents **myoglobin**, which has a much higher affinity for oxygen than hemoglobin. It binds oxygen at very low partial pressures and releases it only when oxygen levels are significantly depleted, as in active muscle tissue. - Myoglobin's dissociation curve is typically **hyperbolic** due to its single oxygen-binding site, reflecting its role in oxygen storage rather than transport. *Purple* - The **purple curve** represents normal **hemoglobin**, which exhibits a **sigmoidal** shape due to its **cooperative binding** of oxygen. This allows hemoglobin to efficiently load oxygen in the lungs and unload it in tissues. - Hemoglobin has a lower oxygen affinity than myoglobin and is designed for oxygen transport, adapting its binding based on oxygen partial pressure. *Red* - The **red curve** likely represents a **right-shifted hemoglobin dissociation curve**, indicating **decreased oxygen affinity**. This shift facilitates oxygen unloading to tissues. - Right shifts occur due to increased temperature, decreased pH (Bohr effect), increased 2,3-DPG, or increased CO₂. These physiological adaptations help deliver more oxygen to metabolically active tissues. *None* - This option is incorrect because the **green curve** clearly represents the characteristic oxygen dissociation curve for myoglobin.

Question 1

What is incorrect about the shown basement membrane?

Accepted Answer

Only molecules which are larger than 50,000 Daltons can traverse the filtration barrier

Answer

Part of filtration barrier

Answer

Stained with PAS

Answer

It has Lamina Densa and Lamina Rara

Question 2

Which enzyme marked as $X$ is missing in synthesis of vitamin $D_{3}$ ?

Accepted Answer

17-alpha-hydroxylase

Answer

3-beta-hydroxylase

Answer

21-hydroxylase

Answer

24-hydroxylase

Question 3

The following reaction occurs in which part of kidney?

Accepted Answer

Proximal convoluted tubule

Answer

Distal convoluted tubule

Answer

Loop of Henle

Answer

Collecting duct

Question 4

Name the antigen marked as X determining blood group A.

Accepted Answer

N-Acetyl-Galactosamine

Answer

N-Acetyl-Glucosamine

Answer

Dermatan sulphate

Answer

Keratan sulfate

Question 5

Which of the following will occur on efferent arteriolar constriction?

Accepted Answer

Increased GFR

Answer

Decreased GFR

Answer

Increase flow in vasa recta

Answer

Decreased flow in vasa recta

Question 6

The A wave in His bundle electrogram shows presence of:

Accepted Answer

Atrial depolarization

Answer

Atrial repolarization

Answer

AV node activation

Answer

Atrial depolarization to AV node activation

Question 7

Which of the following is correct about the pressure volume loop of left ventricle?

Accepted Answer

Aortic valve opens at 2

Answer

1 to 2 indicates isovolumetric relaxation

Answer

2 to 3 indicates ventricular diastole

Answer

Pulmonic valve opens at 3

Question 8

Which of the following is correct about the point marked $Z$ on the cardiac cycle?

Accepted Answer

Aortic valve opens

Answer

Mitral valve opens

Answer

Tricuspid valve opens

Answer

Mid systolic click

Question 9

The pressure-volume loop of left ventricle tracing of the patient indicates:

Accepted Answer

Diastolic dysfunction

Answer

Systolic dysfunction

Answer

Decreased atrial compliance

Answer

Increased atrial compliance

Question 10

Which of the following dissociation curve mentioned is for myoglobin?

Accepted Answer

Green

Answer

Purple

Answer

Red

Answer

None

NEET-PG 2017

Anatomy

Biochemistry

Physiology