NEET-PG 2015

1414 Questions — Page 31 of 142

Anatomy

2 questions

Q301

Where are the stretch receptors located in the left atrium?

Q302

Which organ receives dual blood supply with both sources contributing to its primary metabolic function?

NEET-PG 2015 - Anatomy NEET-PG Practice Questions and MCQs

Question 301: Where are the stretch receptors located in the left atrium?

A. None of the options
B. Atrioventricular septum
C. Septum between the atria
D. Entrance of the pulmonary veins (Correct Answer)

Explanation: ***Entrance of the pulmonary veins*** - **Stretch receptors** are mechanoreceptors that detect changes in pressure and volume. In the left atrium, they are primarily located at the **junction of the pulmonary veins and the left atrium** [1]. - These receptors play a crucial role in the **Bainbridge reflex** and the release of **atrial natriuretic peptide (ANP)** in response to increased blood volume [1]. *Atrioventricular septum* - The **atrioventricular septum** separates the atria from the ventricles and primarily contains components of the **cardiac conduction system**, such as the AV node and bundle of His [2]. - While it has specialized tissues, it is not the primary location for **stretch receptors** involved in volume sensing. *Septum between the atria* - The **interatrial septum** primarily separates the right and left atria. - Although it contains some myocardial cells, it is not the main site for **stretch receptors** responsible for monitoring left atrial volume. *None of the options* - This option is incorrect because the **entrance of the pulmonary veins** is indeed the primary location for stretch receptors in the left atrium [1].

Question 302: Which organ receives dual blood supply with both sources contributing to its primary metabolic function?

A. Heart
B. Liver (Correct Answer)
C. Kidney
D. Lung

Explanation: ***Liver*** - The liver receives blood from two sources: the **hepatic artery** (supplying oxygenated blood, ~25% of blood flow) and the **hepatic portal vein** (supplying nutrient-rich, deoxygenated blood from the gastrointestinal tract, ~75% of blood flow). - Both blood supplies are essential for the liver's primary metabolic functions, detoxification, and nutrient processing [1]. - This is the classic example of dual blood supply in medical education. *Heart* - The heart receives its blood supply primarily from the **coronary arteries**, which branch off the aorta. - While it has an extensive arterial network, it has a single primary source of blood supply. *Kidney* - The kidneys receive their blood supply exclusively from the **renal arteries**, which branch directly from the aorta. - Each kidney typically has a single renal artery supplying it for high-pressure filtration. *Lung* - The lungs do receive blood from two sources: **pulmonary arteries** (deoxygenated blood for gas exchange) and **bronchial arteries** (oxygenated blood for tissue nourishment, <5% of flow). - However, the primary function (gas exchange) is served by pulmonary circulation alone, while bronchial circulation only nourishes lung tissue. - The liver is the standard answer for dual blood supply where both sources serve the organ's primary function.

Internal Medicine

1 questions

Q301

What does the measurement of Glomerular Filtration Rate (GFR) help determine in kidney function?

Physiology

7 questions

Q301

Which of the following is the primary factor involved in mesangial cell contraction?

Q302

Tubuloglomerular feedback is for regulation of?

Q303

Which of the following is the MOST important factor determining whether a substance can be filtered at the glomerulus?

Q304

Which of the following statements is true about coronary circulation?

Q305

Which of the following statements is true regarding the Bezold-Jarisch reflex?

Q306

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

Q307

Which of the following factors is most commonly targeted therapeutically for blood pressure control?

NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs

Question 301: Which of the following is the primary factor involved in mesangial cell contraction?

A. ANP
B. Endothelin-1
C. Angiotensin II (Correct Answer)
D. Platelet-activating factor (PAF)

Explanation: ***Angiotensin II*** - **Angiotensin II** is a potent vasoconstrictor that directly stimulates **mesangial cell contraction**. - Contraction of mesangial cells reduces the **glomerular surface area** available for filtration, thereby decreasing the **glomerular filtration rate (GFR)**. *Endothelin-1* - **Endothelin-1** is a potent vasoconstrictor produced by endothelial cells, which can also induce mesangial cell contraction. - However, its role in **mesangial cell contraction** is generally considered secondary to **angiotensin II** in physiological regulation. *ANP* - **Atrial natriuretic peptide (ANP)** is a hormone that causes **vasodilation** and relaxation of mesangial cells. - Its primary effect is to **increase GFR** and sodium excretion, opposing the effects of vasoconstrictors. *Platelet-activating factor (PAF)* - PAF is a **phospholipid mediator** involved in inflammation and allergic reactions. - While it can affect renal hemodynamics, its role in directly and primarily causing **mesangial cell contraction** is less significant compared to angiotensin II.

Question 302: Tubuloglomerular feedback is for regulation of?

A. BP
B. Blood volume
C. Na+ reabsorption
D. Renal blood flow (Correct Answer)

Explanation: ***Renal blood flow*** - **Tubuloglomerular feedback (TGF)** is a key mechanism that helps to tightly regulate **renal blood flow** and **glomerular filtration rate (GFR)** by sensing tubular fluid composition. - This mechanism involves the **macula densa** cells in the distal tubule sensing changes in **sodium chloride (NaCl) delivery**, which then signals the afferent arteriole to adjust its caliber. *BP* - While renal blood flow ultimately influences **blood pressure (BP)**, tubuloglomerular feedback is primarily focused on **local autoregulation** within the kidney, not systemic BP control. - Systemic BP is regulated by much broader mechanisms involving the **renin-angiotensin-aldosterone system** and **autonomic nervous system**. *Blood volume* - **Blood volume** is primarily regulated by hormones like **ADH (vasopressin)** and **aldosterone**, which influence water and sodium reabsorption in the collecting ducts and other parts of the nephron. - Although renal function impacts blood volume, tubuloglomerular feedback's direct role is not in regulating the overall volume of blood. *Na+ reabsorption* - While the macula densa senses **Na+ delivery** to the distal tubule and this influences GFR, the primary role of tubuloglomerular feedback is not to modulate the total amount of **Na+ reabsorbed** throughout the nephron. - Na+ reabsorption is regulated by multiple factors and occurs extensively in the **proximal tubule**, **loop of Henle**, and **distal tubule**, often under hormonal control.

Question 303: Which of the following is the MOST important factor determining whether a substance can be filtered at the glomerulus?

A. Lipid solubility of the substance
B. Molecular weight of the substance (Correct Answer)
C. Binding capacity to albumin
D. None of the options

Explanation: ***Molecular weight of the substance*** - The **glomerular filtration barrier** acts as a size-selective filter, generally permeable to substances with a molecular weight less than 5,000-10,000 Daltons - Larger molecules are typically restricted from filtration due to the **size exclusion** property of the glomerular basement membrane and podocyte slit diaphragms - This is the **primary determinant** of whether a substance can be filtered at all, making it the most important factor among the given options *Lipid solubility of the substance* - **Lipid solubility** is more relevant for reabsorption and secretion in the renal tubules, particularly for passive diffusion across tubular cell membranes - It has minimal direct influence on the initial filtration process at the glomerulus, which is primarily a **pressure-driven, size- and charge-selective ultrafiltration** process - The glomerular capillary wall is not a lipid membrane barrier for the filtration process *Binding capacity to albumin* - Substances bound to **large plasma proteins** like albumin (molecular weight ~67,000 Daltons) cannot pass through the glomerular filtration barrier - While important for determining the *free, filterable fraction* of a substance in plasma, the binding itself is secondary to the fundamental molecular weight/size restriction - Only the **free (unbound) fraction** of a substance is available for filtration, and whether it filters depends primarily on its molecular weight *None of the options* - This option is incorrect because **molecular weight** is indeed the most critical factor among the given options for determining whether a substance can be filtered at the glomerulus

Question 304: Which of the following statements is true about coronary circulation?

A. Uniform flow during full cardiac cycle
B. Flow rate is approximately 500 ml/min
C. Major flow during diastole (Correct Answer)
D. All of the above

Explanation: ***Major flow during diastole*** - The **coronary arteries** are compressed during **systole** by the contracting myocardium, significantly reducing blood flow to the heart muscle. - During **diastole**, the myocardium relaxes, allowing the coronary arteries to open fully and deliver the majority (70-80%) of oxygenated blood to the heart. - This is the most distinctive feature of coronary circulation. *Flow rate is approximately 500 ml/min* - The typical **coronary blood flow** at rest is approximately **225-250 ml/min** (about 5% of cardiac output at rest). - 500 ml/min is significantly higher than normal resting coronary flow and would represent a pathological or high-demand state. *Uniform flow during full cardiac cycle* - **Coronary blood flow** is highly variable (phasic) throughout the cardiac cycle, being significantly higher during **diastole** and much lower during **systole**. - This non-uniform flow is a unique characteristic of coronary circulation due to mechanical compression from myocardial contraction. *All of the above* - Not all statements are correct, as the flow rate value is incorrect and flow is non-uniform throughout the cardiac cycle. - The **major flow during diastole** is the most accurate and physiologically important statement regarding coronary circulation.

Question 305: Which of the following statements is true regarding the Bezold-Jarisch reflex?

A. Hypertension
B. Tachycardia
C. Hyperpnea
D. Hypotension (Correct Answer)

Explanation: ***Hypotension*** - The Bezold-Jarisch reflex is a **cardioinhibitory reflex** that is typically activated by strong ventricular contraction or noxious stimuli, leading to a triad of **bradycardia**, **peripheral vasodilation**, and subsequent **hypotension**. - This reflex is thought to be a protective mechanism to prevent excessive cardiac work or to trigger a "fainting" response to remove the body from danger. *Hypertension* - The Bezold-Jarisch reflex primarily causes a **decrease in blood pressure**, making hypertension an incorrect outcome. - Its activation directly opposes the mechanisms that would lead to increased blood pressure. *Tachycardia* - A key component of the Bezold-Jarisch reflex is **bradycardia** (slowing of the heart rate), not tachycardia. - This reflex is mediated by the vagus nerve, which primarily exerts inhibitory control over heart rate. *Hyperpnea* - The Bezold-Jarisch reflex primarily impacts **cardiovascular function** and does not directly cause hyperpnea (increased rate and depth of breathing). - While other reflexes can affect respiration, this particular reflex is not known for its respiratory effects.

Question 306: Which carrier pump is responsible for transporting solutes in the thick ascending limb of the loop of Henle?

A. NaCl cotransporter
B. Na+-H+ exchanger
C. Na+-K+ exchanger
D. Sodium-potassium-chloride cotransporter (Correct Answer)

Explanation: * **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.

Question 307: Which of the following factors is most commonly targeted therapeutically for blood pressure control?

A. Heart rate
B. Peripheral resistance (Correct Answer)
C. Cardiac output
D. Stroke volume

Explanation: ***Peripheral resistance*** - **Peripheral resistance** is primarily determined by the **arteriolar tone**, which can be effectively modulated by various antihypertensive medications. - Medications like **ACE inhibitors**, **ARBs**, **calcium channel blockers**, and **diuretics** all influence peripheral resistance to lower blood pressure. *Heart rate* - While heart rate contributes to **cardiac output** and thus blood pressure, it is not the most common primary target for hypertension management. - **Beta-blockers** reduce heart rate, but they are often used for specific indications beyond essential hypertension, such as angina or post-MI. *Cardiac output* - **Cardiac output** is a product of **heart rate** and **stroke volume**, and while it directly impacts blood pressure, directly targeting cardiac output as a whole is less common than modulating its individual components or peripheral resistance. - Many antihypertensive drugs reduce cardiac output as a secondary effect of reducing blood volume or heart rate, but directly reducing cardiac output is not the primary mechanism for the most common medications. *Stroke volume* - **Stroke volume** is influenced by **preload**, **afterload**, and **contractility**, and while it impacts cardiac output, it is generally less accessible for direct pharmacological manipulation in hypertension management compared to peripheral resistance. - **Diuretics** can indirectly reduce stroke volume by decreasing preload, but this is often considered a mechanism related to volume status rather than a direct myocardial effect.