NEET-PG 2015 - Physiology Practice Questions

Q: Cerebral blood flow is regulated by all, EXCEPT:

Potassium ions. ***Potassium ions*** - While potassium ions play a crucial role in neuronal excitability and membrane potential, they are **not a primary direct regulator** of cerebral blood flow (CBF) in the same way as other factors listed. - Changes in extracellular potassium can affect vascular smooth muscle, but their direct impact on CBF auto-regulation is less pronounced compared to metabolic or pressure-related factors. *Intracranial pressure* - **Increased intracranial pressure (ICP)** can significantly decrease cerebral blood flow due to the **Monro-Kellie doctrine**, which states that an increase in ICP reduces the cerebral perfusion pressure (CPP). - A sustained and significant elevation in ICP can lead to **cerebral ischemia** as it opposes the arterial pressure driving blood into the brain. *Arterial PCO2* - **Arterial PCO2** is a potent regulator of cerebral blood flow, with **hypercapnia (high PCO2)** causing **vasodilation** and increased CBF. - Conversely, **hypocapnia (low PCO2)** leads to **vasoconstriction** and decreased CBF, which is a key mechanism in the management of cerebral edema. *Cerebral metabolic rate* - **Cerebral metabolic rate (CMR)** is directly coupled to cerebral blood flow, meaning that regions of the brain with higher metabolic activity receive increased blood flow. - This **neurovascular coupling** ensures adequate supply of oxygen and nutrients to meet the brain's metabolic demands.

Q: In an ECG the cardiac event corresponding to the ST segment is:

Ventricular repolarisation. ***Ventricular repolarisation*** - The **ST segment** represents the **early phase of ventricular repolarization**, corresponding to the **plateau phase (Phase 2)** of the ventricular action potential. - During this phase, the ventricles are completely depolarized and calcium influx balances potassium efflux, creating an isoelectric (flat) segment on the ECG. - The ST segment extends from the **end of the QRS complex (J point)** to the **beginning of the T wave**, after which rapid repolarization occurs. - Together, the **ST segment and T wave** represent the complete process of ventricular repolarization. *Atrial depolarisation* - **Atrial depolarization** is represented by the **P wave** on the ECG, not the ST segment. - This occurs first in the cardiac cycle, triggering atrial contraction and filling of the ventricles. *Ventricular depolarisation* - **Ventricular depolarization** is represented by the **QRS complex**, which immediately **precedes** the ST segment. - This event triggers ventricular contraction (systole) and occurs before the plateau phase. *Atrial repolarisation* - **Atrial repolarization** occurs during the QRS complex and is **obscured** by the much larger electrical signal from ventricular depolarization. - It is not visible as a separate deflection on the standard ECG.

Q: The ST Segment of an ECG corresponds to which phase of the action potential?

Plateau phase. ***Plateau phase*** - The **ST segment** of the ECG represents the period when the ventricles are completely depolarized and corresponds to the **plateau phase (phase 2)** of the ventricular myocardial action potential. - During this phase, there is a balance between **calcium influx** and **potassium efflux**, maintaining the depolarized state and contributing to the sustained contraction of the ventricles. *Rapid depolarization* - This phase, represented by the **QRS complex** on the ECG, signifies the rapid influx of sodium ions into the ventricular cells. - It corresponds to **phase 0** of the action potential, where there is a sharp upstroke. *Rapid repolarization* - This corresponds to **phase 3** of the ventricular action potential, where potassium ions rapidly exit the cell, leading to repolarization. - On the ECG, this phase is represented by the **T wave**. *Final repolarization* - This is **not a standard electrophysiological term** in cardiac action potential nomenclature. - The complete repolarization process is represented by the **T wave** (phase 3), which returns the ventricle to its resting potential (phase 4). - The term may cause confusion as it doesn't correspond to a specific phase or ECG component.

Q: Which of the following structures contains baroreceptors that detect changes in blood pressure?

Carotid sinus. ***Carotid sinus*** - The **carotid sinus** is a dilation at the bifurcation of the common carotid artery, containing **baroreceptors** sensitive to changes in blood pressure [1]. - These baroreceptors are **mechanoreceptors** that respond to the stretching of the vessel wall due to increased arterial pressure, sending signals to the brainstem to regulate blood pressure. *Carotid body* - The **carotid body** is a chemoreceptor that primarily detects changes in **blood oxygen, carbon dioxide, and pH** levels, not blood pressure [2]. - It plays a crucial role in regulating **respiration** in response to hypoxemia. *Aortic body* - The **aortic body** is a **chemoreceptor** located near the aortic arch that primarily monitors **blood oxygen, carbon dioxide, and pH levels**. - Note: While the aortic body itself is a chemoreceptor, the **aortic arch** (a different structure) does contain baroreceptors [1]. However, this option specifically refers to the aortic body, which is not a baroreceptor. - The aortic body contributes to the regulation of **respiration** in response to hypoxemia, not directly blood pressure. *None of the options* - This option is incorrect because the **carotid sinus** is a well-known site for baroreceptors involved in blood pressure regulation.

Q: Which of the following conditions can lead to a decrease in afterload?

Severe anemia. ***Severe anemia*** - In **severe anemia**, the **blood viscosity** is reduced, and the body compensates by decreasing systemic vascular resistance to maintain tissue perfusion, thereby lowering **afterload**. - The reduced **oxygen-carrying capacity** triggers vasodilation to maximize blood flow to tissues, contributing to decreased afterload. - This represents a **chronic compensatory mechanism** that results in sustained reduction of afterload. *Hypothyroidism* - **Hypothyroidism** typically leads to an **increase in systemic vascular resistance** and thus can increase afterload. - It often results in **bradycardia** and reduced cardiac output, which can further elevate afterload to maintain pressure. *Increased physical activity* - During **physical activity**, there is **vasodilation in exercising muscles**, which acutely decreases systemic vascular resistance. - However, this is accompanied by **increased cardiac output** and **elevated blood pressure** due to sympathetic stimulation, and the afterload reduction is **transient** rather than sustained. - In the context of this question asking about conditions that lead to decreased afterload, **severe anemia** is the better answer as it represents a chronic pathological state with sustained afterload reduction, whereas exercise represents a temporary physiological response. *None of the options* - This option is incorrect because **severe anemia** is a recognized cause of decreased afterload.

Q: What is the typical oxygen saturation level of venous blood?

70%. ***70%*** - Venous blood has a lower oxygen saturation compared to arterial blood because tissues have extracted a significant amount of oxygen for **cellular respiration**. - A typical mixed venous oxygen saturation (SvO2) is around **70-75%**, indicating the amount of oxygen remaining after tissues have taken what they need. *30%* - This level of oxygen saturation is **too low** for typical venous blood and would indicate severe tissue hypoperfusion or extreme oxygen extraction. - Such low levels are usually not compatible with normal physiological function for prolonged periods. *50%* - While lower than normal, a 50% venous oxygen saturation is still indicative of **increased oxygen extraction** by tissues, often seen in conditions of increased metabolic demand or decreased oxygen delivery. - It's not the typical resting value for healthy individuals. *90%* - An oxygen saturation of 90% is more characteristic of **arterial blood** (normal arterial saturation is 95-100%). - Venous blood, having already delivered oxygen to tissues, would normally have a lower saturation.

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

Peripheral resistance. ***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.

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

Hypotension. ***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.

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

Major flow during diastole. ***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 1

What does the ST Segment of an ECG correspond to?

Accepted Answer

Plateau phase between ventricular depolarization and repolarization

Answer

Ventricular depolarization

Answer

Atrial depolarization

Answer

AV Conduction

Question 2

Cerebral blood flow is regulated by all, EXCEPT:

Accepted Answer

Potassium ions

Answer

Intracranial pressure

Answer

Cerebral metabolic rate

Answer

Arterial PCO2

Question 3

In an ECG the cardiac event corresponding to the ST segment is:

Accepted Answer

Ventricular repolarisation

Answer

Atrial depolarisation

Answer

Ventricular depolarisation

Answer

Atrial repolarisation

Question 4

The ST Segment of an ECG corresponds to which phase of the action potential?

Accepted Answer

Plateau phase

Answer

Rapid repolarization

Answer

Final repolarization

Answer

Rapid depolarization

Question 5

Which of the following structures contains baroreceptors that detect changes in blood pressure?

Accepted Answer

Carotid sinus

Answer

Carotid body

Answer

Aortic body

Answer

None of the options

Question 6

Which of the following conditions can lead to a decrease in afterload?

Accepted Answer

Severe anemia

Answer

Hypothyroidism

Answer

Increased physical activity

Answer

None of the options

Question 7

What is the typical oxygen saturation level of venous blood?

Accepted Answer

70%

Answer

30%

Answer

50%

Answer

90%

Question 8

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

Accepted Answer

Peripheral resistance

Answer

Heart rate

Answer

Cardiac output

Answer

Stroke volume

Question 9

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

Accepted Answer

Hypotension

Answer

Hypertension

Answer

Tachycardia

Answer

Hyperpnea

Question 10

Which of the following statements is true about coronary circulation?

Accepted Answer

Major flow during diastole

Answer

Uniform flow during full cardiac cycle

Answer

Flow rate is approximately 500 ml/min

Answer

All of the above

NEET-PG 2015 — Physiology