Cardiovascular System Practice Questions

Q: What are the ECG changes seen in hypocalcemia?

Prolongation of ST segment. **Explanation:** The hallmark ECG finding in **hypocalcemia** is the **prolongation of the ST segment**, which leads to a prolonged **QT interval**. **1. Why the correct answer is right:** Calcium ions play a critical role in the plateau phase (Phase 2) of the cardiac action potential. In hypocalcemia, the reduced extracellular calcium concentration slows the influx of calcium through L-type calcium channels. This delays the completion of the plateau phase, thereby lengthening the duration of the ST segment. Since the T wave (repolarization) remains relatively unchanged, the overall effect is a **prolonged QT interval** (specifically due to the long ST segment). **2. Why the incorrect options are wrong:** * **ST segment depression:** This is typically associated with myocardial ischemia, hypokalemia, or digoxin effect, rather than calcium imbalances. * **Inversion of T wave:** This is a sign of myocardial ischemia, ventricular hypertrophy, or bundle branch blocks. In hypocalcemia, the T wave is usually upright and normal. * **Prolongation of PR segment:** This indicates a delay in AV node conduction, commonly seen in first-degree heart block or hyperkalemia, but not typically associated with hypocalcemia. **High-Yield Clinical Pearls for NEET-PG:** * **Hypocalcemia:** Prolonged ST segment $\rightarrow$ Prolonged QT interval (can predispose to Torsades de Pointes, though less common than in hypomagnesemia). * **Hypercalcemia:** Shortened ST segment $\rightarrow$ **Shortened QT interval** (the "Osborn wave" or J wave is more specific to hypothermia but can rarely be seen here). * **Mnemonic:** "Hypo-Long, Hyper-Short" (referring to the QT interval). * **Clinical Signs:** Look for Trousseau’s sign and Chvostek’s sign in the clinical stem.

Q: Blood pressure is defined as the product of which of the following?

Cardiac output and peripheral resistance. **Explanation** **1. Why Option D is Correct:** The fundamental hemodynamic equation for blood pressure is derived from Ohm’s Law ($V = I \times R$), where Pressure ($P$) is the product of Flow ($Q$) and Resistance ($R$). In the cardiovascular system, this translates to: **Mean Arterial Pressure (MAP) = Cardiac Output (CO) × Total Peripheral Resistance (TPR)** * **Cardiac Output:** Represents the volume of blood pumped by the heart per minute. It primarily determines the systolic blood pressure. * **Peripheral Resistance:** Primarily determined by the diameter of the arterioles (resistance vessels). It is the chief determinant of diastolic blood pressure. **2. Why Other Options are Incorrect:** * **Options A & B:** Systolic and Diastolic pressures are *components* of blood pressure, not factors that multiply to define it. Pulse rate is a component of Cardiac Output ($CO = Stroke\ Volume \times Heart\ Rate$), but it is not the sole determinant of BP. * **Option C:** Pulse pressure is the difference between systolic and diastolic pressure ($SBP - DBP$). Multiplying it by pulse rate does not yield a physiological measurement for blood pressure. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Poiseuille’s Law:** Resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). This means small changes in arteriolar diameter lead to massive changes in BP. * **MAP Calculation:** $MAP = DBP + 1/3\ (Pulse\ Pressure)$. This is a frequent numerical MCQ topic. * **Determinants:** Systolic BP is mainly affected by **Stroke Volume** and **Aortic Compliance**, while Diastolic BP is mainly affected by **TPR** and **Heart Rate**. * **Baroreceptor Reflex:** This is the primary short-term regulator of BP, sensing changes in "stretch" in the carotid sinus and aortic arch.

Q: Which of the following is FALSE regarding the funny current in the heart?

It is a Na-K ATPase pump. ### Explanation **1. Why Option A is the Correct (False) Statement:** The **funny current ($I_f$)** is not a pump; it is a **non-specific cation channel** (HCN channel - Hyperpolarization-activated Cyclic Nucleotide-gated channel). Unlike the Na-K ATPase, which requires ATP to move ions against their gradient, the funny current allows the passive influx of sodium ($Na^+$) and a minor efflux of potassium ($K^+$) down their electrochemical gradients. **2. Analysis of Other Options:** * **Option B (True):** The funny current is the primary driver of **Phase 4 (diastolic depolarization)** in pacemaker cells (SA and AV nodes). It slowly brings the membrane potential from the maximum diastolic potential toward the threshold. * **Option C (True):** Because $I_f$ initiates the spontaneous depolarization that leads to an action potential without external nerve stimulation, it is responsible for the **autorhythmicity** (automaticity) of the heart. * **Option D (True/Contextual):** While $I_f$ is modulated by cAMP (sympathetic/parasympathetic activity), it is fundamentally **voltage-gated**. Uniquely, it is activated by **hyperpolarization** (becoming more negative) rather than depolarization, which is why it was named "funny." **3. NEET-PG High-Yield Pearls:** * **Location:** Primarily found in the SA node, AV node, and Purkinje fibers. * **Activation:** It activates when the membrane potential reaches approximately **-60 mV** (at the end of repolarization). * **Clinical Correlation:** **Ivabradine** is a specific $I_f$ channel blocker used in heart failure and stable angina. It reduces heart rate without affecting myocardial contractility (negative chronotrope without being a negative inotrope). * **Ion Permeability:** It is more permeable to $Na^+$ than $K^+$, leading to net inward positive charge.

Q: Local control of blood flow is seen in all except which of the following?

Skin. **Explanation:** The regulation of blood flow in the body is divided into **Local (Autoregulation)** and **Humoral/Neural (Extrinsic)** control. **Why Skin is the Correct Answer:** The primary function of cutaneous (skin) blood flow is **thermoregulation**, not the metabolic demands of the tissue itself. Therefore, skin blood flow is predominantly under **extrinsic neural control** via the sympathetic nervous system. When the body temperature rises, sympathetic tone decreases to allow vasodilation and heat loss. Because it lacks significant intrinsic metabolic autoregulation, it is the exception among the options provided. **Analysis of Incorrect Options:** * **B. Muscle:** During exercise, skeletal muscle blood flow is governed by **local metabolic factors** (e.g., increased $K^+$, $H^+$, lactate, and adenosine). This "active hyperemia" ensures oxygen delivery matches metabolic demand. * **C. Splanchnic vessels:** The gastrointestinal tract exhibits significant local control, especially postprandially (after meals), where metabolic products and GI hormones trigger local vasodilation to aid digestion. * **D. Cerebrum:** The brain has the most highly developed **autoregulation** mechanism. Cerebral blood flow remains constant despite fluctuations in mean arterial pressure (60–140 mmHg) and is exquisitely sensitive to local $PCO_2$ levels. **High-Yield Clinical Pearls for NEET-PG:** * **Most potent local vasodilator** in the brain: **$CO_2$** (via $H^+$ ions). * **Most potent local vasodilator** in skeletal muscle: **Adenosine** (during ischemia) and **$K^+$ ions** (during exercise). * **Organs with best autoregulation:** Brain, Kidney, and Heart. * **Organs with least autoregulation:** Skin.

Q: All of the following factors normally increase the length of the ventricular cardiac muscle fibers except?

Lying to standing change in posture. ### Explanation The length of ventricular cardiac muscle fibers is determined by the **End-Diastolic Volume (EDV)**, also known as **Preload**. According to the **Frank-Starling Law**, an increase in venous return leads to increased ventricular filling, which stretches the myocardial fibers. **Why Option D is Correct:** When a person moves from a **lying to a standing position**, gravity causes blood to pool in the highly distensible veins of the lower extremities (venous pooling). This significantly **decreases venous return** to the heart, leading to a decrease in EDV and, consequently, a **decrease** in the length of the ventricular muscle fibers. **Why the Other Options are Incorrect:** * **A. Increased venous tone:** Sympathetic stimulation causes venoconstriction, which decreases the capacitance of veins and pushes more blood toward the heart, increasing preload and fiber length. * **B. Increased total blood volume:** Conditions like IV fluid resuscitation or polycythemia increase the overall circulating volume, thereby increasing venous return and fiber stretch. * **C. Increased negative intrathoracic pressure:** During deep inspiration, the intrathoracic pressure becomes more negative. This creates a "suction effect" on the vena cava, drawing more blood into the right atrium and increasing ventricular fiber length. **High-Yield NEET-PG Pearls:** * **Frank-Starling Law:** States that the force of ventricular contraction is proportional to the initial length of the muscle fiber (within physiological limits). * **Preload vs. Afterload:** Preload is the degree of stretch (EDV); Afterload is the resistance the heart must pump against (MAP). * **Postural Hypotension:** The initial drop in BP upon standing is normally compensated by the **Baroreceptor Reflex**, which increases heart rate and peripheral resistance.

Question 1

What are the ECG changes seen in hypocalcemia?

Accepted Answer

Prolongation of ST segment

Answer

ST segment depression

Answer

Inversion of T wave

Answer

Prolongation of PR segment

Question 2

All of the following events occur at or shortly after birth EXCEPT?

Accepted Answer

The ductus arteriosus closes, allowing blood to bypass the lungs.

Answer

The ductus arteriosus closes, ending shunting of blood from the aorta to the lungs.

Answer

The foramen ovale closes, ending the shunting of blood from the right to the left atrium.

Answer

Blood pressure in the left atrium increases.

Question 3

In a study to measure blood pressure (BP) in a dog, one student measures BP using a mercury sphygmomanometer on the right femoral artery, while another student uses a pressure transducer and pulse tracing on the left femoral artery. The mean arterial pressure measured by both methods is initially 100 mmHg. After 5 minutes of adrenaline injection, the first student measures blood pressure as 130 mmHg and the second student as 120 mmHg. This difference of 10 mmHg is best explained by which of the following?

Accepted Answer

Falsely high values at low pressure in pulse tracing

Answer

Femoral artery is more sensitive to adrenaline on the right side

Answer

Ventricular filling affects the diastolic period

Question 4

Blood pressure is defined as the product of which of the following?

Accepted Answer

Cardiac output and peripheral resistance

Answer

Systolic pressure and pulse

Answer

Diastolic pressure and pulse rate

Answer

Pulse pressure and pulse rate

Question 5

Which of the following is FALSE regarding the funny current in the heart?

Accepted Answer

It is a Na-K ATPase pump

Answer

They are responsible for diastolic depolarization

Answer

It is responsible for the spontaneous rhythm producing tissue of the heart

Answer

They are voltage-dependent channels only

Question 6

Local control of blood flow is seen in all except which of the following?

Accepted Answer

Skin

Answer

Muscle

Answer

Splanchnic vessels

Answer

Cerebrum

Question 7

Which statement about the 'instantaneous mean vector' is true?

Accepted Answer

Summated vector of generated potential at a particular instant caused by inflowing septal depolarization

Answer

Equal and same as the mean QRS vector

Answer

It is drawn through the center of the vector in a direction from base toward the apex

Answer

When a vector is exactly horizontal and directed toward the person's left side, the vector is said to extend in the direction of 0 degrees

Question 8

All of the following factors normally increase the length of the ventricular cardiac muscle fibers except?

Accepted Answer

Lying to standing change in posture

Answer

Increased venous tone

Answer

Increased total blood volume

Answer

Increased negative intrathoracic pressure

Question 9

Blood is flowing through a circuit with an inflow pressure of 100 mmHg and an outflow pressure of 10 mmHg. Each of the parallel circuits (R1, R2, R3, R4, and R5) has a resistance of 5 mmHg/mL/min. What is the blood flow across this circuit?

Accepted Answer

90 ml/min

Answer

3.6 ml/min

Answer

45 ml/min

Answer

135 ml/min

Question 10

Tachycardia is caused by hypoxia due to which of the following mechanisms?

Accepted Answer

Secondarily after hyperventilation

Answer

Reflexly through peripheral chemoreceptors

Answer

Diffuse vasodilation

Answer

Through the central chemoreceptor

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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