Cardiovascular System Practice Questions

Q: Which of the following is expected to increase in response to hemorrhage?

Sympathetic activity. **Explanation:** Hemorrhage leads to a decrease in blood volume (hypovolemia), which causes a drop in mean arterial pressure (MAP). This triggers the **Baroreceptor Reflex**, the body’s primary short-term compensatory mechanism. **Why Sympathetic Activity Increases:** Decreased stretch of baroreceptors in the carotid sinus and aortic arch leads to a reduction in their firing rate to the medulla. This results in: 1. **Increased sympathetic outflow:** Leading to tachycardia (increased HR), increased myocardial contractility, and peripheral vasoconstriction. 2. **Decreased parasympathetic (vagal) tone.** These changes aim to restore cardiac output and systemic vascular resistance to maintain perfusion to vital organs. **Analysis of Incorrect Options:** * **A. Arteriolar dilation in skeletal muscle:** In response to hemorrhage, sympathetic stimulation causes **vasoconstriction** (via $\alpha_1$ receptors) in non-essential beds like skeletal muscle and skin to divert blood to the brain and heart. * **C & D. Sodium and Water excretion:** Hemorrhage activates the **Renin-Angiotensin-Aldosterone System (RAAS)** and stimulates **ADH (Vasopressin)** release. These hormones act on the kidneys to increase sodium and water **reabsorption** (decreasing excretion) to restore intravascular volume. **NEET-PG High-Yield Pearls:** * **Earliest sign of compensated shock:** Tachycardia. * **The "Goldman’s Rule":** In hemorrhage, the body prioritizes MAP over local tissue perfusion. * **Bainbridge Reflex vs. Baroreceptor Reflex:** While baroreceptors increase HR during hypotension, the Bainbridge reflex increases HR in response to increased venous return (atrial stretch). In hemorrhage, the Baroreceptor reflex dominates. * **Key Hormone:** Angiotensin II is a potent vasoconstrictor and also stimulates the thirst center in the hypothalamus.

Q: The shift of the oxygen dissociation curve to the left is facilitated by all except?

Decrease in pH. The **Oxygen-Hemoglobin Dissociation Curve** represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. ### **Why "Decrease in pH" is the Correct Answer** A **decrease in pH** (acidosis) indicates an increase in $H^+$ ion concentration. This stabilizes the "Tense" (T) state of hemoglobin, reducing its affinity for oxygen and causing the curve to shift to the **RIGHT**. This is known as the **Bohr Effect**. A right shift facilitates oxygen unloading to tissues, which is the opposite of what the question asks. ### **Analysis of Incorrect Options (Left Shift Factors)** A **Left Shift** indicates an increased affinity of hemoglobin for oxygen (holding onto $O_2$ more tightly). * **Fetal Hemoglobin (HbF):** HbF lacks the ability to bind effectively with 2,3-DPG. This results in a higher affinity for $O_2$ compared to adult hemoglobin (HbA), shifting the curve to the **left** to ensure oxygen uptake from the placenta. * **Decrease in 2,3-DPG:** 2,3-Bisphosphoglycerate normally stabilizes the T-state. Its absence or decrease shifts the curve to the **left**. * **Decrease in Temperature:** Lower temperatures stabilize the bond between oxygen and hemoglobin, increasing affinity and shifting the curve to the **left**. ### **High-Yield NEET-PG Pearls** * **Mnemonic for Right Shift (CADET, face Right!):** * **C** – $CO_2$ increase * **A** – Acidosis (Decrease in pH) * **D** – 2,3-**D**PG increase * **E** – Exercise * **T** – Temperature increase * **P50 Value:** The $PO_2$ at which Hb is 50% saturated. Normal is **26.6 mmHg**. A **Right shift** increases P50; a **Left shift** decreases P50. * **Carbon Monoxide (CO):** Causes a **Left shift** and a downward shift (decreases oxygen-carrying capacity).

Q: Which of the following vessels has the function of capacitance?

Vein. **Explanation:** The correct answer is **Vein**. In the cardiovascular system, vessels are classified based on their primary physiological function. **1. Why Veins are Capacitance Vessels:** Capacitance refers to the ability of a vessel to accommodate a large volume of blood with a relatively small increase in pressure. Veins have thin, highly distensible walls with high compliance. At any given time, approximately **60-70% of the total blood volume** resides in the venous system, acting as a reservoir. This "capacitance" allows the body to adjust venous return to the heart by mobilizing this stored blood through sympathetic stimulation (venoconstriction). **2. Why the other options are incorrect:** * **Arterioles (Resistance Vessels):** These possess thick smooth muscle layers and are the primary site of peripheral resistance. They regulate blood flow into capillaries and determine arterial blood pressure. * **Capillaries (Exchange Vessels):** These have the thinnest walls (single layer of endothelium) and the largest total cross-sectional area, optimized for the diffusion of gases, nutrients, and waste. * **Arteries (Distribution/Windkessel Vessels):** Large arteries like the aorta are elastic; they dampen the pulsatile output of the heart to maintain continuous flow during diastole. **High-Yield NEET-PG Pearls:** * **Compliance Formula:** $C = V/P$. Veins are roughly **24 times** more compliant than arteries. * **Velocity of Flow:** Is lowest in the capillaries (due to the highest total cross-sectional area), facilitating exchange. * **Stressed vs. Unstressed Volume:** Blood in the arteries is "stressed volume" (high pressure), while blood in the veins is "unstressed volume" (low pressure).

Q: Which of the following groups of contrast agents may be safely injected intrathecally?

Water-soluble non-ionic monomers. **Explanation:** The safety of a contrast agent for intrathecal injection (myelography) is primarily determined by its **neurotoxicity**, which is directly linked to its **osmolality** and **ionic charge**. **1. Why Water-soluble non-ionic monomers are correct:** Non-ionic monomers (e.g., **Iohexol, Iopamidol**) do not dissociate into ions in solution. This results in lower osmolality compared to ionic agents. Because they lack an electrical charge and are closer to the osmolality of cerebrospinal fluid (CSF), they do not interfere with the electrical potential of neuronal membranes. This significantly reduces the risk of neurotoxic complications such as seizures, arachnoiditis, or meningeal irritation. **2. Why the other options are incorrect:** * **Water-soluble ionic monomers (A) & dimers (C):** These agents dissociate into cations (sodium/meglumine) and anions. The high ionic charge and hyperosmolality are highly neurotoxic; they can trigger massive neuronal depolarization, leading to severe convulsions and even death if injected intrathecally. * **Oil-based iodinated contrasts (D):** (e.g., Ethiodol, Pantopaque) These were used historically but are now obsolete for myelography. They are not resorbed by the body, require manual removal, and carry a high risk of causing chronic adhesive arachnoiditis. **Clinical Pearls for NEET-PG:** * **Iohexol (Omnipaque)** is the most commonly used non-ionic agent for myelography. * **Osmolality Rule:** The lower the osmolality and the lower the ionicity, the safer the contrast for the CNS. * **Contraindication:** Never use **Ionic** contrast (like Diatrizoate/Urografin) for myelography; it is considered a "never event" due to fatal neurotoxicity. * **Non-ionic Dimers:** While even lower in osmolality (e.g., Iodixanol), non-ionic monomers remain the standard for intrathecal use due to established safety profiles.

Q: Which of the following causes an increase in conduction velocity of impulse through the heart?

Sympathetic stimulation. **Explanation:** The conduction velocity of the cardiac impulse is primarily regulated by the autonomic nervous system. This property of the heart is known as **Dromotropy**. **1. Why Sympathetic Stimulation is Correct:** Sympathetic stimulation (via the release of Norepinephrine acting on **$\beta_1$ receptors**) increases conduction velocity (Positive Dromotropy). This occurs because it increases the rate of rise of the action potential (Phase 0) and increases the excitability of the conducting tissues, particularly at the **AV node**. By increasing the permeability to $Ca^{2+}$ and $Na^+$, it shortens the AV nodal delay, allowing the impulse to travel faster from the atria to the ventricles. **2. Why Other Options are Incorrect:** * **Vagal/Parasympathetic Stimulation (Options A & B):** These are essentially the same. Vagal fibers release Acetylcholine (ACh), which acts on **$M_2$ receptors**. This increases $K^+$ conductance (hyperpolarization) and decreases $Ca^{2+}$ conductance. This leads to a **decrease** in conduction velocity (Negative Dromotropy), primarily at the SA and AV nodes. In extreme cases, strong vagal stimulation can lead to a transient heart block. **High-Yield Clinical Pearls for NEET-PG:** * **Dromotropy:** Refers to conduction velocity. * **Inotropy:** Refers to contractility. * **Chronotropy:** Refers to heart rate. * **Bathmotropy:** Refers to excitability. * **AV Node Delay:** The slowest conduction velocity in the heart (approx. 0.01–0.05 m/s) occurs at the AV node to allow for ventricular filling. * **Purkinje System:** Possesses the **fastest** conduction velocity (approx. 1.5–4.0 m/s) to ensure near-simultaneous ventricular contraction.

Q: Right axis deviation is seen in:

Thin and tall individuals. The electrical axis of the heart is primarily determined by its anatomical orientation within the thoracic cavity. **Explanation of the Correct Answer:** **B. Thin and tall individuals:** In ectomorphic (thin and tall) individuals, the diaphragm sits lower in the chest. This causes the heart to hang more vertically (a "vertical heart"). Since the electrical depolarization follows the anatomical long axis, the mean QRS vector shifts downward and to the right, resulting in **Right Axis Deviation (RAD)**. **Explanation of Incorrect Options:** * **A. Lying down position:** When a person lies supine, the abdominal contents push the diaphragm upward. This pushes the apex of the heart upward and to the left, leading to a more horizontal orientation or **Left Axis Deviation (LAD)**. * **C. Obese persons:** In obesity, increased intra-abdominal pressure and fat displacement push the diaphragm cranially. This rotates the heart transversely, causing **Left Axis Deviation (LAD)**. * **D. At the end of peak expiration:** During expiration, the diaphragm rises. This elevates the heart and rotates it to the left, resulting in **Left Axis Deviation (LAD)**. (Conversely, deep inspiration causes RAD). **High-Yield Clinical Pearls for NEET-PG:** * **Normal QRS Axis:** -30° to +90°. * **RAD (>+90°):** Seen in Right Ventricular Hypertrophy (RVH), Left Posterior Hemiblock (LPH), Pulmonary Embolism, and COPD. * **LAD (<-30°):** Seen in Left Ventricular Hypertrophy (LVH), Left Anterior Hemiblock (LAH), and Ascites/Pregnancy. * **Mnemonic:** **REACH** (Right Expiration—Wait, no): Remember **"Left Leaves, Right Reaches."** In LAD, QRS complexes in Lead I and Lead aVF point away from each other; in RAD, they point toward each other.

Q: Which of the following statements is TRUE regarding hemorrhage?

Pulse pressure decreases.. **Explanation:** Hemorrhage leads to a reduction in total blood volume (hypovolemia), which triggers a sequence of compensatory and pathological changes in the cardiovascular system. **Why Option A is Correct:** Pulse pressure is the difference between systolic and diastolic blood pressure ($PP = SBP - DBP$). It is directly proportional to **Stroke Volume (SV)** and inversely proportional to arterial compliance. In hemorrhage, the decrease in venous return (preload) leads to a significant drop in SV (Frank-Starling law). This reduction in SV is the primary driver for the **decrease in pulse pressure**, making it one of the earliest signs of clinical shock. **Analysis of Incorrect Options:** * **Option B:** Hematocrit actually **decreases** (though not immediately). Following hemorrhage, the body initiates "capillary refill" where interstitial fluid shifts into the intravascular compartment to restore volume, hemodiluting the remaining red cells. * **Option C:** While Heart Rate (HR) increases (tachycardia) via the baroreceptor reflex to compensate for low BP, **Stroke Volume decreases** due to reduced filling pressure. * **Option D:** Sinus nerves (branches of the glossopharyngeal nerve) carry inhibitory impulses from the carotid sinus baroreceptors. In hemorrhage, the drop in MAP reduces the stretch on these receptors, leading to a **decrease in the firing rate** of sinus nerves to the medulla, which then triggers sympathetic outflow. **High-Yield Clinical Pearls for NEET-PG:** * **Baroreceptor Reflex:** The most rapid compensatory mechanism in acute hemorrhage. * **Class of Shock:** A decrease in pulse pressure is typically seen starting in Class II Hemorrhage (15-30% blood loss). * **Reverse Stress Relaxation:** A delayed compensatory mechanism where blood vessels constrict around the remaining volume to maintain pressure.

Q: In which type of blood vessel is the mean linear velocity of a red blood cell the lowest?

Capillaries. **Explanation:** The velocity of blood flow is governed by the principle of continuity, which states that velocity ($V$) is inversely proportional to the **total cross-sectional area** ($A$) of the vascular bed ($V = Q/A$, where $Q$ is cardiac output). 1. **Why Capillaries are Correct:** Although an individual capillary has a tiny diameter, the human body contains billions of them. When arranged in parallel, their **total combined cross-sectional area** is the largest in the entire circulatory system (approximately 1000 times that of the aorta). Consequently, the velocity of blood flow reaches its minimum (approx. 0.03 cm/s) in the capillaries. This slow transit is physiologically essential to allow sufficient time for the exchange of gases, nutrients, and waste products between blood and tissues. 2. **Why Other Options are Incorrect:** * **Aorta and Large Arteries:** These have the smallest total cross-sectional area. Therefore, the mean linear velocity is **highest** here (approx. 20-40 cm/s) to ensure rapid distribution of blood. * **Arterioles and Small Arteries:** As blood moves from the aorta toward the periphery, the total cross-sectional area gradually increases. While velocity decreases in these vessels compared to the aorta, it remains significantly higher than in the capillaries. **NEET-PG High-Yield Pearls:** * **Velocity vs. Resistance:** Do not confuse velocity with resistance. The **arterioles** are the site of highest peripheral resistance and the greatest pressure drop, but the **capillaries** have the lowest velocity. * **Sequence of Velocity:** Aorta > Arteries > Arterioles > Venules > Veins > Capillaries (Lowest). * **Sequence of Cross-sectional Area:** Capillaries (Highest) > Venules > Arterioles > Veins > Arteries > Aorta (Lowest).

Question 1

Which of the following is expected to increase in response to hemorrhage?

Accepted Answer

Sympathetic activity

Answer

Arteriolar dilation in skeletal muscle

Answer

Sodium excretion

Answer

Water excretion

Question 2

The shift of the oxygen dissociation curve to the left is facilitated by all except?

Accepted Answer

Decrease in pH

Answer

Fetal hemoglobin

Answer

Decrease in 2,3 DPG

Answer

Decrease in temperature

Question 3

Which of the following vessels has the function of capacitance?

Accepted Answer

Vein

Answer

Arteriole

Answer

Capillary

Answer

Artery

Question 4

Which of the following groups of contrast agents may be safely injected intrathecally?

Accepted Answer

Water-soluble non-ionic monomers

Answer

Water-soluble ionic monomers

Answer

Water-soluble ionic dimers

Answer

Oil-based iodinated contrasts

Question 5

Which of the following causes an increase in conduction velocity of impulse through the heart?

Accepted Answer

Sympathetic stimulation

Answer

Vagal stimulation

Answer

Parasympathetic stimulation

Answer

All of the above

Question 6

Right axis deviation is seen in:

Accepted Answer

Thin and tall individuals

Answer

Lying down position

Answer

Obese persons

Answer

At the end of peak expiration

Question 7

Which of the following statements is TRUE regarding hemorrhage?

Accepted Answer

Pulse pressure decreases.

Answer

Hematocrit ratio increases.

Answer

Stroke volume and heart rate increase.

Answer

The number of impulses traveling in the sinus nerves increases.

Question 8

In which type of blood vessel is the mean linear velocity of a red blood cell the lowest?

Accepted Answer

Capillaries

Answer

Aorta and large arteries

Answer

Arterioles

Answer

Small arteries

Question 9

Carotid baroreceptors are important in the regulation of arterial blood pressure. Which of the following statements best describes their function?

Accepted Answer

They are important in the rapid, short-term regulation of arterial blood pressure.

Answer

They do not fire until a pressure of approximately 100 mm Hg is reached.

Answer

They adapt over 1 to 2 weeks to the prevailing mean arterial pressure.

Answer

Their reflexive action decreases cerebral blood flow.

Question 10

Which of the following events causes closure of the ductus arteriosus in a newborn?

Accepted Answer

Fall in pulmonary arterial pressure

Answer

Compression of the thorax during delivery

Answer

Compression of the pulmonary vessels during delivery

Answer

Fall in systemic arterial pressure

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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