Cardiovascular System Practice Questions

Q: Which of the following causes a decrease in blood pressure?

Nitric Oxide (NO). **Explanation:** Blood pressure is primarily determined by the product of Cardiac Output (CO) and Total Peripheral Resistance (TPR). A decrease in blood pressure is typically achieved through **vasodilation**, which reduces TPR. **1. Why Nitric Oxide (NO) is correct:** Nitric Oxide, formerly known as Endothelium-Derived Relaxing Factor (EDRF), is a potent vasodilator. It is synthesized from L-arginine by the enzyme Nitric Oxide Synthase (NOS). NO diffuses into vascular smooth muscle cells and activates **soluble guanylyl cyclase**, increasing levels of **cGMP**. This leads to dephosphorylation of the myosin light chain, resulting in smooth muscle relaxation and vasodilation, which decreases blood pressure. **2. Why the other options are incorrect:** * **Thromboxane A2:** Produced by platelets, it is a potent vasoconstrictor and platelet aggregator. It increases TPR and, consequently, blood pressure. * **Vasopressin (ADH):** Acts on $V_1$ receptors in vascular smooth muscle to cause profound vasoconstriction (hence the name "vasopressin") and on $V_2$ receptors in the kidney to increase water reabsorption, both of which elevate blood pressure. * **Prostaglandin F2 (PGF2):** This is a member of the eicosanoid family that acts as a potent vasoconstrictor in most vascular beds (though it is primarily known for its role in uterine contraction). **High-Yield Clinical Pearls for NEET-PG:** * **Nitroglycerin** works by being converted into Nitric Oxide, making it the drug of choice for angina. * **Sildenafil (Viagra)** inhibits Phosphodiesterase-5 (PDE-5), preventing the breakdown of cGMP, thereby prolonging the vasodilatory effects of NO. * **Septic Shock:** The massive hypotension seen in sepsis is largely due to the overproduction of NO via Inducible Nitric Oxide Synthase (iNOS).

Q: What percentage of the total blood volume is typically found in the capillaries?

5%. ### Explanation **Correct Option: A (5%)** The distribution of blood volume across the vascular system is determined by the total cross-sectional area and the compliance of the vessels. Although **capillaries** are the primary site of nutrient and gas exchange and have the largest **total cross-sectional area** (approx. 2500–4500 cm²), they contain only about **5% of the total blood volume** at any given time. This is because each individual capillary is microscopic in length and diameter, and the velocity of blood flow is at its slowest here to facilitate exchange. **Analysis of Incorrect Options:** * **B, C, and D:** These percentages are too high for the capillary bed. The majority of the blood volume (approx. **64%**) resides in the **systemic veins and venules**, which act as the body’s "blood reservoir" due to their high compliance. The systemic arteries hold about 13%, the heart holds 7%, and the pulmonary circulation holds 9%. **NEET-PG High-Yield Pearls:** 1. **The "Reservoir" Concept:** Systemic veins are called **Capacitance vessels** because they hold ~64% of blood volume. 2. **The "Resistance" Concept:** Arterioles are the **Resistance vessels**; they provide the maximum peripheral resistance and cause the largest pressure drop. 3. **Velocity vs. Area:** Blood flow velocity is **inversely proportional** to the total cross-sectional area. Therefore, velocity is highest in the aorta and lowest in the capillaries. 4. **Exchange Vessels:** Capillaries are known as **Exchange vessels** because their walls consist of a single layer of endothelial cells, optimized for diffusion.

Q: What is the normal cerebral blood flow per 100 grams of brain tissue per minute?

55 mL/100gm/min. **Explanation:** The brain is one of the most metabolically active organs in the body. Under normal physiological conditions, the **average cerebral blood flow (CBF)** is approximately **50–55 mL per 100 grams of brain tissue per minute**. Given that the average adult brain weighs about 1400 grams, the total CBF is roughly 750–800 mL/min, representing 15% of the total cardiac output. **Analysis of Options:** * **A (55 mL/100gm/min):** This is the standard physiological value. This flow rate is critical to maintain the high oxygen and glucose demands required for neuronal activity. * **B (400 mL/100gm/min):** This value is far too high for the brain. However, it is characteristic of the **Kidneys** (approx. 360–400 mL/100g/min), which receive the highest blood flow per unit mass for filtration purposes. * **C & D (100–200 mL/100gm/min):** These values exceed normal cerebral perfusion. While gray matter has a higher flow (approx. 70–90 mL/100g/min) than white matter (approx. 20–30 mL/100g/min), the average remains around 55 mL. **High-Yield Clinical Pearls for NEET-PG:** 1. **Critical Thresholds:** * **Ischemic Penumbra:** CBF falls to **20 mL/100g/min**. * **Irreversible Infarction:** CBF falls below **10–12 mL/100g/min**. 2. **Autoregulation:** CBF remains constant between a Mean Arterial Pressure (MAP) of **60 to 140 mmHg**. 3. **Chemical Regulation:** The most potent physiological regulator of CBF is **Partial Pressure of CO₂ (PaCO₂)**. Hypercapnia causes vasodilation, increasing CBF, while hypocapnia (via hyperventilation) causes vasoconstriction.

Q: Ventricular filling begins at which point?

Point D. ***Point D*** - Ventricular filling begins when the **mitral valve opens** after **isovolumetric relaxation** is complete, allowing blood to flow from the atrium into the ventricle. - At this point, **ventricular pressure** drops below **atrial pressure**, creating the pressure gradient necessary for ventricular filling to commence. *Point A* - Represents the beginning of **systole** when the **mitral valve closes**, marking the end of ventricular filling, not its beginning. - This corresponds to the **first heart sound (S1)** and the start of **isovolumetric contraction**. *Point B* - Occurs during **isovolumetric contraction** when both **aortic and mitral valves** are closed and ventricular pressure is rapidly rising. - No blood flow occurs into or out of the ventricle during this phase, making ventricular filling impossible. *Point C* - Represents **aortic valve opening** at the beginning of the **ejection phase** when blood is pumped out of the ventricle. - This is when the ventricle is **emptying** rather than filling, opposite to what the question asks.

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: 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: Calf compartment pressure rises to _________ on walking?

200-300 mmHg. ### Explanation **The Correct Answer is D: 200-300 mmHg** **Underlying Medical Concept:** The calf muscles (gastrocnemius and soleus) act as the **"Peripheral Heart."** During walking, the contraction of these muscles within the tight, non-distensible deep fascia of the leg creates a powerful pumping mechanism. This contraction significantly increases the intramuscular pressure to levels between **200-300 mmHg**. This high pressure is physiological and essential to overcome gravity, compress the deep veins, and propel venous blood upward toward the heart. Once the muscle relaxes, the pressure drops, allowing blood to flow from the superficial system to the deep system via perforators. **Analysis of Incorrect Options:** * **Option A (20-30 mmHg):** This represents the normal resting pressure of a muscle compartment. If resting pressure exceeds 30 mmHg persistently, it is suggestive of **Compartment Syndrome**. * **Option B & C (60-100 mmHg):** While these pressures are higher than resting levels, they are insufficient to effectively empty the deep venous system against the hydrostatic pressure of the blood column in a standing adult. **High-Yield Clinical Pearls for NEET-PG:** * **Venous Pump Efficiency:** A normal calf muscle pump can reduce the venous pressure at the ankle from 90 mmHg (standing) to less than 30 mmHg during walking. * **Ambulatory Venous Hypertension:** Failure of this pump (due to muscle weakness or valvular incompetence) leads to chronic venous insufficiency and venous ulcers. * **Compartment Syndrome:** Diagnosis is clinical, but a **Delta pressure** (Diastolic BP minus Compartment pressure) of **<30 mmHg** is a strong indication for fasciotomy. * **Deep Posterior Compartment:** This is the most common site for compartment syndrome in the leg.

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.

Question 1

Which of the following causes a decrease in blood pressure?

Accepted Answer

Nitric Oxide (NO)

Answer

Thromboxane A2

Answer

Vasopressin

Answer

Prostaglandin F2 (PGF2)

Question 2

What percentage of the total blood volume is typically found in the capillaries?

Accepted Answer

5%

Answer

10%

Answer

15%

Answer

20%

Question 3

What is the normal cerebral blood flow per 100 grams of brain tissue per minute?

Accepted Answer

55 mL/100gm/min

Answer

400 mL/100gm/min

Answer

100 mL/100gm/min

Answer

200 mL/100gm/min

Question 4

Ventricular filling begins at which point?

Accepted Answer

Point D

Answer

Point A

Answer

Point B

Answer

Point C

Question 5

Lymph flow from the foot is:

Accepted Answer

Increased by massaging the foot

Answer

Increased when an individual rises from the supine to standing position

Answer

Increased when capillary permeability is decreased

Answer

Decreased when the valves of the leg veins are incompetent

Question 6

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 7

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 8

Calf compartment pressure rises to _________ on walking?

Accepted Answer

200-300 mmHg

Answer

20-30 mmHg

Answer

60-80 mmHg

Answer

80-100 mmHg

Question 9

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 10

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.

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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