Cardiovascular System Practice Questions

Q: The second heart sound is due to which of the following?

Closure of semilunar valves. **Explanation** The **second heart sound (S2)** is produced by the vibrations initiated by the sudden **closure of the semilunar valves** (Aortic and Pulmonary valves). This occurs at the beginning of **isovolumetric ventricular relaxation**, marking the end of ventricular systole and the start of diastole. The closure is triggered when the pressure in the great arteries (Aorta and Pulmonary artery) exceeds the pressure in the relaxing ventricles, causing blood to flow back toward the heart and snapping the valve cusps shut. **Analysis of Incorrect Options:** * **Option A (Closure of AV valves):** This produces the **first heart sound (S1)**. It occurs at the onset of ventricular systole (isovolumetric contraction) when the Mitral and Tricuspid valves close. * **Option C (Inflow of blood):** Rapid ventricular filling during early diastole produces the **third heart sound (S3)**. While normal in children, it often indicates volume overload (e.g., heart failure) in adults. * **Option D (Contraction of atria):** Atrial contraction against a stiff, non-compliant ventricle produces the **fourth heart sound (S4)**, which is always pathological (e.g., ventricular hypertrophy). **High-Yield NEET-PG Pearls:** * **Physiological Splitting:** S2 has two components: **A2** (Aortic) and **P2** (Pulmonary). A2 normally precedes P2. During inspiration, the split widens because increased venous return delays the closure of the pulmonary valve. * **Fixed Splitting:** A classic sign of **Atrial Septal Defect (ASD)**. * **Duration:** S2 is higher-pitched and shorter in duration (approx. 0.11 sec) compared to S1.

Q: Cardiac output decreases in all the following conditions except?

Sleep. **Explanation:** The correct answer is **Sleep**. Contrary to common assumption, cardiac output (CO) remains **unchanged or shows no significant decrease** during normal sleep. While the heart rate and blood pressure may drop due to increased parasympathetic tone, the stroke volume often increases slightly to compensate, maintaining a stable cardiac output. **Analysis of Options:** * **Sleep (Correct):** Standard physiological teaching (e.g., Guyton, Ganong) states that CO does not decrease during sleep. It is one of the few resting states where CO remains stable despite a lower metabolic rate. * **Heart Disease:** Conditions like myocardial infarction, valvular heart disease, or heart failure directly impair the heart's pumping ability (contractility), leading to a decrease in CO. * **Sitting from Supine:** When moving from a lying to a sitting or standing position, gravity causes blood to pool in the lower extremities (venous pooling). This reduces venous return (preload), which, according to the Frank-Starling law, decreases stroke volume and CO by approximately 20-30%. * **Arrhythmias:** Tachyarrhythmias (due to shortened diastolic filling time) and bradyarrhythmias (due to low heart rate) both result in a reduction of effective cardiac output. **High-Yield NEET-PG Pearls:** * **CO Increases in:** Anxiety, eating (digestion), exercise, pregnancy, high altitude, and anemia (hyperdynamic circulation). * **CO Decreases in:** Rapid arrhythmias, hemorrhage, and sudden change in posture (supine to standing). * **Formula:** $CO = \text{Stroke Volume} \times \text{Heart Rate}$. * **Index:** Cardiac Index is CO per square meter of body surface area (Normal: $3.2 \, \text{L/min/m}^2$).

Q: What is the normal electrical axis of the heart?

-30 to +90 degrees. ### Explanation **1. Understanding the Correct Answer (A: -30 to +90 degrees)** The electrical axis of the heart represents the net direction of the ventricular depolarization wave (QRS complex) in the frontal plane. In a healthy individual, the heart is positioned anatomically with the apex pointing downward and to the left. Because the left ventricle is significantly more muscular than the right, the mean electrical vector is pulled toward it. Most international guidelines (including Guyton and Ganong) define the normal range as **-30° to +90°**. Some texts extend this to +110°, but for NEET-PG, -30° to +90° is the standard accepted range. **2. Analysis of Incorrect Options** * **B (+90 to +120 degrees):** This represents **Right Axis Deviation (RAD)**. It is commonly seen in right ventricular hypertrophy (RVH), pulmonary embolism, or in thin, tall individuals. * **C (+120 to -30 degrees):** This range encompasses **Extreme Axis Deviation** (also known as "No Man's Land" or Northwest axis), typically seen in ventricular tachycardia or severe emphysema. * **D (+60 to -60 degrees):** This is an arbitrary range that does not align with standard physiological definitions of the cardiac axis. **3. Clinical Pearls for NEET-PG** * **Left Axis Deviation (LAD):** Axis +90°. Causes: Right Ventricular Hypertrophy (RVH), Left Posterior Fascicular Block (LPFB), or lateral wall MI. * **Quick Rule of Thumb:** * Normal Axis: QRS is positive (upright) in both Lead I and Lead aVF. * LAD: QRS is positive in Lead I and negative in Lead aVF ("Leaving" each other). * RAD: QRS is negative in Lead I and positive in Lead aVF ("Reaching" for each other).

Q: Stimulation of the medial portion of the vasomotor center results in which of the following?

Decreased cardiac output. ### Explanation The **Vasomotor Center (VMC)**, located bilaterally in the reticular substance of the medulla and lower third of the pons, is functionally divided into three distinct areas: the vasoconstrictor area, the vasodilator area, and the sensory area. **1. Why the Correct Answer is Right:** The **medial portion** of the VMC corresponds to the **inhibitory (depressor) area**. When stimulated, it sends inhibitory signals to the lateral (pressor) areas of the VMC. This inhibition results in: * **Decreased Sympathetic Outflow:** Leading to peripheral vasodilation and decreased myocardial contractility. * **Increased Parasympathetic (Vagal) Tone:** Via the nucleus ambiguus and dorsal motor nucleus of the vagus. The net effect of reduced contractility and a lower heart rate is a **decrease in Cardiac Output (CO)**. **2. Why the Incorrect Options are Wrong:** * **A & B (Increased Peripheral Resistance & Blood Pressure):** These are functions of the **lateral (pressor) portion** of the VMC. Stimulation of the lateral area increases sympathetic discharge, causing vasoconstriction (increased resistance) and a subsequent rise in blood pressure. * **C (Increased Heart Rate):** Stimulation of the medial area increases vagal activity, which leads to **bradycardia** (decreased heart rate), not tachycardia. **3. High-Yield Facts for NEET-PG:** * **Location:** The VMC is primarily in the **Medulla Oblongata**. * **Sensory Input:** The **Nucleus Tractus Solitarius (NTS)** in the sensory area receives input from the glossopharyngeal (IX) and vagus (X) nerves regarding baroreceptor status. * **Neurotransmitter:** The inhibitory signals from the medial area to the lateral area are primarily mediated by **GABA**. * **Baroreceptor Reflex:** An increase in BP stimulates the NTS, which then excites the medial (inhibitory) area to lower BP and heart rate.

Q: Reynolds number describes the relationship between all of the following, EXCEPT:

Direction of flow. **Explanation:** The **Reynolds number (Re)** is a dimensionless quantity used in fluid dynamics to predict whether blood flow is **laminar** (silent, streamlined) or **turbulent** (noisy, chaotic). It is mathematically expressed by the formula: $$Re = \frac{\rho \cdot v \cdot d}{\eta}$$ Where: * **$\rho$ (Rho):** Density of the fluid * **$v$:** Velocity of flow * **$d$:** Diameter of the vessel * **$\eta$ (Eta):** Viscosity of the fluid **Why "Direction of flow" is the correct answer:** The Reynolds number determines the **nature** or **type** of flow (laminar vs. turbulent) based on physical properties and velocity. It does not provide information regarding the vector or direction in which the fluid is moving. **Analysis of Incorrect Options:** * **A. Viscosity:** Inversely proportional to Re. A decrease in viscosity (e.g., severe anemia) increases Re, predisposing to turbulence. * **B. Density:** Directly proportional to Re. Higher density increases the inertial forces of the fluid. * **C. Velocity:** Directly proportional to Re. This is the most dynamic variable; as velocity increases (e.g., during exercise), flow is more likely to become turbulent. **Clinical Pearls for NEET-PG:** * **Critical Threshold:** If $Re 3000$, flow is turbulent. * **Anemia & Murmurs:** In anemia, blood viscosity decreases ($\downarrow \eta$), leading to an increased Reynolds number. This causes functional "hemic" murmurs due to turbulent flow. * **Bruits:** Turbulence in large arteries (like the carotid) caused by narrowing (decreased $d$ but significantly increased $v$) creates sounds called bruits. * **Korotkoff Sounds:** These sounds heard during BP measurement are a result of turbulent flow created by the partial occlusion of the brachial artery.

Q: Which of the following best describes the Anrep effect?

Increased afterload increases cardiac contractility. ### Explanation The **Anrep effect** is an intrinsic autoregulation mechanism of the heart where an **increase in afterload** (e.g., a sudden rise in aortic pressure) leads to a gradual **increase in myocardial contractility** (inotropism). #### 1. Why the Correct Answer is Right When afterload increases, the left ventricle initially cannot eject the full stroke volume, leading to an increase in end-systolic volume. This stretches the myocardial fibers (Frank-Starling mechanism). However, over the next 1–2 minutes, a secondary response occurs: the **Anrep effect**. * **Mechanism:** The increased wall tension activates stretch-activated sodium-hydrogen exchangers ($NHE-1$). This leads to an accumulation of intracellular $Na^+$, which subsequently slows the $Na^+/Ca^{2+}$ exchanger ($NCX$). The resulting increase in **intracellular calcium** levels enhances contractility, allowing the heart to maintain stroke volume despite the higher pressure. #### 2. Why Other Options are Wrong * **Option A:** Increased preload actually *increases* contractility (Frank-Starling Law), not decreases it. * **Option C & D:** These options confuse contractility (systolic function) with relaxation (diastolic function). While the **Bowditch effect** (Treppe phenomenon) and Anrep effect deal with inotropy, they are not primarily defined by changes in relaxation phases. #### 3. Clinical Pearls for NEET-PG * **Frank-Starling vs. Anrep:** Frank-Starling is an **instantaneous** response to preload (heterometric autoregulation). The Anrep effect is a **delayed** response to afterload (homeometric autoregulation). * **Bowditch Effect (Treppe Phenomenon):** An increase in heart rate leads to increased contractility due to the inability of $Na^+/K^+$ ATPase to keep up, leading to calcium accumulation. * **Key Mediator:** Remember that the Anrep effect is mediated by **intracellular Calcium** secondary to $Na^+/H^+$ exchange.

Q: What is the largest compliance in the circulatory system?

Veins. **Explanation:** **1. Why Veins are the Correct Answer:** Compliance (or capacitance) is defined as the change in volume per unit change in pressure ($C = \Delta V / \Delta P$). In the circulatory system, **veins** have the highest compliance—approximately **24 times** that of arteries. This is due to their thin, distensible walls and larger luminal diameters. Because of this high compliance, veins can accommodate large volumes of blood (about 60-70% of total blood volume) with minimal increases in pressure, acting as the body’s primary **blood reservoir**. **2. Why Other Options are Incorrect:** * **Arteries & Aorta:** These are "resistance" and "conduit" vessels, respectively. They have thick, muscular, and elastic walls designed to withstand high pressures. Consequently, they are much stiffer (less compliant) than veins. A small increase in arterial volume leads to a significant rise in pressure. * **Capillaries:** While numerous, individual capillaries have very small diameters and lack the distensible wall structure required for high compliance. Their primary function is exchange, not storage. **3. NEET-PG High-Yield Pearls:** * **Capacitance Vessels:** Veins are known as capacitance vessels, while arterioles are known as resistance vessels. * **Formula:** Compliance is the inverse of **Elastance** ($E = 1/C$). As age increases or in conditions like atherosclerosis, arterial compliance decreases (vessels become stiffer). * **Sympathetic Effect:** Sympathetic stimulation decreases venous compliance (venoconstriction), shifting blood from the peripheral veins into the heart to increase stroke volume (Frank-Starling mechanism). * **Specific Ratio:** Systemic veins are about 8 times more distensible than systemic arteries, and their volume is 3 times larger, leading to the 24x total compliance figure.

Question 1

The second heart sound is due to which of the following?

Accepted Answer

Closure of semilunar valves

Answer

Closure of atrioventricular valves

Answer

Inflow of blood into the ventricles

Answer

Contraction of the atria

Question 2

Cardiac output decreases in all the following conditions except?

Accepted Answer

Sleep

Answer

Heart disease

Answer

Sitting from supine

Answer

Arrhythmias

Question 3

What is the normal electrical axis of the heart?

Accepted Answer

-30 to +90 degrees

Answer

+90 to +120 degrees

Answer

+120 to -30 degrees

Answer

+60 to -60 degrees

Question 4

Stimulation of the medial portion of the vasomotor center results in which of the following?

Accepted Answer

Decreased cardiac output

Answer

Increased peripheral resistance

Answer

Increased blood pressure

Answer

Increased heart rate

Question 5

Reynolds number describes the relationship between all of the following, EXCEPT:

Accepted Answer

Direction of flow

Answer

Viscosity of fluid

Answer

Density of fluid

Answer

Velocity of flow

Question 6

Which of the following represents a site of local control in blood flow?

Accepted Answer

Skin

Answer

Muscle

Answer

Splanchnic vessels

Answer

Cerebrum

Question 7

Which of the following best describes the Anrep effect?

Accepted Answer

Increased afterload increases cardiac contractility

Answer

Increased preload decreases cardiac contractility

Answer

Increased preload decreases cardiac relaxation

Answer

Decreased afterload decreases cardiac relaxation

Question 8

Which among the following is a false statement about fetal circulation?

Accepted Answer

Blood in the inferior vena cava has lower oxygen concentration compared to the superior vena cava

Answer

Ductus venosus receives blood with high oxygen saturation

Answer

Pressure in the right and left ventricles are equal

Answer

Brain receives blood with high oxygen saturation

Question 9

What is the largest compliance in the circulatory system?

Accepted Answer

Veins

Answer

Arteries

Answer

Capillaries

Answer

Aorta

Question 10

Closure of the fetal circulatory adjustments occurs functionally in the following sequence?

Accepted Answer

Ductus venosus > Foramen ovale > Ductus arteriosus

Answer

Ductus arteriosus > Foramen ovale > Ductus venosus

Answer

Ductus venosus > Ductus arteriosus > Foramen ovale

Answer

Ductus arteriosus > Ductus venosus > Foramen ovale

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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