Cardiovascular System Practice Questions

Q: Which one of the following neurotransmitters functions to increase cardiac output?

Norepinephrine. **Explanation:** **Norepinephrine (Option C)** is the correct answer because it is the primary neurotransmitter of the postganglionic sympathetic nervous system. It increases cardiac output through its action on **$\beta_1$-adrenergic receptors** located in the myocardium and the sinoatrial (SA) node. This binding triggers a G-protein-mediated increase in cAMP, leading to: 1. **Positive Inotropy:** Increased force of contraction. 2. **Positive Chronotropy:** Increased heart rate. Since Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR), both mechanisms contribute to a significant rise in CO. **Analysis of Incorrect Options:** * **GABA (Option A):** The primary inhibitory neurotransmitter in the CNS. While it can influence central blood pressure regulation, it does not have a direct peripheral stimulatory effect on cardiac output. * **Serotonin (Option B):** Primarily involved in mood regulation and platelet aggregation. While it has complex effects on the vasculature (vasoconstriction/dilation), it is not the physiological mediator for increasing cardiac output. * **Glutamate (Option D):** The major excitatory neurotransmitter in the CNS. It is involved in synaptic plasticity and memory but does not act directly on the heart to increase output. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor Specificity:** While Norepinephrine acts on $\alpha_1$ and $\beta_1$ receptors, **Epinephrine** (from the adrenal medulla) acts on $\alpha_1, \beta_1,$ and $\beta_2$. * **Parasympathetic Control:** Acetylcholine (ACh) acts on **$M_2$ receptors** to decrease heart rate (negative chronotropy), thereby decreasing cardiac output. * **Bowditch Effect:** An increase in heart rate leads to an increase in the force of contraction due to the inability of Na+/K+ ATPase to keep up, leading to higher intracellular calcium.

Q: Thrombin activity is inhibited by which of the following?

Heparin. ### Explanation **Correct Option: B (Heparin)** Thrombin (Factor IIa) is a central protease in the coagulation cascade. Its activity is primarily regulated by **Antithrombin III (AT-III)**, a naturally occurring plasma protein. Heparin acts as an indirect anticoagulant by binding to AT-III, inducing a conformational change that increases AT-III’s affinity for Thrombin by nearly **1,000-fold**. This complex rapidly inactivates Thrombin and other serine proteases (Factors IXa, Xa, XIa, and XIIa), effectively halting clot formation. **Analysis of Incorrect Options:** * **A. Chymotrypsin:** This is a digestive proteolytic enzyme produced in the pancreas. It functions in the small intestine to break down proteins into peptides and has no physiological role in inhibiting the blood coagulation cascade. * **C. Alpha 2 antitrypsin:** While it is a serine protease inhibitor (Serpin), its primary clinical role is inhibiting **neutrophil elastase** in the lungs. Deficiency leads to emphysema and liver cirrhosis, not coagulation disorders. * **D. Alpha 2 macroglobulin:** This is a broad-spectrum protease inhibitor that can neutralize various enzymes, including thrombin, but its role is minor compared to the potent AT-III/Heparin mechanism. It serves more as a secondary backup inhibitor. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Heparin does not dissolve existing clots; it prevents the formation and extension of new clots. * **Monitoring:** The efficacy of Unfractionated Heparin (UFH) is monitored using **aPTT** (Intrinsic pathway). * **Antidote:** The specific antagonist for Heparin overdose is **Protamine Sulfate** (derived from salmon sperm). * **LMWH vs. UFH:** Low Molecular Weight Heparin (e.g., Enoxaparin) has a higher affinity for inhibiting **Factor Xa** than Thrombin (IIa).

Q: During exercise, what happens to blood flow to the brain?

Unaltered. **Explanation:** The correct answer is **Unaltered (C)**. **1. Why it is correct:** During exercise, there is a massive increase in total cardiac output to meet the metabolic demands of skeletal muscles. However, the brain requires a constant, steady supply of oxygen and glucose to maintain consciousness and neurological function. This is achieved through **Cerebral Autoregulation**. Despite fluctuations in systemic blood pressure and the redistribution of blood to muscles and skin, the cerebral blood flow (CBF) remains remarkably constant at approximately **750 mL/min (or 15% of resting cardiac output)**. While the *percentage* of total cardiac output directed to the brain decreases, the *absolute volume* of blood flow remains unchanged. **2. Why other options are incorrect:** * **A. Decreased:** The brain is a vital organ; any significant decrease in flow would lead to syncope (fainting). Autoregulation prevents this during the sympathetic surge of exercise. * **B. Increased:** While blood flow to the heart and skeletal muscles increases significantly, the rigid cranium and autoregulatory mechanisms (myogenic and metabolic) prevent hyperperfusion of the brain. * **D. Initially increased and then decreases:** There is no physiological basis for this biphasic response in a healthy individual during standard exercise. **3. NEET-PG High-Yield Pearls:** * **Most sensitive factor for CBF:** Arterial $PCO_2$. Hypercapnia causes vasodilation (increasing flow), while hypocapnia (hyperventilation) causes vasoconstriction. * **Autoregulation Range:** Cerebral blood flow remains constant between a Mean Arterial Pressure (MAP) of **60 to 140 mmHg**. * **Organ with the highest blood flow per 100g tissue:** Carotid bodies (followed by the Kidneys). * **Organ with the highest oxygen extraction ($A-V O_2$ difference):** The Heart.

Q: What is the normal CO2 content in arterial blood?

49 mL/dL. **Explanation:** The correct answer is **49 mL/dL** (Option D). In cardiovascular physiology, it is essential to distinguish between the partial pressure of a gas ($PCO_2$) and its actual volume content in the blood. **1. Why 49 mL/dL is Correct:** In a healthy adult, arterial blood typically contains approximately **48–50 mL of $CO_2$ per 100 mL (dL)** of blood. This $CO_2$ exists in three forms: dissolved in plasma (approx. 5%), carbamino compounds bound to hemoglobin (approx. 5%), and the majority as bicarbonate ions ($HCO_3^-$) (approx. 90%). When blood passes through systemic tissues, it picks up an additional 4 mL/dL, bringing the **venous $CO_2$ content to approximately 52–54 mL/dL**. **2. Analysis of Incorrect Options:** * **Option A (19 mL/dL):** This value represents the approximate **Oxygen ($O_2$) content** in arterial blood (Normal: 19–20 mL/dL). * **Option B (29 mL/dL):** This is a distractor; however, 24–30 mEq/L is the normal range for plasma bicarbonate concentration, not total gas content. * **Option C (36 mL/dL):** This value does not correspond to standard physiological gas constants in arterial blood. **3. High-Yield NEET-PG Pearls:** * **Arterial-Venous (A-V) Difference:** The A-V difference for $CO_2$ is small (**4 mL/dL**) compared to $O_2$ (**5 mL/dL**). * **Haldane Effect:** Deoxygenation of blood increases its ability to carry $CO_2$. This is crucial in the tissues. * **Chloride Shift (Hamburger Phenomenon):** To maintain electrical neutrality, $Cl^-$ enters RBCs as $HCO_3^-$ leaves them in systemic capillaries. * **Partial Pressures:** Do not confuse *content* with *pressure*. Normal arterial $PCO_2$ is **40 mmHg**, and venous $PCO_2$ is **46 mmHg**.

Q: Which of the following causes vasoconstriction in all vascular beds?

TXA2. **Explanation** The correct answer is **TXA2 (Thromboxane A2)**. **Why TXA2 is correct:** Thromboxane A2 is a potent eicosanoid synthesized primarily by platelets via the cyclooxygenase (COX) pathway. Its primary physiological roles are **platelet aggregation** and **potent vasoconstriction**. Unlike other prostaglandins which may have varying effects depending on the tissue or receptor subtype, TXA2 acts via the TP receptor to cause generalized vasoconstriction across all vascular beds, including the renal, coronary, and pulmonary circulations. **Why the other options are incorrect:** * **PGE2 (Prostaglandin E2):** This is primarily a **vasodilator** in most vascular beds. While it can cause constriction in specific areas (like the ductus arteriosus or certain segments of the renal vasculature under specific conditions), it is generally known for its role in inflammatory vasodilation and maintaining the patency of the ductus arteriosus. * **PGF2α (Prostaglandin F2 alpha):** While PGF2α is a vasoconstrictor (especially in the pulmonary and uterine vessels), it is primarily known for its potent **smooth muscle contracting** effects on the uterus and bronchi. It does not exert a universal vasoconstrictive effect across all vascular beds as consistently as TXA2. * **PGI2 (Prostacyclin):** Produced by vascular endothelial cells, PGI2 is the functional antagonist to TXA2. It is a potent **vasodilator** and inhibitor of platelet aggregation. **High-Yield NEET-PG Pearls:** * **Aspirin's Mechanism:** Low-dose aspirin irreversibly inhibits COX-1, shifting the balance in favor of **PGI2 (vasodilator)** over **TXA2 (vasoconstrictor)**, which explains its cardioprotective effect. * **Vasoactive Mnemonic:** Remember **"I"** for **I**nhibition (PGI2 inhibits aggregation/constriction) and **"TX"** for **T**hrombus (TXA2 promotes thrombus/constriction). * **Ductus Arteriosus:** PGE2 keeps it open; NSAIDs (Indomethacin) close it by inhibiting PGE2 synthesis.

Q: Nitric oxide (NO) is secreted by which of the following?

Endothelium. **Explanation:** **Nitric Oxide (NO)**, formerly known as **Endothelium-Derived Relaxing Factor (EDRF)**, is a potent vasodilator synthesized primarily in the **vascular endothelium**. 1. **Why Endothelium is Correct:** In the vascular system, the enzyme **Endothelial Nitric Oxide Synthase (eNOS)** acts on the amino acid **L-arginine** to produce NO. Once released, NO diffuses into the underlying vascular smooth muscle cells, where it activates **guanylyl cyclase**. This increases intracellular **cGMP**, leading to smooth muscle relaxation and vasodilation. This process is crucial for regulating blood pressure and regional blood flow. 2. **Why Other Options are Incorrect:** * **Ectoderm and Endoderm:** These are primary germ layers formed during embryogenesis. While they give rise to various tissues (e.g., Ectoderm forms the nervous system; Endoderm forms the GI tract lining), they are not direct "secretory sites" for NO in the context of cardiovascular physiology. * **Bones:** Bone tissue provides structural support and mineral storage. While some NO production occurs in bone cells (osteoblasts/osteoclasts) for remodeling, it is not the primary or classic physiological source associated with systemic NO secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Precursor:** L-arginine is the essential amino acid required for NO synthesis. * **Isoforms of NOS:** There are three types: **nNOS** (Neuronal), **iNOS** (Inducible/Macrophages), and **eNOS** (Endothelial). * **Mechanism:** NO → ↑ cGMP → Protein Kinase G → Dephosphorylation of Myosin Light Chain → **Vasodilation**. * **Clinical Link:** Nitroglycerin works by being converted into NO, providing rapid relief in angina pectoris. * **Septic Shock:** Overproduction of NO by **iNOS** (induced by cytokines) leads to the massive peripheral vasodilation seen in sepsis.

Q: Pacemaker potential occurs due to which of the following?

Opening of transient, rapid T-type Ca2+ channels. **Explanation:** The **Pacemaker Potential** (also known as the prepotential or Phase 4 depolarization) is the slow, spontaneous depolarization of the SA node that brings the membrane potential to the threshold, triggering an action potential. **1. Why Option A is Correct:** The pacemaker potential occurs in three sequential ionic steps: * **Initial Phase:** Triggered by the opening of **"Funny" Na+ channels ($I_f$)**, which allow sodium influx. * **Late Phase:** As the membrane depolarizes, **T-type (Transient) Ca2+ channels** open. These channels provide the final push (calcium influx) to reach the threshold potential (approx. -40 mV). * Once the threshold is reached, **L-type (Long-lasting) Ca2+ channels** open to cause the actual depolarization (Phase 0). Therefore, the opening of T-type channels is a critical component of the pacemaker potential. **2. Why Other Options are Incorrect:** * **Option B:** Opening of K+ channels causes **repolarization** (Phase 3), as K+ leaves the cell, making the interior more negative. * **Option C:** Closure of Ca2+ channels would stop depolarization; it is the *opening* of these channels that drives the potential toward the threshold. * **Option D:** The prepotential begins with the **opening** of funny Na+ channels, not their closure. **Clinical Pearls & High-Yield Facts:** * **SA Node:** The primary pacemaker because it has the steepest prepotential slope. * **Autonomic Influence:** Sympathetic stimulation increases the slope (faster heart rate), while Parasympathetic (Vagus) stimulation decreases the slope and hyperpolarizes the cell (slower heart rate). * **Ivabradine:** A clinical drug that selectively blocks the **$I_f$ (funny) channels**, used to reduce heart rate in angina and heart failure. * **Phase 0 in SA Node:** Unlike ventricular muscle (where Phase 0 is Na+ dependent), the SA node's Phase 0 is **Ca2+ dependent**.

Q: The shape of the arterial pulse is influenced by which of the following?

Arterial wall elasticity. **Explanation:** The shape and contour of the arterial pulse are primarily determined by the **elasticity of the arterial walls** (compliance) and the stroke volume. When the left ventricle ejects blood into the aorta, the energy is stored by the expansion of the elastic arterial walls (Potential Energy). During diastole, the elastic recoil (Windkessel effect) converts this into kinetic energy, maintaining continuous blood flow and shaping the pulse wave. A decrease in elasticity, such as in atherosclerosis, leads to a steeper rise and a higher pulse pressure. **Why other options are incorrect:** * **Viscosity of blood (A):** Viscosity primarily affects peripheral resistance and the *rate* of flow (Poiseuille’s Law) rather than the specific morphological shape of the pressure wave. * **Velocity of blood (B):** While velocity relates to flow, the pulse is a *pressure wave* that travels significantly faster (5–12 m/s) than the actual blood flow (0.5 m/s). Velocity does not dictate the contour of the wave. * **Cross-sectional area (D):** This determines the velocity of flow (Inversely proportional) but does not influence the characteristic dicrotic notch or the upstroke of the arterial pulse. **High-Yield Clinical Pearls for NEET-PG:** * **Anacrotic Notch:** Seen in the ascending limb in Aortic Stenosis. * **Dicrotic Notch:** Caused by the closure of the aortic valve; it marks the beginning of diastole. * **Pulsus Bisferiens:** A double-peaked pulse seen in AR + AS or Hypertrophic Obstructive Cardiomyopathy (HOCM). * **Windkessel Effect:** The process where elastic recoil of central arteries maintains diastolic pressure; loss of this effect causes isolated systolic hypertension in the elderly.

Question 1

Which one of the following neurotransmitters functions to increase cardiac output?

Accepted Answer

Norepinephrine

Answer

GABA

Answer

Serotonin

Answer

Glutamate

Question 2

Thrombin activity is inhibited by which of the following?

Accepted Answer

Heparin

Answer

Chymotrypsin

Answer

Alpha 2 antitrypsin

Answer

Alpha 2 macroglobulin

Question 3

All of the following statements regarding the heart are true EXCEPT?

Accepted Answer

The sinoatrial node receives a nerve supply and thus initiates the heart beat autonomously.

Answer

The nerve fibers that conduct the pain associated with ischemia accompany the sympathetic nerve supply to the heart.

Answer

The atrioventricular node is located in the interatrial septum.

Answer

The diaphragmatic surface of the heart is composed primarily of the left ventricular wall.

Question 4

During exercise, what happens to blood flow to the brain?

Accepted Answer

Unaltered

Answer

Decreased

Answer

Increased

Answer

Initially increased and then decreases

Question 5

What is the normal CO2 content in arterial blood?

Accepted Answer

49 mL/dL

Answer

19 mL/dL

Answer

29 mL/dL

Answer

36 mL/dL

Question 6

Thrombomodulin-thrombin complex prevents clotting because it:

Accepted Answer

Activates protein C, which inactivates activated factors V and VIII, and also removes thrombin

Answer

Inhibits prothrombin activator

Answer

Activates anti-thrombin III

Answer

Activates heparin

Question 7

Which of the following causes vasoconstriction in all vascular beds?

Accepted Answer

TXA2

Answer

PGE2

Answer

PGF2α

Answer

PGI2

Question 8

Nitric oxide (NO) is secreted by which of the following?

Accepted Answer

Endothelium

Answer

Ectoderm

Answer

Endoderm

Answer

Bones

Question 9

Pacemaker potential occurs due to which of the following?

Accepted Answer

Opening of transient, rapid T-type Ca2+ channels

Answer

Opening of K+ channels

Answer

Closure of Ca2+ channels

Answer

Closure of funny Na+ channels

Question 10

The shape of the arterial pulse is influenced by which of the following?

Accepted Answer

Arterial wall elasticity

Answer

Viscosity of blood

Answer

Velocity of blood

Answer

Cross-sectional area of the artery

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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