Cardiovascular System Practice Questions

Q: A sudden increase in total peripheral resistance has all of the following effects EXCEPT:

Increase cardiac output. ### Explanation The correct answer is **D. Increase cardiac output.** **1. Why Option D is correct (The Concept):** Total Peripheral Resistance (TPR) is the resistance against which the left ventricle must pump to eject blood (Afterload). According to the formula **Mean Arterial Pressure (MAP) = Cardiac Output (CO) × TPR**, if TPR increases suddenly, the heart must work against a higher resistance. This increase in afterload leads to a **decrease in Stroke Volume (SV)**, which subsequently **decreases Cardiac Output**. Therefore, a sudden increase in TPR cannot increase cardiac output; it typically reduces it or keeps it stable at the cost of increased myocardial oxygen demand. **2. Why the other options are incorrect:** * **A. Increase the diastolic blood pressure:** Diastolic blood pressure is primarily determined by the tone of the arterioles (TPR). When TPR increases, the rate at which blood leaves the arterial system during diastole decreases, leading to a higher diastolic pressure. * **B. Reduce the stroke volume:** As mentioned, TPR is a major component of afterload. An increase in afterload increases the end-systolic volume, thereby reducing the stroke volume. * **C. Increase the mean arterial blood pressure:** Since MAP is directly proportional to TPR (MAP = CO × TPR), an increase in resistance leads to an immediate rise in arterial pressure. **3. NEET-PG High-Yield Pearls:** * **Afterload vs. CO:** In a healthy heart, the Frank-Starling mechanism may partially compensate, but in a failing heart, an increase in TPR significantly drops CO. * **Determinants of BP:** Systolic BP is primarily determined by **Stroke Volume** and aortic compliance, while Diastolic BP is primarily determined by **TPR** and heart rate. * **Vessel Type:** The **Arterioles** are the primary site of TPR in the systemic circulation.

Q: Which of the following physiological changes can occur when there is vagal stimulation of the heart?

Increased R-R interval. **Explanation:** Vagal stimulation involves the release of **Acetylcholine (ACh)** from the parasympathetic nerve endings (Vagus nerve). ACh binds to **M2 muscarinic receptors** in the Sinoatrial (SA) node, leading to the opening of K+ channels (GIRK channels) and inhibition of Adenylyl Cyclase. This causes hyperpolarization and a decreased rate of phase 4 spontaneous depolarization, resulting in **Bradycardia** (decreased heart rate). 1. **Why Option A is Correct:** The **R-R interval** on an ECG represents the time between two successive heartbeats. Since vagal stimulation slows the heart rate, the time between beats increases, leading to an **increased R-R interval**. 2. **Why Options B & C are Incorrect:** Vagal stimulation decreases the heart rate (Negative Chronotropy). Since Cardiac Output (CO) is the product of Heart Rate and Stroke Volume ($CO = HR \times SV$), a decrease in heart rate typically leads to a **decreased cardiac output**. 3. **Why Option D is Incorrect:** Vagal fibers primarily innervate the SA and AV nodes with sparse innervation to the ventricles. While it has a weak negative inotropic effect on the atria, it does **not increase** the force of contraction. **NEET-PG High-Yield Pearls:** * **Vagal Tone:** At rest, the heart is under constant inhibitory influence of the vagus nerve. If the vagus is blocked (e.g., by Atropine), the resting heart rate increases to the intrinsic rate of the SA node (~100 bpm). * **Vagal Escape:** If the vagus is stimulated intensely, the heart may stop, but it eventually starts beating again at a slow rate due to the emergence of a ventricular pacemaker. * **AV Node:** Vagal stimulation also decreases conduction velocity through the AV node (Negative Dromotropy), which can increase the **P-R interval**.

Q: Prepotential of the SA node is due to all except:

Fast sodium channels opening. The **prepotential** (or pacemaker potential) is the slow, spontaneous depolarization of the SA node that occurs during Phase 4 of the action potential. This phase is responsible for the heart's automaticity. ### Why "Fast Sodium Channels Opening" is Correct Fast sodium channels ($I_{Na}$) are responsible for the rapid depolarization (Phase 0) in **ventricular and atrial myocytes**. However, in the SA node and AV node, these channels are **absent or permanently inactivated** due to the relatively less negative resting membrane potential (approx. -60 mV). Therefore, fast sodium channels play no role in the SA node's prepotential or its action potential. ### Explanation of Other Options * **K+ decay (Option C):** This is the initial trigger for the prepotential. As the cell repolarizes, potassium efflux decreases, reducing the outward positive charge and allowing the membrane potential to drift upward. * **Transient Ca2+ channel opening (Option D):** T-type (Transient) calcium channels open toward the end of the prepotential, providing the final push to reach the threshold. * **Ca2+ spark (Option A):** Localized releases of calcium from the sarcoplasmic reticulum (via ryanodine receptors) occur during late diastole. This "calcium clock" mechanism activates the Na+-Ca2+ exchanger (NCX), contributing to the depolarizing current. ### High-Yield NEET-PG Pearls * **Funny Current ($I_f$):** The prepotential is primarily initiated by $I_f$, a slow inward sodium current through HCN channels. * **Phase 0 in SA Node:** Unlike myocytes, the upstroke in the SA node is due to **L-type (Long-lasting) Ca2+ channels**, not fast sodium channels. * **Parasympathetic Effect:** Acetylcholine increases $K^+$ conductance and decreases $I_f$, hyperpolarizing the cell and slowing the heart rate. * **Sympathetic Effect:** Norepinephrine increases $I_f$ and $Ca^{2+}$ currents, increasing the slope of the prepotential and heart rate.

Q: What is the mean pulmonary artery pressure?

15 mm Hg. **Explanation:** The pulmonary circulation is a **low-pressure, low-resistance system** compared to the systemic circulation. The normal pressures in the pulmonary artery are approximately **25 mm Hg (systolic)** and **8 mm Hg (diastolic)**. The **Mean Pulmonary Artery Pressure (mPAP)** is calculated using the formula: $mPAP = Diastolic + 1/3 (Systolic – Diastolic)$ $mPAP = 8 + 1/3 (25 – 8) = 8 + 5.6 = 13.6 \text{ mm Hg}$ In clinical practice and standard physiological texts (like Guyton), the normal mPAP is rounded to **15 mm Hg**. **Analysis of Options:** * **Option A (10 mm Hg):** This is too low for a mean pressure; however, it is closer to the normal **Left Atrial Pressure (LAP)**, which averages around 5–10 mm Hg. * **Option B (15 mm Hg):** **Correct.** This represents the physiological average for a healthy adult at rest. * **Option C (20 mm Hg):** This is the upper limit of normal. Pressures between 20–24 mm Hg are considered "borderline." * **Option D (25 mm Hg):** This is the normal **Systolic** Pulmonary Artery Pressure. If the *mean* pressure exceeds 25 mm Hg at rest, it is the diagnostic threshold for **Pulmonary Hypertension**. **High-Yield NEET-PG Pearls:** 1. **Pulmonary Hypertension Definition:** mPAP >20 mm Hg (Updated guidelines) or >25 mm Hg (Classic definition). 2. **Driving Pressure:** The pressure gradient required to move blood through the lungs is only ~10 mm Hg (mPAP minus Left Atrial Pressure). 3. **Vascular Resistance:** Pulmonary vascular resistance is roughly **1/10th** of systemic vascular resistance. 4. **Hypoxic Vasoconstriction:** Unlike systemic vessels, pulmonary arterioles **constrict** in response to low $O_2$ to shunt blood to better-ventilated areas.

Q: Which of the following statements about Nitric Oxide is FALSE?

Acts through cyclic GMP. **Explanation:** The question asks for the **FALSE** statement regarding Nitric Oxide (NO). While NO does indeed act through the cyclic GMP (cGMP) pathway, the phrasing of the options suggests a nuance in the mechanism of action or a potential error in the question's premise. However, based on standard physiological principles, let’s analyze the facts: 1. **Mechanism of Action (Option D):** Nitric Oxide is a gas that diffuses across membranes and binds to **soluble Guanylyl Cyclase (sGC)**. This enzyme converts GTP to **cyclic GMP (cGMP)**. cGMP then activates Protein Kinase G (PKG), leading to dephosphorylation of myosin light chains and subsequent smooth muscle relaxation. Since this is a **true** statement, its selection as the "False" answer in some question banks often stems from a technicality (e.g., it acts *via* sGC to *produce* cGMP, rather than being cGMP itself) or a misprint in the source material. 2. **Synthesis (Option A):** This is **TRUE**. NO is synthesized from the amino acid **L-arginine** by the enzyme Nitric Oxide Synthase (NOS), requiring oxygen and NADPH as cofactors. 3. **Isoforms (Option B):** This is **TRUE**. There are three isoforms of NOS: **nNOS** (Neuronal/Type 1), **iNOS** (Inducible/Type 2), and **eNOS** (Endothelial/Type 3). 4. **EDRF (Option C):** This is **TRUE**. NO was historically identified as **Endothelium-Derived Relaxing Factor** by Furchgott, Ignarro, and Murad (Nobel Prize 1998). **Clinical Pearls for NEET-PG:** * **Vasodilation:** NO is the most potent endogenous vasodilator. * **Therapeutic use:** Nitroglycerin works by releasing NO to treat angina. * **Sildenafil (Viagra):** Inhibits Phosphodiesterase-5 (PDE-5), the enzyme that breaks down cGMP, thereby prolonging the effects of NO. * **Septic Shock:** Overproduction of NO by **iNOS** leads to the profound hypotension seen in sepsis.

Q: Pre-capillary sphincter relaxation is caused by what?

Local metabolites. **Explanation:** The pre-capillary sphincter is a ring of smooth muscle located at the junction of the metarteriole and the capillary. Its primary function is to regulate the micro-perfusion of tissues based on metabolic demand. **1. Why Local Metabolites are Correct:** Pre-capillary sphincters are unique because they are **not** under direct autonomic (nervous) control. Instead, they exhibit **autoregulation** via local metabolic factors. When a tissue becomes metabolically active, it produces substances such as **CO₂, H⁺ (decreased pH), Adenosine, Lactate, and K⁺ ions**, alongside a decrease in local **O₂** tension. these metabolites act as potent vasodilators, causing the sphincter to relax to increase blood flow (hyperemia) and meet the tissue's metabolic needs. **2. Why the Other Options are Incorrect:** * **B & C (Catecholamines and Sympathetic Activity):** While large arterioles are heavily innervated by the sympathetic nervous system (α1 receptors), pre-capillary sphincters lack sympathetic innervation. They respond to local tissue environment rather than systemic neural or hormonal signals. * **D (Fall in Capillary Pressure):** A fall in pressure would typically trigger a myogenic response (constriction/dilation to maintain flow), but the primary driver for *relaxation* in this context is the accumulation of waste products, not the pressure gradient itself. **High-Yield Clinical Pearls for NEET-PG:** * **Vasomotion:** The intermittent opening and closing of pre-capillary sphincters is called vasomotion. * **Law of Laplace:** Capillaries can withstand high internal pressures without bursting because their small radius results in very low wall tension ($T = P \times r$). * **Most Potent Vasodilator:** In the heart, **Adenosine** is the most important local metabolite; in skeletal muscle, it is often **Lactate and K⁺**.

Q: Triggered automaticity leads to the development of which of the following rhythm disorders?

Torsades de pointes. ### Explanation **Underlying Concept: Triggered Activity** Triggered automaticity (or triggered activity) refers to abnormal action potentials generated by **afterdepolarizations**. These are oscillations in membrane potential that occur before the cell has fully repolarized. There are two types: 1. **Early Afterdepolarizations (EADs):** Occur during Phase 2 or 3 of the action potential. They are associated with a prolonged QT interval. 2. **Delayed Afterdepolarizations (DADs):** Occur during Phase 4, often due to intracellular calcium overload (e.g., Digoxin toxicity). **Torsades de Pointes (TdP)** is the classic example of a rhythm caused by **EADs**. When the ventricular repolarization is delayed (long QT), EADs can reach the threshold, triggering a series of rapid, polymorphic ventricular beats. **Analysis of Incorrect Options:** * **A & B (Sinus Bradycardia/Tachycardia):** These are disorders of **enhanced or depressed normal automaticity** at the SA node, not triggered activity. * **D (Ischemic Ventricular Fibrillation):** While ischemia can involve multiple mechanisms, the primary mechanism for VF in the setting of acute ischemia is **re-entry** or enhanced automaticity in Purkinje fibers, rather than triggered activity. **High-Yield Pearls for NEET-PG:** * **EADs** are exacerbated by **slow heart rates** (bradycardia-dependent) and are the hallmark of **Long QT Syndrome**. * **DADs** are exacerbated by **fast heart rates** (tachycardia-dependent) and are the mechanism behind **Digoxin toxicity** and **CPVT** (Catecholaminergic Polymorphic Ventricular Tachycardia). * **Re-entry** is the most common mechanism for most clinical tachycardias (e.g., PSVT, Atrial Flutter).

Question 1

A sudden increase in total peripheral resistance has all of the following effects EXCEPT:

Accepted Answer

Increase cardiac output

Answer

Increase the diastolic blood pressure

Answer

Reduce the stroke volume

Answer

Increase the mean arterial blood pressure

Question 2

Which of the following physiological changes can occur when there is vagal stimulation of the heart?

Accepted Answer

Increased R-R interval

Answer

Increased heart rate

Answer

Increased cardiac output

Answer

Increased force of contraction

Question 3

Peripheral vascular resistance is best represented by which of the following parameters?

Accepted Answer

Diastolic blood pressure, as it decreases progressively towards the mid-thoracic aorta.

Answer

Mean arterial pressure, which is responsible for blood flow to organs.

Answer

Pulse pressure, as it relates to stroke volume and aortic compliance.

Answer

Systolic pressure, as it increases in the descending aorta.

Question 4

Prepotential of the SA node is due to all except:

Accepted Answer

Fast sodium channels opening

Answer

Ca2+ spark

Answer

K+ decay

Answer

Transient Ca channel opening

Question 5

During the 'fight or flight' reaction, which of the following is responsible for an increase in local blood flow?

Accepted Answer

Sympathetic system-mediated cholinergic release

Answer

Local hormones

Answer

Parasympathetic cholinergic activity

Answer

Endocrine factors only

Question 6

The SA node acts as the pacemaker of the heart because?

Accepted Answer

Its resting excitability is the highest among all cardiac tissues.

Answer

It is the only excitable node in the heart.

Answer

It is the only node sensitive to vagal stimulation.

Answer

It is the largest pacemaker tissue in the heart.

Question 7

What is the mean pulmonary artery pressure?

Accepted Answer

15 mm Hg

Answer

10 mm Hg

Answer

20 mm Hg

Answer

25 mm Hg

Question 8

Which of the following statements about Nitric Oxide is FALSE?

Accepted Answer

Acts through cyclic GMP

Answer

Produced from arginine

Answer

Nitric oxide synthase has three isoforms

Answer

Also known as endothelium-derived relaxing factor

Question 9

Pre-capillary sphincter relaxation is caused by what?

Accepted Answer

Local metabolites

Answer

Circulating catecholamines

Answer

Sympathetic activity

Answer

Fall in capillary pressure

Question 10

Triggered automaticity leads to the development of which of the following rhythm disorders?

Accepted Answer

Torsades de pointes

Answer

Sinus bradycardia

Answer

Sinus tachycardia

Answer

Ischemic ventricular fibrillation

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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