Cardiovascular System Practice Questions

Q: Which part of the action potential in cardiac pacemaker cells is primarily affected by calcium channel blockers?

Phase 0. ***Phase 0*** - In cardiac pacemaker cells (SA and AV nodes), **Phase 0 (rapid depolarization)** is mediated by **L-type calcium channels**, NOT the fast sodium channels seen in ventricular myocytes. - Calcium channel blockers primarily inhibit these **L-type calcium channels**, leading to a **slower rate of depolarization** and **reduced conduction velocity** through the AV node. - This is the **primary mechanism** by which these drugs slow heart rate and cause AV nodal blockade. *Phase 1* - Phase 1 (initial rapid repolarization) is **absent in pacemaker cells** because they lack the fast sodium channels and transient outward potassium currents characteristic of ventricular myocytes. - This phase is not relevant to pacemaker cell action potentials. *Phase 2* - Phase 2 (plateau phase) is also **absent or minimal in pacemaker cells**. - Pacemaker action potentials lack the prolonged plateau seen in ventricular myocytes. - This phase is not the primary target of calcium channel blockers in pacemaker tissue. *Phase 3* - Phase 3 (repolarization) occurs in pacemaker cells and is mediated by **potassium efflux**. - Calcium channel blockers do **not directly affect** this phase, as it is driven by potassium channels, not calcium channels. - Their effect on Phase 3 is minimal compared to their direct action on Phase 0.

Q: Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?

Norepinephrine. ***Norepinephrine*** - **Norepinephrine** is the primary neurotransmitter released by **postganglionic sympathetic neurons** directly onto the heart to increase heart rate and contractility in response to a drop in blood pressure. - It acts on **beta-1 adrenergic receptors** in the sinoatrial (SA) node, atria, and ventricles, leading to increased chronotropy (heart rate) and inotropy (contractility). *Dopamine* - While **dopamine** can have cardiovascular effects, particularly at high doses, it is not the primary neurotransmitter released by the sympathetic nervous system for direct heart rate regulation. - Dopamine is a precursor to norepinephrine and epinephrine, but its main physiological roles involve **renal blood flow regulation** and central nervous system functions. *Acetylcholine* - **Acetylcholine** is the primary neurotransmitter of the **parasympathetic nervous system**, which generally acts to **decrease heart rate** (bradycardia) through muscarinic receptors. - It is also released by **preganglionic sympathetic fibers**, but these do not directly innervate the heart to produce the desired effect of increasing heart rate. *Epinephrine* - **Epinephrine** (adrenaline) is primarily a **hormone** released from the **adrenal medulla** into the bloodstream, not directly from postganglionic sympathetic nerve terminals to the heart. - Although it has strong effects on beta-1 receptors in the heart, its release is more generalized and slower than the direct neuronal release of norepinephrine.

Q: Which of the following statements about cardiac muscle is incorrect?

Cardiac muscle has a short refractory period.. ***Cardiac muscle has a short refractory period.*** - This statement is **incorrect** because cardiac muscle has a **long refractory period** (~250 ms), which prevents summation and tetanus by ensuring that the muscle relaxes completely before another action potential can be initiated. - The long refractory period is crucial for maintaining the heart's **pumping efficiency** and preventing arrhythmias. *Cardiac muscle obeys the all or none law.* - This statement is **correct**. Individual **cardiac muscle cells** obey the **all-or-none law**; when a stimulus reaches threshold, the cell contracts fully. - The heart as a whole organ can grade its contraction force through recruitment of more fibers and the Frank-Starling mechanism, but at the cellular level, the all-or-none principle applies. *Cardiac muscle exhibits the Frank-Starling mechanism* - This statement is **correct**. The **Frank-Starling mechanism** describes the heart's ability to increase its force of contraction and stroke volume in response to an increase in **venous return** or end-diastolic volume. - This intrinsic regulatory mechanism allows the heart to match its output to the venous return, optimizing cardiac efficiency. *Cardiac muscle has automaticity and rhythmicity* - This statement is **correct**. **Automaticity** refers to the ability of specialized cardiac cells (e.g., in the sinoatrial node) to spontaneously generate action potentials without external nervous stimulation. - **Rhythmicity** is the regular, cyclical discharge of these action potentials, which drives the rhythmic beating of the heart.

Q: Which phases occur in the sequence: rapid filling followed by atrial contraction?

Rapid filling, Atrial contraction. ***Rapid filling, Atrial contraction*** - **Rapid filling** is the early diastolic phase when blood flows passively from the atria into the ventricles immediately after the AV valves open. - **Atrial contraction** (atrial systole) is the final phase of ventricular filling, contributing the last 20-30% of ventricular volume. - These two phases occur in this exact sequence during ventricular diastole, directly matching the question. *Atrial systole, Ejection* - While **atrial systole** is the same as atrial contraction, **ejection** does not immediately follow it. - Between atrial systole and ejection, there is an **isovolumic contraction** phase where ventricular pressure rises with all valves closed. - This sequence skips a critical intermediate phase. *Isovolumic contraction, Diastasis* - **Isovolumic contraction** occurs after atrial contraction but before ejection. - **Diastasis** is the slow filling phase that occurs between rapid filling and atrial contraction. - This sequence does not represent the phases mentioned in the question. *Isovolumic relaxation, Ejection* - **Isovolumic relaxation** occurs immediately after ejection ends, when ventricular pressure drops with all valves closed. - **Ejection** precedes isovolumic relaxation, not follows it. - This sequence is physiologically incorrect and unrelated to the question.

Q: What is the correct sequence of phases that follows isovolumic contraction in the cardiac cycle?

Ejection, Isovolumic relaxation. ***Ejection, Isovolumic relaxation*** - Following **isovolumic contraction**, ventricular pressure exceeds aortic pressure, causing the aortic valve to open and blood to be ejected from the ventricle. - After ejection, the aortic valve closes, and the ventricle relaxes without a change in volume, leading to **isovolumic relaxation**. *Rapid filling, Diastasis* - These phases occur during **ventricular diastole**, specifically after isovolumic relaxation, when the mitral valve opens and blood flows from the atria into the ventricles. - They represent the filling stages of the cardiac cycle, not the immediate phases after isovolumic contraction. *Diastasis, Atrial systole* - **Diastasis** is a late phase of ventricular filling, where blood flows slowly into the ventricles. - **Atrial systole** (atrial contraction) occurs at the very end of ventricular diastole, just before isovolumic contraction, to push the final volume of blood into the ventricles. *Atrial systole, Isovolumic contraction* - **Atrial systole** precedes **isovolumic contraction** in the cardiac cycle. - Isovolumic contraction is the phase where ventricular pressure rapidly increases while volume remains constant, just before blood is ejected.

Q: During the cardiac cycle, which phase corresponds to the period when the ventricles are contracting but no blood is being ejected?

Isovolumetric contraction phase. ***Isovolumetric contraction phase*** - During this phase, the **ventricular muscles contract**, leading to a rapid increase in intraventricular pressure. - Both the **mitral/tricuspid (AV) valves** and the **aortic/pulmonic (semilunar) valves** are closed, preventing blood ejection. *Isovolumetric relaxation phase* - This phase occurs during **diastole** when the ventricles are relaxing; therefore, no contraction is happening. - All four heart valves are closed, and ventricular pressure is decreasing, allowing for ventricular filling to occur next. *Ventricular ejection phase* - In this phase, the **semilunar valves are open**, and blood is actively ejected from the ventricles into the aorta and pulmonary artery. - This occurs *after* isovolumetric contraction, once ventricular pressure exceeds arterial pressure. *Atrial contraction phase* - This phase involves the **atria contracting** to push the last bit of blood into the ventricles, representing the final stage of ventricular filling. - The ventricles are relaxed and filling during this time, not contracting.

Q: The Bainbridge reflex is triggered by:

Stretching of the atria. ***Stretching of the atria*** - The Bainbridge reflex, also known as the **atrial reflex**, is a neurogenic reflex initiated by an increase in intravascular volume, which leads to **distension of the right atrial wall**. - This stretching activates **stretch receptors** in the atria, primarily the right atrium, sending signals via the vagus nerve to the medulla oblongata, resulting in an **increase in heart rate**. *Baroreceptor reflex activation* - The **baroreceptor reflex** is primarily triggered by changes in **arterial blood pressure**, detected by stretch receptors in the carotid sinus and aortic arch. - Its main function is to stabilize blood pressure, often leading to a **decrease in heart rate** in response to high blood pressure, which is opposite to the Bainbridge reflex. *Decreased venous return* - **Decreased venous return** would lead to reduced filling of the atria and ventricles, which would **not stimulate atrial stretch receptors** to activate the Bainbridge reflex. - Instead, decreased venous return typically **reduces cardiac output** and can trigger other compensatory mechanisms like vasoconstriction and increased heart rate via different pathways. *Increased ventricular activity* - While increased ventricular activity is a result of an increased heart rate, it is **not the trigger** for the Bainbridge reflex itself. - The reflex is initiated by changes in **atrial volume and stretch**, not ventricular action.

Q: In the cardiac pressure-volume loop, which phase corresponds to isovolumetric contraction?

Phase B to C. ***Phase B to C*** - This phase represents the period after the **mitral valve** closes and before the **aortic valve** opens, during which the ventricular pressure rapidly increases without a change in volume. - The start of this phase (point B) is marked by the closure of the **mitral valve**, signaling the beginning of systole. *Phase A to B* - This phase represents **diastolic filling**, where the ventricle fills with blood from the atrium, and its volume increases while pressure remains low. - The end of this phase (point B) indicates the **closure of the mitral valve**, marking the transition to isovolumetric contraction. *Phase C to D* - This phase represents **ejection**, where the **aortic valve** is open, and blood is expelled from the ventricle, causing a decrease in ventricular volume. - The end of this phase (point D) is marked by the **closure of the aortic valve**, signaling the end of systole. *Phase D to A* - This phase corresponds to **isovolumetric relaxation**, during which the ventricle relaxes, and pressure drops rapidly without a change in volume, after the **aortic valve** has closed and before the **mitral valve** opens. - The end of this phase (point A) is marked by the **opening of the mitral valve**, allowing ventricular filling to begin again.

Q: A 70-year-old male with a history of hypertension has elevated plasma renin levels. Which of the following physiological mechanisms is most likely responsible for his hypertension?

Increased aldosterone secretion. ***Increased aldosterone secretion*** - Elevated plasma renin levels lead to increased production of **angiotensin II**, which stimulates the adrenal cortex to secrete **aldosterone**. - **Aldosterone** causes sodium and water retention by the kidneys, leading to increased blood volume and consequently **hypertension**. *Decreased sympathetic activity* - **Decreased sympathetic activity** would typically lead to a reduction in heart rate, contractility, and peripheral vasoconstriction, which would tend to **lower blood pressure**, not cause hypertension. - Furthermore, decreased sympathetic activity would generally lead to **decreased renin release**, which contradicts the patient's elevated renin levels. *Increased natriuresis* - **Natriuresis** is the excretion of sodium in the urine; an increase in natriuresis would lead to **decreased total body sodium** and thus a **reduction in blood pressure**. - Elevated renin levels would promote sodium retention (via aldosterone), thus suppressing natriuresis, which is counter to this option. *Decreased angiotensin II levels* - **Elevated renin levels** would lead to **increased production of angiotensin I** and subsequently **increased angiotensin II levels**, not decreased. - **Angiotensin II** is a potent vasoconstrictor and stimulates aldosterone release, both of which contribute to hypertension.

Question 1

Which part of the action potential in cardiac pacemaker cells is primarily affected by calcium channel blockers?

Accepted Answer

Phase 0

Answer

Phase 1

Answer

Phase 2

Answer

Phase 3

Question 2

Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?

Accepted Answer

Norepinephrine

Answer

Dopamine

Answer

Acetylcholine

Answer

Epinephrine

Question 3

Which of the following statements about cardiac muscle is incorrect?

Accepted Answer

Cardiac muscle has a short refractory period.

Answer

Cardiac muscle obeys the all or none law.

Answer

Cardiac muscle exhibits the Frank-Starling mechanism

Answer

Cardiac muscle has automaticity and rhythmicity

Question 4

Which phases occur in the sequence: rapid filling followed by atrial contraction?

Accepted Answer

Rapid filling, Atrial contraction

Answer

Isovolumic contraction, Diastasis

Answer

Isovolumic relaxation, Ejection

Answer

Atrial systole, Ejection

Question 5

What is the correct sequence of phases that follows isovolumic contraction in the cardiac cycle?

Accepted Answer

Ejection, Isovolumic relaxation

Answer

Rapid filling, Diastasis

Answer

Atrial systole, Isovolumic contraction

Answer

Diastasis, Atrial systole

Question 6

How does pulmonary hypertension contribute to hemoptysis?

Accepted Answer

Increased bronchial artery pressure

Answer

Increased alveolar pressure

Answer

Elevated pulmonary venous pressure

Answer

Vasoconstriction of pulmonary arteries

Question 7

During the cardiac cycle, which phase corresponds to the period when the ventricles are contracting but no blood is being ejected?

Accepted Answer

Isovolumetric contraction phase

Answer

Isovolumetric relaxation phase

Answer

Ventricular ejection phase

Answer

Atrial contraction phase

Question 8

The Bainbridge reflex is triggered by:

Accepted Answer

Stretching of the atria

Answer

Baroreceptor reflex activation

Answer

Decreased venous return

Answer

Increased ventricular activity

Question 9

In the cardiac pressure-volume loop, which phase corresponds to isovolumetric contraction?

Accepted Answer

Phase B to C

Answer

Phase A to B

Answer

Phase C to D

Answer

Phase D to A

Question 10

A 70-year-old male with a history of hypertension has elevated plasma renin levels. Which of the following physiological mechanisms is most likely responsible for his hypertension?

Accepted Answer

Increased aldosterone secretion

Answer

Decreased sympathetic activity

Answer

Increased natriuresis

Answer

Decreased angiotensin II levels

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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