Cardiovascular System MCQs

Cardiac Output (C.O.) refers to the amount of blood pumped by each ventricle of the heart in one minute. It is typically measured in liters per minute. This measurement is important in assessing the overall efficiency of the heart and its ability to meet the body's demands for oxygen and nutrients. A normal resting cardiac output is around 5 liters per minute, with each ventricle contributing approximately 2.5 liters. In certain conditions, such as exercise or exposure to cold, the cardiac output may increase to meet the increased demand for oxygen and heat distribution. However, denervation of the heart, which involves the interruption of nerve supply, can lead to a lack of response in cardiac output during exercise.

When the end-diastolic ventricular filling pressure rises, it means that there is an increased volume of blood filling the left ventricle during diastole. This increased volume stretches the ventricular muscle fibers, leading to a stronger contraction during systole. As a result, the strength of contraction of the left ventricular muscle increases. This is known as the Frank-Starling mechanism, which ensures that the heart pumps out the same amount of blood that it receives.

When the parasympathetic nervous system, specifically the parasympatheticus, is activated, it leads to bradycardia. Bradycardia refers to a slower than normal heart rate. This occurs because the parasympatheticus releases acetylcholine, which slows down the electrical signals in the heart and decreases the heart rate. As a result, the heart beats at a slower pace, leading to bradycardia.

Sino-atrial node cells are able to self-generate impulses because their membrane potential is unstable. This means that these cells have the ability to spontaneously depolarize and generate electrical impulses without any external stimulation. This is a crucial characteristic of the sino-atrial node, as it serves as the natural pacemaker of the heart, initiating the electrical signals that regulate the heartbeat. The unstable membrane potential allows for the regular and rhythmic contractions of the heart, ensuring its proper functioning.

When the end-diastole length of the ventricular fiber increases, it means that the heart muscle is stretched more during diastole, which allows it to contract more forcefully during systole. This increased contractility leads to a higher stroke volume, which is the amount of blood pumped out of the left ventricle with each heartbeat. Therefore, the correct answer is that the left ventricular stroke volume increases when the end-diastole length of the ventricular fiber increases.

When the vagus nerve is stimulated, it releases acetylcholine, which binds to muscarinic receptors on the heart. This activation leads to a decrease in heart rate through a series of intracellular signaling pathways. Therefore, the correct answer is vagus is stimulated.

When the arm is raised above head level, the gravitational force causes blood to flow downwards, away from the brachial artery. This reduces the amount of blood in the artery and therefore decreases the pressure within it. As a result, the pressure falls when the arm is raised above head level.

As the distance from the heart increases, the arterial walls contain relatively more smooth muscle fibers than elastic. This is because the smooth muscle fibers provide the necessary contractility and control of blood flow in the smaller arteries and arterioles, which are located further away from the heart. The elastic fibers, on the other hand, are more abundant in the larger arteries closer to the heart, allowing them to stretch and recoil to accommodate the pulsatile flow of blood.

Diastolic blood pressure is the pressure in the arteries when the heart is at rest between beats. Peripheral vascular resistance refers to the resistance that the blood encounters as it flows through the blood vessels. It is determined by factors such as the diameter of the blood vessels, the elasticity of the vessel walls, and the viscosity of the blood. When peripheral vascular resistance is high, it causes an increase in diastolic blood pressure. Therefore, peripheral vascular resistance is the main factor determining diastolic blood pressure.

The absolute refractory period in the heart refers to the period of time during which the cardiac muscle is unable to respond to any additional stimulation, regardless of the strength of the stimulus. This period lasts until the end of the first third of cardiac relaxation, meaning that the heart cannot be excited or contract during this time. This is important for ensuring that the heart has enough time to relax and refill with blood before the next contraction.

Excessive secretion of aldosterone can cause systemic hypertension. Aldosterone is a hormone produced by the adrenal glands that regulates the balance of salt and water in the body. When there is an excessive secretion of aldosterone, it can lead to an increase in sodium reabsorption and water retention, which in turn raises blood pressure. This can occur in conditions such as primary aldosteronism or adrenal adenoma, where there is an abnormal overproduction of aldosterone.

The first heart sound corresponds in time with a rise in ventricular pressure. This is because the first heart sound, also known as S1, is produced by the closure of the atrioventricular valves (mitral and tricuspid valves) when the ventricles contract and the pressure inside them increases. This closure prevents the backflow of blood into the atria and marks the beginning of systole, the contraction phase of the cardiac cycle.

Arterioles form the resistance against the ventricular contractions. This means that they regulate the flow of blood from the heart to the capillaries by constricting or dilating. By constricting, arterioles increase resistance and reduce blood flow, while by dilating, they decrease resistance and increase blood flow. This resistance is important for maintaining blood pressure and ensuring that blood is distributed appropriately to different tissues and organs in the body.

In atrial fibrillation, the normal electrical signals in the heart are disrupted, causing the atria to quiver instead of contracting properly. This results in the absence of coordinated atrial activity, which is reflected in the electrocardiogram (ECG) as no evidence of atrial activity. Additionally, in atrial fibrillation, the ventricular rate (heartbeat) is typically lower than the atrial rate because the irregular and chaotic electrical signals from the atria fail to reach and fully activate the ventricles. Therefore, the correct answer is "The ventricular rate is lower than the atrial rate."

During exercise, there is an increased demand for oxygen and nutrients in the skeletal muscles. This leads to vasodilation in the exercising muscles, allowing for increased blood flow to meet the increased demand. However, this vasodilation can also lead to a decrease in blood pressure. In order to maintain blood pressure and ensure adequate blood flow to other organs, reflex vasoconstriction occurs in other vascular beds. This vasoconstriction helps redistribute blood flow and maintain overall blood pressure during exercise.