Cardiac Physiology Exam Quiz! MCQ

The sinoatrial (SA) node is responsible for initiating the electrical impulses that regulate the heart's rhythm. It acts as the natural pacemaker of the heart and sets the pace for the rest of the cardiac conduction system. The SA node has the most prominent prepotential, which is the gradual depolarization that occurs before an action potential is generated. This prepotential allows the SA node to reach the threshold for firing an action potential and initiate the contraction of the heart.

The second heart sound is caused by the closure of the aortic and pulmonary valves. This occurs during diastole, when the ventricles are relaxed and filling with blood. As the ventricles fill, the pressure inside them increases, causing the valves to close. This closure produces the second heart sound, which can be heard as a "dub" sound. The closure of the mitral and tricuspid valves occurs during systole, when the ventricles contract to pump blood out of the heart. Vibrations in the ventricular wall and ventricular filling are not directly responsible for the second heart sound. Retrograde flow in the vena cava is unrelated to the closure of the valves.

K+ channels contribute to the repolarization phase of the action potential of ventricular muscle fibers. During the action potential, K+ channels open, allowing K+ ions to move out of the cell, leading to repolarization. This movement of K+ ions helps restore the cell's resting membrane potential and prepares it for the next action potential. The other channels listed (Na+, Cl-, Ca2+, and HCO3-) are not primarily involved in the repolarization phase of the action potential.

The relatively slow conduction through the atrioventricular (AV) node allows sufficient time for filling of the ventricles. The AV node serves as a delay mechanism, slowing down the electrical signal between the atria and ventricles. This delay ensures that the atria have enough time to contract and pump blood into the ventricles before the ventricles contract. This allows for efficient filling of the ventricles with blood, ensuring an adequate cardiac output.

The cardiac output of a ventricle can be calculated by multiplying the stroke volume (the volume of blood pumped out of the ventricle with each heartbeat) by the heart rate. In this case, the stroke volume can be calculated by multiplying the ventricle volume (100 ml) by the ejection fraction (75%), which gives us a stroke volume of 75 ml. The heart rate is given as 70 beats/min. Therefore, the cardiac output is 75 ml/beat x 70 beats/min = 5250 ml/min, which is equivalent to 5.25 L/min.

During moderate exercise, the body's demand for oxygen increases, leading to vasodilation in the muscles and a decrease in total peripheral resistance (TPR). TPR is the resistance to blood flow in the systemic circulation, and when it decreases, it allows for easier blood flow and delivery of oxygen to the muscles. Arteriovenous O2 difference, heart rate, cardiac output, and pulse pressure typically increase during exercise to meet the increased oxygen demands of the body.

The correct answer is an increase in Na+ conductance. In the sinoatrial (SA) node, phase 4 depolarization is the pacemaker potential responsible for initiating the heartbeat. During this phase, there is an increase in Na+ conductance, which leads to the influx of Na+ ions into the cell. This causes the membrane potential to become more positive, leading to depolarization and the generation of an action potential. This increase in Na+ conductance is essential for the SA node's ability to spontaneously generate electrical impulses and regulate the heart's rhythm.

During Phase 2 of the ventricular action potential, the conductance to Ca2+ is highest. This phase is known as the plateau phase and is characterized by a slow influx of calcium ions into the cell. This influx of calcium ions helps to sustain the depolarization of the cell membrane, prolonging the action potential. The high conductance to Ca2+ during Phase 2 is essential for the proper contraction of the ventricles and the pumping of blood.

Starling's law of the heart states that the force of contraction of the heart increases as the volume of blood returning to the heart, known as venous return, increases. This means that when there is an increase in venous return, the heart will pump out a greater volume of blood, resulting in an increase in cardiac output. Therefore, the given answer correctly explains the relationship between Starling's law and the increase in cardiac output that occurs when venous return is increased.

The second heart sound is caused by the closure of the aortic and pulmonic valves. The aortic valve is located on the left side of the heart and the pulmonic valve is located on the right side. During inspiration, there is increased blood flow to the lungs, causing the pulmonic valve to close slightly later than the aortic valve. This time delay in closure results in the splitting of the second heart sound.

The cardiac output of the right side of the heart is equal to the cardiac output of the left side of the heart. This means that both sides of the heart pump the same amount of blood, resulting in an equal distribution of cardiac output. Therefore, the correct answer is 100%.

The arterioles have the greatest resistance in the circulation. Resistance is a measure of how difficult it is for blood to flow through a blood vessel. The arterioles are small blood vessels that regulate blood flow to capillaries. They have a smaller diameter compared to arteries and veins, which increases the resistance to blood flow. This resistance helps to regulate blood pressure and control the distribution of blood to different tissues and organs. Therefore, the greatest pressure decrease occurs across the arterioles due to their high resistance.

Phase 4 of the ventricular action potential coincides with diastole. Diastole is the relaxation phase of the cardiac cycle when the ventricles are filling with blood. During phase 4, the membrane potential of the ventricular cells is relatively stable and at a negative resting potential. This allows for the passive filling of the ventricles with blood from the atria. Once the ventricles are filled, the next phase (phase 0) begins, which is the depolarization phase and initiates systole.

phase 4 is REST, phase 0 is the steep upstroke on the curve

When a person moves from a supine position to a standing position, the body needs to adjust to maintain blood flow to the brain and prevent a drop in blood pressure. One compensatory change that occurs is increased contractility of the heart. This means that the heart pumps with more force, allowing it to maintain an adequate cardiac output and blood pressure. This compensatory change helps to counteract the effects of gravity and ensure proper blood flow to the brain and other organs while standing.

Isovolumic Relaxation - The ventricle is now at rest and because both valves are closed, the
volume is constant and at its lowest value (see ventricular volume curve).

The ventricles of the heart undergo complete depolarization during the QRS complex on the electrocardiogram (ECG). This brief but critical phase represents the moment when the electrical signal rapidly spreads through the ventricular muscle cells, initiating their contraction and the subsequent pumping of blood to the rest of the body. The QRS complex is a distinctive feature on the ECG, signaling the onset of ventricular depolarization, while other parts of the ECG waveform represent different phases of the cardiac cycle, such as atrial depolarization, repolarization, and relaxation.

During exercise, the local metabolites produced by the skeletal muscles, such as adenosine, potassium ions, and carbon dioxide, cause the arterioles in the skeletal muscles to dilate. This dilation increases blood flow to the muscles, allowing for increased oxygen and nutrient delivery, as well as the removal of waste products. As a result, the total peripheral resistance (TPR) decreases, as the resistance to blood flow in the skeletal muscle arterioles decreases. This allows for improved circulation and oxygenation of the muscles during exercise.

During exercise, the body requires more oxygen to meet the increased metabolic demands. The man consumes 1.8 L of oxygen per minute, which is the amount of oxygen he takes in. The arterial O2 content is 190 ml/L, indicating the amount of oxygen in his arterial blood. The O2 content of his mixed venous blood is 134 ml/L, indicating the amount of oxygen in his venous blood. The difference between the arterial and venous oxygen content represents the amount of oxygen consumed by the tissues. By dividing the oxygen consumption by the difference in oxygen content, we can calculate the cardiac output. In this case, the cardiac output is approximately 32 L/min.

When the ejection fraction increases, it means that a larger proportion of blood is being pumped out of the heart with each contraction. This indicates that the heart is able to pump more efficiently. Since end-systolic volume refers to the amount of blood left in the heart after contraction, an increase in ejection fraction would result in a decrease in end-systolic volume.

The fourth heart sound is caused by ventricular filling. During this phase, the ventricles are filling with blood and preparing to contract. The sound is produced by the vibrations created as blood rushes into the ventricles and causes the valves to close. This sound is typically heard during late diastole, just after the atria contract and blood is pushed into the ventricles.

During isovolumetric ventricular relaxation, the mitral valve opens. This phase occurs after the ventricles have contracted and ejected blood into the aorta and pulmonary artery. The mitral valve opens to allow blood to flow from the left atrium into the relaxed left ventricle, preparing for the next cardiac cycle.

Pulse pressure is determined by stroke volume. Pulse pressure is the difference between the systolic and diastolic blood pressure. Stroke volume is the amount of blood pumped out of the heart with each heartbeat. When stroke volume increases, more blood is ejected into the arteries, leading to a higher systolic pressure and therefore a larger pulse pressure. Conversely, if stroke volume decreases, there is less blood being pumped into the arteries, resulting in a lower systolic pressure and a smaller pulse pressure. Therefore, pulse pressure is directly influenced by stroke volume.

The afterload refers to the resistance that the ventricle must overcome in order to eject blood. If the afterload is greater in the left ventricle compared to the right ventricle, it means that the left ventricle has to work harder to overcome this resistance. This results in the left ventricle performing more work compared to the right ventricle.

The renal artery is the blood vessel that supplies oxygenated blood to the kidneys. The kidneys play a crucial role in regulating blood pressure. When blood flows through the renal artery, it undergoes filtration and reabsorption processes in the kidneys. These processes help maintain the balance of fluids and electrolytes in the body, which in turn helps regulate blood pressure. Therefore, the systolic blood pressure is the highest at the renal artery site due to the kidneys' role in blood pressure regulation.