A&p Chapter 20 - The Cardiovascular System: The Heart

The left ventricle of the heart has the thickest myocardium compared to the other chambers. This is because the left ventricle is responsible for pumping oxygenated blood to the rest of the body, which requires more forceful contractions. The thick myocardium allows the left ventricle to generate the necessary pressure to propel blood throughout the systemic circulation.

The Frank-Starling law of the heart states that the more the cardiac muscle fibers are stretched during diastole, the more forcefully they contract during systole. This law helps to equalize the output of the right and left ventricles, ensuring that the same volume of blood flows to both the systemic and pulmonary circulations. Therefore, the statement is true.

The correct route of blood through the heart starts with the right atrium, where deoxygenated blood from the systemic circulation enters. From there, it passes through the tricuspid valve into the right ventricle. The right ventricle then pumps the blood through the pulmonary semilunar valve into the pulmonary circulation, where it picks up oxygen. The oxygenated blood then returns to the heart through the left atrium. It passes through the mitral valve into the left ventricle, which pumps it out through the aortic semilunar valve back into the systemic circulation.

The correct pathway for conduction of an action potential through the heart starts with the SA node (sinoatrial node), which is the natural pacemaker of the heart. The electrical signal then travels to the AV node (atrioventricular node), which acts as a delay to allow the atria to contract before the ventricles. From the AV node, the signal passes through the AV bundle (bundle of His) and then into the bundle branches. Finally, the signal spreads through the Purkinje fibers, which are specialized cardiac muscle fibers that rapidly transmit the electrical signal to the ventricles, causing them to contract.

During systole, the heart muscles contract, pushing blood out of the chambers and into the arteries. This is the phase of heart contraction. On the other hand, during diastole, the heart muscles relax, allowing the chambers to fill with blood. This is the phase of relaxation.

The correct answer is False. In auscultation, the "lubb" sound represents the closing of the atrioventricular valves (mitral and tricuspid valves), while the "dupp" sound represents the closing of the semilunar valves (aortic and pulmonary valves).

The correct answer is 1, 2, and 4. The autonomic nervous system (ANS) regulates heart rate, and its control center is located in the cardiovascular center of the medulla oblongata in the brainstem (1). Proprioceptor input, which is sensory information from muscles and joints, is a major stimulus for the rapid increase in heart rate during physical activity (2). The vagus nerves release acetylcholine, not norepinephrine, which slows down the heart rate (3 is false). Hormones from the adrenal medulla, such as epinephrine, and the thyroid gland can increase heart rate (4 is true). Hypothermia, which is low body temperature, actually decreases heart rate, so statement 5 is false. Therefore, the correct answer is 1, 2, and 4.

The stroke volume is the amount of blood pumped out of the heart with each heartbeat. To calculate the stroke volume, we need to know the cardiac output and the heart rate. The cardiac output is given as 5.0 liters per minute and the heart rate is given as 50 beats per minute. To find the stroke volume, we can divide the cardiac output by the heart rate: 5.0 liters per minute / 50 beats per minute = 0.1 liters per beat = 100 mL. Therefore, the stroke volume is 100 mL.

The correct answer is coronary sulcus. The coronary sulcus is the external boundary between the atria and ventricles of the heart. It is a groove that encircles the heart and contains the coronary blood vessels, including the right coronary artery and the left coronary artery. The interventricular septum separates the ventricles, the interatrial septum separates the atria, and the anterior and posterior interventricular sulci are grooves on the surface of the heart that mark the boundary between the left and right ventricles.

Increased K+ in the interstitial fluid would not increase stroke volume. Stroke volume is the amount of blood pumped by the heart with each contraction. Increased Ca2+ in the interstitial fluid, epinephrine, increase in venous return, and a slow resting heart rate can all increase stroke volume. However, increased K+ in the interstitial fluid would not have this effect.

The correct answer is 2, 3, 4, and 5. This means that the binding of Ca2+ to troponin allows the interaction of actin and myosin filaments, resulting in contraction. Repolarization occurs when the voltage-gated K+ channels open and calcium channels are closing. Opening of voltage-gated fast Na+ channels results in depolarization. Opening of voltage-gated slow Ca2+ channels results in a period of maintained depolarization, known as the plateau.