Which valves close during ventricular systole and open during ventricular diastole?

Correct Answer: B

Rationale: During ventricular systole, the atrioventricular valves (AV valves) close to prevent blood from flowing back into the atria. This allows the ventricles to contract and pump blood out of the heart. During ventricular diastole, the AV valves open to allow blood to flow from the atria into the ventricles. The other choices are incorrect because semilunar valves (choice A) close to prevent blood from flowing back into the ventricles during ventricular diastole, and the mitral valve (choice C) and tricuspid valve (choice D) are specific types of AV valves.

Correct Answer: A

Rationale: The correct answer is A: Excitability. Excitability refers to the ability of cardiac cells to respond to an impulse by generating an action potential and contracting. This is the fundamental property that allows the heart to beat. Contractility (B) is the ability of cardiac muscle to contract once stimulated, but it does not specifically refer to the response to an impulse. Rhythmicity (C) is the ability of cardiac cells to generate spontaneous electrical impulses, not directly related to responding to an impulse. Conductivity (D) is the ability of cardiac cells to transmit electrical impulses, not specifically related to the response of cells contracting.

Correct Answer: A

Rationale: Contractility is the correct answer as it specifically refers to the ability of the heart muscle to contract with a given force without changing its length. This term is used to describe changes in the inotropic state of the muscle, which affects the strength of contraction. Excitability, refractoriness, and automaticity do not directly relate to changes in muscle contraction force without altering fiber length. Excitability is the ability of the muscle to respond to stimuli, refractoriness is the recovery period after a muscle contraction, and automaticity is the ability of certain cells to generate spontaneous electrical activity.

Correct Answer: A

Rationale: The correct answer is A: Carotid body. The carotid body is the major chemoreceptor of the heart, detecting changes in oxygen levels in the blood. It sends signals via the glossopharyngeal nerve to regulate heart rate and blood pressure. The aortic body primarily monitors blood pressure, not chemoreception. The vagus nerve plays a role in regulating heart rate but is not a chemoreceptor. The SA node is the pacemaker of the heart, responsible for initiating the electrical signals for heart contraction, not chemoreception. Therefore, the carotid body is the correct choice for the major chemoreceptor of the heart.

Correct Answer: A

Rationale: Automaticity is the ability of cardiac cells to generate an electrical impulse spontaneously without external stimulation. It is a fundamental property of specialized cardiac cells like pacemaker cells. Contractility refers to the ability of muscle cells to contract in response to an electrical stimulus. Conductivity is the ability of cardiac cells to transmit electrical impulses. Refractoriness is the period during which cardiac cells are unable to respond to a new stimulus. Therefore, in this context, the correct answer is A: Automaticity.