If Mr. Simpson begins to have pain that is worse with inspiration and relieved by sitting up, your assessment of his situation is that he has developed

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: A

Rationale: The correct answer is A: Right atrium. The right atrium receives venous blood returning to the heart via the superior and inferior vena cava. Blood from the body enters the right atrium through the vena cavae, then flows into the right ventricle and eventually gets pumped to the lungs for oxygenation. Choices B, C, and D are incorrect because the left atrium receives oxygenated blood from the lungs, the right ventricle pumps blood to the lungs, and the left ventricle pumps oxygenated blood to the rest of the body.

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: SA node. The SA node is known as the natural pacemaker of the heart because it initiates the electrical impulses that regulate the heartbeat. It is located in the right atrium and generates the electrical signals that coordinate the heart's contractions. The other choices, B: AV node, C: Purkinje fibers, and D: Atria, do play roles in the heart's electrical conduction system, but they do not serve as the primary pacemaker. The AV node delays the electrical impulses, the Purkinje fibers distribute the impulses to the heart muscles, and the atria contract to pump blood into the ventricles. However, none of these structures serve as the primary pacemaker like the SA node does.

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.