Correct Answer: A

Rationale: Pulmonary hypertension is a condition characterized by the thickening and stiffening of the arteries in the lungs, resulting in elevated blood pressure in the pulmonary arteries. This condition is distinct from the other choices provided. Pulmonary fibrosis involves scarring of lung tissue, pulmonary embolism is a blockage in the pulmonary artery, and pulmonary edema is the accumulation of fluid in the lungs.

Correct Answer: A

Rationale: Mitral regurgitation is the condition where the heart's mitral valve does not close properly, allowing blood to leak backward into the left atrium. This can result in symptoms like shortness of breath and fatigue. Choices B, C, and D are incorrect because aortic stenosis, tricuspid regurgitation, and pulmonary hypertension involve different heart valves or conditions, not the mitral valve specifically.

Correct Answer: A

Rationale: The correct answer is to hold the digoxin and notify the healthcare provider. A potassium level of 2.8 mEq/L indicates hypokalemia, which can increase the risk of digoxin toxicity. Holding the medication and informing the healthcare provider is crucial to prevent adverse effects. Choice B is incorrect because increasing the dose of digoxin would further raise the risk of toxicity. Choice C is incorrect as continuing the current dose could exacerbate the toxicity risk. Choice D is incorrect because administering potassium supplements alone is not sufficient to address the potential digoxin toxicity; the first step should be to hold the digoxin and seek further guidance.

Correct Answer: A

Rationale: The correct answer is A, the carotid body. The carotid body is the major chemoreceptor of the heart responsible for detecting changes in blood oxygen, carbon dioxide, and pH levels. This specialized structure helps regulate the cardiovascular system's response to maintain appropriate oxygen levels in the blood. Choices B, C, and D are incorrect as they are not directly involved in chemoreception in the heart. The aortic body is primarily involved in blood pressure regulation, the vagus nerve is a cranial nerve responsible for parasympathetic innervation, and the SA node is known as the heart's natural pacemaker.

Correct Answer: A

Rationale: Heart block is the correct answer because it specifically refers to a condition where the heart's electrical impulses are delayed or blocked, resulting in a slower or irregular heartbeat. Tachycardia (choice B) is a condition characterized by a fast heart rate, Bradycardia (choice C) is a slow heart rate, and Arrhythmia (choice D) is a general term used to describe any abnormal heart rhythm, which may or may not involve delays or blocks in electrical impulses.