Correct Answer: D

Rationale: The sinoatrial node (SA node) in the atrium is indeed responsible for initiating the electrical impulse that starts the heart's rhythm. The SA node is known as the heart's natural pacemaker. Choices A, B, and C are incorrect because while the Purkinje fibers, bundle branches, and atrioventricular node play crucial roles in the conduction of the electrical impulse throughout the heart, the SA node is specifically responsible for initiating this impulse.

Correct Answer: A

Rationale: The correct answer is A: Tachycardia. Tachycardia, which is an increased heart rate, is a classic clinical manifestation of hyperthyroidism. In hyperthyroidism, there is an excess production of thyroid hormones, leading to an increased metabolic rate. This increased metabolism can cause symptoms such as a rapid heart rate. Choices B, C, and D are incorrect because constipation, weight gain, and fatigue are more commonly associated with hypothyroidism, where there is a deficiency of thyroid hormones leading to a slower metabolic rate.

Correct Answer: A

Rationale: The correct answer is A: Decreased plasma proteins. Edema can be caused by decreased plasma proteins, which reduce the osmotic pressure that keeps fluid in the blood vessels. Hypotension (choice B) is low blood pressure and is not a direct cause of edema. Dehydration (choice C) involves a lack of body fluid, but it is not a direct cause of edema. Polyuria (choice D) is excessive urination and not a direct cause of edema.

Correct Answer: B

Rationale: The correct answer is B: Insufficient circulating blood volume. Hypovolemia is a condition characterized by a decrease in the volume of blood plasma. This reduction in circulating blood volume can lead to inadequate perfusion of tissues and organs, potentially resulting in shock if left untreated. Choices A, C, and D are incorrect because increased urine retention, bounding peripheral pulses, and crackles auscultated in the lungs are not typical manifestations of hypovolemia.

Correct Answer: C

Rationale: The correct answer is C. Influenza immunization works by introducing a weakened or inactivated form of the virus into the body, allowing the immune system to recognize it as foreign. This recognition triggers the production of antibodies specific to the virus. Choice A is incorrect as the virus in the vaccine does not remain in the body until the end of the season. Choice B is incorrect as an attenuated virus does not cause immune system suppression but rather stimulates an immune response. Choice D is incorrect because the vaccine does not stay at the injection site but rather prompts a systemic immune response throughout the body.