Which electrolyte is important in the formation of the thyroid hormones?

Correct Answer: B

Rationale: Iodine is the correct answer because it is essential for the synthesis of thyroid hormones. The thyroid gland incorporates iodine into thyroid hormones such as thyroxine (T4) and triiodothyronine (T3). These hormones are crucial for regulating metabolism, growth, and development. Sodium, iron, and chloride are not directly involved in the formation of thyroid hormones, making them incorrect choices.

Correct Answer: A

Rationale: The correct answer is A: Kidneys. The kidneys play a crucial role in regulating the amount of sodium in the body. They achieve this by filtering blood and controlling the excretion or reabsorption of sodium. The small intestine is primarily responsible for nutrient absorption, not sodium regulation. The large intestine is mainly involved in water absorption and waste elimination, not sodium balance. The skin helps regulate body temperature through sweating and does not directly regulate sodium levels.

Correct Answer: C

Rationale: Aldosterone increases the reabsorption of sodium in the kidneys, which leads to an increase in blood volume and blood pressure. Choice A is incorrect as aldosterone does not regulate body temperature. Choice B is incorrect as aldosterone increases blood pressure by increasing sodium reabsorption. Choice D is incorrect as aldosterone promotes water retention by increasing sodium reabsorption.

Correct Answer: B

Rationale: The correct answer is 'Intracellular fluid.' Intracellular fluid refers to the fluid contained within the cells, constituting a significant portion of the body's total water content. Choices A, C, and D are incorrect. Plasma is the liquid component of blood outside the cells, interstitial fluid is the fluid surrounding cells in tissues, and the combination of plasma and intracellular fluid is not the specific term for the fluid inside the cell.

Correct Answer: C

Rationale: The correct answer is C: 'plasma and interstitial fluid.' Extracellular fluid consists of all body fluids outside the cells, primarily including plasma (the liquid component of blood) and interstitial fluid (the fluid between cells). Choices A, B, and D are incorrect because intracellular fluid is located within the cells, not in the extracellular fluid compartment.