Which of the following is the main cation in the extracellular fluid (ECF)?

Correct Answer: B

Rationale: The correct answer is B: Sodium (Na). Sodium is the main cation in the extracellular fluid (ECF) due to its high concentration relative to other cations in the ECF. Sodium plays a crucial role in maintaining fluid balance, nerve function, and muscle contractions. Potassium (A) is the main intracellular cation, while Calcium (C) and Magnesium (D) are also important cations but are not the main cation in the ECF. Therefore, Sodium is the correct answer as it is the primary cation present in the extracellular fluid.

Correct Answer: C

Rationale: The normal arterial blood pH is around 7.35-7.45. Option C, 7.45 falls within this range, making it the correct answer. A pH of 7.25 (option A) is considered acidic, while a pH of 7.55 (option D) is alkaline, both outside the normal range. Option B, 7.35, is towards the lower end of the normal range but still within it. Overall, option C is the most appropriate choice as it aligns with the typical arterial blood pH range.

Correct Answer: B

Rationale: Certainly! The correct answer is B: Promote sodium and water excretion. Atrial natriuretic peptide (ANP) is released by the heart in response to high blood pressure or volume overload. ANP acts to dilate blood vessels, increase glomerular filtration rate, and promote sodium and water excretion by the kidneys. This results in a decrease in blood volume and blood pressure. Choices A, C, and D are incorrect because ANP does not have the function of increasing blood pressure, retaining sodium and water, or increasing thirst.

Correct Answer: B

Rationale: The correct answer is B: High serum sodium. Dehydration leads to an increase in serum sodium concentration due to the loss of water without a proportional loss of sodium. This results in hypernatremia. Low hematocrit (A) is seen in anemia, not dehydration. Low serum osmolality (C) and low serum potassium (D) are not typically associated with dehydration.

Correct Answer: A

Rationale: Rationale: Low serum magnesium levels can lead to cardiac arrhythmias due to its role in regulating heart muscle function. Magnesium deficiency can disrupt electrical conduction in the heart, potentially causing arrhythmias. Hypokalemia (Choice B), hypercalcemia (Choice C), and hypertension (Choice D) are not directly associated with low magnesium levels. Potassium and calcium imbalances have different physiological implications, while hypertension is more commonly linked to sodium levels. Therefore, the correct answer is A: Cardiac arrhythmias.