The most important regulator of electrolyte concentrations in extracellular fluids is ________.

Correct Answer: B

Rationale: The correct answer is B: aldosterone. Aldosterone is a hormone produced by the adrenal glands that plays a key role in regulating electrolyte concentrations in extracellular fluids. It specifically acts on the kidneys to increase the reabsorption of sodium and water while promoting the excretion of potassium. This helps to maintain the balance of electrolytes in the body. Insulin, glucagon, and cortisol do not directly regulate electrolyte concentrations in extracellular fluids. Insulin regulates blood sugar levels, glucagon regulates glucose release from the liver, and cortisol is involved in stress response and metabolism. Therefore, aldosterone is the most important regulator of electrolyte concentrations in extracellular fluids.

Correct Answer: A

Rationale: The correct answer is A: humoral. Humoral regulation refers to the control of physiological processes by substances in the blood, such as hormones. In this case, the production and release of hormones in response to a chemical like calcium is an example of humoral mechanism. This choice is correct because it specifically involves the blood-borne substances affecting hormone production. Choices B, C, and D are incorrect because neural regulation (B) involves the nervous system controlling physiological processes, sensory regulation (C) refers to sensory input influencing responses, and hormonal regulation (D) involves feedback loops within the endocrine system, not directly related to blood-borne substances like calcium.

Correct Answer: C

Rationale: The correct answer is C: diabetes insipidus. The inability to produce ADH (antidiuretic hormone) results in diabetes insipidus, characterized by excessive thirst and urination. ADH plays a crucial role in regulating water retention by the kidneys. Without ADH, the kidneys are unable to concentrate urine, leading to increased urine output and dehydration. A: Diabetes mellitus is not caused by the inability to produce ADH. It is a condition characterized by high blood sugar levels due to insufficient insulin production or ineffective use of insulin. B: Uterine contractions are not related to the production of ADH. Uterine contractions are primarily controlled by hormones such as oxytocin during labor. D: Decreased urine volume is the opposite of what occurs in diabetes insipidus. In this condition, there is an increase in urine volume due to the inability to concentrate urine.

Correct Answer: B

Rationale: Calcitonin is the correct answer because it is released from the thyroid gland in response to high blood calcium levels to deposit the excess calcium into the bones, decreasing blood calcium levels. Parathyroid hormone (A) works in the opposite way, increasing blood calcium levels by releasing calcium from bones. Oxytocin (C) is a hormone involved in labor and breastfeeding, not calcium regulation. Glucagon (D) is released from the pancreas to increase blood glucose levels, not calcium levels. Therefore, calcitonin is the most suitable choice for regulating high blood calcium levels by promoting calcium deposition in the bones.

Correct Answer: D

Rationale: Step-by-step rationale: 1. Cushing syndrome is characterized by hypersecretion of adrenal cortex hormones, not hyposecretion. 2. Option D states hyposecretion, which is incorrect for Cushing syndrome. 3. Trunk obesity, moon-shaped face, and alkalosis (basic blood pH) are characteristic features of Cushing syndrome. 4. Thus, option D is the correct answer because it is not a true characteristic of Cushing syndrome. Summary: Option D is incorrect because Cushing syndrome is associated with hypersecretion of adrenal cortex hormones, not hyposecretion. Options A, B, and C are true characteristics of Cushing syndrome, making them incorrect choices.