Oxytocin:

Correct Answer: A

Rationale: Oxytocin is a hormone produced by the hypothalamus and released by the pituitary gland. In the bloodstream, oxytocin is mostly bound to a carrier protein called neurophysin. This binding helps to protect oxytocin from being degraded too quickly in the bloodstream, thus allowing it to exert its effects on target tissues such as the uterus and mammary glands. Oxytocin plays important roles in stimulating uterine contractions during labor, facilitating milk letdown during breastfeeding, and promoting social bonding and emotional connections.

Correct Answer: D

Rationale: The most common cause of Cushing's syndrome is a pituitary adenoma, specifically a corticotroph adenoma. This adenoma leads to excessive secretion of adrenocorticotropic hormone (ACTH) by the pituitary gland, which in turn stimulates the adrenal glands to produce high levels of cortisol. This results in the symptoms and signs characteristic of Cushing's syndrome. Pituitary adenomas are responsible for around 70-80% of cases of Cushing's syndrome, making it the most common cause.

Correct Answer: D

Rationale: Increased serum aldosterone level is typically associated with conditions such as Conn's syndrome or primary hyperaldosteronism. These conditions lead to an excess of aldosterone, which results in increased sodium resorption and potassium excretion by the kidneys. This imbalance can lead to hypertension (Choice A), hypernatraernia (elevated sodium level) (Choice B), and hypokalaemia (low potassium level) (Choice C). However, metabolic acidosis (Choice D) is not directly associated with increased aldosterone levels. Instead, metabolic acidosis may be seen in conditions like renal tubular acidosis or diabetic ketoacidosis.

Correct Answer: C

Rationale: Tetany is a condition characterized by involuntary muscle spasms and contractions due to low levels of calcium in the blood. The signs associated with tetany include Trousseau's sign, which is the carpal spasm elicited by inflating a blood pressure cuff above systolic pressure, and Chvostek's sign, which is the facial muscle spasm elicited by tapping on the facial nerve. Peroneal sign is not specifically associated with tetany but can be seen in conditions like peroneal nerve injury. Erb's sign, on the other hand, is not a recognized sign of tetany. It is associated with Erb's palsy, a condition resulting from injury to the brachial plexus nerves, typically during childbirth. Tinel's sign, which is a tingling sensation elicited by tapping over a compressed nerve, is also not a characteristic sign of tetany.

Correct Answer: A

Rationale: Cirrhosis is not a potential cause of elevated LDL cholesterol levels. The liver plays a significant role in cholesterol metabolism, and liver disease like cirrhosis can actually lead to decreased levels of LDL cholesterol. Elevated LDL cholesterol levels can be caused by conditions such as hypothyroidism, nephrotic syndrome, or the use of certain medications like thiazide diuretics.