**Question:** Appetite is stimulated by all except

A. Insulin
B. Leptin
C. Thyroid hormones
D. Cortisol

**Correct Answer:** D. Cortisol

**Core Concept:** Appetite is regulated by a complex interplay of hormones and neurotransmitters in the brain and peripheral tissues. Several hormones and neurotransmitters play a role in stimulating or inhibiting appetite.

**Why the Correct Answer is Right:** Cortisol is a glucocorticoid hormone produced by the adrenal cortex in response to stress or high blood glucose levels. Its primary function is to maintain glucose homeostasis by stimulating gluconeogenesis and inhibiting glycogenolysis and lipolysis. In the context of appetite, cortisol suppresses appetite as it counteracts the anorexigenic effects of thyroid hormones and increases energy expenditure, leading to a decrease in body weight.

**Why Each Wrong Option is Incorrect:**

**A. Insulin:** Insulin is a hormone secreted by the pancreas that lowers blood glucose levels by promoting glucose uptake into cells and inhibiting gluconeogenesis. Insulin does not directly influence appetite regulation.

**B. Leptin:** Leptin is a hormone produced by adipocytes (fat cells) that suppresses appetite by signaling satiety to the hypothalamus. Leptin's role in appetite regulation directly opposes the correct answer (cortisol).

**C. Thyroid hormones:** Thyroid hormones (triiodothyronine and thyroxine) stimulate the hypothalamus to release the orexigenic (appetite-stimulating) hormones like cortisol would have an opposing effect, inhibiting appetite.

**Clinical Pearl:** Understanding the regulation of appetite helps in interpreting various clinical presentations, including weight loss or gain in different diseases, such as Cushing's syndrome (hypercortisolism) and hypothyroidism (low thyroid hormone levels).

In the context of the question, the core concept is that appetite is regulated by a balance of various hormones, including cortisol, leptin, insulin, and thyroid hormones. Cortisol is known to stimulate appetite suppression, while the other options (insulin, leptin, and thyroid hormones) work to stimulate appetite. In the presence of high cortisol levels, as in Cushing's syndrome, the appetite-stimulating effects of thyroid hormones, leptin, and insulin are suppressed, leading to decreased appetite.