Which hormone is primarily secreted by the pineal gland?

• A. Melatonin
• B. Thyroxine
• C. Insulin
• D. Cortisol

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by identifying the function of the pineal gland. The pineal gland is a small, pea-shaped gland located in the brain. Its primary role is to regulate biological rhythms, such as the sleep-wake cycle, through hormone secretion.
2. Step 2: Review the hormones listed in the options and their primary functions. For example: Melatonin is involved in regulating sleep cycles, Thyroxine is secreted by the thyroid gland and regulates metabolism, Insulin is secreted by the pancreas and regulates blood sugar levels, and Cortisol is secreted by the adrenal glands and helps manage stress.
3. Step 3: Match the hormone that aligns with the pineal gland's function of regulating biological rhythms. Melatonin is the hormone directly associated with the pineal gland and its role in controlling sleep-wake cycles.
4. Step 4: Eliminate the other options based on their functions and the glands that secrete them. Thyroxine, Insulin, and Cortisol are not secreted by the pineal gland and serve different physiological roles.
5. Step 5: Conclude that the hormone primarily secreted by the pineal gland is Melatonin, as it is directly involved in regulating sleep and circadian rhythms.