Which of the following hormones is secreted by the pineal gland and plays a key role in regulating the circadian rhythm (sleep-wake cycle)? MCQ with Answer and Explanation
Which of the following hormones is secreted by the pineal gland and plays a key role in regulating the circadian rhythm (sleep-wake cycle)?
A. Melatonin
B. Calcitonin
C. Thymosin
D. Oxytocin
Answer: Option A
Solution (By JKExamLibrary)
Melatonin is a hormone secreted by the pineal gland, a small endocrine gland located in the brain. Its secretion is highly sensitive to light and dark cycles, being produced in higher amounts at night. Melatonin is crucial for regulating the circadian rhythm (sleep-wake cycle), maintaining biological clocks, and influencing seasonal reproductive functions in some animals. Thymosin is from the thymus, oxytocin from the posterior pituitary.
Explanation:
A mid-cycle surge in LH (luteinizing hormone) from the anterior pituitary triggers ovulation—the release of the secondary oocyte from the mature Graafian follicle. FSH stimulates follicle development. Estrogen levels rise before ovulation and provide positive feedback for the LH surge. Progesterone is secreted after ovulation by the corpus luteum.
Explanation:
Spectrin is a cytoskeletal protein that lines the inner surface of the RBC membrane, maintaining its biconcave shape and providing elasticity to squeeze through capillaries. Hemoglobin carries oxygen, myosin is a motor protein, keratin is structural in skin/hair. Defects in spectrin cause spherocytosis.
Explanation:
Iodine is essential for the synthesis of thyroid hormones T₃ and T₄. Deficiency causes hypothyroidism and goiter (enlarged thyroid gland). Iodized salt is a preventive measure.
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