Q.93 Which one of the following hormones is INCORRECTLY paired with its function?
(A) Melatonin – biological rhythm
(B) Glucagon – increases blood glucose levels
(C) Prolactin – stimulates milk secretion
(D) Calcitonin – increases blood calcium level
Calcitonin is incorrectly paired with increasing blood calcium level. Calcitonin actually lowers blood calcium by inhibiting osteoclast activity and promoting calcium deposition in bones.
Options Explained
Melatonin – Biological Rhythm (A)
Melatonin from the pineal gland synchronizes circadian rhythms with light-dark cycles via suprachiasmatic nucleus signaling, correctly regulating sleep-wake cycles and seasonal reproduction.
Glucagon – Increases Blood Glucose Levels (B)
Pancreatic alpha cells release glucagon during hypoglycemia, stimulating hepatic glycogenolysis and gluconeogenesis to raise blood glucose—standard counter-regulatory hormone function.
Prolactin – Stimulates Milk Secretion (C)
Anterior pituitary prolactin induces mammary gland alveolar development and milk synthesis post-partum, inhibited by dopamine during pregnancy—correct lactogenic function.
Calcitonin – Increases Blood Calcium Level (D)
INCORRECT: Thyroid C-cells secrete calcitonin to decrease serum calcium/phosphate by suppressing osteoclast bone resorption and enhancing renal calcium excretion. Parathyroid hormone (PTH) performs the opposite function.
Calcitonin hormone incorrectly paired with increasing blood calcium defines calcium homeostasis confusion in NEET endocrinology questions.
Calcium Regulation Hormones Comparison
| Hormone | Source | Blood Calcium Effect | Mechanism |
|---|---|---|---|
| Calcitonin | Thyroid C-cells | Decreases | Inhibits osteoclasts, renal Ca excretion |
| PTH | Parathyroid | Increases | Bone resorption, renal Ca reabsorption |
| Vitamin D | Skin/liver/kidney | Increases | Gut absorption, bone mobilization |
| Melatonin | Pineal gland | Neutral (rhythm) | Circadian regulation |
Hormone-Effector Pathways
Calcitonin: Hypocalcemia → C-cell activation → cAMP ↓ in osteoclasts → reduced bone breakdown → serum Ca 9.0-10.5 mg/dL restoration.
PTH (opposite): Hyperparathyroidism → bone cysts, kidney stones (“stones, bones, groans”).
Why Option (D) is Correct
Textbook physiology confirms calcitonin as hypocalcemic (not hypercalcemic) hormone; common exam distractor confusing it with PTH function.
