Which hormone decreases serum calcium level?

Appeared in: AIIMS Delhi NO - 2017

Explanation

Calcitonin is a peptide hormone secreted by the parafollicular cells (C-cells) of the thyroid gland.
Its main function is to lower serum calcium levels, acting in opposition to Parathyroid Hormone (PTH).
Calcitonin achieves this by directly inhibiting the activity of osteoclasts, the cells responsible for bone resorption (breakdown).
It also decreases the reabsorption of calcium in the renal tubules, leading to increased calcium excretion in the urine.

Option A: Parathyroid hormone (PTH) has the opposite effect; it increases serum calcium levels.
Option B: This option is too general. The primary thyroid hormones (T3 and T4) regulate metabolism, not calcium. While the thyroid gland does produce calcitonin, 'Thyroid' hormone itself is not the correct answer.
Option D: Motilin is a hormone produced in the gastrointestinal tract that regulates gut motility, particularly initiating the migrating motor complex. It has no role in calcium homeostasis.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Hormonal regulation of serum calcium as background academic context rather than a clinical decision trigger.
Understanding the roles of calcitonin and PTH is crucial for nurses caring for patients with endocrine disorders like hyperparathyroidism, hypoparathyroidism, or medullary thyroid carcinoma.
Nurses must monitor serum calcium levels in at-risk patients and recognize the signs of hypocalcemia (e.g., tetany, Chvostek's sign) and hypercalcemia (e.g., lethargy, constipation, bone pain).
Calcitonin (derived from salmon) is used therapeutically to treat hypercalcemia, Paget's disease, and postmenopausal osteoporosis due to its ability to inhibit bone resorption.

How to Approach the Question

First, identify the key concept in the question: the hormonal decrease of serum calcium.
Recall the two primary hormones involved in calcium balance: Parathyroid Hormone (PTH) and Calcitonin.
Remember their opposing functions. A simple mnemonic is: PTH 'Puts' calcium 'To' the 'H'eavens (raises it), while Calcitonin 'tones down' the calcium.
Evaluate the options based on this knowledge. PTH increases calcium, so it is incorrect.
Calcitonin decreases calcium, which matches the question, making it the correct choice.
Eliminate the remaining distractors. 'Thyroid' is too general, as its main hormones (T3/T4) control metabolism. Motilin is a gut hormone unrelated to calcium.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 163-165

E6 Pharmacology KD Tripathi Essentials 9e Part 2 p. 12-14

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 1239-1241

Practise the full AIIMS Delhi NO - 2017

Attempt every question from this paper in a timed mock, then review the full solution for each one.