Question

49 a deficiency of calcium in the diet would lead to: a an increase in parathyroid hormone in the blood b increased secretion of growth hormone c an increase in calcitonin secretion d an increase in melatonin levels in the blood

Explanation:

• Parathyroid hormone (PTH) is secreted by the parathyroid glands. Its main function is to regulate calcium levels in the blood. When there is a deficiency of calcium in the diet (leading to low blood - calcium levels), the parathyroid glands sense this and secrete more PTH. PTH acts on bones (to release calcium from bone matrix), kidneys (to re - absorb more calcium and excrete more phosphate), and intestines (to increase calcium absorption, though this is mainly through increasing vitamin D activation).
• Growth hormone is secreted by the anterior pituitary and is mainly involved in growth, metabolism (anabolic effects on proteins, etc.), and not directly in calcium regulation.
• Calcitonin is secreted by the parafollicular cells (C cells) of the thyroid. It has the opposite effect of PTH. Calcitonin is secreted when blood calcium levels are high (to lower blood calcium by inhibiting bone resorption and increasing renal calcium excretion). So, in a calcium - deficient state (low blood calcium), calcitonin secretion would not increase.
• Melatonin is secreted by the pineal gland and is mainly involved in regulating the sleep - wake cycle and has no direct role in calcium homeostasis.

Answer:

A. An increase in parathyroid hormone in the blood