Which of the Following is the Response to Low Plasma

Question

Which of the following is the response to low plasma levels of calcium?
A) Secretion of calcitonin
B) Secretion of the beta cells of the islets of Langerhans
C) Inhibition of the adenohypophyseal release of ACTH
D) Secretion of PTH

Accepted Answer

Low plasma levels of calcium stimulate the secretion of parathyroid hormone (PTH) from the parathyroid glands. PTH acts to increase plasma calcium levels by stimulating bone resorption, increasing renal reabsorption of calcium, and promoting the activation of vitamin D, which increases intestinal absorption of calcium. Secretion of calcitonin by the thyroid gland, choice A, is stimulated by high plasma levels of calcium and acts to decrease plasma calcium levels by inhibiting bone resorption, promoting calcium deposition in bone, and increasing renal excretion of calcium. Secretion of the beta cells of the islets of Langerhans, choice B, is not involved in the regulation of calcium levels. Inhibition of the adenohypophyseal release of ACTH, choice C, is not directly involved in the regulation of calcium levels.