Given a serum calcium value that falls from 9.8 mg/dL to 7.6 mg/dL, predict the coordinated endocrine responses and resulting effects on bone, kidney, and intestine.

Parathyroid glands increase PTH secretion causing bone resorption to release calcium, kidneys increase calcium reabsorption and activate vitamin D, and activated vitamin D increases intestinal calcium absorption

Adrenal medulla secretes catecholamines to directly increase intestinal absorption and deposit calcium into bone as hydroxyapatite

Pancreatic insulin secretion increases to stimulate osteoblasts and promote net bone calcium uptake until serum calcium normalizes

Thyroid releases calcitonin causing immediate bone mineralization, kidneys to excrete more calcium, and intestines to decrease calcium uptake