rav endocrinology regulation of Ca metabolism

Maintenance of the body calcium stores depends on dietary calcium intake, absorption of calcium from the gastrointestinal tract, and regulation of renal calcium excretion. I

in a balanced diet, roughly 1000 mg/d of calcium is ingested. Depending on the concentration of circulating vitamin D, 200 to 400 mg of calcium is absorbed from the intestine each day, with the remainder appearing in the stool.

Calcium balance is maintained through renal calcium excretion, which averages 200 mg/24 h (5 mmol/24h).

Normal total serum calcium levels range from 9.0 to 10.5 mg/dL (2.3 to 2.6 mmol/L).

Despite its important intracellular roles, roughly 99% of body calcium exists in bone, mainly as hydroxyapatite crystals, and approximately 1% of bone calcium is freely exchangeable with the extracellular fluid, which makes it available for buffering changes in calcium balance.

Approximately 40% of the total blood calcium is bound to plasma proteins, primarily albumin; the remaining 60% includes ionized calcium and calcium complexed with phosphate and citrate. The total calcium level is usually determined by clinical laboratory measurement
The ionized calcium level is generally assumed to be roughly 50% of the total serum calcium level.

Calcitonin is secreted by the thyroid parafollicular C cells. The effect of calcitonin on bone metabolism is weak and is clinically significant only in pharmacologic amounts.