Endocrine Control of Calcium:
Blood clotting and neural excitability, bones, muscle contractions are all dependent upon calcium level.
Controlled at 10mg/100mL, 50% free and 50 bound to albumin in the cellular and extracellular fluids.
99% of the calcium in the body is kept in the bone, with the bone serving as a reservoir.
Absorbed by the intestine and the kidney, with maintenance of plasma calcium is by the exchange of
bone and plasma levels due to hormones.
PTH increase circulating levels of Ca.
Calcitonin is produced by parafolicular or C cells of the thyroid gland, opposite of the PTH.
Vitamin increases circulating levels of Ca.
Eaten and absorbed by the duodenum and upper jejunum. Vit D and PTH increases absorption.
Calcitonin increases calcium deposition to the bones or other reservoirs. When the conc. Drops
bellows 10mg/mL, PTH leads to reabsorption and conscription of the calcium of the bone calcium.
Hormonal influences stabilizes calcium level of the blood.
Parathyroid Hormones (PTH): secreted from chief cells of the parathyroid. 84 aa in total, 34 of the N
terminus NECESSARY for recognition by the receptors. 3-18 min half-life. First produced as
preproparathyroid hormone, whch is then cleaved into the PTH.
PTH will cause an increase in rate of vit D production, from 25-hydroxyvit D into 1,25 dihydroxyvit D.
Hypofunction: low PTH, low plasma Ca, vit D production drops. Tetany, convulsions and spasms.
Hyperfunction: parathyroid adenoma, benign growth of the parathyroid. Opposite of the hypofunction,
lead to kidney stones and other forms of incorrect ca deposition (blood vessel walls), cardiac
Vitamin D: available from things that we don’t want to eat. Strictly speaking, not a real vitamin, can be
synthesized from cholesterol, need sunlight to make. Skin colour affects rate of production. 2 step
modification to activate. 25 hydroxylation in the liver, with long-half life. 1 hdyroxyxlation in the kidney
and some other tissues to activate into 1,25 dihydroxyvit D. Increases ca absorption in the intestine,
regulates immune system (anti inflammatory) with some anticancer properties. Osteomalacia is not
enough calcium, osteoporosis is not enough proteins. Renal failure causes failure to activation.
Vit D receptor issues also prevents hair growth. Only receptor issue