Vitamin D — is a steroid hormone involved in the intestinal absorption of calcium and calcium homeostasis regulation. Synthesize vitamin hydroxylated in the liver to form 25-OH vitamin D.
Known for two forms of vitamin D - D3 and D2. The level of D3 depends on its receipt of food and synthesis in the skin under the influence of UV sun rays. D2 comes largely as a synthetic product of fortified food products.
Refers to vitamins, as it is vital, but can not completely synthesized in the body (mandatory food).
Synthesized by the body from dehydrocholesterol under the influence of sunlight. Zhirorastvorim. Inactive forms are activated in the kidneys and liver.
Biological functions of vitamin D:
- maintains normal levels of calcium and phosphorus in the blood
- increases calcium absorption in the intestine
- supports osteoid mineralization, together with other vitamins, hormones and minerals
- necessary for bone formation
Deficiency of vitamin D is usually the cause of secondary hyperparathyroidism. Increased PTH, especially in older people with vitamin D deficiency can lead to osteomalacia, increased bone turnover, reduced bone mass and risk of bone fractures. Low concentrations of vitamin D are also associated with low bone density.
Minimum level of vitamin D (25-OH) required to maintain a healthy bone should be in the range between 20-32 ng / ml (50-80 nmol / L).
Parathyroid hormone (parathormone, PTH)
Parathyroid hormone (parathormone, PTH) — synthesized parathyroid glands regulate calcium concentration in the blood through the organs of the target - the bones, intestines and kidneys.
Pparatgormon (PTH) enhances:
- reabsorption of calcium in the kidneys
- calcium absorption in the intestine (through the activation of vitamin D)
- bone resorption (by stimulating osteoclasts), reinforcing the lower levels of blood calcium and phosphate
- excretion of phosphorus in the kidney