CALCIUM AND THE HUMAN BODY

ROLE OF CALCIUM AND VITAMIN D IN BONE HOMEOSTASIS: Calcium is the primary mineral responsible for bone formation and for maintaining bone health throughout the life span. This major mineral constitutes about 2% of our body weight and is also critical to proper functioning of the nervous, muscular, and cardiovascular systems. To maintain homeostasis, calcium balance in the body is regulated by parathyroid hormone (PTH), calcitonin, and vitamin. Acting together, these three substances regulate the rate of absorption of calcium from the gastrointestinal (GI) tract, the excretion of calcium from the kidney, and the movement of calcium into and out of bone.

BONE RESORPTION AND DEPOSITION: Secreted by the parathyroid glands, PTH stimulates bone cells called osteoclasts. These cells accelerate the process of bone resorption, demineralization that breaks down bone into its mineral components. Once bone is broken down (resorbed), calcium becomes available for transport to areas in the body where it is needed. The opposite of this process is bone deposition, or bone building, accomplished by cells called osteoblasts. This process, which removes calcium from the blood to be placed in bone, is stimulated by the hormone calcitonin. When serum calcium levels become elevated, calcitonin is released by the thyroid gland.

ROLE OF VITAMIN D IN CALCIUM METABOLISM: Vitamin D and calcium metabolism are intimately related: Absorption of calcium is increased in the presence of vitamin D, and inhibited by vitamin D deficiency. Thus, calcium disorders are often associated with vitamin D disorders. Vitamin D is unique among vitamins because the body is able to synthesize it from precursor molecules. Several steps, however, are required before vitamin D can act on target tissues. The inactive form of vitamin D, cholecalciferol, is synthesized in the skin from cholesterol. Exposure of the skin to sunlight or ultraviolet light increases the level of cholecalciferol in the blood. Cholecalciferol can also be obtained from dietary products such as milk or other foods fortified with vitamin D. Enzymes in the kidneys metabolize calcifediol to calcitriol, the active form of vitamin D. Parathyroid hormone stimulates the formation of calcitriol at the level of the kidneys. Patients with extensive kidney disease are unable to adequately synthesize calcitriol and thus frequently experience calcium and vitamin D abnormalities. The primary function of calcitriol is to increase calcium absorption from the GI tract. Dietary calcium is absorbed more efficiently in the presence of active vitamin D and parathyroid hormone, resulting in higher serum levels of calcium, which is then transported to bone, muscle, and other tissues.

ROLES OF CALCIUM IN THE BODY: The importance of proper calcium balance in the body cannot be overstated. Calcium ion influences the excitability of all neurons. When calcium concentrations are too high (hypercalcemia), sodium permeability decreases across cell membranes. This is a dangerous state, because nerve conduction depends on the proper influx of sodium into cells. When calcium levels in the bloodstream are too low (hypocalcemia), cell membranes become hyperexcitable. If this situation becomes severe, convulsions or muscle spasms may result. Calcium is also important for the normal functioning of other body processes such as blood coagulation and muscle contraction.

RELATED;

1.  Magnesium

2.  Vitamin D

3.  Osteoporosis 

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