"Calcium metabolism - first part -
INTESTINAL RESORPTION, KIDNEY, THYROID AND PARATHYROIDS
PARATHYROIDS SECURE PARATORMONE: → hypercalcemizing IN RESPONSE TO LOW CALCIUM LEVELS IN THE BLOOD (hypocalcemia)
THE THYROID SECRETS CALCITONIN → hypocalcemizing IN RESPONSE TO HIGH LEVELS OF CALCIUM IN THE BLOOD (hypercalcemia)
THESE HORMONES ALSO AFFECT CALCIUM ALTITUDE REABSORBED AT THE KIDNEY LEVEL
BIOLOGICAL ACTIONS ORGAN PARATORMONE CALCITONIN Kidney It increases the reabsorption of calcium in the distal tubule, reducing its excretion.
Reduces tubular reabsorption of phosphorus.
It increases the activation of Vitamin D.
It decreases the reabsorption of calcium by the kidneys, increasing its excretion in the urine. Bone
Increases the reabsorption of calcium and phosphate from bone to extracellular fluids; enhances the activity of osteoclasts while calcitonin reduces it.
It decreases bone resorption and stimulates the deposition of calcium in the bone tissue. Intestine It indirectly increases the absorption of calcium
and phosphate acting on the synthesis of Vitamin D
It hinders the absorption of calcium
80% SKIN SYNTHESIS (following sun exposure).
20% FOOD SUPPLY: meat of some fatty fish, egg yolk, liver, fish oils (especially cod liver oil).
IN BOTH CASES IT NEEDS ACTIVATION AT THE LIVEL AND THEN KIDNEY LEVEL (favored by parathyroid hormone), AFTER ":
- favors the absorption of calcium and phosphorus in the intestine
- increases bone resorption (stimulates osteoclast differentiation), but its overall effect on the bone is to promote mineralization
- increases the ability of parathyroid hormone to reabsorb calcium in the kidney.
BONE MASS OR DENSITY:
It reaches its highest levels around 25 years of age and decreases with aging
INCREASED FROM DECREASED BY Physical load-bearing activity (running, dancing, weights, etc.) Sedentary lifestyle Dietary intake of calcium and vitamin D Insufficient calcium and vitamin D intake or malabsorption disease Solar exposure Reduced sun exposure Male and especially female hormones Deficiency of androgens and especially estrogen (late menarche; early menopause; secondary amenorrhea). Normal or high body mass index Smoking and alcohol, anorexia nervosa Estrogen replacement therapy, anabolic steroids, GH. Therapy with cortisone, loop diuretics, thyrotoxicosis
AND "DATE FROM" BALANCE BETWEEN THE "ACTIVITY OF:
Osteoblasts: cells that lay down bone
Osteoclasts: cells that resorb bone
Osteocytes: cover the surfaces of the non-growing bone