Hormonal Control of Calcium ppt **

The calcium in the plasma is present in three forms:vitamin D or calcitriol is a steroid hormone . Cholecalciferol D3 is generated in the skin of animals when light energy is absorbed by a precursor molecule 7-dehydrocholesterol. Vitamin D3, does not have significant biological activity. Rather, it must be metabolized within the body to the hormonally-active form known as 1,25-dihydroxycholecalciferol. This transformation occurs in two steps,
• Within the liver, cholecalciferal is hydroxylated to 25-hydroxycholecalciferol by the enzyme 25-hydroxylase.
• Within the kidney, 1-alpha-hydroxylase act on 25-hydroxycholecalciferol, yielding 1,25-dihydroxycholecalciferol, the biologically active form.
1-alpha-hydroxylase in the kidney is tightly regulated and serves as the major control point in production of the active hormone. The major inducer of 1-alpha-hydroxylase is parathyroid hormone.
Physiological Effects of Vitamin D
Vitamin D is well known as a hormone involved in mineral metabolism and bone growth.
• Its most dramatic effect is to facilitate intestinal absorption of calcium. Vitamin D stimulates the expression of a number of proteins involved in transporting calcium from the lumen of the intestine, across the epithelial cells and into blood (calcium transporters - calbindin).
• The crutial effect of vitamin D on bone is to provide the proper balance of calcium and phosphorus to support mineralization.
• It stimulates tubular reabsorption of calcium and phosphate
Disease States
Vitamin D deficiency: The classical manifestations of vitamin D deficiency is rickets, which is seen in children and results in bony deformaties including bowed long bones. Deficiency in adults leads to the disease osteomalacia. Both rickets and osteomalacia reflect impaired mineralization of newly synthesized bone matrix, and usually result from a combination of inadequate exposure to sunlight and decreased dietary intake of vitamin D.
Osteoporosis is characterized by demineraIization of bone resulting in the progressive loss of bone mass . This is reflected in demineralization After the age of 60, osteoporosis is seen . There is reduced bone strength and an increased risk of fractures
Vitamin D toxicity: Vitamin D toxicity is inevitably the result of overdosing on vitamin D supplements.
Calcitonin hormone
Calcitonin is a peptide hormone known to participate in calcium and phosphorus metabolism. It is from the parafollicular or C cells in the thyroid gland

Physiologic Effects of Calcitonin
• Bone: Calcitonin suppresses resorption of bone by inhibiting the activity of osteoclasts.
• Kidney: Calcitonin inhibits tubular reabsorption of these two ions, leading to increased rates of their loss in urine.
Calcium imbalance:



Hypercalcemia : The serum Ca2+ level >11 mg/dl
Causes: Hyperparathyroidism and overdose .
Clinical features
• Neurological symptoms such as depression, confusion, inability to concentrate
• Generalized muscle weakness
• Gastrointestinal problems such as anorexia, abdominal pain, nausea, vomiting & constipation
• Renal feature such as polyuria & polydipsia
• Cardiac arrhythemias

Treatment
Intravenous fluids hydrate you and lower calcium levels in the blood.
Corticosteroids : mechanism?
Loop diuretic medications : mechanism?
Hypocalcemia: Decreased serum Ca2+ < 8.8 mg/dl
Causes: Hypoproteinaemia , neck surgery, idiopathic , Vitamin D deficiency: • May be due to malabsorption or an inadequate diet with little exposure to sunlight , Renal disease:
Clinical features of hypocalcemia:
• Enhanced neuromuscular irritability
• Neurologic features such as tingling, tetany, numbness (fingers and toes), muscle cramps
• Cardiovascular signs such as an abnormal ECG
Treatment focuses on restoring normal blood calcium concentrations by calcium infusions, oral calcium supplements and vitamin D therapy.