Hormonal control of calcium and phosphate metabolism 18012022

Hormonal control of calcium and phosphate metabolism 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Parathyroid Hormone 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

PTH producing cells 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Calcium – Phosphate Homeostasis 1 g/d Ca 2+ PTH Food 10% Ca 2+ 100% PO 4 - Calcitonin Calcium Absorption Phosphate Filtration Bone Turnover reabsorption Feces 90% Ca 2+ Urine 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Different Forms of Calcium Most of the Calcium in the body is stored in the bones as hydroxyapatite (99%) Calcium in the plasma (1%) 1. Free ionized form – 50% Physiologically active 2. Bound to proteins (albumin) - 41% 3. Complexed with anions (phosphate, citrate)– 9% 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Different Forms of Phosphate Most of the Phosphate in the body is stored in the bones (85%) Most of the remainder is intracellular (14%) as a component of phospholipids in cell membranes, DNA, RNA, ATP and ADP The small fraction of phosphate that is in the serum exists as circulating phospholipids, and inorganic phosphate Inorganic Phosphate 18/01/2022 HPO 4 -H 2 PO 4 Dr. Omary Chillo (MD, Ph. D) Physiologically active

Hormones involved in Ca 2+ and PO 4 Balance Parathyroid Hormone Calcitriol (active Vit D) Composed of 84 aa polypeptide Produced by parathyroid gland Net effect Derived from diet or a cholesterolderived precursor with help from UV light Enzymes from the liver and kidney are essential for active vit. D formation Net effect Serum Calcium Serum Phosphate 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Synthesis and Regulation of PTH Parathyroid Hormone Secreted by the chief cells PTH is primarily regulated by serum calcium Serum Calcium PHT Magnesium also regulates PTH release just like serum calcium 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Synthesis and Regulation of Calcitriol Serum Phosphate 7 -dehydrocholesterol Vit. D 25 -hydroxylase Cholecalciferol (vit. D 3) PTH Vit. D 1ɑ-hydroxylase 25(OH)cholecalciferol (Calcidiol) Ergocalciferol (vit. D 2) Dietary Sources e. g. Fish 18/01/2022 Phosphate Dr. Omary Chillo (MD, Ph. D) 1, 25(OH)cholecalciferol (Calcitriol)

Hormonal Action in Calcium – Phosphate Homeostasis PTH Ca 2+/PO 4 Calcitriol Ca 2+/PO 4 Blood + Filtration + - PTH Calcitriol Calcium Ca 2+/PO 4 PTH Calcitonin + Phosphate Net Effect PTH: 18/01/2022 Urine Dr. Omary Chillo (MD, Ph. D) Calcium, Phosphate Calcitriol: Calcium, Phosphate

The p. H effect on Calcium – Phosphate Metabolism Serum p. H PTH Urinary excretion of Phosphate Buffering of H+ excretion in distal tubule Serum p. H 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Disorders of Calcium and Phosphate Metabolism Hypercalcemia PTH excess production (tumors of the parathyroid gland) Vitamin D excess Excessive dietary intake of Ca 2+ Thiazide diuretics 18/01/2022 Dr. Omary Chillo (MD, Ph. D) 1. Depresses nervous system 2. Decreases muscle activity 3. Constipation 4. Lack of appetite

Disorders of Calcium and Phosphate Metabolism Hypocalcemia Aging Malnutrition Menopause Hypothyroidism 18/01/2022 Dr. Omary Chillo (MD, Ph. D) 1. Increases Nervous system excitement 2. Tetanic contrations 3. Seizures 4. Increases muscle activity

The Bone Physiology 18/01/2022 Dr. Omary Chillo (MD, Ph. D)

Thanks 18/01/2022 Dr. Omary Chillo (MD, Ph. D)