1. Hormonal control of calcium and phosphate metabolism
19/09/2018
Dr. Omary Chillo (MD, PhD)

2. Dr. Omary Chillo (MD, PhD)
Parathyroid Hormone
19/09/2018
Dr. Omary Chillo (MD, PhD)

3. Dr. Omary Chillo (MD, PhD)
PTH producing cells
19/09/2018
Dr. Omary Chillo (MD, PhD)

4. Dr. Omary Chillo (MD, PhD)
Calcium – Phosphate Homeostasis
PTH
Calcitonin
1g/d Ca2+
Food
10% Ca2+
Calcium
Bone Turnover
Absorption
100% PO4-
Phosphate
Filtration
reabsorption
Feces
90% Ca2+
Urine
19/09/2018
Dr. Omary Chillo (MD, PhD)

5. 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%
19/09/2018
Dr. Omary Chillo (MD, PhD)

6. 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
HPO4--
Inorganic Phosphate
Physiologically active
H2PO4
19/09/2018
Dr. Omary Chillo (MD, PhD)

7. Hormones involved in Ca2+ and PO4 Balance
Parathyroid Hormone
Calcitriol (active Vit D)
Derived from diet or a cholesterol-derived precursor with help from UV light
Composed of 84 aa polypeptide
Produced by parathyroid gland
Enzymes from the liver and kidney are essential for active vit. D formation
Net effect
Serum Calcium
Serum Phosphate
Net effect
Serum Calcium
Serum Phosphate
19/09/2018
Dr. Omary Chillo (MD, PhD)

8. Synthesis and Regulation of PTH
Parathyroid Hormone
Secreted by the chief cells
PTH is primarily regulated by serum calcium
PHT
Serum Calcium
Serum Calcium
PHT
Magnesium also regulates PTH release just like serum calcium
19/09/2018
Dr. Omary Chillo (MD, PhD)

9. Synthesis and Regulation of Calcitriol
Serum Phosphate
Serum Phosphate
PTH
Vit.D
25-hydroxylase
Vit.D
1ɑ-hydroxylase
1, 25(OH)cholecalciferol
(Calcitriol)
7-dehydrocholesterol
Cholecalciferol
(vit.D3)
25(OH)cholecalciferol
(Calcidiol)
Ergocalciferol
(vit.D2)
Dietary Sources e.g. Fish
19/09/2018
Dr. Omary Chillo (MD, PhD)

10. Dr. Omary Chillo (MD, PhD)
Hormonal Action in Calcium – Phosphate Homeostasis
PTH
Ca2+/PO4
Calcitriol
Blood
Ca2+/PO4
Ca2+/PO4
Calcium
Phosphate
PTH + -
PTH
Calcitonin + +
Filtration
Calcitriol
Net Effect
PTH: Calcium, Phosphate
Calcitriol: Calcium, Phosphate
Urine
19/09/2018
Dr. Omary Chillo (MD, PhD)

11. The pH effect on Calcium – Phosphate Metabolism
Serum pH
PTH
Urinary excretion of Phosphate
Buffering of H+ excretion in distal tubule
Serum pH
19/09/2018
Dr. Omary Chillo (MD, PhD)

12. Disorders of Calcium and Phosphate Metabolism
Hypercalcemia
PTH excess production (tumors of the parathyroid gland)
Depresses nervous system
Decreases muscle activity
Constipation
Lack of appetite
Vitamin D excess
Excessive dietary intake of Ca2+
Thiazide diuretics
19/09/2018
Dr. Omary Chillo (MD, PhD)

13. Hypocalcemia Disorders of Calcium and Phosphate Metabolism
Increases Nervous system excitement
Tetanic contrations
Seizures
Increases muscle activity
Aging
Malnutrition
Menopause
Hypothyroidism
19/09/2018
Dr. Omary Chillo (MD, PhD)

14. Dr. Omary Chillo (MD, PhD)
The Bone Physiology
19/09/2018
Dr. Omary Chillo (MD, PhD)

15. Dr. Omary Chillo (MD, PhD)
Thanks
19/09/2018
Dr. Omary Chillo (MD, PhD)