LMP301 Introduction to the Biochemistry of Human Disease Lecture 15 – Calcium  Homeostasis o Net gain at intestine = net loss at kidney (150 mg/d) o No net change at bone formation/resorption (500 mg/d)  Hormones o PTH  Produced by the parathyroid glands behind the thyroid  Stimulated by low serum Ca and inhibited by high Ca 2+  Bone: ↑ bone resorption  Kidney: ↑ Ca reabsorption, ↓ PO rea4sorption  Stimulate 1,25 (OH) 2itD o 1,25 (OH) 2itD  Plants: from vitD2; Animals: from vitD3  ProvitD 3 vitD 325-OH D  1,35(OH) D (act2 3)  Side products: 24,25(OH) 2 3nd 1,24,25(OH) D 3 3active) st  1 step: UV  2 step: 25-hydroxylase (liver) rd  3 step: 1α-hydroxylase (kidney, pancreas, etc.)  Inactivation: 24-hydroxylase  Autocrine: regulation of cell growth  Paracrine: immune modulation  Endocrine: calcium homeostasis, muscle and bone health 2+ -  Intestine: ↑ Ca and PO ab4orption  Bone: ↑ bone resorption  Feedback: inhibit PTH  Bound to vitD-binding protein in circulation and targets nuclear vitD receptor o Calcitonin  From the parafollicular/C cells of the thyroid  Stimulated by high Ca , gastrin, and pentagastrin  Inhibit bone resorption by osteoclasts and ↓ Ca and PO (clinically 4 insignificant)  Treatment of osteoporosis  Marker of medullary thyroid carcinoma (C cells)  Bone o Osteoclasts (resorption) and osteoblasts (formation)  Resorption markers: deoxypyridinoline  Formation markers: alkaline phosphatase, ost