Metabolism - Session 11, Lecture 1 Calcium metabolism The endocrine system, J. Hinson, P. Revan and S. Chew., ( Elsevier 2007) Marks’ Essential of Medical Biochemistry p 19, , Ganong’s Review of Medical Physiology Chapter 22, 23 DR. Hasanat A. Aljabery

 Hormone secretion  Muscle contraction  Nerve conduction  Exocytosis  Activation and inactivation of enzymes  Intracellular second messenger

 Cellular energy metabolism.  It also plays crucial roles in the activation and deactivation of enzymes.

 Why calcium and phosphate homeostasis are inter-related?  First: they are the principal components of hydroxyapatite crystals [Ca10(PO4)6(OH)2)], which constitute the major portion of the mineral phase of bone.  Second: both are regulated by the same hormones.

1. Intestine 2. Bone 3. kidney

1. Free ionized calcium : 45% 2. Bound to albumin: 45% 3. Complex with citrate and oxalate: 10%  Total calcium = mM ( mmg/dl)  The free ionized calcium is the physiologically active form  Common labrotory tests measure serum total calcium, the level then corrected according to serum albumin

 Hypocalcemia:  Hyper-excitability in nervous system ( including neuromuscular junction) leading to paraesthesia, then tetany, paralysis and convulsion.  Hypercalcaemia:  Formation of kidney stones ( calculi)  Constipation  Dehydration  Kidney damage  Tierdness  deppression

1. Parathyroid hormone :raise serum Calcium, short term regulation 2. Vitamine D : raise serum calcium, long term regulation 3. Calcitonin: lower serum calcium in animal

 Peptide produced by tumours  Cause humeral hypercalceamia of malignancy (HHM)  Commonly produced in patient with breast or prostatic cancer, some time in melanoma  PTHrP lead to increase calcium release from the bone Reduce renal renal calcium excretion Reduced renal phosphate reabsorption