BIOM 3200 Chapter Unit 2: BIOM 3200 Chapter Unit : BIOM 3200 Chapter : BIOM 3200 unit2
11 May 2020
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2. 01 identify three hormones that mediate calcium homeostasis: calcitonin from thyroid gland, parathyroid hormone (pth) from parathyroid gland, 1,25-dihydroxyvitamin d3 (1,25-dihydroxycholecalciferol) from kidneys, all 3 also involved in phosphate metabolism. 2. 02 describe the effects of vitamin d on calcium absorption and indicate the cellular mechanism: unlike phosphorous (po4. 3-), calcium (ca2+) poorly absorbed into git (unless in excess: active vit d3 promotes ca2+ and po4. 2. 04 discuss the effects on homeostasis of hyper- and hypo-calcaemia: plasma [ca2+] regulated by pth within narrow range ~2. 4 mmol/l, 3 different forms: 1. 0 mmol/l combined w plasma proteins won"t diffuse through capillary membrane. 1. 2 mmol/l diffusible and ionized: hypocalcaemia: low blood [ca2+], results in spontaneous ap in peripheral nerves to muscles, ca2+ important for na+ permeability regulation. Low extracellular [ca2+] neuron membrane permeability to na+ increases easy initiation of ap depolarized muscle cells: muscles begin to twitch may lead to tetany. Associated w paralysis in cows w milk fever (downer cow)
