BISC307 Lecture Notes 3.07.2008

BISC307 Lecture Notes 3.07.2008 - BISC307 Dr. Herrera...

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BISC307 Dr. Herrera Friday 3/07/08 (Lecture 17, slide 7) Hormones That Regulate Body Calcium 3 hormones with principle effects 1. Parathyroid hormone (aka parathormone, PTH): secreted from parathyroid glands, little clusters tissue on the posterior aspects of the thyroid gland; required for life; if one must surgically remove thyroid gland, it’s important to preserve the parathyroid gland tissue; PTH raises plasma calcium concentrations 2. Calcitriol (aka Vitamin D3, 1,25-dihyroxy-cholecalciferol): steroid hormone made of vitamin D- either from diet or made in skin from precursors with the action of sunlight- causes skin cells to make vitamin D; problem: doctors say avoid sun exposure because of damaging effects, those overly conscious of it are vitamin D deficient; doesn’t need to be all of your skin; 10-15 minutes a day is enough; or take vitamin D supplement Vitamin D converted by liver into intermediate compound which is taken by kidney; w/ stimulation of PTH action of kidney in converting the intermediate into calcitriol, which reinforces the action of PTH raises plasma calcium indirectly 3.Calcitonin lowers plasma calcium; secreted by C-cells embedded in the thyroid gland. Ca balance in the body Small intestine: where dietary Ca is absorbed into body Bone: ca reservoir into which it can be deposited by action of the cell called “osteoblast” (causes mineral formation of new bone); also release ca under action of osteoclasts in process called bone resorption Kidney either excretes Ca or not Ca in body exists in bone, ECF, and ICF Input of ca from small intestine and excreted from body here Kidneys reabsorb or excrete ca according to need where regulation occurs PTH: raises plasma ca by stimulating resorption of bone by osteoclasts; stimulating reasorption of ca from tubular fluid back into the blood, ca that was previously filtered out of the blood, back into ECF; stimulates excretion pf Phosphate can’t lower plasma ca without lowering plasma phosphate b/c ca phosphate is an insoluble salt that would precipitate; 3
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BISC307 Lecture Notes 3.07.2008 - BISC307 Dr. Herrera...

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