Phayrngeal Region Endocrine Glands Parathyroid Control of Calcium Homeostasis

Phayrngeal Region Endocrine Glands Calcitonin –Produced in the intrafollicular cells of the thyroid –Produced by C-cells that are present in the thyroid, thymus, and parathyroid –Chemistry Single chain protein 32 amino acids Entire molecule required for biological activity 3-12

Phayrngeal Region Endocrine Glands Calcitonin –Function Lowers circulating Ca + Targets bone, kidney, gut –Lowers ca by »Blocking absorption in the gut »Promoting its excretion in the kidney »Depositing it on the bone 3-22

Phayrngeal Region Endocrine Glands Calcitonin Regulation and secretion –No neural or neuroendocrine regulation –Calcium level is the most important regulator –Other hormones stimulate it CCK, gastrin 3-22

Regulation of Ca mg % 11 mg % [Ca + ] PTHCT Normal Ca level

Phayrngeal Region Endocrine Glands Parathyroid Anatomy Embedded in surface of thyroid Removal leads to death Chief cells make PTH Parathormone –Single chain 84 amino acids –Active core of 34 AA’s 3-8

Phayrngeal Region Endocrine Glands Parathormone –Functions »Maintains Ca in body »Essential for life »Not stored, used readily »Supports all functions requiring Ca »muscular and nervous function »Bone structure »Blood clotting »2 nd messenger systems »Egg shells 3-22

Phayrngeal Region Endocrine Glands Parathormone –Mechanisms Increase or decrease: » deposition in bone »Absorption in kidney and GI tract Primary control –Calcitonin, vitamin D 3, PTH Secondary control –Adrenal steroids, thyroid 3-22

Ca balance Total body Ca = Kg Ca –Tissues = 12g –Body fluids =1g (50% bound) –99% is in the bone! Bone is a major Ca reservoir –1% readily availible –99% slowly available

Ca balance Pathways –Gut –Kidney –Liver –Ovary –Hormones PTH, Calcitonin,Vitamin D 3

Ca balance Vitamin D 3 Works primarily on GI tract Secondarily on the Bone –Source = Diet and Sunlight –PTH and Vitamin D are intimately related –Precursor is cholesterol –Fig 9.6, 9.8