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Lecture #31 - Endocrine System II.doc

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Queen's University
Anatomy and Cell Biology
ANAT 101
Richard Oko

Lecture #31 - Endocrine System II Thyroid Gland TSH causes release of thyroid hormones • majority are transported by plasma proteins • derived from a.a. tyrosine and iodine • Thyroxine (T4) tetraiodothyrine has 4 atoms of iodine • Triiodothyronin (T3) has 3 atoms of iodine and is more potent (has a stronger affect) Effects of Thyroid Hormones • activate nearly every cell in body • increase rate of ATP production in mitochondria -activate genes coding for enzyme synthesis -calorigenic effect: cells uses more energy (measured in calories) and heat is produced C Cells of Thyroid Gland (aka parafollicular cells) • found between follicles • produce calcitonin (CT) -stimulated by increases in plasma calcium -inhibits osteoclasts in bone -stimulates calcium excretion by kidneys -essential for normal bone growth in children and last trimester of pregnancy *DECREASES CALCIUM CONCENTRATION IN BODY FLUIDS Calcium Imbalances • Hypercalcemia causes: -decreased sodium permeability of excitable membranes Lecture #31 - Endocrine System II -less responsive muscles and nerves • Hypocalcemia causes: -increased sodium permeability -highly excitable, spasmodic muscles and nerves *parathyroid glands prevent hypocalcemia Parathyroid Glands • Chief cells produce parathyroid hormone (PTH) -stimulated by decrease in plasma calcium -activates osteoclasts in bone -reduces calcium excretion by kidney -stimulates kidney to secret calcitriol (increases calcium absorption in digestive tract) *INCREASES CALCIUM CONCENTRATION IN BODY FLUIDS Adrenal Cortex • contains high levels of cholesterol and fatty acids • produces more than 24 steroid hormones called coricosteroids -essential for metabolic functions -transported in plasma bound to proteins -3 zones of cortex produce
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