Test 3 - Thyroid Gland Synthesizes two hormones...

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Thyroid Gland Synthesizes two hormones: tetradothyronine (T4) and tridothyronine (T3). The thyroid gland rests on the esophagus in the neck. Almost every cell in the body responds to thyroid hormones. 1. Hormones a. Tetradothyronine (T4) -has 4 iodine molecules attached to it -inactive until converted to T3 -more T4 released than T3 -not lost in urine b. Tridothyronine (T3) -3 iodine molecules attached to it -active form of thyroid hormone and acts like steroid hormone -only 10% is T3 -T3 is fat soluble and travels through membrane easily -once in cell membrane it binds to a protein carrier that takes it to the nucleus so it can bind to an intracellular nuclear receptor called a hormone response element -hormone response element (HRE) -stimulate transcription of RNA c. Thyrotropin Releasing Hormone (TRH) -synthesized by hypothalamus -when released it stimulates the release of thyroid stimulating hormone (TSH) from the adenohypophysis -major regulator thyroid stimulating hormone in body -regulation of TRH secretion -decrease in T (cooler) = body releases more TRH -increase in body T = decrease in TRH release -in animals they being to shed -TRH secretion increases with low thyroid levels, low metabolic rate, pregnancy, and high altitude d. Thyroid Stimulating Hormone (TSH) -stimulates the releases of thyroid hormones from thyroid gland -four effects of TSH 1. Increases amount of idodie taken into a follicle cell of the thyroid gland 2. Increases thyroglobulin synthesis 3. Increases thyroid peroxidase synthesis 4. Increases uptake of thyroglobulin through the follicle cell of the thyroid gland 2. Synthesis of Thyroid Hormones -thyroid gland is made up of thousands of cells called thyroid follicles -each thyroid follicle is filled with a substance called colloid a. 7 steps: 1. Iodide trapping by follicular cells
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-follicle cells of the thyroid gland absorb iodide into the cell and release it into the colloid 2. Thyroglobulin -the follicle cells synthesize the protein thyroglobulin -the colloid is made of thyroglobulin and contains the protein tyrosine 3. Thyroid Peroxidase -the enzyme thyroid peroxidase oxidizes iodide and forms iodine -this occurs in the lumen of the follicle cell -iodine is needed to form thyroid hormone 4. Iodination of Tyrosine -once iodine is in the colloid, tyrosine takes up iodine -if the tyrosine protein takes up one iodine molecule it is called monoiodotyrosine (MIT) -if the tyrosine protein takes up two iodine molecules it is called diiodotyrosine (DIT) 5. Forming Thyroid Hormones -the thyroid hormones can now form - if one monoiodotyrosine (MIT) and one diiodotyrosine (DIT) join together they for T3 hormone -if two diiodotyrosine (DIT) join together they form T4 6. Endocytosis -TSH (thyroid stimulating hormone) stimulates the follicle cell to take up T3 or T4 from the colloid through pinocytosis -pinocytosis is a form of endocytosis that takes in liquid (the colloid plus hormones) -once in the follicle cell, the hormone moves to the lysosome -the lysosome removes thyroglobulin (colloid) from the hormone
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Test 3 - Thyroid Gland Synthesizes two hormones...

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