Thyroid Gland Flashcards

Question

Synthesis & secretion of T3 & T4 2. Synthesis of thyroglobulin

Answer 1

- While the follicular cells are trapping iodide ions, they are also synthesizing thyroglobulin (TGB), a large glycoprotein that is produced in the rough ER, modified in the Golgi complex, & packaged into secretory vesicles. - Vesicles then undergo exocytosis, which releases TGB into the lumen of the follicle.

Answer 2

- Some of the amino acids in TBG are tyrosines that will become iodinated. - Negatively charged iodide ions can't bind to tyrosine until they undergo oxidation (removal of electrons) to iodine. - As the iodide ions are being oxidized, they pass through the membrane into the lumen of the follicle.

Answer 3

- As iodine molecules, they react with tyrosines that are part of TGB molecules. - Binding of 1 iodine atom yields monoiodotyrosine (T1) & a second iodination produces diiodotyrosine (T2). - Colloid - the TGB with attached iodine atoms, a sticky material that accumulates & is stored in the lumen of the thyroid follicle.

Answer 4

During the last step in the synthesis of thyroid hormone, 2 T2 molecules join to form T4 1 T1 & 1 T2 molecules join to form T3

Answer 5

- Droplets of colloid reenter follicular cells by pinocytosis & merge with lysosomes. - Digestive enzymes in the lysosomes break down TGB, cleaving off molecules of T3 & T4.

Answer 6

- Because T3 & T4 are lipid-soluble, they diffuse through the plasma membrane into interstitial fluid & then into the blood. - T4 normally is secreted in greater quantity than T3, but T3 is several times more potent. - After T4 enters a body cell, most of it is converted to T3 by removal of one iodine.

Answer 7

More than 99% of both the T3 and the T4 combine with transport proteins in the blood, mainly thyroxine-binding globulin (TBG).

Answer 8

Thyroglobulin (TGB)

Answer 9

- Increase basal metabolic rate (BMR) - Maintenance of normal body temperature - Regulation of metabolism - Enhance actions of catecholamines - Accelerates body growth

Answer 10

- BMR = rate of energy expenditure under standard or basal conditions (awake, at rest, & fasting). - Increases rate of O2 consumption under standard or basal conditions by stimulating the use of cellular O2 to produce ATP.

Answer 11

The cellular metabolism of carbohydrates, lipids, & proteins increases.

Answer 12

- As cells produced & use more ATP, BMR increases, more heat is given off, & body temp rises = a calorigenic effect.

Answer 13

- they have permissive effects on the catecholamines bc they up-regulate beta-adrenergic receptors. - catecholamines bind to beta-adrenergic receptors to promote sympathetic responses. - symptoms of excess levels of thyroid hormones = increased HR, increased BP.

Answer 14

- stimulates protein synthesis & increases the use of glucose & fatty acids for ATP production. - increases lipolysis & enhances cholesterol excretion, thus decreasing cholesterol level.

Answer 15

- Nervous system = promotes synapse formation, myelin production & growth of dendrites. - Skeletal system = promotes formation of ossification centers in developing bones, synthesis of many bone proteins, & secretion of GH & insulin-like growth factors (IGF).

Answer 16

TRH, TSH, anterior

Answer 17

1. Low blood levels of T3 & T4 OR lo metabolic rate stimulates the hypothalamus to secrete TRH. 2. TRH enters the hypophyseal portal veins & flows to the anterior pituitary gland = which stimulates thyrotrophs to secrete TSH. 3. TSH stimulates all aspects of thyroid follicular cell activity. 4. The thyroid follicular cells release T3 and T4 into the blood until the metabolic rate returns to normal. 5. An elevated level of T3 inhibits release of TRH and TSH (negative feedback inhibition).

Answer 18

- cold environment - hypoglycemia - high altitude - pregnancy

Answer 19

Calcitonin (CT)

Answer 20

- catalyzes iodide oxidation to form iodine atoms which are added onto tyrosine residues on thyroglobulin for the production of thyroxine or triiodothyronine.

Answer 21

Decreases the level of Ca2+ in the blood by inhibiting the action of osteoclasts (breaks down bone extracellular matrix)

Answer 22

negative feedback system

Answer 23

- decreases the amount of blood Ca2+ & phosphates by inhibiting bone resorption (breakdown of bone extracellular matrix) by osteoclasts. - by accelerating uptake of Ca2+ & phosphates into bone extracellular matrix.