Thyroid Hormones

Question 1

thyroid hormones are comprised of:

Answer 1

colloid and follicular cells

Question 2

colloid (protein) solution

Answer 2

contains thyroglobulin and stored thyroid hormone

Question 3

Synthesis of T3 and T4 by thyroid gland

Answer 3

requires intake of iodine
- enters thyroid gland follicular cells via iodide trapping by sodium-iodide symporter (NIS)
- goes through pendrin protein than transport iodide in colloid
- thyroglobulin combines with iodide and attaches to TG
- iodide is coupled to make T3 and T4

Question 4

fxn of thyroperoxidase

Answer 4

• catalyzes oxidation of iodide
• iodination of tyrosine
• coupling of iodotyrosines

Question 5

secretion of thyroid hormones

Answer 5

• TSH stimulates synthesis and secretion
• enzymes hydrolyze bonds between thyroid hormones and thyroglobulin
• T3 and T4 enter circulation
• iodide recycled

Question 6

regulation on thyroid hormone secretion

Answer 6

temp. has effect on TRH and thus thyroid hormone
stress decreases thyroid hormone

Question 7

thyroid hormone transport

Answer 7

• thyroxine-binding globulin
• thyroid hormone half lives
• T3: 1 day
• T4: 6 days

Question 8

T3 production

at tissue level

Answer 8

by de-iodination of T4 by type 1 and type 2 deiodinases

Question 9

Type 1 deiodinase produces

kidney, liver

Answer 9

T3 by:
removing outer iodide
activity can be altered by burns, tramua, cancer, etc

Question 10

Type 2 deiodinase produces

muscle, brain

Answer 10

T3 by:
removing outer iodide

Question 11

Type 3 deiodinase produces

Answer 11

reverse T3 by:
removing inner iodide

Question 12

at tissue level, T4 can be deiodinated by type 3 deiodinase to produce

Answer 12

reverse T3
inactive hormone

Question 13

Intracellular effects of TH

Answer 13

• increased basal metabolic rate
• increased synthesis and activity of NaKATPase
• increased synthesis of metabolic enzymes: heat production, O2 consumption, ATP generation

Question 14

systemic effects of TH

Answer 14

• mobilization of substrates for ATP generation by cells
• increased delivery of substrates to cells
• increased delivery of O2 to cells; CO2 removal from cells

Question 15

thyroid hormone increases availability of substrates for cells

Answer 15

• exogenous substrates increase food intake
• endogenous substrates increase mobilization
• increased delivery of substrates to cells: increased CO
• increased respiratory rate

Question 16

TH is permissive for full physiological effects of:

Answer 16

EPI, insulin, GH

Question 17

hyperthyroidism

Answer 17

• weight loss
• tachycardia
• sweating
• diarrhea
• graves’ disease
• tumor of follicular cells
• abnormal TRH and/or TSH secretion

Question 18

treatment of hyperthyroidism

Answer 18

decrease synthesis of TH
- inhibit iodide trap
- inhibit activity of thyroperoxidase
- surgical removal
- radioactive iodine to ablate tissue

Question 19

Hypothyrodism

Answer 19

weight gain
bradycardia
cold intolerance
constipation
autoimmune destruction of thyroid gland: hashimoto disease
surgical removal of gland
hypothalamic or pituitary failure
diet low in iodine