Thyroid Gland (lec 23)

Question 1

Thyroid is what kind of hormone gland?

Answer 1

endocrine

Question 2

Thyroid regulates?

Answer 2

growth
maturation
metabolic rate/heat
energy mobilization

Question 3

Thyroid hormones synthesis requires?

Answer 3

requires both intracellular and extracellular actions

Question 4

Thyroid hormones synthesis: Step 1?

Answer 4

Uptake of iodide thru iodide trap: Na+/I- cotrans

Trap activity run by diet (iodine)

Question 5

Thyroid hormones synthesis: Step 2?

Answer 5

Oxidation:

iodide from cell to lumen via pendrin ->
Δ to I2 via peroxidase

Question 6

Thyroid hormones synthesis: Step 3?

Answer 6

Organification:

I2 + tyrosine + thyroglobulin (TG)

Question 7

Thyroid hormones synthesis: Step 4?

Answer 7

Coupling via peroxidase:

DIT + DIT -> thyroxine (T4)

or

MIT + DIT -> triiodothyronine (T3)

T4»T3

Question 8

Thyroid hormones synthesis: Step 5?

Answer 8

Secretion stim by TSH:

Follicular cell engulfs colloid/TG complex via Megalin ->
lysosomes split T3/4 from complex ->
out to blood

rest deiod/recycled

Question 9

T3 more bio active than T4, why? (3)

Answer 9

1) thyroid hormone receptors in nucleus more affinity for T3
2) T4 binds more tightly to plasma protein
3) T4 peripheral conversion

Question 10

Peripheral conversion is?

Answer 10

Δ of T4 into T3 at target cell

Question 11

Thyroid hormone action on target cell?

Answer 11

Free T3/4 enter cell ->
most T4 Δd to T3 ->
bind DNA TH receptor ->
makes many kinds of proteins

Question 12

Thyrotrophin Releasing Hormone (TRH) acts on?

Action?

Answer 12

thyrotrophs of ant pit

Binds G protein -> IP3 -> Ca2+ release -> exocytosis of TSH

Question 13

Thyrotropin (TSH) role?

Answer 13

Stim every step of TH synth in thyroid except step 2

Stim thyroid gland to grow (trophic)

Question 14

T3 regulates TH secretion how?

Answer 14

down-reg thyrotroph TRH receptors = ↓ TSH release from ant pit

inhib hypothal release of TRH

Question 15

Action of TH on Basal Metabolic Rate (BMR)

Answer 15

↑ Na+/K+ATPase =

↑ O2 consumption, ↑ temp, ↑ CO, ↑ BMR

Question 16

Action of TH on CV?

Answer 16

T3 -> chronotrophic/inotrophic
T4 -> ↑ vascular resistance

= ↑ CO and vent

Question 17

Action of TH on SNS?

Answer 17

↑ synth of β-adrenergic receptors in cardiac/skeletal mm/fat

NO Δ in catacholmines

= ↑ temp

Question 18

Action of TH on CNS?

Answer 18

necessary for fetal CNS development (mother diet of iodide)

Cretinism

Question 19

Action of TH on growth?

Answer 19

synergistic w/ GH for bones

degrades proteins

Question 20

Iodine deficiency results in?

Answer 20

thyroid Φ maintain feedback reg ->

pit ↑ TSH -> stim growth of gland -> hypothyroidism (decrease T4 secretion)/goiter

Question 21

Adult Onset Hypothyroidism caused by?

Early labs?

Answer 21

antithyroid antibodies destroy gland
(U) Hashimoto thyroiditis

↑ TSH, N T3/4

Question 22

Antibody-induced Graves caused by?

Answer 22

hyperthyroidism

ABs mimic TSH (TSH levels will be low) -> ↑ TH prdxn -> lose feedback control

Question 23

Type I peripheral conversion happens where?

↓ by?

Results in?

Answer 23

liver, kidney, thyroid

↓ calories, severe stress

becomes unresponsive to TH = ↓ metabolic rate