Lecture 7 - Thyroid Phys (Also a Pharm lecture)

Question 1

How much iodine do you need from your diet per day?

Answer 1

150 ug/d

this is needed for T4 production

Question 2

The production of T3 and T4 is dependent on…

Answer 2

Iodine

Selenium

Question 3

What are factors that can inhibit deiodination?

Answer 3

drugs 
selenium deficiency 
burns
trauma
disease
diet

Question 4

What is the effect of starvation on T3 levels?

Answer 4

goes down

Question 5

Most circulating TH is bound to….

Answer 5

plasma proteins
>99% bound

mainly thyroxin binding globulin

0. 03% free T4
1. 3% free T3

Question 6

Thyroxine

Answer 6

T4

Question 7

What is the mechanism by which iodine is accumulated into the follicle cell?

Answer 7

NIS

sodium - iodine symporter

Question 8

What is the most abundant form of thyroid hormone released by the thyroid?

Answer 8

T4

Question 9

What influences the production of T4?

Answer 9

TRH levels released from the hypothalamus

Question 10

What factors alter the production of TRH released from the hypothalamus?

Answer 10

cold increases it
acute psychosis increases it
circadian and pulsatile rhythms increase it

severe stress decreases it

Question 11

TRH

Answer 11

Thyroid releasing hormone

released from the hypothalamus to activate the pituitary gland

Question 12

TSH

Answer 12

thyroid stimulating hormone released by the pituitary in response to TRH from hypothalamus

Question 13

If you remove the pituitary gland, what will happen to the thyroid?

Answer 13

hypothyroidism because you don’t have TSH stimulating the thyroid

Question 14

What happens if you administer synthetic TSH post removal of pituitary?

Answer 14

you will have thyroid function restored

Question 15

What might happen in the long term if you administer TSH?

Answer 15

goiter

Question 16

Wolff - Chaikoff Effect

Answer 16

thyroid gland autoregulation

when there is really high iodine levels it actually suppress the production of thyroglobulin

Question 17

What does thyroid escape mean in regards to autoregulation?

Answer 17

If a pt is exposed to high levels of iodine for a long period of time (roughly 10 days) they will eventually down regulate the NIS so that they can return to normal levels of synthesis (escape)

Question 18

What are mechanisms by which thyroid activity is regulated?

Answer 18

hypothalamus
pituitary
autoregulation

Question 19

What happens when the thyroid hormone reaches its target organ?

Answer 19

it binds to the thyroid hormone receptor (TR) and disassociates from protein used to transport and protect hormone in plasma. Then the hormone gets into the cell where it goes into the nucleus.
T 4 is converted to T3 in the nucleus by D1

Question 20

What has the highest affinity to the thyroid hormone receptor?

Answer 20

T3

Question 21

Where is T3 and T4 degraded and where is it excreted?

Answer 21

degraded in liver

excreted in bile

Question 22

What are the sxs of hyperthyroidism?

Answer 22

nervousness
weight loss
hyperphagia
heat intolerance
warm, soft skin 
high BMR

Question 23

Subclinical hypothyroidism

Answer 23

normal free T4 and T3 and increase TSH

asymptomatic

Levothyroxine ONLY if they have hyperlipidemia