4_Thyroid

Question 1

Describe the location of the thyroid gland.

Answer 1

below larynx of either side, anterior to trachea in an H-shape

Question 2

What percentage of thyroid hormone does T3 make up?

Answer 2

7%

Question 3

t1/2 of T3

Answer 3

1 day

Question 4

t12 of T4

Answer 4

6 days

Question 5

Describe the relative potencies of T3 & T4.

Answer 5

T3 4x more potent

Question 6

Describe the cell structure of the thyroid gland.

Answer 6

follicles of cuboidal epithelium surrounded by colloid

Question 7

How is iodine trapped?

Answer 7

Na/K ATPase & TSH-linked NIS (Na/I symporter)

Question 8

Where is TRH synthesized?

Answer 8

PVN of hypothalamus (affected by emotion, temp, etc)

Question 9

Where is TSH secreted?

Answer 9

anterior pituitary

Question 10

Other name for TSH?

Answer 10

thyrotropin

Question 11

Describe the receptor pathway for TSH.

Answer 11

G-alpha-S

Question 12

What is the effect of TSH binding its receptor in the thyroid?

Answer 12

increased activity of NIS, iodination of Tyr, Tg proteolysis; thyroid hyperplasia

Question 13

What is the feedback circuit for TSH?

Answer 13

T3 & T4 only

Question 14

Describe the steps in the formation of thyroid hormones.

Answer 14

1) TSH-dependent I trapping, 2) peroxidase oxidation, 3) Tg precursor secretion, 4) peroxidase iodization, 5) Tg auto-coupling, 5) pinocytosis, 6) proteolysis and secretion

Question 15

Where is peroxidase located in the thyroid cuboidal cell?

Answer 15

at the apical membrane (colloid side)

Question 16

Describe the action of peroxidase in the thyroid?

Answer 16

1) oxidizes iodide to yield I2 or I3-, 2) iodizes Tyr

Question 17

What are the products of Tg auto-coupling?

Answer 17

1) MIT + DIT = T3; 2) DIT + MIT = RT3; 3) DIT + DIT = T4

Question 18

What is the chemical numbering name for T3?

Answer 18

3,5,3’-T3

Question 19

What is the chemical numbering name for RT3?

Answer 19

3,3’,5-T3

Question 20

What is the physiologic function of RT3?

Answer 20

none known

Question 21

Describe the structure of Tg precursor.

Answer 21

chain of Tyr

Question 22

How is Tg proteolyzed after reuptake via pinocytosis?

Answer 22

fusion with a lysosome

Question 23

Describe the relative concentrations of T3 and T4 in the plasma.

Answer 23

T4 much greater than T3

Question 24

How are T3 & T4 transported in the plasma?

Answer 24

thyroxine-binding globulin

Question 25

How are T3 & T4 imported?

Answer 25

via AA transporters

Question 26

Describe the storage of T3 & T4.

Answer 26

stored for days-week intracellularly

Question 27

Why is T3 more potent?

Answer 27

T4 binds stronger intracellularly

Question 28

What are the adverse effects brought about by the T3/T4 receptor?

Answer 28

CV: increased HR, contractility, tissue flow, CO

Question 29

What is the function of T3/T4 via its receptor?

Answer 29

increase BMR (via increased Na/K-ATPase, increased plasma glucose, increased protein turnover, increased mitochondria)

Question 30

Describe the receptor action of T3/T4.

Answer 30

nuclear hormone receptor forms a homodimer or heterodimer with RXR at specific thryoid HREs

Question 31

What is graves disease?

Answer 31

a toxic goiter

Question 32

What is TSI?

Answer 32

thyroid-stimulating immunoglobulin, an antibody that mimics TSH

Question 33

How is hyperthyroidism caused?

Answer 33

by a toxic goiter (Graves Disease)

Question 34

How is hyperthyroidism diagnosed?

Answer 34

1) increased T3 or T4, 2) TSI, 3) BMR +30 to +60

Question 35

How is hyperthyroidism treated?

Answer 35

surgery or propylthiouracil

Question 36

How does propylthiouracil work?

Answer 36

blocks MIT/DIT coupling and iodination via inhibiting peroxidase

Question 37

What is a side effect of propylthiouracil?

Answer 37

can increase TSH and cause a goiter

Question 38

What are non-obvious symptoms of hyperthyroidism?

Answer 38

sweating, fatigue, fine hand tremor, diarrhea, exophthalmos

Question 39

What is exophthalmos?

Answer 39

protrusion of eyeball caused by swelling of retro-orbital tissues and degeneration of extra-ocular muscles

Question 40

How is an endemic nontoxic colloid goiter caused?

Answer 40

iodine deficiency

Question 41

How is an endemic nontoxic colloid goiter treated?

Answer 41

iodine

Question 42

What causes an idiopathic nontoxic colloid goiter?

Answer 42

thyroiditis: inflammation causes hypothyroidism, which increases TSH; or T3/T4 synthetic enzyme defects

Question 43

What is myxedema?

Answer 43

facial swelling due to increased proteoglycans and hyaluronic acid

Question 44

What are the effects of hypothyroidism?

Answer 44

failure of trophic functions (less hair, scaly skin, husky voice), myxedema, arteriosclerosis, altered lipid metabolism, less bile/cholesterol secretion

Question 45

What is cretinism?

Answer 45

extreme hypothyroidism in infance or early childhood leading to growth failure

Question 46

What are the various forms of cretinism?

Answer 46

1) congenital, 2) genetic, 3) endemic

Question 47

What causes congenital cretinism?

Answer 47

no thyroid

Question 48

What causes genetic cretinism?

Answer 48

no T3/T4 production

Question 49

What causes endemic cretinism?

Answer 49

inadequate dietary iodine