Chapter 122: Disorders of the Thyroid Gland

Question 1

at least this amount of daily dietary intake of iodine is needed to ensure adequate production of thyroid hormone

Answer 1

100 ug

Question 2

leading cause of thyroid - related disorders

Answer 2

iodine deficiency

Question 3

Components of Pendred syndrome

Answer 3

mild hypothyroidism
goiter
hearing loss

Question 4

function of Tg

Answer 4

tissue specific protein that serves as a matrix for the synthesis of hormone and as a vehicle for its storage

Question 5

enzyme responsible for coupling of iodotyrosine residues

Answer 5

Thyroperoxidase (TPO)

Question 6

plasma protein which accounts for nearly 75% of circulating hormone.

What is the affinity of this protein to T4 and T3?

Answer 6

TBG

T4: high
T3: lower

Question 7

Proteins that bind thyroid hormones

Answer 7

TG (75%)
Transthyretin (10%)
Albumin: (10 - 20%)

Question 8

METABOLISM of THYROID HORMONES:

What action must occur first before T4 can exert most of its biologic actions?

Answer 8

Deiodination of T4 to T3

Question 9

METABOLISM of THYROID HORMONES:

Types I deiodinase:
- found in tissues of _______, _____, and ______

Positively regulated by: ______
Reduced: _______

Inhibited by antithyroid drug: _______

Answer 9

Tissues of
KIDNEY, LIVER and THYROID
(KI LI T1)

(+) regulation: by Thyroid Hormone
(-): by pathophysiologic conditions such as starvation and non - thyroidal illness

Inhibited by: PROPYLTHIOURACIL

Question 10

METABOLISM of THYROID HORMONES:

Types IIdeiodinase:
- found in tissues of _______, _____, ______ and _____; has more recently been found in _____

negatively regulated by : _____

Answer 10

skin, placenta, pituitary, CNS; thyroid

(-) regulated by: THYROID hormone (as opposed to deiodinase I)

unaffected by PTU

Question 11

Type III deiodinase found in
____, ____ and ____
present in high levels in ____

Answer 11

brain
skin
placenta

high levels in FETAL TISSUE

Question 12

alpha subunit of TSH is similar to what other hormones? (4)

Beta unit function: ________

Answer 12

1. pituitary hormones
2. FSH
3. LH
4. Chorionic Gonadrotopin

B for binding. responsible for the binding of the hormone to its receptor in the basal membrane of the thyroid cell

Question 13

CONTROL OF THYROID FUNCTION:

Primary internal regulatory of thyroid function, and it influences virtually all phases of thyroid metabolism.

Answer 13

Anterior Pituitary

Question 14

CONTROL OF THYROID FUNCTION:

what happens to T4, T3 and TSH when you withdraw iodide from diet?

Answer 14

rapid DECREASE in serum T4

and

INCREASE in serum TSH

T3 initially unaffected, but eventually DECLINE with prolonged withdrawal

Question 15

How does goiter occur with prolonged iodine deficiency?

Answer 15

Prolonged iodine deficiency –> TSH - stimulated cell proliferation –> goiter

Question 16

Components of cretinism:

Answer 16

mental retardation

deafness

mutism

stunted growth

Question 17

THYROID HORMONE MECHANISM OF ACTION:

Most effects of thyroid hormone are now believed to be
exerted by interactions with specific nuclear thyroid hormone
receptors, which result in the altered expression of specific
genes. What event related to the thyroid hormones must occur before they can be effective?

Answer 17

Conversion of T4 to T3

Question 18

STEPS in Synthesis and Release of Thyroid Hormone:

Answer 18

1. Iodide transport into thyrocyte (c/o NA - I symporter)
2. TG synthesized in ER
3. Uniodinated TG travels to apical surface
4. Tg is IODINATED
5. Coupling of Iodotyrosyls to form T3 and T4
6. Tg retrieved by micropinocytosis, enters endosome - lysosomal pathway - where PROTEOLYSIS and HORMONE release Occurs

OR Tg retrieved by MACRO pinocytosis travels to lysosomes in colloid droplets

7. Thyroid hormones and precursors leave the lysosomes - T4 and T3 enter the bloodstream
8. MIT and DIT deiodinated Iodide is recirculated.