Thyroid

Question 1

What inhibits the iodine/sodium transporter into the follicular lumen?

Answer 1

Thiocyanate, perchlorate anions

Question 2

What catalyzes oxidation of I- to I2?

What inhibits this enzyme?

Answer 2

Peroxidase enzyme

PTU (propylthiouracil)

Question 3

What is the Wolff-Chaikoff effect?

Answer 3

High levels of I- inhibit organification (I2 combining with tyrosine on thryoglobulin), or formation of MIT and DIT –> inhibit thyroid hormone synthesis

(High doses of I- will only increase hormone synthesis initially)

Question 4

How are T3 and T4 made?

Answer 4

DIT + DIT = T4
DIT + MIT = T3

thyroglobulin digested and T3, T4 released into circulation (mostly bound to thyroid binding globulin)

Question 5

What converts T4 to T3?

Answer 5

5-iodinase

T3 3-4x as potent as T4

Question 6

Most T4 and T3 in the blood is free. T4 is mostly bound to…

Answer 6

TBG (thyroid binding globulin)

Also to TBPA, albumin

• Very small changes in T4 will affect TSH

Question 7

Iodide _____ regulates its uptake

Answer 7

negatively

Question 8

What is the Jod-Basedow Effect?

Answer 8

Excessive iodine induced hyperthyroidism (opposite Wolff-Chaikoff)
- Seen in disease: Graves, toxic multinodular goiter, toxic adenoma

Question 9

What increases in pregnancy?

Answer 9

TBG

hCG (increase intrinsic thyrotropic activity - activate TSH receptor)

Question 10

Thyroid hormone increases…

Answer 10

Basal metabolic rate (and contractility/SV) via:

• Na/K ATPase
• beta-1 adrenergic receptors

Question 11

Causes of hypothyroidism:

Answer 11

• I- deficiency
• Autoantibody destruction of thyroid
• Hypothalamic or pituitary disease (less TRH, TSH)
• Removal of thyroid
• Diseases that interfere with thyroid hormone production

**If problem in the thyroid gland, goiter will result (low T3 and T4 stimulate TSH)

Question 12

What is myxedema?

Answer 12

Adult-onset hypothyroidism

• tiredness, lethargy, decreased metabolic rate
• slowing of mental fxn / motor activity
• cold intolerance
• weight gain
• goiter (stimulation of follicular cells and increased blood flow)
• hair loss, dry skin

maybe coma

Question 13

Primary vs. secondary hypothyroidism:

Answer 13

Primary: thyroid can’t produce (is stimulated)
Secondary: thyroid isn’t being stimulated (TSH/TRH deficiency)

Question 14

Treatment of hypothyroidism?

Answer 14

Levothyroxine

Question 15

Graves’ Disease has ________ of adenyl cyclase

Answer 15

“locked” activation

IgG autoantibody stimulates TSH receptor

Question 16

Symptoms of Graves’

Answer 16

• nervousness, irritability
• fatigue
• heat intolerance
• weight loss
• diffuse goiter
• atrial fibrillation (beta-1 adrenergic receptors)
• risk of osteoporosis, decreased muscle mass

Question 17

Why do exophthalmos and dermopathy result from Graves’?

Answer 17

Fibroblasts in orbit and overlying shin express TSH receptor

- glycosaminoglycan buildup, inflammation, fibrosis, edema

Question 18

Treatment of hyperthyroidism?

Answer 18

• Beta-blockers
• Surgery or radioactive iodine or PTU/methimazole

PTU blocks: peroxidase-mediated oxidation, organification, and coupling steps, as well as peripheral conversion of T4 to T3

Question 19

Drugs that block iodine uptake?

Answer 19

• Pertechnetate
• Perchlorate
• Thiocyanate
• Nitrate

Question 20

What does lithium do in the thyroid?

Answer 20

Inhibit iodination of thyroglobulin

Question 21

What is a key differential point of subacute (granulomatous) thyroiditis?

Answer 21

IT REALLY HURTS

(DeQuervain’s)

• transient hyperthyroidism
• follows a viral illness
• self-limited (doesn’t progress to hypothyroidism)

Question 22

What is Reidel’s fibrosing thyroiditis?

Answer 22

Extensive fibrosis, chronic inflammation (“hard as wood”)

- can extend to airway