Thyroid Gland

Question 1

Which hormone, T3 or T4 is active?

Answer 1

T3

Question 2

Which thyroid hormone is the main secretory product?

Answer 2

T4 (90%)

Question 3

What is the secretory product of the thyroid gland?

Answer 3

Iodothyronines

Question 4

How is T4 converted to T3?

Answer 4

Peripheral conversion w/ deiodinase

enzyme = 5’ - iodinase

Question 5

Iodide =

Answer 5

I-

Inside follicular cell

Question 6

Iodine =

Answer 6

I2

In apical lumen

Question 7

What is a treatment for hyperthyroidsm?

Answer 7

PTU –> Inhibits peroxidase + NIS

Wolff-Chiakoff Effect –> increased levels of I- (iodide) prevents the synthesis of thyroid hormones cause you need decreased iodide for deiodinase to convert

T4 –> T3 and get them out of storage form and into blood stream

Question 8

How is iodine stored?

Answer 8

It is stored in follicular colloids iodinated as tyrosines attached to thyrogobulin (need to use deiodinase to break them apart)

Question 9

How can you assess the activity of the thyroid gland?

Answer 9

By radioactive iodine uptake

Question 10

Which thyroid hormone has a longer half life?

Answer 10

T4 –> 6 days

vs. 1 day for T3

thats why T4 = most circulating hormone

Question 11

How can we assess circulating levels of TBG?

Answer 11

With a resin uptake test

Thyroid function involves the interaction of many hormones, including triiodothyronine (T3) and thyroxine (T4). Both of these hormones exist in two forms in the blood. The more abundant forms are bound to a carrier protein called thyroxin-binding globulin (TBG), which helps transport the hormones through the body. The less abundant forms circulate unattached or “free.” Only the free forms of the thyroid hormones (free T4 and free T3) are available to affect body processes.

The T3 resin uptake is used by doctors to estimate the amount of TBG in the blood, and how much T4 and T3 in the blood is free form and available to affect the body.

Question 12

Explain what happens to TBG, T4, and T3 in these disorders during the resin uptake test:

Hyperthyroidism

Hypothyroidism

High TBG

Low TBG

Hepatic Failure

Preganancy

Answer 12

Question 13

What enzyme converts Iodide to Iodine?

Answer 13

Thyroid Peroxidase (via pendrin transporter)

Question 14

What factors stimulate thyroid hormone secretion?

Answer 14

TSH

Thyroid stimulating immunogobulins

Increased TBG levels –> ex = pregnancy

Question 15

What factors inhibit thyroid hormone secretion?

Answer 15

I- deficiency –> can’t make T3

Deiodinase deficiency

Excessive I- intake (Wolff-Chaikoff effect)

Perchlorate + thiocyanate –> inhibit Na + I- cotransport

Propylthiouracil (PTU) –> inhibits peroxidase enzyme

Decreased TBG levels –> ex = liver disease

Question 16

What do people with hypothyrodism take?

Answer 16

Thyroxine (T4) injection, increases BMR

Question 17

Review this chart (good things to look for in stem)

Answer 17

Question 18

Are TSH levels low or high in hyperthyroidism?

Answer 18

Low

Question 19

Are TSH levels low or high in hypothyroidism?

Answer 19

High

Question 20

What is the other name for hyperthyroidism?

Answer 20

Thyrotoxicosis

Question 21

What is primary hyperthyroidism?

Answer 21

Grave’s Disease

Question 22

What causes Grave’s disease?

Answer 22

Thyroid stimulating immunogobulins (TSI’s) stimulate the TSH receptor without actually having the TSH hormone.

Soooo TSH receptor is being constantly stimulated!

But, you still have low TSH hormone cause all the high T3 + T4 hormones are stopping it from making more through negative feedback.

Remember main symptom = exophthalmos

Question 23

What causes Hashimoto’s Thyroiditis?

Answer 23

Usually thyroid gland destrction –> causing impaired thyroid hormone synthesis and decreased T3 + T4 levels

TSH = high –> causes trophic effect (Goiter)

Question 24

What is caused by untreated postnatal hypothyroidism?

Answer 24

Cretinism

Question 25

The TSH test is used for diagnosing both hyperthyroidism and hypothyroidsim.

What would the levels of TSH, T3/T4, TSI, and Radioactive Iodine Uptake test be for these diseases:

Hyperthyroidism

1. Grave’s
2. Thyroditis (w/ hyperthyroidism)
3. Thyroid nodules

Hypothyroidism

1. Hashimoto’s disease
2. Pituitary abnormality

Answer 25