Thyroid

Question 1

What is the primary constituent of the colloid of the thyriod gland?

Answer 1

Thryroglobulin (TG)

Question 2

What do parafollicular cells (C cells) secrete?

Answer 2

Calcitonin

Question 3

Which is considered the “thyroid hormone:” T3 or T4?

Answer 3

T3

Question 4

Which is considered the “prohormone:” T3 or T4?

Answer 4

T4

Question 5

What are the two ingredients for thyroid hormone (TH)?

Answer 5

Iodide and tyrosine

Question 6

What anion acts as a competitive inhibitor or iodide uptake?

Answer 6

Perchlorate (ClO4)

Question 7

Where does organification of iodide occur?

Answer 7

At the follicular cell-colloid interface

Question 8

Which enzyme catalyzes iodination of thyroglobulin?

Answer 8

Thyroperoxidase

Question 9

Where is thyroglobulin produced?

Answer 9

In the follicular cell

Question 10

What is the source of the tyrosine used to make thyroid hormone?

Answer 10

Thyroglobulin

Question 11

Where do all of the iodination and coupling reactions of TH synthesis occur?

Answer 11

On tyrosyl residues of TG

Question 12

Is most TH carried in bloodstream bound or unbound? To what is it bound?

Answer 12

99% exists bound to TBG

Question 13

Which inhibitory compound leads to goiter?

Answer 13

Thiourea drugs

Question 14

Why is T3 considered to be the active form of TH?

Answer 14

Because its affinity for the Th receptor is 10 fold greater for T3 than for T4

Question 15

What is the main action of TH?

Answer 15

Maintain basal metabolic rate

Question 16

What can congenital hypothyroidism lead to in a neonate?

Answer 16

Severe and irreversible mental retardation

Question 17

Define cretinism

Answer 17

Severely stunted physical and mental growth due to congenital hypothyroidism

Question 18

What are the CV effects of TH?

Answer 18

Upregulates beta adrenergic activity

Question 19

How does T3 provide negative feedback?

Answer 19

Free T3 and T4 can influence the response of the anterior pituitary to TRH (high levels reduce response, low levels sensitize response)

Question 20

Describe the Wolff-Chaikoff effect

Answer 20

Iodine deficient diets will lead to a decrease in TH synthesis, but paradoxically, a short term effect of high doses of iodine will also lead to a decrease in TH release. This is the Wolff-Chaikoff effect. This happens because high iodide will diminish the response to TSH.

Question 21

Is high iodide intake used for chronic management of hyperthyroidism?

Answer 21

No, because the Wolff-Chaikoff effect is only transient

Question 22

What is the pathophysiology of Graves’ Disease?

Answer 22

Autoantibodies mimic actions of TSH leading to hyperthyroidism

Question 23

Does the thyroid produce more T4 or T3?

Answer 23

Much more T4, but then T4 is later converted to T3

Question 24

In cases of severe illness, stress, or starvation, is more or less T3 produced?

Answer 24

Much less; advantageous to have a lower BMR

Question 25

What is the half-life of T4?

Answer 25

7 days

Question 26

What is the half-life of T3?

Answer 26

1 day

Question 27

What is the main cause of increased TOTAL (not free) T4 and T3?

Answer 27

Increased binding proteins

Question 28

What is the main cause of increased FREE T4 and T3?

Answer 28

Hyperthyroidism/Thyrotoxicosis

Question 29

What is the main cause of decreased TOTAL T4 and T3?

Answer 29

Hypothyroidism

Question 30

How can liver disease cause low total or free T3/T4?

Answer 30

Liver produces the binding proteins. Less binding proteins means less hormone.

Question 31

How can kidney disease cause low total or free T3/T4?

Answer 31

Proteins can leak out in urine. Less binding proteins means less hormone.

Question 32

The level of what is the primary indicator of someone's thyroid status (aka what do you check)?

Answer 32

TSH

Question 33

Is TSH elevated or reduced in primary hypothyroidism?

Answer 33

Elevated

Question 34

Is TSH elevated or reduced in primary hyperthyroidism?

Answer 34

Reduced

Question 35

When can we not rely on the TSH?

Answer 35

Anytime there is an abnormal pituitary gland

Question 36

Define thyrotoxicosis

Answer 36

High circulating levels of TH (does not always mean it's hyperthyroidism)

Question 37

What is true hyperthyroidism/

Answer 37

OVERPRODUCTION of T4 and T3

Question 38

How can radioactive iodine uptake and scan help us distinguish between true hyperthyroidism and thyrotoxicosis?

Answer 38

When TSH is low, there should be no uptake of iodine. A normal or elevated uptake of iodine in the setting of a low TSH indicated true hyperthyroidism.

Question 39

What is the most common cause of thyrotoxicosis?

Answer 39

Hashimoto's thyroiditis

Question 40

What are the most common causes of true hyperthyroidism?

Answer 40

Graves' disease and toxic nodules

Question 41

What is the pathophysiology of Graves' ophthalmopathy?

Answer 41

There are fibroblasts behind the eye that express TSH receptors. Binding of auto-antibodies to these receptors can cause the fibroblasts to differentiate into adipocytes.

Question 42

What is the skin finding of Graves' disease?

Answer 42

Pretibial myxedema

Question 43

What are the two medications used to treat Graves' disease? What is their mechanism?

Answer 43

Methimazole adn propylthiouracil; inhibit synthesis of thyroid hormone. Beta blockers to counteract systemic effects.

Question 44

What are other ways to treat Graves' disease?

Answer 44

Radioactive iodine and surgery

Question 45

What is the pathophysiology of Hashimoto's?

Answer 45

Autoantibodies against thyroid peroxidase and thyroglobulin

Question 46

What is the treatment for hypothyroidism?

Answer 46

Levothyroxine (synthetic T4)

Question 47

What is myxedema coma?

Answer 47

An extreme form of hypothyroidism. Life-threatening. High mortality rate.

Question 48

What is the most common type of malignant tumor of the thyroid?

Answer 48

Papillary

Question 49

What percentage of nodules are cancer?

Answer 49

10-15%

Question 50

What kind of spread does papillary thyroid cancer have?

Answer 50

Lymph node spread

Question 51

Define central hypothyroidism

Answer 51

A reduction in TH as a result of inadequate stimulation of a normal thyroid gland by TSH and may be secondary, due to pituitary disease, or tertiary, due to hypothalamic dysfunction.

Question 52

What is the prognosis of a papillary carcinoma of the thyroid?

Answer 52

Excellent

Question 53

Optically clear nuclei is indicative of which type of thyroid cancer?

Answer 53

Papillary carcinoma

Question 54

What is the prognosis of a anaplastic carcinoma of the thyroid?

Answer 54

Poor

Question 55

What are the three patterns of anaplastic carcinoma of the thyroid?

Answer 55

Spindle cell, giant cells, and squamoid cells

Question 56

What are the two types of follicular/hurthle cell carcinoma of the thyroid?

Answer 56

Minimally invasive and widely invasive

Question 57

What is the most common pathway that is messed up in thyroid cancer?

Answer 57

MAP kinase pathway

Question 58

What is the most common mutation in all thyroid cancer?

Answer 58

BRAF - leads to papillary carcinoma

Question 59

The thyroid gland arises from what?

Answer 59

Originates as a proliferation of endodermal epithelial cells on median surface of pharyngeal floor between 1st and 2nd arches

Question 60

85% of cases of congenital hypothyroidism are caused by what?

Answer 60

Abnormal development of the thyroid gland (dysgenesis)

Question 61

Those with congenital hypothyroidism due to mutation in PAX8 may also present with what abnormality?

Answer 61

Renal agenesis

Question 62

Those with congenital hypothyroidism due to mutation in TITF2 may also present with what abnormality?

Answer 62

Bamforth-Lazarus syndrome (very rare)

Question 63

Those with congenital hypothyroidism due to mutation in TITF2 may also present with what abnormality?

Answer 63

Respiratory distress and neurologic disorders

Question 64

Those with congenital hypothyroidism due to mutation in SCL26A4 also present with what?

Answer 64

Pendred syndrome - Aut rec disorder characterized by sensorineural congenital deafness and goiter

Question 65

What do THOX1 and THOX2 encode?

Answer 65

NADPH oxidases which are involved in H2O2 generation in the thyroid; H2O2 is an essential cofactor for iodination and coupling reactions