Physiology V

Question 1

What effect do T3/T4 have on the heart?

Answer 1

Increases B1 receptors in the heart. This increases CO, HR, SV, and contractility (p.295)

Question 2

What effect do T3/T4 have on metabolic rate?

Answer 2

Increase basal metabolic rate via increased Na+/K+-ATPase activity. This increases O2 consumption, RR, and body temperature (p.295)

Question 3

What effect do T3/T4 have on glucose metabolism?

Answer 3

Increase glycogenolysis, increase gluconeogenesis, increases lipolysis (p.295)

Question 4

What are the four functions of T3?

Answer 4

Brain maturation, bone growth, beta-adrenergic effects, increased basal metabolic rate (4Bs) (p.295)

Question 5

What binds T3/T4 in the blood?

Answer 5

Thyroxine-binding globulin (TBG) (p.295)

Question 6

What forms of T3/T4 are active?

Answer 6

Only free hormones are active (p.295)

Question 7

What pathologic state decreases Thyroxine-binding globulin (TBG)?

Answer 7

Hepatic failure (p.295)

Question 8

What physiologic state increases Thyroxine-binding globulin (TBG)?

Answer 8

Pregnancy (or OCP use) (p.295)

Question 9

What is the effect of estrogen on Thyroxine-binding globulin (TBG)?

Answer 9

Estrogen increases TBG (p.295)

Question 10

What converts T4 to T3?

Answer 10

T4 is converted to T3 in peripheral tissues by 5’-deiodinase (p.295)

Question 11

Which is the more major thyroid product, T4 or T3?

Answer 11

T4 is the major product (p.295)

Question 12

Compare the receptor binding affinities of T3 vs T4.

Answer 12

T3 binds with greater affinity (p.295)

Question 13

What enzyme is responsible for the oxidation and organification of iodide?

Answer 13

Peroxidase (p.295)

Question 14

What enzyme is responsible for the coupling of MIT and DIT?

Answer 14

Peroxidase (p.295)

Question 15

What is the mechanism of action of Propylthiouracil?

Answer 15

It inhibits both peroxidase and 5’deiodinase to decrease Iodine production and thus to decrease thyroid hormone production (p.295)

Question 16

What is the mechanism of action of Methimazole?

Answer 16

It inhibits peroxidase to decrease Iodine production and thus to decrease thyroid hormone production (p.295)

Question 17

What is the difference in mechanism between Methimazole and Propylthiouracil?

Answer 17

Propylthiouracil inhibits both peroxidase and 5’deiodinase; Methimazole inhibits peroxidase only (p.295)

Question 18

Describe the regulation of thyroid hormones.

Answer 18

TRH from the hypothalamus stimulates TSH in the pituitary. This stimulates folicular cells to release T3 and T4. There is negative feedback by free T3 to the anterior pituitary which decreases sensitivity to TRH (p.295)

Question 19

What role does T3 play in negative feedback?

Answer 19

There is negative feedback by free T3 to the anterior pituitary which decreases sensitivity to TRH (p.295)

Question 20

What do Thyroid stimulating immunoglobulins (TSIs) do?

Answer 20

Stimulate follicular cells (p.295)

Question 21

In what disease state are Thyroid stimulating immunoglobulins (TSIs) elevated?

Answer 21

Graves’ disease (p.295)

Question 22

What is the Wolff Chaikoff effect?

Answer 22

Excess iodine temporarily inhibits thyroid peroxidase which decreases iodine organification and thus decreases T3/T4 production (p.295)

Question 23

What can inhibit the oxidation of I- ions in the production of thyroid hormone?

Answer 23

Anions such as perchlorate and pertechnetate (p.295)

Question 24

What amino acids are needed for thyroid hormone production?

Answer 24

Tyrosine residues; phenylalanine is a precursor to tyrosine so deficiency of either may cause hypothyroidism (p.295)