Unit 2 - Thyroid gland

Question 1

What is the structure of the thyroid gland?

Answer 1

it is made up of follicular cells and parafollicular cells

Question 2

What is in the lumen of follicular cells?

Answer 2

colloid

Question 3

What do parafollicular cells produce?

Answer 3

calcitonin

Question 4

What hormones are secreted from follicular cells?

Answer 4

thyroxine (T4) and triopdpthyronine (T3)

Question 5

What is T3 and T4 synthesized from?

Answer 5

tyrosine and iodide

Question 6

What are T3 and T4 bound to in colloid?

Answer 6

thyroglobulin

Question 7

What is the main function of T3 and T4?

Answer 7

increase the basal metabolic rate (energy production at rest)

Question 8

What is goiter?

Answer 8

Iodine deficiency that leads to the reduction in thyroid hormone production slowing the rate of oxidation of all cells which causes an enlarged thyroid gland

Question 9

What synthesizes thyroglobulin?

Answer 9

follicular cells

Question 10

What synthesizes ‘trap’ I?

Answer 10

follicular cells

Question 11

When I- is released into the lumen of the follicle, what happens?

Answer 11

it is converted into highly reactive I^0

Question 12

What does I^0 do?

Answer 12

it iodinates tyrosine molecules within the thyroglobulin protein

Question 13

If iodinated tyrosinases are adjacent to one another what happens?

Answer 13

they condense and form T3 and T4

Question 14

When T3 and T4 are needed, what occurs within follicular cells to free them?

Answer 14

TG containing T3 and T4 is taken up by phagocytosis and inside of follicular cells it is attacked by proteases, which free T3 and T4.

Question 15

How is the secretion of thyroid hormones regulated?

Answer 15

deviations from homeostasis are detected by the hypothalamus and stimulate its release

Question 16

When deviation from homeostasis is sensed, what is released by the hypothalamus?

Answer 16

TRH

Question 17

What does TRH do?

Answer 17

it stimulates the release of TSH from the anterior pituitary

Question 18

What does TSH do?

Answer 18

it enters the circulation which then tells the thyroid gland to release T3 and T4

Question 19

How do thyroid hormones effect calorigenesis?

Answer 19

increase O2 consumption, increase BMR, increase heat dissipation, increase beta adrenergic receptors, increase vasodilation, increase cardiac output

Question 20

How do thyroid hormones effect carbohydrate metabolism?

Answer 20

they provide more glucose

Question 21

How do thyroid hormones effect lipid metabolism?

Answer 21

provide more fatty acids

Question 22

How do thyroid hormones effect protein synthesis?

Answer 22

stimulates pre-adolescent growth and development and inhibits hyperthyroidism

Question 23

How do thyroid hormones effect bone?

Answer 23

maintain growth and epiphyseal closure

Question 24

How do thyroid hormones effect muscle?

Answer 24

they maintain muscle protein synthesis

Question 25

How do thyroid hormones effect skin?

Answer 25

maintain protein synthesis and turn over, maintain hair coat, and sebaceous gland activity

Question 26

How do thyroid hormones effect brain development?

Answer 26

increase fetal brain development, synapse formation, and myelination

Question 27

In which species will you most likely encounter hyperthyroidism?

Answer 27

older cats

Question 28

What are the most common causes of hyperthyroidism?

Answer 28

Thyroid gland tumors

Question 29

What are common physical manifestations of hyperthyroidism?

Answer 29

poor hair coat, diarrhea, weight loss, heat intolerance, increased nail growth, goiter, vomiting, weak, and nervousness

Question 30

What is hyperthyroidism treated with?

Answer 30

Methimazole, surgery, or radioactive I

Question 31

What does Methimazole do?

Answer 31

inhibits T4 formation

Question 32

In which species will you most likely encounter hypothyroidism?

Answer 32

dogs

Question 33

Are there breeds which are predisposed for hypothyroidism?

Answer 33

yes, especially golden retrievers and doberman pinchers

Question 34

What is primary hypothyroidism caused by and what happens after administering TSH?

Answer 34

it is a thyroid lesion; no increase in T4 after administering TSH

Question 35

What is secondary hypothyroidism caused by and what happens after administering TRH?

Answer 35

pituitary lesion, no increase in TSH after administrating TRH

Question 36

What is tertiary hypothyroidism caused by and what happens after administering TRH?

Answer 36

hypothalamic lesion, increase in TSH after administering TRH

Question 37

What is the most common type of hypothyroidism?

Answer 37

primary

Question 38

What is cretenism?

Answer 38

congenital hypothyroidism

Question 39

how is hypothyroidism treated?

Answer 39

replacement therapy with synthetic thyroxine-levothyroxine