thyroid gland

Question 1

thyroid gland secretes:

Answer 1

• thyroid hormones (T3, T4)
• calcitonin

Question 2

what are the key features of the endocrine system

Answer 2

• release hormones into intercellular or perivascular CT spaces
• cells arranged in clusters or cords
• associated with dense capillary beds and wide thin-walled vessels called sinusoids

Question 3

what are follicles

Answer 3

• functional units of thyroid gland
• spheres of low cuboidal to high columnar cells
• centers filled with colloid

Question 4

what are follicular cells

Answer 4

• acidophilic
• polar cell morphology
• apical microvilli
• golgi, ER
• vaculoes
• large membrane-bound colloid droplets

Question 5

what do follicular cells store

Answer 5

pro-hormone in follicle lumen

Question 6

what do follicular cells secrete

Answer 6

active thyroid hormone (T3 and T4) into pericapillary space

Question 7

what do follicular cells concentrate

Answer 7

iodine from blood

Question 8

what is iodine essential for

Answer 8

T3/T4 synthesis

Question 9

what can an iodine deficiency cause

Answer 9

goiter

Question 10

what is thyroglobuoin

Answer 10

• glycoprotein
• synthesized by ER/golgi complex and secreted via secretory vesicles into follicle lumen

Question 11

where is thyroperoxidase and what does it do

Answer 11

• on apical surface
• iodinates thyroglobulin on tyrosines

Question 12

where is iodinated thyroglobulin taken up

Answer 12

follicular lumen

Question 13

what is thyroglobulin broken down into

Answer 13

• thyroxine (T4) and triiodothyronine (T3)

Question 14

how much of the circulating T3 is formed in the liver

Answer 14

83%

Question 15

what is thyroxine (T4)

Answer 15

• pro-hormone
• converted to T3 by target cells and liver

Question 16

what is thyronamines (TAMs)

Answer 16

family of decarboxylated and deiodinated metabolites of T3 and T4

Question 17

what are the three TH distributor proteins

Answer 17

• thyroxine-binding globulin
• transthyretin
• albumin

Question 18

what do TH distributor proteins form

Answer 18

a buffering network for free T4 in blood - helps protect against hypothyroidism or hyperthyroidism

Question 19

what kind of thyroid hormones enter target cells

Answer 19

only free T4 and T3

Question 20

describe the HPT axis

Answer 20

• TRH from hypothalamus stimulates adenohypophysis to release TSH
• TSH stimulates thryoid follicular cells

Question 21

what are goitrogens

Answer 21

substances that interfere with thyroid hormone production

Question 22

what happens if there is too much iodine

Answer 22

diminish T3/T4 hormone production

Question 23

what is triiodothyronine (T3)

Answer 23

• accelerates metabolic rate of body
• increase cell metabolism, growth, differentiation, development
• increases protein, carbohydrate and fat metabolism

Question 24

what do thyroid hormones influence

Answer 24

metabolism and function of all organs

Question 25

how do thyroid hormones function

Answer 25

via nuclear receptors

Question 26

what do thyroid hormone receptors do

Answer 26

regulate gene expression

Question 27

how are thyroid hormone receptor functions defined

Answer 27

mutations that cause resistance to thyroid hormone: RTH * mutations in TR beta and alpha

Question 28

what does UCP1 do

Answer 28

increases the conductance of the inner mitochondrial membrane to make BAT mitochondria generate heat rather than ATP

Question 29

what does stress do to the HPT axis

Answer 29

shuts it down - net lower TH production

Question 30

what does cold do to the HPT axis

Answer 30

activates expression of thyroid hormone

Question 31

how does T4 regulate cancer

Answer 31

via the plasma membrane associated integrin receptors

Question 32

describe hypothyroidism

Answer 32

* lethargy and obestity (most common) * derm symptoms - alopcecia along trunk or tail head - skin thickened - dull dry hair

Question 33

what are less common signs of hypothyroidism in dogs

Answer 33

* cardiovascular * neuromuscular myopathies and megaesophagus * facial nerve paralysis, vestibular disease, lower motor neuron disorders * repro disorders in females * corneal lipid reposits and GI problems

Question 34

how to treat canine hypothyroidism

Answer 34

levothyroxine = synthetic T4

Question 35

what is the most common type of primary hypothyroidism in dogs

Answer 35

lymphocytic thyroiditis

Question 36

what is lymphocytic thyroiditis

Answer 36

* circulating thyroid autoantibodies * antibodies to follicular cell, colloid, or thyroglobulin antigens

Question 37

what do high doses of glucocorticoids do to thyroid function

Answer 37

reduce conversion of thyroxine (T4) to the more active triiodothyronine (T3)

Question 38

hyperthyroidism

Answer 38

most common endocrinopathy of cats, typically caused by adenomatous hyperplasia of the thyroid gland

Question 39

what are clinical signs of hyperthyroidism

Answer 39

* hypermetabolism * activation of symathetic nervous system * long-standing hyperthyroidism leads to hypertrophic cardiomyopathy, and death * liver hypermetabolism

Question 40

what is toxic nodular goiter caused by

Answer 40

aberrant signal transduction of the thyroid follicular cells

Question 41

what does the TSH receptor activate | hyperthyroidism cats

Answer 41

receptor-coupled guanosine triphosphate-binding proteins (G proteins) in thyroid follicular cells

Question 42

does diet play a role in feline hyperthyroidism

Answer 42

canned cat food has been implicated as a cause because BADGE, substance used to make liner of easy-open cans and cats susceptible to toxic effects of BADGE

Question 43

what is the treatment of choice for cats with hyperthyroidism

Answer 43

radioactive iodine (RAI) therapy

Question 44

what does felimazole (methimazole) do

Answer 44

prevents iodine and perozidase form their normal interactions with thyroglobulin to form T4 and T3

Question 45

what is RAI therapy

Answer 45

* thyroid gland absorbs all iodine in blood * large dose of RAI is taken, the radiation collects in thyroid cells * destroys the thyroid gland and cancer cells

Question 46

what are the advantages and disadvantages to RAI therapy

Answer 46

advantages * gets tid of tumor completely * targets thyroid tumor cells elsewhere in body disadvantages * requires cat to be in tx ward for 2 wks * kitty litter is handles as radioactive waste