Midterm 2 - Importance of Thyroid Hormones

Question 1

where is the thyroid gland located

Answer 1

both side of the trachea, below the larynx

Question 2

what are the 2 lobes of the thyroid gland bridged by

Answer 2

isthmus

Question 3

what are characteristic of the thyroid gland

Answer 3

heavily vascularized
heaviest of pure endocrine glands

Question 4

what is the thyroid gland composed of

Answer 4

numerous follicles

Question 5

what are follicles in the thyroid gland

Answer 5

a single layer of epithelial cells that release thyroid hormones
lumen filled with protein rich fluid (colloid)

Question 6

what occurs between follicles in the thyroid gland

Answer 6

parafollicular cells (C-cells) secrete calcitonin

Question 7

how much of circulating thyroid hormones does TBG bind to

Answer 7

70-80% - remaining binds to other albumins

Question 8

what percentage of T3 and T4 are free in blood

Answer 8

0.03%

Question 9

why is there several days of hormone available bound to TBG

Answer 9

only 0.03% free in blood and diffuse to tissues - only free hormone is active

Question 10

what are free and bound forms in

Answer 10

equilibrium

Question 11

what cells do thyroid hormones act on

Answer 11

all cells of the body

Question 12

what do thyroid hormones act on all cells to do

Answer 12

increase basal metabolic rate by increasing heat production and O2 consumption

Question 13

where does O2 consumption not increase due to thyroid hormones

Answer 13

brain
gonads
spleen

Question 14

what do TH stimulate during development

Answer 14

GH

Question 15

what can a TH deficiency lead to

Answer 15

dwarfism - TH is important for bone and tissue growth

Question 16

when are TH critical for normal maturation of brain function

Answer 16

during the last phase of foetal development and early stage after birth

Question 17

what can a lack of TH lead to

Answer 17

cretinism

Question 18

what do TH increase

Answer 18

the number of adrenalin/noreadrenalin receptors –> boost sensitivity to SNS

Question 19

what are TH essential for

Answer 19

gonadal normal function

Question 20

what does a lack of TH in gonad lead to

Answer 20

reduced sperm produciton
irregular cycles

Question 21

how does TH effect reflexes

Answer 21

increases nerve conduction velocity –> faster reflexes

Question 22

what is hypothyroidism mainly due to in humans

Answer 22

iodine deficiency

Question 23

what can hypothyroidism result in

Answer 23

reduced growth and mental retardation

Question 24

what is hypothyroidism mainly due to in dogs

Answer 24

autoimmune disorders that destroy follicular cells = primary hypothyroidism

Question 25

what do lab tests show in dogs with hypothyroidism

Answer 25

low T4 and T3 with high TSH

Question 26

what is secondary hypothyroidism due to

Answer 26

low secretion of TSH, mainly due to injury to pituitary or hypothalamus

Question 27

what cell types are affected by hypothyroidism

Answer 27

most

Question 28

symptoms of hypothyroidism

Answer 28

reduced heat production and tolerance to cold
sluggish animal, not feeding but gaining weight
impaired reproduction
constipation

Question 29

treatment for hypothyroidism

Answer 29

thyroxine for the rest of life

Question 30

what is a goiter

Answer 30

enlarged thyroid gland

Question 31

what are causes of goiter

Answer 31

iodine deficiency
tumor and inflammation
lack of thyroid hormones increases TRH and TSH release (lack of feedback) which stimulates multiplication (hyperplasia) and volume (hypertrophy) of follicular cells

Question 32

what area of animal are gaiters more frequent in

Answer 32

inland - coastal air, vegetation, and marine organisms are a good source of iodine

Question 33

hyperthyroidism

Answer 33

over-production of thyroid hormones

Question 34

what animal is hyperthyroidism frequent in

Answer 34

cats - unknown cause

Question 35

what does hyperthyroidism target

Answer 35

many target organs

Question 36

symptoms of hyperthyroidism

Answer 36

big appetite associated with weight loss
excitable and nervous
increased heart rate, respiration and digestive passage

Question 37

treatment of hyperthyroidism

Answer 37

surgery, radioactive I2 to destroy follicular cells

Question 38

what is Tgb

Answer 38

a glycoprotein with over 120 tyrosine residues