The Thyroid Gland

Question 1

vertebral extent of thyroid

Answer 1

C5-T1

Question 2

the two thyroid hormones

Answer 2

T3 (triiodothyronine) and T4 (thyroxine)

Question 3

what is contained in the follicles of teh thyroid

Answer 3

colloid

Question 4

what is colloid

Answer 4

a glycoprotein containing supply of thyroid hormones and thyroglobulin

Question 5

2 cells types of thyroid

Answer 5

clear cells and follicular cells

Question 6

what cells surround the colloid

Answer 6

follicular

Question 7

what do clear cells do

Answer 7

secrete calcitonin

Question 8

describe the structure of the thyroid gland

Answer 8

follicles filled with colloid with clear cells and capillary interspersed between them, all enclosed in a connective tissue capsule

Question 9

what do follicular cells do

Answer 9

they secrete thyroglobulin proteins and enzymes which make TH

Question 10

what amino acid forms with iodide to make TH and where does it happen

Answer 10

tyrosine in the colloid

Question 11

how does iodide get into colloid

Answer 11

from diet. absorbed into plasma then to follicular cells by coupling to Na+. it is then transported into colloid by pendrin transporter

Question 12

what is MIT

Answer 12

one iodine and one tyrosine (M for mono)

Question 13

what is DIT

Answer 13

two iodine and one tyrosine (D for di)

Question 14

what combination of MIT and DIT makes T3

Answer 14

1 MIT + 1 DIT = T3 (3 iodines)

Question 15

what combination of MIT and DIT makes T4

Answer 15

2 DIT = T4 (4 iodines)

Question 16

what enzyme secreted by follicular cells catalyses

Answer 16

thyroid peroxidase

Question 17

what stimulates TH release

Answer 17

TSH

Question 18

how is TH released from colloid to plasma

Answer 18

endocytosed into follicular cells –> thyroglobulin cut off –> cross cell membrane into plasma

Question 19

how is TH bound in colloid

Answer 19

attached to thyroglobulin

Question 20

TH is lipid/water soluble

Answer 20

lipid soluble

Question 21

what is TBG

Answer 21

thyroxine binding globulin, binds to TH in plasma

Question 22

which TH has a longer half life

Answer 22

T4, 6 days compared to 1, its because TBG has a greater affinity for it over T3

Question 23

what proportion of circulating TH is protein bound

Answer 23

99.8%

Question 24

which TH binds to more intracellular receptors

Answer 24

T3, despite having shorter life and being far less abundant. cell receptors have a greater affinity for it

Question 25

what action does T4 undergo due to T3's greater receptor affintiy

Answer 25

it get deiodinased in plasma and cells

Question 26

stimuli of TRH release

Answer 26

cold, exercise and pregnancy

Question 27

action of TRH

Answer 27

TSH release

Question 28

action of TSH

Answer 28

TH release

Question 29

what class of hormones that cortisol belongs to inhibits TSH and T4-->T3 conversion

Answer 29

glucocorticoids

Question 30

inhibitory action of somatostatin (GHIH)

Answer 30

inhibits TSH (makes sense because GHIH inhibits GH and GH need TH permissive effects)

Question 31

effects of TH on metabolism

Answer 31

increases metabolic rate and creates heat

Question 32

effect of TH on liver

Answer 32

increases hepatic gluconeogenesis

Question 33

why is TH not a glucose counter regulatory hormone

Answer 33

although it raises gluconeogenesis it has no effect on insulin so BG stays the same

Question 34

effect of TH on protein and fat

Answer 34

proteolysis and lipolysis

Question 35

effect of TH on GH

Answer 35

permissive, without it stunted growth

Question 36

2 causes of hyperthyroidism

Answer 36

graves disease and a thyroid tumour

Question 37

what happens in graves disease to produce hyperthyroidism

Answer 37

antibodies mimic TSH at anterior pituitary and continually stimulates TH release. produces negative feedback on TSH but antiboidies keep on stimulating anyway. Thyroid gland gets hyperplastic (big)

Question 38

given the actions of TH what would you expect in hyperthyroidism presentation

Answer 38

proteolysis/lipolysis --> thin, weak, wasting increased metabolism --> weight loss, heat intolerance? also get exaggerated reflexes, tachycardia, high CO and cardiac failure!

Question 39

why does hyperthyroidism cause heart problems

Answer 39

TH is permissive to epinephrine so b receptors very stimulated

Question 40

causes of hypothyroidism

Answer 40

hashimoto's disease, iodine deficiency and idiopathic

Question 41

what happens in hashimoto's disease

Answer 41

there is an autoimmune attack on the thyroid gland --> reduced TH production

Question 42

what would you expect of a hypothroidism presentation

Answer 42

decreased metabolic --> weight gain, cold intolerance permissive to epinephrine --> reduced CV function Nervous system --> slow speech, reduced reflexes more general --> fatigue, brittle nails, thin skin

Question 43

what is meant by goitre

Answer 43

thyroid enlargement