thyroid gland

Question 1

position and weight of thyroid?

Answer 1

lies across trachea at base pf larynx, ~15-20g

Question 2

is it palpable?

Answer 2

not in health

Question 3

which are the active forms of thyroid hormones?

Answer 3

T3 and T4

Question 4

T3?

Answer 4

triiodothyronine

Question 5

T4?

Answer 5

Thyroxine

Question 6

2 types of cells present in thyroid w function?

Answer 6

C cells - secrete calcitonin

follicular cells - support thyroid hormone synthesis and surround follicles

Question 7

what are thyroid follicles?

Answer 7

spherical structures which walls are made of follicular cells

Question 8

describe centre of follicle?

Answer 8

filled with colloid, a sticky glycoprotein matrix, containing 2-3 months supply of TH

Question 9

function of follicular cells?

Answer 9

manufacture enzymes which make thyroid hormones and thyroglobulin

concentrates iodide

Question 10

residues abundant on thyroglobulin?

Answer 10

tyrosine

Question 11

how are thyroid hormones formed?

Answer 11

iodide and tyrosine are combined in the colloid

Question 12

how does iodide enter follicular cells?

Answer 12

via Na+/I- transporter (symport)

Question 13

how is iodide transported to the colloid?

Answer 13

via pendrin transporter

Question 14

result of addition of 1 iodine to tyrosine?

Answer 14

MIT - monoiodotyrosine

Question 15

result of adding 2 iodines to tyrosine?

Answer 15

DIT - diiodotyrosine

Question 16

how is T3 formed?

Answer 16

MIT + DIT

Question 17

how is T4 formed?

Answer 17

DIT + DIT

Question 18

composition of T3?

Answer 18

2 tyrosine + 3 iodines

Question 19

composition of T4?

Answer 19

2 tyrosine + 4 iodines

Question 20

function of thyroid perioxidase?

Answer 20

catalyse thyroid hormone (T3+4) synthesis

Question 21

solubility of T3+4 and effect of this?

Answer 21

lipid-soluble - pass across follicular cell membrane where they bind to plasma protein thyroxine-binding globulin

Question 22

rare cause of disruption to TH balance?

Answer 22

mutations to thyroxine-binding globulin

Question 23

effect of TBG’s high affinity for T4?

Answer 23

T4 is released slowly into the plasma

Question 24

half-life of T3?

Answer 24

~1 day

Question 25

half-life of T4?

Answer 25

~6 days

Question 26

% of T3+4 are free to act as inhibitors to TSH and TRH?

Answer 26

0.2% - acts via -ve feedback loop

Question 27

is T3/4 more. abundant and by how many times?

Answer 27

T4 - x50 more

Question 28

T3 % of binding of thyroid hormones to receptors in cells?

Answer 28

90%, despite being far less abundant than T4

Question 29

why does T3 bind more than T4 and what is the result of this?

Answer 29

receptors have higher affinity for T3 than T4 - therefore, T3 is x3-5 more physiologically active than T4

Question 30

which can increase TRH secretion from hypothalamus?

Answer 30

pregnancy cold exercise

Question 31

effect of somatostatin on TSH?

Answer 31

inhibitory

Question 32

effect of glucocorticoids on TSH?

Answer 32

inhibitory - also inhibits conversion of T4 to T3

Question 33

functions of thyroid hormone?

Answer 33

raises metabolic rate and promotes thermogenesis increase hepatic gluconeogenesis net increase in proteolysis net increase in lipolysis critical for growth (lack of TH results in retarded growth) brain development in utero

Question 34

result of maternal iodine deficiency?

Answer 34

congenital hypothyroidism

Question 35

name 2 causes of hyperthyroidism?

Answer 35

``` Graves disease (common) Thyroid adenoma (rare) ```

Question 36

3 signs of graves disease?

Answer 36

hyperplasia -> enlarged thyroid gland hyperactivity of cells TSH plasma conc. is very low

Question 37

6 symptoms of hyperthyroidism?

Answer 37

``` weight loss heat intolerance muscle weakness hyper-excitable reflexes psychological disturbances increased HR/contractile force, high output, cardiac failure ```

Question 38

3 causes of hypothyroidism?

Answer 38

Hashimoto's disease (autoimmune) dietary deficiency in iodine idiopathic - related to thyroiditis

Question 39

symptoms of hypothyroidism?

Answer 39

``` weight gain cold intolerance brittle nails/hair thin skin slow speech reflexes fatigue slow heart rate/weaker pulse ```

Question 40

define goitre?

Answer 40

enlargement of thyroid gland due to either hyper/hypo-thyroidism

Question 41

hypo cause of goitre?

Answer 41

increased trophic action of TSH on follicular cells

Question 42

hyper cause of goitre?

Answer 42

overactivity due to graves disease