thyroid function W6

Question 1

where is the thyroid gland?

Answer 1

under thyroid cartilage

Question 2

thyroid disease epidimiology?

Answer 2

2-5% of community
more common in women

Question 3

types of thyroid problems?

Answer 3

overactive
underactive
goitre (enlargement) or nodules (lumps)

Question 4

thyroid anatomy?

Answer 4

follicles - filled with colloid, cuboidal thyroid epithelial cells line outside.
capillaries lie close to follicles so hormones can be secreted
parafollicular cells (c cells) between follicles
sympathetic nerve endings

Question 5

how is T3 and T4 released from the thyroid?

Answer 5

iodide enters cuboidal epithelial thyroid cell, becomes iodine, passes through apical membrane into follicular lumen.
TPO and hydrogen peroxide catalyse addition of iodine to thyroglobulin. (creates hormones MIT, DIT, T3, T4.)
hormones in colloid reabsorbed into cell. lysosomes break down colloid releasing hormone into cell and secreted out into bloodstream.

Question 6

what does MIT, DIT, T3 and T4 stand for

Answer 6

MIT = monoiodotyrosine
DIT = diiodotyrosine
T3 = triiodothyronine
T4 = tetraiodothyronine

Question 7

difference between T3 and T4?

Answer 7

T3 - 3 iodine, active form
T4 - 4 iodine, inactive form

Question 8

which hormone does the thyroid mainly produce and why? what is the ratio

Answer 8

T4 because the body wants more inactive form that can be converted to active T3 when needed

T4:T3 in 14:1 ratio

Question 9

how is T4 converted to T3

Answer 9

removal of one iodine

catalysed by deiodinase enzymes

Question 10

mechanism that buffers cells against too much active hormone?

Answer 10

use of proteins to carry hormones around circulation. this causes hormone to become inactive.

Question 11

thyroid hormone secretion pathway

Answer 11

TSH secreted from pituitary
triggers production of thyroid hormones
thyroid gland secretes T4/3
T4 deiodinated by type 1 and type 2 deiodinase enzymes to form T3
T3 then enters nucleus, bind to nuclear receptor, causes effects

Question 12

negative feedback loops in thyroid hormone production?

Answer 12

T3 and T4 feedback on pituitary and hypothalamus inhibiting release of TRH and TSH

Question 13

actions of the thyroid hormone?

Answer 13

growth development
thermogenesis in brown adipose tissue (production of heat)
basal metabolic rate
activate mental processes