Synthesis, secretion and physiologic functions of the thyroid hormones. Regulation of thyroid hormone secretion

Question 1

synthesis of thyroid hormones - step 1

Answer 1

IODINE UPTAKE

iodine is obtained from diet in form of iodide

Question 2

synthesis of thyroid hormones - step 2

Answer 2

IODINE MOVEMENT

iodide is transported into thyroid follicular cells by sodium-iodide symporter
found on basolateral membrane of cells

Question 3

synthesis of thyroid hormones - step 3

Answer 3

ORGANIFICATION

iodine attaches to thryoglobin tyrosine residues

iodine + tyrosine -> monoiodotyrosine + diiodotyrosine

• catalysed by thyroid peroxidase

Question 4

synthesis of thyroid hormones - step 4

Answer 4

COUPLING

• MIT coupled to form tri-iodo-thyronine (T3)
• DIT coupled to form thyroxine (T4)

Question 5

synthesis of thyroid hormones - step 5

Answer 5

STORAGE

stored in follicular lumen until needed

Question 6

secretion - 1

Answer 6

thyroid follicular cells get activated by TSH
stimulate thyroglobulin to endocytose

Question 7

secretion - 2

Answer 7

endocytosed thyroglobulin + lysosome = proteolysis = T3/T4 relased into bloodstream

Question 8

secretion - 4

Answer 8

T3 + T4 in the bloodstream clipped onto
- albumin
- thyroid binding globulin
- transthyretin

only free forms of T3-T3 are biologically active

Question 9

secretion - 4

Answer 9

T4 -> T3 by deiodinase
- as T3 is more active

Question 10

functions of thyroid hormones - 1

Answer 10

METABOLISM

thyroid hormones increase basal metabolic rate by stimulating more sodium-potassium ATPase pump = more ATP produced

Question 11

functions of thyroid hormones - 2

Answer 11

THERMOGENESIS

• more thermogenesis
• more heat production

Question 12

functions of thyroid hormones - 2

Answer 12

GROWTH

help linear growth in young brain/ bones
by activating insulin like growth factor 1

Question 13

functions of thyroid hormones - 3

Answer 13

SNS

thyroid hormones upregulate the action of beta adrenergic receptors + noadrenaline
- increasing heart rate/ contractility / CO

Question 14

functions of thyroid hormones - 4

Answer 14

DIGESTION

thyroid hormones stimulate gastric motility
by regulating carbohydrate/ protein/ fat metabolism

Question 15

functions of thyroid hormones - 5

Answer 15

REPRODUCTION

correct thyroid hormone levels needed:
- menstrual cycle
- fertility
- pregnancy

Question 16

functions of thyroid hormones - 5

Answer 16

DERMATOLOGICAL

thyroid hormones involved in skin health / hydration / elasticity

Question 17

regulation - 1

Answer 17

hypothyroidism = lack of thyroid hormones

hyperthyroidism = too much thyroid hormones

both are autoimmune diseases

negative feedback mechanisms ensure once sufficient levels of T3 + T4 have been secreted then no more should be released

Question 18

regulation - 2

Answer 18

low iodine levels = low thyroid hormone production = TSH hypersecretions = goiter

Question 19

regulation - 3

Answer 19

hypothalmic control

activated under stress/ temp/ metabolic needed

releases thyrotropin releasing hormone -> APG -> thyroid stimulating hormone released

Question 20

regulation - 4

Answer 20

pituitary control

TSH + TSH receptors = signalling pathways activate
- thyroid hormone synthesis
- more T3/T4 released in cells