4) Hypothyroidism Flashcards
What controls metabolic rate?
Thyroxine
Summarise the hypothalamic pituitary thyroid axis:
TRH released from hypothalamus
TSH released from anterior pituitary gland
TSH stimulates T3/4 production from thyroid gland
T3/4 negatively feedback of APG + hypothalamus
Summarise the cellular structure of the thyroid gland:
Colloids-containing thyroglobulin + stored thyroxine
Surrounded by follicular cells
How do TSH stimulate the thyroid gland to make thyroxine?
1) TSH binds to TSH receptors on follicular cells
2) TSH stimulates follicular cells to take up iodide
3) Iodide oxidised to iodine (by TPO)
4) Iodine taken up to follicular cells
5) Tyrosine residues in thyroglobulin are iodinated=monoiodotyrosine
6) Coupling reactions take place-di/triiodotyrosines
7) T4 secreted into blood
What are the 2 types of hypothyroidism & what are the TSH levels like in each one?
Primary (myxoedema)-issue with thyroid gland (high TSH levels)
Secondary-issue with APG (low TSH levels)
What is primary hypothyroidism also known as?
Myxoedema
T3 vs T4:
T3=active
T4=inactive
T4 must be deiodinised to form T3 (prohormone)
(80% of T3 was T4)
What 2 things can cause primary hypothyroidism?
Autoimmune damage
Thyroid removal
What are TSH levels like in primary hypothyroidism and why?
High as no T3/4 made by thyroid gland (no -ve feedback)
What does T3 do once in cells?
1) binds to receptor
2) receptor T3 complex binds to TRE in DNA
3) alters gene expression
How is thyroxine stored?
In colloids
Heavily PPB-thyroxine binding globulin
How is primary hypothyroidism treated?
T4 given (levothyroxine sodium)
Monitored by TSH levels being measured-should go to normal ranges
When is the only time T3 is given?
Myxoedema coma
-T3 is faster acting
Key features of hypothyroidism:
o Cold o Weight gain o Deepening of voice o Depression o Tiredness o Constipation o Bradycardia
