endocrinology 3 - thyroid hormone Flashcards
What hypothalamic hormone stimulates TSH?
THYROID RELEASE HORMONE
TRH
What does TRH stimulate?
TSH
What does TSH stimulate?
thyroid gland
What are the 2 types of cells in the thyroid gland?
follicular cells
clear (c cells)
What do follicular cells secrete?
TH
T4 + T3
What do C cells secrete?
calcitonin
What cells line the follicles in thyroid gland?
follicular cells
What is the substance in the centre of the follicle?
colloid
Describe the colloid substance?
sicky, glycoprotein-rich matrix
What is the backbone of thyroid hormones?
tyrosine
Name T4?
thyroxine
How many iodine does T4 have?
4 iodine atoms
What do thyroid hormones behave like?
steroid hormones
lipophilic
What is the plasma binding p of thyroid hormone?
TBG
thyroglobulin
half-life for T4/
6 days
half-life for T3?
1 day
What is the primary form of thyroid hormone in plasma?
T4 (inactive)
When is T4 converted to T3?
In target tissue
How is T4 converted to T3?
DEIDONASE
What supply of thyroid hormone does the colloid contain?
2-3 months
When does TH move form the colloid to the follicular cell?
TSH
T4 and T3 release
What type of release is the thyroid hormone?
continuous
driven by TRH in hypo
What factors promote TRH?
cold, exercise, pregnancy
What is the function of thyroid hormone?
raise metabolic rate an produces heat (thermogenic)
provide substrate for oxidative metabolism (AAs, FAs. CHO)
critical for growth
required for foetal brain development
- nervous system function and cognition
How is thyroid hormone involved in growth?
anabolic (involved in synthesis reaction)
stimulates GH receptor expression
What can iodine deficiency in mother cause?
baby deficient in thyroid hormone = cretin
What does hyperthyroidism lead to?
increased metabolic rate and heat production
- heat tolerance/ weight loss
increased protein metabolism
- muscle weakness/weight loss
altered nervous system function
- hypoexcitable reflexes and psychological disturbances
elevated cardiovascular function
- increased HR/contractile force
What causes hyperthyroidism?
hormone-secreting thyroid tumour (rare) or nodules
graves disease (antibodies produced that bind and activate the thyroid)
Graves disease?
hyperthyroidism
(antibodies produced that bind and activate the thyroid)
Treatment for hyperthyroidism?
surgical removal or part of gland
radioactive iodine treatment (destroys TH-producing follicular cells)
thyrostatics (block TH synthesis)
propylthiouracil (blocks T4 -> T3)
propylthiouracil?
(blocks T4 -> T3)
What does hypothyroidism lead to?
decrease metabolic rate and heat production
- cold intolerance/ weight gain
disrupted protein synthesis
- brittle skin/thin skin
altered NS function
- slow speech/reflexes, fatigue
reduced cardiovascular function
- slow HR/weaker pulse
What can cause hypothyroidism?
deficiency in dietary iodine
autoimmune attack on thyroid gland
What is the treatment for hypothyroidism?
oral thyroxine T4
dietary iodine supplements e.g. iodised salt (1 in every10,000 molecules is NaI)
What is a goiter?
enlargement of the thyroid gland
What causes a goiter?
caused by trophic action of TSH on thyroid follicular cells
iodine deficiency - thyroid gland increase
resulting in hypertrophy (overgrowth) of thyroid gland
What ab are present in graves disease?
TSIs
thyroid stimulating hormone
What is a key symptom of graves disease?
enlargement of eye muscles/tissues
