Wk 23 Flashcards
What are the dietary sources of iodine?
Seafood
Dairy
Eggs
Meat
Where is the iodine cleared from body?
98% urine and the rest in faeces
What is the distribution of Iodine in body?
consume from diet, travels through to thyroid which then makes T3 and T4 which goes to liver and other tissues
Cycle of thyroid hormones…
Hypothalamus releases ________ which travels down ______ ______ ____ to the _____ ______ which releases ____ and travels through the blood to the thyroid
_____ ______ cells release T3 and T4
____ inhibits release of ____ and ___ for negative feedback
Thyrotropin releasing hormone (TRH)
hypophyseal portal veins
anterior pituitary
Thyroid stimulating hormone (TSH)
Thyroid follicular cells
TRH and TSH
What do T3 and T4 do?
- Increase basal metabolic rate
- Stimulate protein synth
- Increase body temp
- Increase use of glucose and FAs for ATP production
- Stimulates lipolysis
What receptors (on anterior pituitary) does TRH act on?
What type of receptors are they?
What happens when these receptors are activated?
TRHRs (thyrotropin releasing hormone receptors)
GPCRs
When activated, intracellular Ca increases which causes secretion of TSH
What does TSH do to thyroid follicular cells?
Stimulates the follicular cells to make thyroglobulin (hormone precursor) which is stored in colloid in follicular cell
Also increases follicle cells to uptake iodine
What do T3 and T4 refer to and what is the structure?
T3= triiodothyronine
T4= thyroxine
iodine atoms attached to modified tyrosine (AA)
Thyroid hormones…
What is the precursor and where is it stored?
Which is the main secreted form?
Which is more potent?
Which has the longest half life?
Which is enzymatically cleaved to what at target tissues?
Precursor is thyroglobulin, it is stored in colloid
T4 is main secreted form
T3 is more potent
T4 has longer half life
T4 cleaved to T3 at target tissues
What carrier proteins transport thyroid hormones?
Are they lipid or water sol hormones?
How do they get into target cell?
What receptor do they activate?
Mostly Thyroxine binding globulin (TBG) (but also albumin)
Lipid sol
Simple diffusion
Nuclear receptor to activate genes or mitochondria receptors to accelerate ATP production
What percentage of thyroid hormone is bound (what are they bound to) and what percentage is free?
Bound= 99.96% (bound to plasma proteins or tissue proteins)
Free= 0.04%
What are the main effects of T3?
Growth and development
- brain development
- cell growth and differentiation
Increased catecholamine effect (sympathetic stimulation)
Increased basal metabolic rate
- increased O2 and energy consumption
- increased heat production
- increased HR and contraction force
- accelerates turnover of minerals in bone
What happens in hypothyroidism?
Decreased metabolism= decreased secretion and synthesis and release of T4/T3, which leads to increased thyroid stimulating hormone synthesis and release (because no neg feedback to stop it and also to try and increase T3/T4 to restore homeostasis)
What is the main cause of hypothyroidism?
Iodine deficiency
Primary hypothyroidism…
TSH level?
Free T4 level?
Subclinical hypothyroidism…
TSH level?
Free T4 level?
Primary:
TSH: elevated
Free T4: low
Subclinical:
TSH: elevated
Free T4: normal
What is hyperthyroidism?
Increased metabolism= increased synthesis and release of T4/T3 so decreased TSH synthesis and release through feedback loop to try and decrease T3/T4
What is the primary cause of hyperthyroidism?
Graves’ disease (autoimmune)
Hyperthyroidism…
TSH levels?
Free T4 levels?
TSH= decreased
Free T4= elevated
Adrenalin…
Lipid or water sol?
What are the 4 precursors to adrenalin?
Water sol
Tyrosine -> DOPA -> Dopamine -> Noreadrenalin -> Adrenalin
What do catecholamines bind to on heart cell and what does this cause an increase of?
What is the effect?
B adrenergic receptors
Increases cAMP
Increases rate and force of contraction of cardiac muscle
What is Pheochromocytoma?
What are symps similar to?
Tumor of adrenal gland causing excess adrenalin
Symps similar to hyperthyroidism
How does adrenalin cause breakdown of glucogen to glucose in liver and muscle cells?
Adrenalin activates cAMP signalling which causes reduced glycogen synthase activity and increased glycogen phosphorylase activity = release of glucose into blood
In prolonged fasting state, liver starts producing glucose from what?
Lactate from muscle (cori cycle)
Amino Acids from muscle (proteolysis)
Glycerol from adipose tissue (lipolysis)
What hormone promotes lipolysis in adipocytes?
What are the 2 products of lipolysis and what does each product go on and do?
Adrenalin
Triglycerides break down into glycerol (glucose production in liver) and fatty acids (provides energy for gluconeogenesis through B oxidation)
When prolonged fasting or glucose depleted, lipolysis is enhanced, generating massive amounts of FFAs which turn to what in the Kreb’s cycle?
What is this process promoted by?
Where does it occur?
Ketone bodies
Ketogenesis promoted by glucagon
Occurs in the liver
