thyroid physiology Flashcards
what do the parafollicular C cells secrete?
calcitonin
where is thyroglubulin stored?
colloid
explain the steps in the synthesis of the thyroid hormones?
- iodine taken up by follicular cells
- iodine attaches to tyrosine residues on thyroglobulin to form MIT and DIT (building blocks)
- coupling of the building blocks
- stored in colloid until required
MIT+DIT=
T3
DIT+DIT=
T4
which thyroid hormone is most biologically active?
T3
which thyroid hormone is more potent?
T3
in what form are the thyroid hormones biologically active?
unbound
what to T3 and T4 bind to?
plasma proteins
what molecule to most thyroid hormones bind to?
thyroid binding globulin (TBG)
when might there be increased thyroid binding globulin?
pregnancy new born state Hep A Biliary Cirrhosis taken heroin
what will happen to the total T4 when there is increased TBG?
increased total T4 but not free T4
what will happen to total T4 when there is decreased TBG?
decrease total T4 but not free T4
when might there be decreased TBG?
cushings
acromegaly
chronic liver disease
adrogens
roles of thyroid hormones?
increase basal metabolic rate increase thermogenisis carb metabolism- increase blood glucose lipid metabolism- increase lipolysis protein metabolism- increase synthesis
growth
development of foetal and neonatal brain
normal central nervous activity
how do thyroid hormones increase responsiveness to adrealine and noradrenaline?
by increasing number of receptors
affect of thyroid hormones on heart?
increase heart rate and stroke volume
what stimulates the release of thyroid hormones?
TSH from anterior pituitary
what stimulates the release of TSH?
TRH- thyrotrophin releasing hormone from hypothalamus
what does stress do to the release of TRH and TSH?
inhibits it
when are thyroid hormone levels highest?
at night
what can cause a goitre?
gland failure
iodine deficiency
symptoms of hypothyroidism?
reduced BMR slow pulse rate fatigue, lethargy slow reflexes cold intolerance weight gain reduced appetite
symptoms of hyperthyroidism?
increased BMR very fast pulse increased nervousness insomnia sweating heat intolerance weight loss increased appetitie
