the thyroid gland Flashcards
(23 cards)
describe the structure of the thyroid
in neck below thyroid cartilage
made of 2 lobes (left and right) and an isthmus joining them
some people have a pyramidal lobe
describe the cellular arrangement of a thyroid
follicular cells surround the colloid creating a follicle
parafollicular cells scattered about
what nerve runs close to the thyroid
left recurrent laryngeal nerve
what glands are embedded in the thyroid
parathyroid glands
outline the embryology of the thyroid gland
1: midline outpouching from the floor of the pharynx(originates from the base of the tongue)
2: development of the thyroglossal duct
3: divides into 2 lobes
4: duct disappears leaving the foramen caecum
5: week 7 is at its final position and gland develops
explain what happens when thyroid stimulating hormone binds to thyroid stimulating receptor
1: Na+ and I- enter follicular cell. thyroglobulin(TG) is also produced
2: I- , TG and TPO diffuse into the colloid
3: TG is iodinated
4: coupling reactions between MIT and DIT occur
5: the TG with T3/T4 attached go into the follicular cell into a lysosome
6: T3 and T4 released into the blood
what does MIT and DIT stand for?
Mono/Di Iodo Tyrosine
what is T3 comprised of?
a DIT and MIT ( 3,5,3’-tri-iodothyronine)
what is T4 (thyroxine) comprised of?
2 DIT ( 3,5,3’,5’-tetra-iodothyronine)
what happens when T4 is deiodinated in target tissues?
produces T3 or reverse T3( inactive) depending on which iodine is removed
outline what happens when TRH is released and how it is controlled
TSH levels rise from pituitary to thyroid
T4 and T3 levels rise
T4 provides negative feedback to hypothalamus and pituitary and is also converted into T3
T3 is active in target tissues
iodide also reduces thyroid output(wolff-chaikoff effect)
what are the names of the plasma proteins that transport thyroid hormones in he blood?
thyroid-binding globulin
albumin
prealbumin(transthyretin)
what is the effect of binding to thyroid receptors?
gene expression is altered
what is the action of thyroid hormones?
fetal growth and development (especially CNS)
increases basal metabolic rate
protein, carbohydrate and fat metabolism increase
potentiate action of catecholamines( tachycardia, lipolysis)
growth and bone maturation
increased cardiac output
how is thyroid hormone levels measured in babies?
heel prick test
who are thyroid diseases more common in?
women (4:1)
what are the main causes of hypothyroidism?
autoimmune damage (hashimoto's thyroiditis)
what are the symptoms and signs of hypothyroidism?
deepening of voice depression and tiredness cold intolerance weight gain and reduced appetite constipation bradycardia(slow heart rate) eventual myxoedema coma shaggy hair/ hair loss memory impairment swollen face, eye socket dry rough skin muscle cramps paraesthesia(tingling) diminished potency and fertility low sex drive menstrual cycle disorders
what medication can be used for hypothyroidism?
include common dose and complications
levothyroxine oral tablets 100micrograms( dose is adjusted)
minor side effects- weight loss and headache
major complications- heart attack/ rapid heart rate
what is the issue with giving liothyronine(T3) tablets?
no more effective than T4
combination tablets of T4 and T3 may cause toxicity(palpitations, tremor, anxiety) TSH is often supressed by this
what are the main causes of hyperthyroidism?
grave’s disease
toxic multinodular goitre
solitary toxic nodule
what are signs of grave’s disease?
diffuse goitre of thyroid
eyes stick out exophthalmos
growth of soft tissue shins- pretibial myxoedema
what are the signs and symptoms of hyperthyroidism?
heat intolerance weight loss with increased appetite myopathy mood swings diarrhoea tremor of hands palpitations sore eyes goitre broken hair/ hair loss nervousness insomnia depression fragile nails arrhythmia(irregular heart rate) increased heart rate high blood pressure warm moist skin muscle cramps and weakness menstrual cycle disorders
