Thyroid Physiology & Pathology Flashcards
what is the thyroid composed of?
follicles
colloid
tyrosine containing thyroglobulin filled spheres enclosed by follicular cells
parafollicular C cells
secrete calcitonin
T4
thyroxine
T3
triiodothyronine
major biologically active thyroid hormone
which is more potent, T3 or T4?
T3
how is T3 created?
T4 converted to T3 by liver & kidney
what makes T3 & T4 able to bind plasma proteins?
hydrophobic/lipophillic
is the bound or unbound form of T3 & T4 biologically active?
unbound
what do thyroid hormones do to basal metabolic rate?
increase
what do thyroid hormones do to thermogenesis?
increase
what do thyroid hormones do to blood glucose?
increase due to stimulation of glycogenolysis & gluconeogenesis
what do thyroid hormones do to insulin dependent glucose uptake into cells?
increase
what do thyroid hormones do to lipid metabolism?
mobilise fats from adipose tissue & increase fatty acid oxidation in tissues
what do thyroid hormones do to protein synthesis?
increase
the production & secretion of which hormone requires thyroid hormones?
growth hormone releasing hormone
glucocorticoid-induced GHRH release
which hormones require the presence of thyroid hormone for activity?
GH/somatomedins
how do thyroid hormones affect the development of foetal & neonatal brain?
myelinogenesis & axonal growth require thyroid hormones
what does stress do to TRH & TSH?
inhibits their release
what rhythm of secretion do thyroid hormones exhibit?
circadian
what does exposure to cold environments do to TRH release?
stimulates it
what does TRH release stimulate?
TSH release
what does TSH release increase?
T3 & T4 release from thyroid
what can primary deficiency of thyroid hormones be associated with?
enlarged thyroid
wat can secondary deficiency of thyroid hormones be due to?
TRH or TSH
what is the other cause of deficiency of thyroid hormones?
lack of iodine in diet
what is grave’s disease?
autoimmune hyperthyroidism
what symptoms are common in Grave’s disease?
exopthalmos
goitre
what is each follicle in the thyroid gland surrounded by?
flat to cuboidal follicular epithelial cells
what’s at the centre of each follicle?
dense amorphsc pink material containing thyroglobulin
C cells
parafollicular cells
how are C cells arranged in the thyroid?
occasionally scattered
what do C cells look like?
slightly larger cells with clearer cytoplasm
what do the symptoms of hyperthyroidism occur as a result of?
excess of T3 & T4
what’s the most common cause of hyperthyroidism?
Grave’s disease
what are the other causes of hyperthyroidism excluding Grave’s disease?
hyperfunctioning nodules
tumours
thyroiditis
what are the triad of features of Grave’s disease?
Hyperthyroidism with diffuse enlargement of the thyroid
Eye changes (exophthalmos)
Pretibial myxoedema.
what do the eye changes in Grave’s disease result from?
fibroblasts etc expressing TSH receptors
what are the symptoms & signs of hypothyroidism dir to?
low levels of T3 & T4
what are the majority of cases of hypothyroidism due to?
hashimoto’s thyroiditis
what is hashimoto’s thyroiditis?
gradual failure of thyroid function due to auto-immune destruction of thyroid tissue
what may hashimoto’s thyroiditis be preceded by?
transient hyperfunction (hashitoxicosis)
goitre
any enlargement of the thyroid gland
adenomas
Discrete solitary mass
Encapsulated by a surrounding collagen cuff
Composed of neoplastic thyroid follicles
