the thyroid gland Flashcards
what are the hormones released by this gland
calcitonin and T3, T4
what is calcitonin
a polypeptide hormone produced by c cells that functions in regulating blood calcium levels in conjunction with parathyoid hormone
what is calcitonin secretion dependent on
blood calcium levels
how does calcitonin lower blood calcium levels
inhibit the rate of decalcification of bone by osteoclastic resorption
what produces calcitonin
c cells
what are T3 and T4
iodine containing hormones
what is T3
tri-iodothyronine
what is T4
tetraiodothyronine
how is T4 converted to T3
in general circulation by removal of one iodothyronine
what is the function of T4
regulate basal metabolic rate
what is T4 in relation to T3
the metabolically active form of T3
what is thyroxine
T4
what is secretion of t4 regulated by
thyroid stimulating hormone
what does the thyroid hormone do
store lots of inactive hormone within the extracellular compartments in the centre of the follicles
what is thyrotoxosis
excess of circulating thyroid hormone which causes symptoms due to systemic effect of the thyroid hormone
what can thyrotoxicosis lead to
graves disease
what is graves disease
hyperfunction of the thyroid gland, an autoimmune disease
what are the symptoms of graves disease
exophthalmos (puffy eyes) and non pitting edema of the lower limbs (fluid accumulation)
what is hypothyroidism
lack of production of thyroid hormone leading to weight gain, tiredness and poor tolerance to cold weather
what is hashimotos disease
the thyroid acini are destroyed as the gland is infiltrated by lymphocytes and plasma cells. leads to fatigue, weight gain and depression
which epithelium lines the thyroid follicles
simple cuboidal
what do the septa of the gland convey
blood supply, lymphatics and nerves
what do thryoid follicles store
thryoglobulin and iodinated glycoprotein
what is the storage form of T4
thyroglobulin
what is the storage form of T3
iodinated glycoprotein
what is the epithelium of the inactive follicles
simple squamous or cuboidal
what is the epithlium of the actively secreting or synthesising follicles
columnar
where are the c cells found in the thyroid glands
as scattered individual cells in the follicle lining or as small clumps in the interstices between the follicles
how do follicular cells concentrate iodide from the body
iodine pump in the basal plasma membrane
how are T3 and T4 formed
iodide taken in from the blood via iodide pump in the plasma membrane of follicular cells and oxidised to iodine to be transported to the follicular plasma membrane where it is released into the follicular lumen where it combines with tyrosine residues of the follicular lumen
what is pinocytosis
ingestion of liquid into the cell by budding of small vescicles in the cell membrane
describe the process of secretion of thyroxin
ingestion of liquid into the thyroglobulin hormone complex to form cytoplasmic vacuoles which fuse with lysosomes of the follicular cell cytoplasm.
hydrolytic enzymes cleave the hormone from the thryoglobulin and they are released in the basal cytoplasm, where they diffuse into the bloodstream
