The thyroid gland; control of secretion Flashcards
where does thyroid tissue arise during development
foramen caecum
what connects the developing thyroid to the tongue
thyroglossal duct
what cells are found in the thyroid
follicular cells and parafollicular cells
what hormone does the thyroid produce apart from T3 and 4
calcitonin (calcium homeostasis)
describe the triggers of thyroid hormone release
Thyrotropin releasing hormone (hypothalamus)
thyroid stimulating hormone (anterior pituritary)
what is the most common cause of hypothyroidism
iodine
what two chemicals make thyroid hormone
iodine and tyrosine
describe the formation of thyroid hormones
addition of successive iodide ions to thyroglobulin (precursor)
describe the regulation of thyroid hormones
negative feedback loop
increased by cold temps
decreased by dopamine and somatostatin
what is the function of calcitonin
parafollicular cells produce calcitonin in response to high blood calcium
calcitonin decreases the release of calcium from bone
what is the function of parathyroid hormone
increases blood calcium by stimulating bone break down
what part of the hypothalamus secretes TRH
arcuate nucleus and median eminence
where is TRH released
anterior pituitary
what is the other name for T4
thyroxine
it is a prohormone of T3
what is the other name for T3
triiodothyronine
describe synthesis and secretion of T3 and 4
TSH stimulates sodium iodide co transporter resulting in iodine trapping
iodide leaves the cell and enters the lumen
the follicular cell secretes thyroglobulin
TSH stimulates iodination of thyroglobulin in the lumen and conjugates iodinated tyrosines
TSH stimulates endocytosis of thyroglobulin
thyroglobulin undergoes proteolysis forming t4 and 3
TSH stimulate secretion into the circulation
where is TSH made
anterior pituitary gland
where is TSH made
anterior pituitary gland
what hormone causes hyperplasia of the thyroid gland
TSH
What molecule are thyroid hormones bound to in the circulation
thyroxin binding globulin
what is the function of 5’ 3’ monoiodinase
converts T4 to T3
what is the function of TBG and other binding proteins
buffers free T3 and T4 in the blood
what are the functions of thyroid hormones
increase glucose uptake from the GI tract
increase glucose utilization
increase liver glycogenolysis and gluconeogenesis
increased lipolysis
increase oxidation of free fatty acid
permissive action for other hormones essential for normal development and function
what are the effects of fetal hypothyroidism
neuronal hypoplasia
delayed myelination
mental retardation
what are goitrogens
excess iodine, thiocyanate or perchlorate causes excess TSH secretion so hypertrophy of thyroid
what is the effect of pituitary tumours on the thyroid
may cause over or underproduction of TSH
what is Grave’s disease
Long acting thyroid stimulator - autoimmune stimulation of the thyroid
what is hashimoto’s disease
autoimmune destruction of the thyroid
