Thyroid Gland Physiology Flashcards
what is the basic functional unit of the thyroid gland and what are they made up of
the follicle, made up of tubular follicular cells on the outside, surrounding the collide inside
what cells lie outside the follicles of the thyroid gland
the C cells and parafollicular cells
describe the control of the thyroid gland by the brain
hypothalamus releases TRH, which regulates TSH secretion from anterior pituitary, TSH controls secretion from thyroid gland(of T3 and T4)
describe the negative feedback loop of the thyroid gland
T3 and T4 are produced by the thyroid gland, if in excess they have negative feedback and reduce TSH secretion from pituitary and TRH from hypothalamus, decreasing thyroid gland secretion
what is thyroglobulin and what function does it have in the thyroid gland
it is a tyrosine rich protein, made only in follicular cells of thyroid
thyroglobulin is first step of thyroid hormone synthesis
describe the role of iodide and iodine in thyroid hormone synthesis
iodide ions move into the lumen of the follicle cell, where they are oxidised, oxidation of 2I- result in I2(iodine), which can pass through the follicle cell membrane into the colloid
describe the role of thyroid peroxidase enzymes(TPO) in thyroid hormone synthesis
in the colloid, TPOs link iodine to the tyrosine amino acids in thyroglobulin to produce 2 intermediaries; a tyrosine attached to 1 iodine, and a tyrosine attached to 2 iodines
what are T3 and T4
they are thyroid hormones
T3 = triiodothyronine
T4 = thyroxine
describe how T3 is formed
when one MIT unit and one DIT unit are joined by a covalent bond
(so has 3 iodines)
describe how T4 is formed
when 2 DIT units are joined by a covalent bond
(so has 4 iodines)
(much more common than T3)
what are MIT and DIT in thyroid hormone synthesis
MIT = monoiodotyrosine(made up of one iodine attached to one tyrosine) DIT = diiodotyrosine(made up of two iodines attached to one tyrosine)
where are thyroid hormones stored in the thyroid gland until needed
in colloid thyroglobulin
describe the secretion of thyroid hormones from the thyroid gland
colloid is enveloped by microvilli on cell surface to form colloid vesicles within the cell that fuse with lysosomes, enzymes break down the lysosomes resulting in hormone secretion
which of T3 and T4 is more common and which is more potent
T4 makes up 90% of thyroid hormone secretion, T3 only 10%
T3 4 times more potent and much more biologically active
where in the body is T4 converted to T3
the liver and kidneys
