18.4 & 18.5 Thyroid & Parathyroid Flashcards
thyroid gland location
anterior surface of trachea, inferior to thyroid cartilage
isthmus
slender connection between two lobes of thyroid gland
thyroid follicles
Surround what?
hollow spheres lined by simple cuboidal epithelium.. surround follicle cavity.
-each follicle is surrounded by a network of capillaries
follicle cavity
holds colloid, fluid containing dissolved proteins
thyroglobulin
Secreted by?
globular protein secreted by follicle cells into the colloid
thyroid gland requires _____ for hormone synthesis
iodide
thyroid hormone synthesis
TSH-sensitive proteins transports iodide into cytoplasm. I- is converted to I+ by thyroid peroxidase at apical membrane surface. Iodide is attached to tyrosine portions of thyroglobulin. these are linked together to form hormones
thyroid peroxidase
converts I- to I+, and attaches iodide to tyrosine portions of thyroglobulin at apical membrane surface
thyroxine AKA, % of thyroid secretion?
tetraiodothyronine (T4)
-makes up 90% of all thyroid secretions
Thyroid-binding globulins (TBG)
transport proteins in the bloodstream that ~70% T3 and T4 attach to.
transthyretin
AKA thyroid-binding prealbumin (TBPA)… most of remaining T3 and T4 binds to this in circulation
thyroid hormones bind to receptors…where?
in cytoplasm (storage), on mitochondrial surfaces (increase ATP production), and in nucleus (activates genes involved in energy utilization)
calorigenic effect of thyroid hormones
cell consumes more energy and generates more heat due to an increased metabolic rate
observed effects of thyroid hormones.. Which hormone is most responsible?
strong, immediate, and short-lived increase in rate of cellular metabolism
-T3 is primarily resposible
minimum amount of iodine needed each day to maintain normal thyroid funtion
120-150 micrograms I-
C cells
Aka?
(clear cells) aka parafollicular cells
-produce the hormone calcitonin
CT stimulation, effects, and target cells
- stimulated by elevation of Ca2+ in blood
- CT inhibits osteoclasts, slowing the rate of Ca2+ release from bone, and stimulates Ca2+ secretion by kidneys
- stimulates bone growth & mineral deposition in children
- targets bone and kidneys
Four parathyroid glands are embedded in the ____ surface of thyroid gland
posterior
parathyroid (chief) cells produce..
parathyroid hormone PTH
two cell populations in parathyroid glands
parathyroid (chief) cells and oxyphils
PTH stimulation, effects, and target cells
- stimulated by low Ca2+ levels
- mobillizes calcium from bone, enhances reabsorption of Ca2+ by kidneys, stimulates secretion of calcitrol by the kidneys (also enhances reabsorption)
- targets bone and kidneys
T3 & T4 stimulation, effects, and target cells
- stimulated by TSH
- increases energy utilization, oxygen consumption, growth, and development
- targets most cells
