thyroid and parathyroid glands Flashcards
(24 cards)
the ascending pyramidal lobe is present in
50% of the population
arterial supply of the thyroid
superior thyroid artery
inferior thyroid artery
thyroid ima artery
the thyroid ima artery is present in
Anatomical variant in ∼ 10% of the population. If overlooked during surgery and injured, serious bleeding complications may occur.
thyroid follicles
smallest functional units of the thyroid
lined with epithelium with follicular lumen (central cavity) filled with colloid for storage of thyroglobulin
function of calcitonin
lowers calcium in the serum
inhibits osteoclast activity
increases excretion of calcium and phosphate in the kidneys
lowers calcium absorption in the intestine
calcitonin is released in response to
increased serum calcium levels
clinical significance of calcitonin
Important as a tumor marker for medullary thyroid cancer
Acts as a synthetic analog for the treatment of osteoporosis (minimises bone resorption)
procalcitonin is a marker for
The precursor procalcitonin plays a role as a marker for bacterial infection (e.g., sepsis).
thyroxine is produced from
tyrosine and iodine
T3 is
triiodithyronine
T4 is
thyroxine,
or tetraiodothyronine
which cells are responsible for the synthesis of T3 and T4
thymocytes in the thyroid follicles
what is thyroglobulin
an iodine free hormone precursor stored in the follicular lumen with tyrosine residues
which thyroid hormone is more potent
the thyroid gland produces more T4, but T3 is more potent
how does T4 get converted into T3
Peripheral 5’-deiodinase (or type II iodothyronine deiodinase) in the thyroid, pituitary gland, muscle, and brown fat converts T4 into the biologically active T3.
where does most T3 come from
About 80% of the total plasma T3 comes from T4 conversion, whereas about 20% is released from the thyroid gland directly.
what is the half life of T3
20 hours
what is the half life of T4
190 hours
function of the parathyroid glands
secretion of parathyroid hormone (PTH) in response to low calcium serum levels
cells of the parathyroid gland are called
chief cells
chief cells produce
produce and secrete parathyroid hormone
when to chief cells secrete parathyroid hormone
Have calcium-sensing receptors (CaSR), which detect changes in calcium concentration and modulate PTH secretion
what is the function of parathyroid hormone
PTH increases serum calcium and decreases serum phosphate
High extracellular calcium → activation of calcium-sensitive receptors → ↓ PTH excretion
Low extracellular calcium → inhibition of calcium-sensitive receptors → ↑ PTH excretion
