18.8 PARATHYROID GLANDS Flashcards
where are the parathyroid glands located?
partially embedded in the posterior surface of the lateral lobes of the thyroid gland - several small round masses of tissue
how many parathyroid glands are there?
one superior and one inferior are attached to each lateral thyroid lobe - total of 4
parathyroid glands contain 2 kinds of epithelial cells which are
- chief cells (or principle cells)
- oxyphil cell
chief cells produce which hormone
parathyroid hormone (PTH) also called parathormone
what is the oxyphil cell
not known in a normal parathyroid gland. Presence helps to identify histology, cancer of parathyroid glands - oxyphil cells secrete excess PTH
parathyroid hormone is the major regulator of levels of which 3 ions in the blood
calcium, magnesium, phosphate
how does blood release ionic calcium and phosphates into the blood
action of PTH is to increase number & activity of osteoclasts –> bone resorption
how does PTH act on the kidneys?
slows rate at which Ca2+ & Mg2+ are lost from blood into urine
increases loss of phosphate from blood into urine
more phosphate is lost in urine than is gained from bones there for PTH increases or decreases phosphate level and increases or decreases calcium and magnesium level
decreases blood phosphate level
increases blood calcium & magnesium levels
3rd effect of PTH on kidneys is to promote formation of the hormone
calcitriol (active form of vitamin D)
calcitriol increase or decreases rate of calcium, phosphate, magnesium levels
increase
how does calcitriol increase the rate of calcium phosphate and magnesium
absorption of ca2+ from food (absorption in GI tract)
High level of calcium in blood
stimulates parafollicular cells of the thyroid gland to release more calcitonin
a lower level of calcium in the blood
stimulates chief cells of the parathyroid gland to release more PTH
