9 Parathyroid Flashcards
what does a vitamin D deficiency cause in children? adults?
children=rickets
adults=osteomalacia
what do chief cells do?
secrete PTH
what do oxyphil cells do?
fuction unknown
what are the normal levels of calcium in the blood?
9-10mg/dl
what does PTH do the calcium and phosphate?
increases calcium levels by bone reabsorbtion, gut absorption, and increased reabsorbtion in kidney.
increases phosphate reabsorbtion from bone, but increases renal secretion of phosphate.
what are the normal phosphate levels in the blood?
2.5-4.5 mg/dl
T/F Only free Ca+ is active?
true
how does PTH increase reabsorbtion of phosphate and calcium from the bone?
1) rapid osteolysis
2) activates osteoclasts (new and old ones indirectly through osteoblasts)
3) innactivates osteoblastic activity
4) increases calcium pump activity moving Ca+ out of bone.
how do the osteoclasts attach to the bone?
they use integrins to bind to vitronectins.
PTH causes the kidney to do what?
1) decrease reabsorbtion of phosphate
2) increase Ca+ reabsorbtion
3) conversion of 25 hydroxycholecalciferol to 1,25 dihydroxycholecalciferol which acts on the gut to help reabsorb both calcium and phosphate.
what is another name for 1,25 dihydrocholecalciferol?
calcitriol
what mainly regulates PTH secretion?
Ca+ levels in the blood.
what effect do PKC and internal calcium have on PTH?
They both inhibit the release of PTH. They prevent synthesis and exocytosis.
How does calcium inhibit secretion of more PTH?
it binds to the calcium receptor of the chief cell and activates a G protein. The G protein activates PLC which makes DAG and IP3. IP3 increases intracellular calcium levels and DAG increases PKC. Both (Ca+ and PKC) inhibit PTH synthesis and secretion.
an inactivation mutation in the calcium receptor of a chief cell would lead to what?
hypercalcemia because of too much PTH release.
what disease should you think of when you see increased neuromuscular excitability with increased tingling in fingers and toes?
hypoparathyroidism with associated hypocalcemia
what is carpopedal tetany?
muscle twitch/spasm in arm and leg
how do you treat hypoparathyroidism?
active form of vitamin D and exogenous Ca+
dont give PTH because its broken down too quickly
what do you usually see with hyperparathyroidism?
depression of CNS muscle weakness cystic fibrosis osteitis rise in alkaline phosphatase activity elevation of urinary cAMP levels
where do you get calcitonin? what does it do?
parafollicular cells (C cells) Works opposite to PTH
what does calcium do in the adult?
very little. only acts as a short term regulator of calcium ion concentrations in the blood.
does calcitonin have an effect on phosphate?
yes like PTH it lowers phosphate levels.
Alternate expression of the Calcitonin gene can yield CGRP which does what? and where?
It acts as a vasodilator in the brain.
what are the steps to make active vitamin D starting with 7dehydrocholesterol in the skin? Liver? Kidney?
7 dehydrocholesterol
cholecalciferol [Vitamin D3]
25 hydroxycholecalciferol
1,25 dihydroxycholecalciferol
what enhances the conversion of 25 hydocholecalciferol to 1,25 dihydrocholecalciferol?
vitamin D deficiency
calcium deficiency
phosphate deficiency
increased PTH secretion
what factors influence 25 hydroxycholecalciferol to be converted to its inactive form of 24,25 dihydrocholecalciferol?
vitamin D sufficiency
hypercalcemia
hyperphosphatemia
what effects does 1,25 dihydrocholecalciferol have on the intestines?
1) induces the calcium binding protein calbindin to form in the cytoplasm
2) increases Ca+/Na+ exchanges on basolateral membrane
T/F calbindin is an important blood transport protein that helps increase Ca+ half life in the blood?
false, Calbindin is only found in the cell’s cytoplasm
what is the major mechanism in which calcium enters the gut?
through paracellular transport
which cells have Vitamin D receptors?
every tissue in the body except osteoclasts. They rely on osteoblast and paracrine hormones.
what do you see with rickets in children?
malabsorbtion of vitamin D
bones lacking tensile strength
tetany of respiratory muscles
what do you see with osteomalacia?
1) steatorrhea (failure to absorb fat)
2) renal rickets (kidney cant make active vitamin D)
3) congenital hypophosphatemia (failure of the kidneys to reabsorb adequate amounts of phosphate)
how do you treat someone with congenital hypophosphatemia?
give them phosphate
T/F PTH is only involved in Ca+ and PO4 regulation?
false, it has a lot to do with overall health and disorders can lead to some types of cancers
does vitamin D stimulate serotonin release?
yes, and it causes changes in mood.
