Endocrine system 3 Flashcards
What is the function of Trabeculae in spongy bones?
a lattice of rods, filled with marrow, provide strength with minimal weight
Function of Ca(2+)
Na permeability, NT release, muscle contraction, Bone composition, Blood clotting, protein secretion, enzyme activity
Function of PO4
pH buffering, the composition of bone, a constituent of macromolecules
How do we lose Ca in our body and where is it consumed?
net +150 mg/day
loss mostly in feces, also through urine
consumed in cells, and bones, also through digestive secretions
How do we lose and consume PO4(-3) in our body
net +1100 mg/day
more loss in urine, because efficient absorption
consumed in cells and bones (no increased uptake to the bone or loss due to bone growth or bone loss(osteoporosis))
Which hormones influence Ca and PO4
Parathyroid hormone: increase plasma Ca, decrease PO4
stimulates production of active Vitamin D
Vitamin D: increases Ca and PO4
inhibits PTH
stimulates FGF 23
Fibroblast growth factor 23
decreases PO4
inhibits production of active Vitamin D
Where and how is PTH secreted?
Secreted by Parathyroid glands, located on Thyroid glands
Where is Calcitonin produced?
in extrafollicular cells (next to follicle cells)
What is the function of Calcitonin?
it decreases plasma level of Ca and PO4
Name forms of Vitamin D
Vitamin D3: Cholecalciferol
Vitamin D2: Ergocalciferol
How is Vitamin D taken up and activated?
Uptake of Vitamin D2 and D3 by diet and Vitamin D3 through the skin
Activation in the liver (addition of hydroxyl group), in the kidney (addition of hydroxyl group) to produce 1,25-(OH)2-D
How is the activation of Vitamin D regulated?
by regulating 1-hydroxylase in the kidney through PTH(+) and FGF-23(-)
Effect of Vitamin D?
goes to the GI tract and increases absorption of Ca and PO4 into blood
Pathway of Parathyroid hormone
low level of Ca promotes PTH secretion
-> PTH mostly works in the kidney and promotes reabsorption of Ca (filtering Ca back) and thereby increases urinary secretion of PO4
->it increases the level of active Vitamin D (increase absorption of Na and PO4 intestine) by increasing 1-hydroxylase
->in the bone it promotes resorption (breakdown) of Ca and PO4 into the plasma
—> all resolves in restoration of plasma Ca back to normal
How does FGF-23 decrease PO4 and Vitamin D
it decreases the reabsorption of PO4 in the kidney and inhibits 1-hydroxylase (enzyme for Vitamin D), causing Ca to go down
because Vitamin D stimulates Ca absorption in GI
