Endocrine Regulation of Calcium II Flashcards
What hormone functions to lower plasma calcium? What cell produces it?
Calcitonin
Parafollicular (C-cells) of the thyroid
What hormones function to raise plasma calcium? What cell produces them?
PTH
Parathyroid chief cells
What is the distribution of calcium in the body?
99% in bone (hydroxyapatite)
1% in blood and soft tissues
What are the different forms of calcium in the blood?
45-50% ionized
5-10% Ca-salt complex
40-50% protein bound
What is the synthesis/activation pathway of Vitamin D2?
Ergosterol photooxidized by UV to Vit D2
Causes Beta ring to open
What is the synthesis/activation pathway of Vitamin D3?
7 dehydrocholesterol photooxidized by UV in the skin to vit D3
Causes Beta ring to open
What modification does the liver do to vitamin D?
25-hydroxylation
In what organ does 1alpha-hydroxylation and 24-hydroxylation of vitamin D?
Kidney
Under what circumstances is 24, 25-OH vitamin D formed?
Hypercalcemia
Under what circumstances is 1,25-OH vitamin D formed?
PTH, Estrogen and low serum Phosphate
What is the normal relationship between serum phosphorus and various forms of Vit-D?
High PO4 = 1,25-OH vit D
Low PO4 = 24,25-OH vit D
What are the causes post-menopausal and senile bone loss?
Low iPTH, estrogen, androgen, and 1alpha-hydroxylase result in inadequate 1,25 vitamin D.
This, in turn, reduces calcium absorption.
What form of Calcium is biologically active?
Free ionized Calcium
What are the effects of increased PTH?
Increases serum calcium and decreases phosphate
Increases bone reabsorption, Ca reabsorption from distal tubule and intestine, and P excretion from proximal tubule
What increases OPG secretion? What does OPG do?
Estrogen
OPG binds to RANKL preventing osteoblasts from stimulating osteoclast activity.
