Regulation of Calcium Flashcards
(22 cards)
What is Chovstek Sign?
Twitching of the facial nerve subsequent to ipsilateral tapping; indicates hypocalcemia
What is Trousseau sign?
Carpopedal spasms when a blood pressure cuff is increased higher than the systolic value; indicates hypercalcemia
What is the resulting change with ionized calcium, in regards to increased plasma protein concentration?
No change (it does increase total Ca2+ concentration)
What can result from Alcoholism, in terms of PTH?
Alcoholism: Causes Mg2+ deficiency (hypomagnesemia) –> inhibition of PTH synthesis
What are the general mechanisms via which PTH affects Ca2+ & K+ levels?
1) Stimluates Ca2+ reabsorption
2) Stimulates K+ Secretion
What is the last step in the mechanism of action, regarding PTH action, on the kidney?
PTH: Inhibits Na+/Phosphate cotransport along the lumen side of proximal tubule cell & distal convoluted tubule; results in increase phosphate excretion
What are the resulting actions of PTH on RANKL and OPG levels?
PTH= Increased RANKL and Decreased OPG
What are the resulting actions of Vitamin D on RANKL levels?
They decreased RANKL levels
What is RANKL?
1) RANKL = Produced via osteoblasts and dying osteoclasts –> primary mediator for osteoclast formation
What is OPG?
OPG= Soluble protein, produced via osteoblasts that acts as a decoy for the RANKL receptor –> prevents RANKL/RANK interaction
Overall: Inhibits Osteoclast function
What is M-CSF?
It induces stem cells to differentiate into osteoclast percursors
What is Vitamin D’s effect in the small intestine?
It increases Ca2+ and Phosphate absorption via increased expression of Calbindin
What are Vitamin D’s effects on bone?
1) Sensitizes Osteoblasts to PTH’
2) Regulates Osteoid production and Calcification
What is the effect of Vit D on the Kidney?
It stimulates NPT2a expression; increasing phosphate reabsorption
What are Vit D’s effects on the Parathyroid gland?
1) Directly inhibits PTH expression
2) Directly stimulates CaSR gene expression
What are the three effects of PTH in the kidney?
1) Stimulates 1a-hydroxylase activity
2) Stimulates Ca2+ reabsorption along the TAL & Distal tubule
3) Inhibits Phosphate reabsorption via repressing NPT2a expression
In regards to the thyroid role of release of Calcitonin and its affect on calcium levels.
A) What is its function?
B) What is the effect on Ca2+ metabolism with a thyroidectomy & thyroid tumor, respectively?
1) Calcitonin: Inhibits Ca2+ reabsorption
2) Calcitonin has no effect on Ca2+ metabolism; doesn’t play role in the immediate regulation
What is the etiology of Albright Hereditary Osteodystrophy?
Also, what is the resulting pathology?
AKA: Pseudohypoparathyroidism type Ia
Etiology: Gs for PTH in bone and kidney is defective
Pathology: Hypocalcemia and hyperphosphatemia
What is the etiology and pathology of Humoral Hypercalcemia of Malignancy?
Etiology: Increased PTHrP (Parathyroid related peptides); same action as PTH
Pathology: Same as PTH; except there is:
Decreased Vit D
Decreased PTH
Decreased bone formation
What is the etiology and pathology of Familial Hypocalciuric Hypercalcemia?
Etiology: Mutations that inactive CaSR and Ca2+ receptors in the TAL of the kidney
Pathology: Decreased urinary Ca2+ excretion and increased serum Ca2+ concentration
Vitamin D dependent Rickets Type I; characterized by?
Decreased activity of 1a- hydroxylase
Vitamin D dependent Rickets type II; characterized by?
Decreased Vitamin D receptor
