calcium homeostasis - notes Flashcards
essential physiological roles of calcium
1: muscle contraction
2: neural excitation
3: enzyme cofactor
4: cellular secretion
5: structural role in bone
essential physiological roles of phosphorus
1: intermediate metabolism
2: atp
3: structural role in bone
symptoms of hypocalcemia
1: hyperexcitability
2: paresthesias/tingling
3: muscle cramps
4: tetany
5: seizures
6: signs: chvestok and trousseau
hypercalcemia
1: hypoexcitability
2: lethargy
3: confusion
4: coma
5: no specific signs
effects of albumin levels on Ca
increased albumin => total Ca increases, ca2+ doesn’t change
decreased albumin => total Ca decreases, free ca doesn’t change
effects of pH on Ca levels
increased pH => total Ca doesn’t change but free Ca goes down
decreased pH => total ca doesn’t change but free ca goes up
hormones involved in ca regulation
parathyroid hormone
vitamin D metabolites
calcitonin
1,25(OH)2D
active vitamin D metabolite that mediates 90% of ca absorption
in duodenum and jejunum
(rest of Ca absorbed by passive diffusion)
also controls 10% of PO4 absorption
PO4 absorption
90% passive
10% controlled by 1,25(OH)2D
factors increasing bone resorption
1: parathyroid hormone (resorption and turnover)
2: parathyroid hormone-related peptide
3: cytokines and growth factors
4: excess thyroid hormones
5: excess 1,25 vitamin D or vitamin A
factors decreasing bone resorption
1: estrogens and SERMS (selective estrogen receptor modulators
2: bisphosphonates - eg alendroate (fosamax)
3: calcitonin (weak)
factors increasing bone formation
parathyroid hormone (formation and turnover)
hormonal factors affecting renal ca handling
parathyroid hormones => decreased ca excretion
glucocorticoids => increased ca excretion
dietary factors affecting renal ca handling
sodium => increased ca excretion
protein => increased ca excretion
drugs affecting renal ca handling
furosemide => increased ca excretion
hydrochlorothiazide => decreased ca excretion
activity level effects on renal ca handling
inactivity => increased ca excretion
factors that increase ca excretion via renal ca handling
glucocorticoids
dietary sodium and protein
furosemide
inactivity
factors that decrease ca excretion via renal ca handling
parathyroid hormone
hydrochlorothiazide
factors affecting vitamin D3 production
degree of skin pigmentation
amount of sunlight or uv exposure
regulation of vitamin D metabolism
25-hydroxylase in liver unregulated - 25(OH)D levels indicative of general vitamin D status
1-hydroxylase in renal proximal tubular cells highly regulated
regulation of 1-hydroxylase
PTH stimulates
low ca stimulates
low PO4 stimulates
1,25(OH)2D inhibits (directly and indirectly via PTH)
