Exam 5: Calcium Metabolism Flashcards
What is the calcium distribution?
99% bones/teeth
1% intracellular
0.1% extracellular fluid/plasma
What are the different types calcium in extracellular fluid/plasma?
Protein-bound (30-40%)
Ionized (50-60%; unbound)
Complexed
Describe ionized calcium
Biologically active
Fraction dependent on pH
Where is complexed calcium found?
Citrate
Lactate
Bicarbonate
Phosphate
What are the functions of calcium?
Nerve impulses
Muscle contraction
Coagualtion
What does calcium do for nerve impusles
Membrane stabilization
What does calcium do for muscle contraction?
Release of AcCh at NMU
Skeletal
Smooth
Cardiac (ionotropic and chronotropic)
99% of filtered calcium is normally reabsorbed by the renal tubules. 90% of that is reabsorbed in proximal tubules, loops of Henle, and early distal tubules. The remaining 10% is reabsorbed. What is different about this reabsorption?
It is very selective
What are the target tissues of parathyroid hormone?
Bone
Kidney
Small intestine
What does PTH do to bone?
Resorption (release of Ca, P from bone)
Effect on blood levels (increase Ca, increase P)
What does PTH do to kidney?
Reabsorption of Ca (increase Ca)
Excretion of P (decrease P)
What does PTH do to small intestine?
Increase vitamin D3
Increase Ca and P
Where is P excreted from in the kidneys?
Proximal tubules
What is the net effect of PTH on the kidneys?
Increase serum Ca
Decrease serum P
What are the target tissues of calcitriol?
Small intestine
Bone
Parathyroid
What does calcitriol do to small intestine?
Increase Ca
Increase P
What does calcitriol do to parathyroid?
Decrease PTH
What does calcitriol do to bone in large quantities?
Stimulates bone resorption
Increase Ca in blood
Increase P in blood
What does PTH regulation involve?
Feedback inhibition
What is PTH secretion decreased by?
Hypercalcemia
Calcitriol
What is PTH secretion increased by?
Hypocalcemia
Hyperphoshatemia
What does vitamin D cause?
Renal activation
What is the most important site of vitamin D regulation?
Renal activation
What enzyme is involved in renal activation?
1α-hydroxylase
What does calcitriol increase in response to in renal activation?
Increased PTH
Decreased P
What does calcitriol decrease in response to in renal activation?
Increased P
In regulation, what does PTH increase in response to?
Decreased Ca
Increased P
In regulation, what does PTH decrease in response to?
Increase Ca
Increase calcitriol
What is the effect of PTH on the kidney?
Resorption, increase Ca
Excretion, decrease P
What is the effect of PTH on the small intestine?
Increase calcitriol, which increases Ca and P
What is the effect of PTH on bone?
Resorption, which increases Ca and P
What secretes calcitonin?
Parafollicular cells (C cells) of thyroid
What does calcitonin do?
Decrease Ca concentrations
What are the effects of PTH on bone?
Decrease osteocytic membrane activity
Decrease osteoclast formation
