Calcium And Renal Stones Flashcards
What is the plasma concentration of calcium normally?
1.0-1.3mmol/L
Why is calcium important?
Hormone secretion Nerve conduction Muscle contraction Exocytosis Inactivation/activation of enzymes
How is calcium found in the plasma and in what proportions?
45% free ionised species
45% bound to proteins (80% to albumin)
10% complexed (eg citrates, phosphate etc.)
What percentage of dietary calcium is a doe ed and from where?
20-40%
Intestine
When does calcium absorption increase and decrease?
Increases: growth, pregnancy and lactation
Decreases: advancing age
What is calcium absorption regulated by?
1,25-dihydroxyvitamin D
Calcitriol
How much calcium is filtered by the kidney a day?
250 mmol
What percentage of calcium filtered is reabsorbed by the kidney? Where?
95-98%
65% PCT
20-25% ascending loop
10% in DCT
Which part of the kidney tubules does PTH affect in calcium absorption?
Distal convoluted tubule
How do we get vitamin D?
Absorbed in the gut
Synthesised in the skin with UV radiation
Once absorbed, what happens to vitamin D?
Vitamin D -> calciferol
-done in the liver (due to short half life of vit D)
Calciferol -> calcitriol
-in the kidneys
What does calcitriol do?
Binds to calcium in the gut to increase its absorption along with phosphate
How does PTH regulate production of calcitriol?
It regulates the conversion of calciferol to calcitriol
I guess increases the conversion!
How does PTH directly affect calcium levels?
Increases its release from bones by stimulating osteoclasts
Increases its reabsorption in the thick ascending limb and distal tubules of kidneys
Decreases reabsorption of phosphate and bicarbonate in the PCT to allow there to be more free plasma calcium
How is PTH regulated?
Negative feedback of calcium
