Keef Lecture Flashcards
There are about 1,300 grams of calcium in the body. What percentage goes to bones & teeth? To ECF? ICF?
Bones & Teeth: 99%
ECF: 0.1%
ICF: 0.9%
What are some things that calcium is used for in the body?
bone enzyme cofactor nerve excitability muscle contraction NT release
There are about 600 grams of phosphorus in the body. What percentage goes to bones & teeth? To ECF? ICF?
Bones & Teeth: 86%
ECF: 0.08%
ICF: 14%
What are some things that phosphorus is used for in the body?
Phosphoproteins
Buffering pH
DNA, RNA
Bone
What is the plasma variation of calcium per day?
1-2%/day
What is the plasma variation of phosphorus per day?
50-150%/ day
50% of calcium is found in what form? What about the other 50%?
50%: Ca++ (ionized)
40%: Protein bound
10%: bound to anions
80% of phosphorus is found in what form? What about the other 20%?
80%: HPO42-
20%: H2PO4-
What are the 3 main target organs of calcium & phosphorus?
kidney
bone
GI tract
How much calcium is found in your diet? How much is excreted in feces? How much is excreted in urine?
Calcium in diet: 1000mg/day
Excreted in Feces: 850 mg/day
Excreted in Urine: 150 mg/day
What are ways to get calcium into the ECF?
Absorption from GI tract
Resorption from bone
Reabsorption in the kidney
coming out of cells
What are ways to get calcium out of the ECF?
Secretion into the GI tract
Glomerular Filtration
Deposition in Bone
Going into cells
About how much calcium is usu found in the ECF?
900mg
How much phosphate is found in your diet? How much is excreted in feces? How much is excreted in urine?
900 mg is found in your diet
300 mg is excreted in feces
600 mg is excreted in urine
What are ways to get phosphate into the ECF?
Absorption from the GI tract
Resorption from the bone
Reabsorption from the kidney
Coming out of cells
What are ways to get phosphate out of the ECF?
Glomerular Filtration
Deposition in Bone
Going into cells
Is phosphate usu secreted into the GI tract?
NO
Where is calcium absorbed in the GI tract? is this an active or passive process?
In the small intestine
Duodenum & jéjunum: active process
Ileum: passive process
What are the 2 basic ways that calcium can be absorbed?
paracellularly (b/w the cells)
transcellularly (thru cells)
Where is phosphate absorbed in the GI tract?
In the small intestine
everywhere in the SI it is an active process
Can phosphate be absorbed in the GI tract both transcellularly & paracellularly?
No. Just transcellularly, an active process.
Describe how phosphate is absorbed in the SI.
It goes thru a sodium phosphate cotransporter on the luminal side of the enterocyte. This is up its electrochemical gradient–>why it is active. Then it goes thru to the interstitial space down a gradient. There is a sodium potassium pump.
In the kidney: what percentage of calcium is reabsorbed in the PCT? In the thick ascending limb? In the DCT? In the collecting duct?
PCT: 70%
thick ascending limb: 20%
DCT: 8-9%
Collecting Duct: 1%
How is calcium reabsorbed in the PCT?
Mainly passively, which means paracellularly.
Also, some active transport (transcellularly).
How is calcium reabsorbed in the thick ascending limb & the DCT? In the collecting duct?
Only actively, transcellularly
What affect does parathyroid hormone have on calcium reabsorption in the kidney?
It increases it!
It acts on the active processes in the thick ascending limb, DCT, & collecting duct
What is the percentage of calcium excretion in the kidney?
1%
Explain specifically how parathyroid hormone helps in the active calcium reabsorption in the kidney.
It activates a Gs protein. This increases cAMP levels & activates PKA.
PKA phosphorylates the calcium transporters on the luminal side, making them more receptive.
Once calcium gets in the cells of the nephron, how do they get out?
via an active Ca++ pump & a calcium sodium exchanger.
What is the name of the calcium channels in the kidney?
Epithelial calcium channels (ECaC)
OR TRP channels
Vitamin D also assists in calcium reabsorption in the kidney. How?
It is a steroid hormone, so it diffuses across the cell’s plasma membrane & gets into the nucleus. There it increases transcription of TRP channels & calbindin.
What is the role of calbindin in calcium reabsorption?
it binds the Ca++ once it gets into the cell. Then it can get to its transporters on the other side.
In the kidney, what percentage of phosphate is reabsorbed in the PCT? In the thick ascending limb? DCT? Collecting Duct?
PCT: 80%
Thick ascending limb: 0%
DCT: 10%
Collecting duct: 0%
What is the percentage of phosphate excreted in the nephron?
10-20%
What is the effect of parathyroid hormone on phosphate reabsorption in the kidney?
It inhibits the active process.
How is phosphate reabsorbed in the kidney? Transcellularly? ParacellularlY?
ALL transcellularly
Explain how phosphate is reabsorbed in the kidney at the cellular level.
Phosphate goes up its electrochemical gradient as it goes into the cell. It goes thru a sodium phosphate exchanger. Then it gets out via some sort of anion exchanger. This part is more passive & down an electrochemical gradient. There is also a sodium potassium pump.
