Keef Lecture

Question 1

There are about 1,300 grams of calcium in the body. What percentage goes to bones & teeth? To ECF? ICF?

Answer 1

Bones & Teeth: 99%
ECF: 0.1%
ICF: 0.9%

Question 2

What are some things that calcium is used for in the body?

Answer 2

bone
enzyme cofactor
nerve excitability
muscle contraction
NT release

Question 3

There are about 600 grams of phosphorus in the body. What percentage goes to bones & teeth? To ECF? ICF?

Answer 3

Bones & Teeth: 86%
ECF: 0.08%
ICF: 14%

Question 4

What are some things that phosphorus is used for in the body?

Answer 4

Phosphoproteins
Buffering pH
DNA, RNA
Bone

Question 5

What is the plasma variation of calcium per day?

Answer 5

1-2%/day

Question 6

What is the plasma variation of phosphorus per day?

Answer 6

50-150%/ day

Question 7

50% of calcium is found in what form? What about the other 50%?

Answer 7

50%: Ca++ (ionized)
40%: Protein bound
10%: bound to anions

Question 8

80% of phosphorus is found in what form? What about the other 20%?

Answer 8

80%: HPO42-

20%: H2PO4-

Question 9

What are the 3 main target organs of calcium & phosphorus?

Answer 9

kidney
bone
GI tract

Question 10

How much calcium is found in your diet? How much is excreted in feces? How much is excreted in urine?

Answer 10

Calcium in diet: 1000mg/day
Excreted in Feces: 850 mg/day
Excreted in Urine: 150 mg/day

Question 11

What are ways to get calcium into the ECF?

Answer 11

Absorption from GI tract
Resorption from bone
Reabsorption in the kidney
coming out of cells

Question 12

What are ways to get calcium out of the ECF?

Answer 12

Secretion into the GI tract
Glomerular Filtration
Deposition in Bone
Going into cells

Question 13

About how much calcium is usu found in the ECF?

Answer 13

900mg

Question 14

How much phosphate is found in your diet? How much is excreted in feces? How much is excreted in urine?

Answer 14

900 mg is found in your diet
300 mg is excreted in feces
600 mg is excreted in urine

Question 15

What are ways to get phosphate into the ECF?

Answer 15

Absorption from the GI tract
Resorption from the bone
Reabsorption from the kidney
Coming out of cells

Question 16

What are ways to get phosphate out of the ECF?

Answer 16

Glomerular Filtration
Deposition in Bone
Going into cells

Question 17

Is phosphate usu secreted into the GI tract?

Answer 17

NO

Question 18

Where is calcium absorbed in the GI tract? is this an active or passive process?

Answer 18

In the small intestine
Duodenum & jéjunum: active process
Ileum: passive process

Question 19

What are the 2 basic ways that calcium can be absorbed?

Answer 19

paracellularly (b/w the cells)

transcellularly (thru cells)

Question 20

Where is phosphate absorbed in the GI tract?

Answer 20

In the small intestine

everywhere in the SI it is an active process

Question 21

Can phosphate be absorbed in the GI tract both transcellularly & paracellularly?

Answer 21

No. Just transcellularly, an active process.

Question 22

Describe how phosphate is absorbed in the SI.

Answer 22

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.

Question 23

In the kidney: what percentage of calcium is reabsorbed in the PCT? In the thick ascending limb? In the DCT? In the collecting duct?

Answer 23

PCT: 70%
thick ascending limb: 20%
DCT: 8-9%
Collecting Duct: 1%

Question 24

How is calcium reabsorbed in the PCT?

Answer 24

Mainly passively, which means paracellularly.

Also, some active transport (transcellularly).

Question 25

How is calcium reabsorbed in the thick ascending limb & the DCT? In the collecting duct?

Answer 25

Only actively, transcellularly

Question 26

What affect does parathyroid hormone have on calcium reabsorption in the kidney?

Answer 26

It increases it!

It acts on the active processes in the thick ascending limb, DCT, & collecting duct

Question 27

What is the percentage of calcium excretion in the kidney?

Answer 27

1%

Question 28

Explain specifically how parathyroid hormone helps in the active calcium reabsorption in the kidney.

Answer 28

It activates a Gs protein. This increases cAMP levels & activates PKA.
PKA phosphorylates the calcium transporters on the luminal side, making them more receptive.

Question 29

Once calcium gets in the cells of the nephron, how do they get out?

Answer 29

via an active Ca++ pump & a calcium sodium exchanger.

Question 30

What is the name of the calcium channels in the kidney?

Answer 30

Epithelial calcium channels (ECaC)

OR TRP channels

Question 31

Vitamin D also assists in calcium reabsorption in the kidney. How?

Answer 31

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.

Question 32

What is the role of calbindin in calcium reabsorption?

Answer 32

it binds the Ca++ once it gets into the cell. Then it can get to its transporters on the other side.

Question 33

In the kidney, what percentage of phosphate is reabsorbed in the PCT? In the thick ascending limb? DCT? Collecting Duct?

Answer 33

PCT: 80%
Thick ascending limb: 0%
DCT: 10%
Collecting duct: 0%

Question 34

What is the percentage of phosphate excreted in the nephron?

Answer 34

10-20%

Question 35

What is the effect of parathyroid hormone on phosphate reabsorption in the kidney?

Answer 35

It inhibits the active process.

Question 36

How is phosphate reabsorbed in the kidney? Transcellularly? ParacellularlY?

Answer 36

ALL transcellularly

Question 37

Explain how phosphate is reabsorbed in the kidney at the cellular level.

Answer 37

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.