35 Potassium Calcium Phosphate Balance

Question 1

how is glucose handled in the kidney?

Answer 1

The kidneys freely filter glucose, and then reabsorb it, so that only trace amounts normally appear in the urine

Question 2

what parts of the tubule reabsorb the glucose?

Answer 2

● The proximal tubule reabsorbs nearly all the filtered load of glucose, and more distal segments reabsorb almost all the remainder

Question 3

what is glucose plasma concentration?

Answer 3

70-110 mg/dl

Question 4

glucose reabsorption is trans cellular, T/F? if so how?

Answer 4

T via Na/glucose cotransporter on the apical membrane, and via facilitated diffusion on the basolateral side

Question 5

At what plasma glucose concentration does glucose start appearing in the urine? how does this happen?

Answer 5

For the purposes of this test: 250 mg/dL (if looking at ultrafiltrate: 450 mg/min)

This happens because all of the sodium-glucose transporters are saturated

Question 6

How is calcium handled in the kidneys?

Answer 6

Binding of plasma proteins and formation of calcium-anion complexes influence the filtration and reabsorption of calcium

Question 7

what is the total concentration of calcium in plasma?

Answer 7

normally 8.8-10.6 mg/dl

15% of the filterable portion (60%) complexes with small anions such as carbonate, citrate, phosphate, and sulfate

Question 8

T/F, Tubule cells poorly reabsorb Ca-anion complexes?

Answer 8

T, but can take up free Ca2+

Question 9

how much calcium is reabsorbed in the PT?

Answer 9

Reabsorbs ~ 65% of the filtered Ca2+, a process that is not subject to hormonal control

Question 10

Most proximal tubule Ca2+ reabsorption occurs via the _____ route?

Answer 10

paracellular route and this is due to the high Ca2+ permeability of the tubule, as well as the sensitivity of Ca2+ transport to changes in the transepithelial electrochemical gradient for Ca2+

Question 11

in the PT, what is the effect of the lumen negative transepithelial voltage?

Answer 11

induces Ca2+ secretion, whereas a lumen-positive voltage induces reabsorption

Question 12

how much of the calcium is reabsorbed in the TAL?

Answer 12

25% of the filtered Ca2+

Question 13

what percent of the Ca2+ reabsorption in the TAL occurs passively and via what route? what drives this? What NT acts on this?

Answer 13

o 50% of the Ca2+ reabsorption in the TAL occurs passively via a paracellular route, driven by the lumen-positive voltage

AVP, indirectly increase Ca2+ reabsorption by making the transepithelial voltage more positive

Question 14

so still in the TAL, where does the other half of the Ca2+ reabsorption occur, like what pathway and what hormone is active?

Answer 14

The other half of the Ca2+ reabsorption occurs via the transcellular pathway, which PTH stimulates

Question 15

how much of the DCT reabsorbs calcium?

Answer 15

DCT reabsorbs ~ 8% of the filtered Ca2+ load

Question 16

what is the major regulatory site for Ca2+ excretion?

Answer 16

DCT is a major regulatory site for Ca2+ excretion

Question 17

what route does the DCT reabsorb Ca2+?

Answer 17

In contrast to the proximal tubule and TAL, the DCT reabsorbs Ca2+ predominantly via an active, transcellular route

Question 18

what is the most important regulator for renal Ca2+ reabsorption?

Answer 18

PTH, which stimulates Ca2+ reabsorption in the TAL, the DCT, and the connecting tubule

Question 19

how does PTH work?

Answer 19

PTH increases the open probability of apical Ca2+ channels. This increase in Ca2+ permeability increases [Ca2+]i, then stimulate basolateral Ca2+ extrusion mechanisms, increase Ca2+ reabsorption, and raise plasma [Ca2+]

Question 20

how is Vitamin D important for calcium reabsorption?

Answer 20

In renal tubule cells, vitamin D upregulates the Ca2+–binding protein, which contributes to enhanced Ca2+ reabsorption by keeping [Ca2+]i low during increased Ca2+ traffic through the cell

Question 21

what decreases Ca2+ reabsorption?

Answer 21

Diuretics and high plasma [Ca2+]