35 Potassium Calcium Phosphate Balance Flashcards Preview

MABS Physiology > 35 Potassium Calcium Phosphate Balance > Flashcards

Flashcards in 35 Potassium Calcium Phosphate Balance Deck (21)
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1
Q

how is glucose handled in the kidney?

A

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

2
Q

what parts of the tubule reabsorb the glucose?

A

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

3
Q

what is glucose plasma concentration?

A

70-110 mg/dl

4
Q

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

A

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

5
Q

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

A

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

6
Q

How is calcium handled in the kidneys?

A

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

7
Q

what is the total concentration of calcium in plasma?

A

normally 8.8-10.6 mg/dl

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

8
Q

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

A

T, but can take up free Ca2+

9
Q

how much calcium is reabsorbed in the PT?

A

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

10
Q

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

A

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+

11
Q

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

A

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

12
Q

how much of the calcium is reabsorbed in the TAL?

A

25% of the filtered Ca2+

13
Q

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

A

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

14
Q

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

A

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

15
Q

how much of the DCT reabsorbs calcium?

A

DCT reabsorbs ~ 8% of the filtered Ca2+ load

16
Q

what is the major regulatory site for Ca2+ excretion?

A

DCT is a major regulatory site for Ca2+ excretion

17
Q

what route does the DCT reabsorb Ca2+?

A

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

18
Q

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

A

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

19
Q

how does PTH work?

A

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+]

20
Q

how is Vitamin D important for calcium reabsorption?

A

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

21
Q

what decreases Ca2+ reabsorption?

A

Diuretics and high plasma [Ca2+]

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