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Flashcards in L18 Deck (26):
1

The proximal tubule is concerned with....

the uptake and secretion of several solutes and water, but the fluid in the tubule remains
isotonic throughout.

2

The apical ( .... ) surface of the cells have
numerous .... which enhance their transport
function.

(tubule side)
microvilli

3

The proximal tubule has several important functions: (3)

•Reabsorption of the bulk of filtered NaCl as isotonic NaCl solution essential solutes, e.g. glucose and all amino acids

•Regulation of body fluid pH (by bicarbonate reabsorption).

•Secretion of some organic molecules.

4

Reabsorption is the net movement
from ...

apical to baso-lateral
membrane

5

Secretion is the net movement
from....

baso-lateral to apical membrane

6

About ....% of the filtered load of NaCl is reabsorbed, but tubular fluid remains isotonic

80

7

Describe NaCl and Water Reabsorption

•Na+ are transported into the epithelial cell by secondary active transport

• coupled co-transport with other molecules

• coupled counter-transport

• the Na+ are removed from the baso-lateral surface by active transport-the Na pump

• Cl-and H2O follow passively.

• Therefore isotonic NaCl reabsorption has occurred.

8

Przypomnienie:

In normal individuals, all the filtered load of glucose and other vital metabolites (amino acids, etc.) are reabsorbed in the proximal tubule.

9

Describe Glucose Clearance
Glucose is:

• freely filtered
• absorbed by the tubule from lumen to blood
• not metabolised
• does not affect GFR itself

If the Pglu is not high all the glucose in the glomerular filtrate is reabsorbed and the urine excretion is zero:

Cglu=0!!!!
This is a physiologically useful function of the tubule: to reabsorb useful substrates from the filtrate that otherwise would be lost in the urine.

10

Glucose re-absorption is a carrier-mediated process, and therefore has a maximum transport rate called:

The tubular transport maximum or Tmax

11

The kidney can reabsorb completely the filtered glucose load at normal plasma (and therefore filtrate levels) ~=...

4-6mM or 70-110 mg/dl

12

Explain what happens in diabetes mellitus

If the concentration exceeds a critical level CARRIERS ARE SATURATED AND THE EXCESS GLUCOSE APPEARS IN THE URINE

This plasma level is ~= 300 mg/dl or ~= 16mM. It is usually lower ~= 11 mM as nephrons have various Tmax

13

Describe the mechanisms used in Reabsorption of Bicarbonate (HCO3-) in Proximal Tubule

•The mechanisms used are secondary active transport
•Are dependent on carbonic anhydrase

14

Describe the process of Reabsorption of Bicarbonate (HCO3-) in Proximal Tubule

•Secretion of H+
•Buffering of H+ within the tubular lumen be reabsorbing HCO3-
•Buffering of H+ within the tubular lumen with HPO42- or NH3
•Resultant urine pH 4.5-8.2 due to balance of H+ and HCO3- secretion.
•Net result all HCO3- is reabsorbed in the PCT.

15

The kidney plays an important role in the regulation of pH through several mechanisms:

•Secretion of H+
•Buffering of H+ within the tubular lumen be reabsorbing HCO3-
•Buffering of H+ within the tubular lumen with HPO42- or NH3

16

RPF measurement by ....

PAH Clearance

17

Explain terms PAH and RPF

Para-aminohippuric acid
Renal plasma flow

18

(PAH) is:

• freely filtered
• secreted by the tubule from blood to lumen
• not metabolised
• does not affect GFR itself

19

If PPAH is not high all the PAH in the
efferent arteriolar blood is ...

is secreted into the tubule so that
PvPAH X RPF = 0.

the clearance of PAH is a means of measuring RPF=625 ml/min'

ogarnąć to z worda

20

LO: Explain the distinction between reabsorption and secretion.

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21

LO: Transport of essential ions, glucose and amino acids

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22

LO: Glucose clearance by the kidney.

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23

LO: The concept of transport maximum.

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24

LO: Bicarbonate reabsorption in the proximal tubule.

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25

LO: Secretory processes in the proximal tubule.

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26

LO: The use of PAH for estimation of renal plasma flow.

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