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Flashcards in PROXIMAL TUBULE Deck (40)
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1

which is the longest part of the kidney tubules?

the proximal convoluted tubules

2

what are the adaptations of the proximal tubule?

simple cuboidal brush border - microvilli
high mitochondria density - active cells

3

why is the proximal tubule vulnerable to ischaemic injury?

due to the distance from the glomerulus

4

what is the function of the proximal tubule?

- bulk reabsorption of Na+, Cl- H2O, glucose, amino acids, HCO3-, lactate and phosphate
- secretion of organic ions

5

how is water reabsorbed in the proximal tubule?

through aquaporin 1 (AQP1) channels on apical and basolateral membranes
movement of water is due to oncotic gradient
tight junctions are leaky so water passes paracellularly

6

how is glucose reabsorbed in the proximal tubule?

- SGLT2 (1 Na and 1 glucose) in early proximal tubule
- works fast but doesn't produce high gradient
- SGLT1 (2Na and 1 glucose) in late proximal tubule
- higher affinity (as lower conc.)
glucose passes out passive on basolateral membrane through own channels (GLUT)

7

how much glucose should be found in urine?

close to zero

8

how is sodium reabsorbed in the proximal tubule?

1. Na+ actively transported out of PCT cell via Na/K ATPase pump (3Na+ out and 2K+ in) into interstitial fluid
2. Na+ transported into cell in exchange for H+ or co-transported (with glucose or phosphate) - secondary active transport
3. Na+ is actively transported by Na/K ATPase transporter or co-transported with HCO3- in to interstitium -

9

what is the predominant method that Na+ is reabsorbed in the proximal tubule?

80% of Na+ is reabsorbed in exchange for H+

10

how is HCO3- reabsorbed in the proximal tubule?

1. H+ in tubular lumen reacts with HCO3- to produce H2CO3 - requires carbonic anhydrase
2. H2CO3 dissociates into H2O and CO2
3. CO2 diffuses through cell wall as it is small and non-polar
4. H2O moves via osmosis through aquaporin 1
5. in cell CO2 and H2O recombine and dissociate to form HCO3-
6. H+ is recycled
7. HCO3- is either co-transported with Na+ or pumped passively in exchange for an anion across the basolateral membrane

11

give 2 ways that HCO3- is transported across the basolateral membrane of the proximal tubule?

- co-transported with Na+ (1 Na+ and 3 HCO3-)
- pumped passively in exchange for an anion

12

how are chloride ions reabsorbed in the proximal tubule?

it moves paracellularly
- Cl- is exchanged for base on apical membrane
- Cl- is exchanged for formate on apical membrane
- the Cl- is then transported in NKCC2 channel on basolateral membrane

13

what happens in formate cycling in chloride reabsorption in the proximal tubule?

formate is exchanged for Cl- on the apical membrane
the formate then becomes formic acid and diffuses across membrane and is reused
the Cl- is transported through NKCC2 channel on basolateral membrane

14

how are amino acids reabsorbed in the proximal tubule?

- there are a range of amino acid transporters that can carry positive/negative/neutral/any amino acids
- co-transported with Na+
- can flow passively on basolateral membrane through own channels

15

what happens in protein endocytosis and degradation in the proximal tubule?

microvilli have specialised sensors which bind to any protein
endocytosis occurs in endosomes and the protein is degraded by lysosomes to produce amino acids

16

why does endocytosis and degradation of proteins occur in the proximal tubule?

proteins shouldn't be in the tubules so the proximal tubule has a method for getting rid of them

17

what happens to the concentration of glucose in the proximal tubule?

they are taken up very quickly so concentration decreases quickly

18

what happens to the concentration of amino acids in the proximal tubule?

they are taken up very quickly so concentration decreases quickly

19

what happens to the concentration of HCO3- in the proximal tubule?

the concentration reduces slower but it has a much higher initial concentration so it takes more time

20

what happens to the concentration of inulin in the proximal tubule?

the concentration keeps going up as it is not being reabsorbed and water is being reabsorbed

21

what does it mean if inulin concentration doubles in the proximal tubule?

roughly 50% of water has been reabsorbed

22

what happens to the concentration of Cl- in the proximal tubule?

it initially gets left behind but then develops a concentration gradient and then gets reabsorbed

23

what happens to Na+ concentration in the proximal tubule?

the concentration stays level because it flows osmotically

24

what is the fluid that enters the loop of henle described as being?

isotonic urine - it gets concentrated by the loop of henle

25

what is inulin?

- a polysaccharide
- it is freely filtered by the kidney
- therefore amount in = amount out
- useful for measuring renal clearance - it is the same as GFR (inulin clearance = GFR)

26

what is paraminohippuric acid (PAH)?

it is actively secreted and freely filtered and not reabsorbed
therefore any that is in renal plasma is going to be excreted and cleared (unless you exceed Tmax for PAH)

27

what can be used to measure renal plasma flow?

PAH - it is excreted rapidly at first and then slows as it approaches Tmax

28

what is the definition of renal clearance?

it is the notional volume of plasma cleared of a substance in a given time (ml/min)

29

what is albumin clearance like?

0

30

what is sodium clearance like?

low (freely filtered but lots of reabsorption)