The proximal tubule and loop of Henle Flashcards Preview

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Flashcards in The proximal tubule and loop of Henle Deck (48):
1

Where does most tubular reabsorption occur?

Proximal tubule

2

Is tubular reabsorption active or passive?

Active

3

Is filtration specific or non specific?

Non-specific

4

Is tubular reabsorption specific or non specific?

Specific

5

Why is fluid reabsorbed in the proximal tubule iso-osmotic with filtrate?

Equal amounts of salt and water are reabsorbed

6

Reabsorption of which substance occurs completely within the proximal tubule?

Glucose

7

What separates the apical and basolateral membranes of tubular epithelial cells?

Tight junctions

8

During transcellular reabsorption which structures must be crossed?

Apical membrane
Cytoplasma
Basolateral membrane
Interstitium
Endothelial cells

9

During paracellular reabsorption which structures must be crossed?

Tight junctions
Interstitium
Endothelium

10

What is primary active transport?

Energy required to fuel the carrier protein to transport the substrate against its concentration gradient

11

What is secondary active transport?

The carrier protein transports the substrate coupled to the concentration gradient of an ion (usually sodium)

12

What is facilitated diffusion?

Passive carrier mediated transport of a substance down its concentration gradient

13

Why is sodium commonly utilised during active transport?

Because there are more sodium ions in the ECF and ICF and most transport is occuring into the cell

14

Diffusion can occur passively through ion channels. T/F

True

15

How does sodium reabsorption occur at the kidney?

Sodium enters tubular cells >
Sodium-potassium ATPase transports 3 sodium into the interstitium and 2 potassium into the cell at the basolateral membrane>
Sodium diffuses across the endothelium

16

Is the sodium-potassium pump energy dependent or independent?

Dependent

17

How does sodium enter tubular cells?

Secondary active transport of sodium and:
-Glucose
-Amino acids

Countertransport of sodium into cell and hydrogen ions out

18

How does chlorine reabsorption occur at the kidney?

The positively charged sodium ions in the interstitium set up and electrochemical gradient which attracts chloride ions paracellularly

19

How does water reabsorption occur at the kidney?

Salt absorbed attracts water (paracellular)

20

How is glucose reabsorbed in the kidney?

Secondary active transport with sodium into tubular cells then facilitated diffusion out of tubular cells

21

What is transport maximum for glucose?

Active transport mechanisms (i.e those which use conformational changes in membrane proteins) can only move a set number of molecules per unit time. Transport maximum occurs when these transport mechanisms become saturated (max glucose molecules per unit time)

22

Clearance of reabsorbed or secreted substances is constant once the transport maximum of that substance is reached. T/F

False - it is NOT constant once transport maximum is reached

23

Do secretory or reabsorptive mechanisms reach a transport maximum?

Both do

24

What is the function of the loop of Henle? How does it achieve this?

Producing concentrated urine. Creating a cortico-medullary solute concentration gradient

25

What is countercurrent flow?

Opposing flow in the two limbs of the loop of Henle

26

The loop of Henle and vasa recta are responsible for creating a hyper-osmotic medullary interstitium. Therefore which type of nephron is involved?

Juxto-medullary

27

What is being reabsorbed at the descending loop of Henle? What is it impermeable to?

Water
Salts

28

What is being reabsorbed at the ascending loop of Henle? What is it impermeable to?

Salts
Water

29

How does reabsorption of salts differ within the ascending loop of Henle?

Thick upper portion - active transport
Thin lower portion - passive

30

What is the effect of the differing permeabilities between the limbs of the loop of Henle?

Enable osmotic gradient to be established within the medulla

31

How are ions reabsorbed within the loop of Henle?

Triple cotransporter

32

Explain the triple cotransporter

Ions are pumped into the tubular cells:
1 sodium
1 potassium
2 choride
(equal charges)

33

At which membrane is the triple cotransporter always found?

Luminal

34

How do loop diuretics work?

By blocking the triple cotransporter at the loop of Henle thereby limiting salt reabsorption and thus water reabsorption (water follows salt)

35

How is potassium important in salt reabsorption at the loop of Henle?

Potassium is involved in the active transport of chloride and sodium ions and is continually recycled (i.e continually moves in and out of the cell)

36

What happens to the fluid as it passes through the loop of Henle?

Isotonic fluid enters descending limb >
Hypertonic fluid enters the ascending limb >
Hypotonic fluid leaves the ascending limb

37

What is countercurrent multiplication?

The effect the loop of Henle has to transform a horizontal concentration gradient into a vertical one within the medulla

38

Describe the concentration gradient produced by the loop of Henle

Osmolarity should be higher deeper within the medulla

39

Apart from the loop of Henle, what is important in creating the corticomedullary concentration gradient?

Urea cycle

40

Hows ADH promote or oppose urea secretion into the proximal tubule?

Promotes

41

Is the distal tubule permeable or impermeable to urea?

Impermeable

42

Why is the cortico-medullary gradient important for urine production?

It allows different concentrations and volumes of urine to be produced

43

What is the countercurrent exchanger?

The vasa recta acts as a countercurrent exchanger for juxtamedullary nephrons allowing blood to equilibrate with the juxtamedullary interstitial gradient

44

What is the countercurrent system?

The combined efforts of the vasa recta and the loop of henle

45

How is the loss of salt and urea from the medulla minimised?

Vasa recta runs in a hairpin loop
Vasa recta capillaries freely permeable to salt and water
Blood flow to vasa recta is low (minimal juxtamedullary nephrons)

46

Passive exchange of salt and water across the vasa recta helps to maintain the juxtamedullary gradient. T/F

True - since the blood equilibrates

47

What is the function of the vasa recta?

To ensure solute is not washed away from the medulla

48

The high medullary gradient allows the production of hypertonic urine in the presence of ADH. T/F

True

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