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Year 2 > The proximal tubule and loop of Henle > Flashcards

The proximal tubule and loop of Henle Flashcards

1
Q

Where does most tubular reabsorption occur?

A

Proximal tubule

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2
Q

Is tubular reabsorption active or passive?

A

Active

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3
Q

Is filtration specific or non specific?

A

Non-specific

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4
Q

Is tubular reabsorption specific or non specific?

A

Specific

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5
Q

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

A

Equal amounts of salt and water are reabsorbed

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6
Q

Reabsorption of which substance occurs completely within the proximal tubule?

A

Glucose

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7
Q

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

A

Tight junctions

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8
Q

During transcellular reabsorption which structures must be crossed?

A 
Apical membrane
Cytoplasma
Basolateral membrane 
Interstitium 
Endothelial cells
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9
Q

During paracellular reabsorption which structures must be crossed?

A

Tight junctions
Interstitium
Endothelium

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10
Q

What is primary active transport?

A

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

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11
Q

What is secondary active transport?

A

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

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12
Q

What is facilitated diffusion?

A

Passive carrier mediated transport of a substance down its concentration gradient

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13
Q

Why is sodium commonly utilised during active transport?

A

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

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14
Q

Diffusion can occur passively through ion channels. T/F

A

True

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15
Q

How does sodium reabsorption occur at the kidney?

A

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

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16
Q

Is the sodium-potassium pump energy dependent or independent?

A

Dependent

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17
Q

How does sodium enter tubular cells?

A

Secondary active transport of sodium and:

  • Glucose
  • Amino acids

Countertransport of sodium into cell and hydrogen ions out

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18
Q

How does chlorine reabsorption occur at the kidney?

A

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

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19
Q

How does water reabsorption occur at the kidney?

A

Salt absorbed attracts water (paracellular)

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20
Q

How is glucose reabsorbed in the kidney?

A

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

21
Q

What is transport maximum for glucose?

A

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
Q

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

A

False - it is NOT constant once transport maximum is reached

23
Q

Do secretory or reabsorptive mechanisms reach a transport maximum?

A

Both do

24
Q

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

A

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

25
Q

What is countercurrent flow?

A

Opposing flow in the two limbs of the loop of Henle

26
Q

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

A

Juxto-medullary

27
Q

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

A

Water

Salts

28
Q

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

A

Salts

Water

29
Q

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

A

Thick upper portion - active transport

Thin lower portion - passive

30
Q

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

A

Enable osmotic gradient to be established within the medulla

31
Q

How are ions reabsorbed within the loop of Henle?

A

Triple cotransporter

32
Q

Explain the triple cotransporter

A 
Ions are pumped into the tubular cells:
1 sodium
1 potassium
2 choride 
(equal charges)
33
Q

At which membrane is the triple cotransporter always found?

A

Luminal

34
Q

How do loop diuretics work?

A

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

35
Q

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

A

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
Q

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

A

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

37
Q

What is countercurrent multiplication?

A

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

38
Q

Describe the concentration gradient produced by the loop of Henle

A

Osmolarity should be higher deeper within the medulla

39
Q

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

A

Urea cycle

40
Q

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

A

Promotes

41
Q

Is the distal tubule permeable or impermeable to urea?

A

Impermeable

42
Q

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

A

It allows different concentrations and volumes of urine to be produced

43
Q

What is the countercurrent exchanger?

A

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

44
Q

What is the countercurrent system?

A

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

45
Q

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

A

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
Q

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

A

True - since the blood equilibrates

47
Q

What is the function of the vasa recta?

A

To ensure solute is not washed away from the medulla

48
Q

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

A

True

Year 2 (72 decks)

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