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renal system > Loop of Henle > Flashcards

Loop of Henle Flashcards

1
Q

What occurs at the proximal tubule?

A
  • major site of reabsorption
  • 65-75% of all NaCl and H2O
    (all nutritionally important substances)
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2
Q

What protein in particular can get filtered?

A

Albumin

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3
Q

What happens to the albumin that is filtered?

A

Completely reabsorbed by a Tm carrier mechanism in the proximal tubule.

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4
Q

How are many drugs which are nonpolar and highly lipid soluble removed?

A
  • removal of H2O in the proximal tubule would establish concentration gradients for their reabsorption
  • thus the liver metabolises them to polar compounds, reducing their permeability and facilitating their excretion.
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5
Q

What type of fluid leaves the proximal tubule?

A

The fluid is isoosmotic with the plasma (300mOmles/l)

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6
Q

Why is the fluid leaving the proximal tubule isomotic with the plasma?

A
  • all solute movements are accompanied by equivalent H2O movements
  • osmotic equilibrium is maintained
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7
Q

Where do all the nephrons have their proximal and distal tubules?

A

In the cortex of the kidney

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8
Q

What do all nephrons share?

A

Common processes for the reabsorption and secretion of solutes of the filtrate

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9
Q

What is a special system essential for water balance attributable to?

A

The loops of Henle of juxtamedullary nephrons

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10
Q

What is the maximum concentration of urine the kidney can produce?

A
  • 1200-1400mOsmoles/l

- 4x more concentrated than plasma (excess of solute over water)

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11
Q

What amounts to 600mOsmoles daily?

A

The urea, sulphate, phosphate and other waste products and non waste ions (Na and K)

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12
Q

What does the ‘waste’ that must be excreted require?

A

A minimum obligatory H2O loss of 500mls

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13
Q

How can one urinate to death?

A

If the kidneys are functioning but there is no H2O intake

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14
Q

What is the minimum [urine]?

A

30-50mOsmoles/l

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15
Q

When will the minimum [urine] be produced?

A

In conditions of excess H2O intake

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16
Q

Why is the kidney able to produce urine of varying concentration?

A

The loops of Henle of juxtamedullary nephrons act as counter-current multipliers

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17
Q

What is counter current?

A

Fluid flows down the descending limb and up the ascending limb

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18
Q

What are the critical characteristics of the loops which make them current multipliers are:

A
  • The ascending limb of the loop of Henle actively co-transports Na+ and Cl- ions out of the tubule lumen into the interstitium. The ascending limb is impermeable to H2O.
  • The descending limb is freely permeable to H2O but relatively impermeable to NaCl
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19
Q

What does the countercurrent multiplier achieve?

A

concentrates fluid on the way down and promptly re-dilutes it on the way back up by removing NaCl not by adding H2O

20
Q

What is the overwhelming significance of the countercurrent multiplier?

A

It creates an increasingly concentrated gradient in the interstitium

21
Q

What does the countercurrent multiplier deliver to the distal tubule?

A

Hypotonic fluid

22
Q

What is the osmolarity of fluid that enters the countercurrent multiplier?

A

300mOsm

23
Q

What is the osmolarity of the fluid that leaves the countercurrent multiplier?

A

100mOsm

24
Q

What gradient exist within the countercurrent multiplier?

A
  • 200 mOsm gradient exists at any horizontal level

- its effect is multiplied by the countercurrent flow

25
Q

What is the countercurrent multiplier all about?

A
  • concentrating medullary interstitium

- delivering hypotonic fluid to distal tubule

26
Q

What is the vasa recta?

A

The specialized arrangement of the peritubular capillaries of the juxtamedullary nephrons

27
Q

What does the vasa recta participate in?

A

The countercurrent mechanism by acting as countercurrent exchangers

28
Q

Why do the medullary capillaries not drain straight through abolishing the gradient?

A

They are arranged as hairpin loops and therefore do not interfere with the gradient

29
Q

Why do the vasa recta equilibrate with the medullary interstitial gradient?

A

The vasa recta are freely permeable to H2O and solutes

30
Q

What are the functions of the vasa recta?

A
  • Provide O2 for medulla.
  • In providing O2 must not disturb gradient.
  • Removes volume from the interstitium, up to 36l/day.
31
Q

What is the balance of Starling’s forces in favour of?

A

reabsorption because of high osmotic pressure, and high tissue pressure due to tight renal capsule which drives fluid into capillaries.

32
Q

Why is the flow rate through the vasa recta very low?

A

So that there is plenty of time for equilibration to occur with the interstitium, further ensuring that the medullary gradient is not disturbed.

33
Q

Where is the site of water regulation?

A

The collecting duct

34
Q

What is the permeability of the collecting duct under control of?

A

Anti-diuretic hormone (ADH aka. vasopressin)

35
Q

What produced ADH?

A

Posterior pituitary

36
Q

Whether or not the dilute urine delivered to the distal tubule is concentrate and to what extent depends on…

A

The presence or absence of ADH

37
Q

What is the key step in the counter current multiplier system?

A

Active removal of NaCl from ascending limb

38
Q

What happens in the counter current multiplier system as NaCl is removed from the ascending limb?

A

The osmolarity decreases and increases in the interstirium

39
Q

What does removal of NaCl from the ascending limb mean for the descending limb?

A
  • It is now exposed to a greater osmolality in the interstirum
  • H2O will move out of the descending limb to equate osmolality
40
Q

What happens to the H2O what moves into the interstitium in the counter current mechanism?

A

It does not stay in the interstitium but is reabsorbed by the high osmotic pressure and tissue pressure into the vasa recta (Starling forces)

41
Q

Where does fluid enter and exit the counter current system?

A

Enters at the proximal tubule and exits via the distal tubule

42
Q

What does the concentrated fluid in the descending limb of the counter current mechanism do?

A

Rounds the bend and delivers a [high] to the ascending limb

43
Q

What does increasing concentration of the descending limb in the counter current system mean?

A

Greater concentration of interstitium by addition of salt from the ascending limb

44
Q

How is the fluid in the counter current system progressively concentrated?

A

The fluid in the tubule is progressively concentrated as it moves down the descending limb and progressively diluted as it moves up the ascending limb.

45
Q

What does the vertical gradient in the interstitium go from?

A

300 to 1200 mOsmol

46
Q

What happens to the counter current system when frusemide is used?

A
  • active transport of NaCl out of the ascending limb is abolished
  • all concentration differences are lost
  • kidney can only produce isotonic urine

renal system (26 decks)

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