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Systems: Urinary AB > 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 isomotic with the plasma (300mOmles/l)

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6
Q

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

A

This is because all the solute movements are accompanied by equivalent H2O movements, so that 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 which is 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 achieved?

A
  • Concentrates fluid on the way down and promptly re-dilutes it on the way back up, NOT by adding H2O, but by removing NaCl.
  • One consequence of this is that 15-20% of the initial filtrate (up to 36 l) is removed from the loop of Henle.
  • Fluid which enters the distal tubule is more dilute than plasma.
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

Only a 200 mOsm gradient exists at any horizontal level, but its effect is multiplied by the countercurrent flow.

25
Q

What is the countercurrent multiplier all about?

A
  • It is all about concentrating the medullary interstitium.

- And delivering hypotonic fluid to the 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

The balance of Starling’s forces are very much in favour of 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

The active transport of NaCl out of the ascending limb is abolished. all concentration differences are lost and the kidney can nly produce isotonic urine

Systems: Urinary AB (26 decks)

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