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MBBS Year 2 - Physiology > RENAL - Loop of Henle Function > Flashcards

RENAL - Loop of Henle Function Flashcards

1
Q

Structurally, compare and contrast cortical and juxtamedullary nephrons.

A
  • Cortical nephrons - glomeruli in outer cortex and Loop of Henle descends into surface of medulla
  • Juxtamedullary nephrons - glomeruli deeper in cortex and long Loops of Henle descends deeper into medulla
  • Both have vasa recta descending into medulla and following Loop of Henle
  • Cortical nephrons more common
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2
Q

Functionally, compare and contrast cortical and juxtamedullary nephrons.

A

Juxtaglomerular nephrons produce more concentrated urine

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3
Q

What is the role of the Loop of Henle?

A
  • Makes urine concentrated by reabsorption of water
  • By forming a hyperosmotic environment in medulla (more osmotic than plasma)
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4
Q

Why is the thick ascending loop of Henle thick?

A
  • High amount of mitochondria
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5
Q

What is the osmolarity of filtrate entering the Loop of Henle and why?

A

300 mOsm (isomotic with plasma and interstitium)
- In PCT, water and salts removed at same rate

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6
Q

What initially occurs once filtrate reaches the thick ascending loop of Henle?

A
  • Cells actively pump out sodium and chloride into interstitium - until difference in osmotic potential around 200 mOsm
  • More concentrated interstitium and more dilute urine
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7
Q

What happens after this in the thin descending loop?

A
  • Gradient between isosmotic filtrate in descending loop and interstitial fluid
  • Water moves out
  • More concentrated filtrate in descending loop until in equilibrium with interstitium
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8
Q

What happens after this?

A
  • Cells of ascending loop maintain osmotic gradient of 200 mOsm - sodium pumped out of filtrate into interstitium until gradient established
  • Water moves out of descending limb to equilibrate
  • Gradient between osmolarity of filtrate and interstitial fluid
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9
Q

What are the consequences of countercurrent multiplication?

A
  • Gradient in transverse direction maintained at 200 mOsm but gradient in longitudinal direction is steeper (900 mOsm in loop - most concentrated part of interstitium around 1200 mOsm)
  • Concentration of filtrate lower than when entering nephron - hypo-osmotic
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9
Q

(a) Describe the Loop of Henle in relation to collecting ducts

(b) How is reabsorption in the collecting ducts regulated?

A
  • Loop travels in parallel to collecting ducts
  • Regulated depending on water needs of organism
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10
Q

(a) When is ADH released?

(b) Where is it released from?

(c) What are the effects of ADH release?

A
  • When plasma osmolarity is high or blood volume is low
  • Released from posterior pituitary
  • Aquaporin insertion into walls of collecting duct - hyperosmolarity of interstitial fluid - greater reabsorption of water down concentration gradient from ducts - urine is more concentrated
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11
Q

Diabetes insipidus is a condition where ADH is not produced. Suggest some effects of this.

A
  • Urine is not concentrated by collecting ducts
  • Dilute urine is produced
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12
Q

Why can humans not drink seawater?

A
  • Salt content in seawater is higher than what can be processed by human body.
  • Human kidneys can only make urine that is less salty than salt water.
  • Therefore, to get rid of all the excess salt taken in by drinking seawater, you have to urinate more water than you drank - dehydration.
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12
Q

(a) What is the highest concentration occurring due to NaCl in the human kidney?

(b) As well as aquaporin insertion, name an effect of ADH.

(c) What is the most concentrated that human urine can be?

A
  • 600 mOsm
  • Insertion of urea channels into walls of collecting ducts - urea moves down concentration gradient - contributes 600 mOsm of concentrating effect on medullary interstitium
  • 1200 mOsm/litre
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13
Q

Why and when does having longer Loops of Henle become beneficial?

A
  • Greater surface area
  • Filtrate spends longer in the loop.
  • More opportunities for sodium (and therefore water) to be reabsorbed into the blood.
  • Water follows sodium, so conserving water depends on the movement of sodium
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14
Q

How are the solutes and water pumped out of the Loop of Henle reabsorbed back into the blood without damaging the concentration gradient? PART 1

A

COUNTERCURRENT EXCHANGE
- Blood vessels that supply the nephron follow same course but in opposite direction
- Blood vessels supplying the Loop are vasa recta - extension of efferent arteriole
- Plasma entering this blood supply isosmotic with filtrate in proximal collecting duct

15
Q

How are the solutes and water pumped out of the Loop of Henle reabsorbed back into the blood without damaging the concentration gradient? PART 2

A
  • Vasa recta descends down ascending Loop of Henle - interacts with concentrated interstitium, NaCl and other ions diffuse down concentration gradient until blood at apex of loop isosmotic with medullary interstitium
  • Blood supply loops back and follows descending loop of Henle - interacts with more dilute interstitium at portion where loop is permeable to water
16
Q

How are the solutes and water pumped out of the Loop of Henle reabsorbed back into the blood without damaging the concentration gradient? PART 3

A
  • Water diffuses into vessels down concentration gradient
  • As blood leaves loop, picked up both solutes and water - exits at same concentration as it entered
  • To maintain hyperosmotic environment of medullary interstitium, ascending loop pumps out NaCl and K from filtrate - maintain solute reabsorption
17
Q

How does the ascending loop create a concentrated interstitium? PART 1

A
  • NKCC2 transports sodium, chloride and potassium into cell
  • Sodium-hydrogen antiporter shuttles sodium into cells - secreting hydrogen into lumen
  • Energy to power processes comes from sodium gradient generated by sodium-potassium ATPase in basolateral membrane
  • Chloride ions diffuse freely down concentration gradient out of basolateral membrane
18
Q

How does the ascending loop create a concentrated interstitium? PART 2

A
  • Potassium flows out of both basolateral and apical membranes
  • As potassium flows out of apical membrane, makes luminal side slightly more positive than interstitium
  • Positive charge drives paracellular transport of ions such as sodium, potassium, magnesium and calcium across membrane into interstitium
  • Process is the basis for loop diuretics e.g furosemide
19
Q

Suggest what would happen if the NKCC2 channel is blocked.

A
  • Hinders ability of Loop of Henle to concentrate the interstitium
  • Reduced osmotic drive for water to leave collecting ducts
  • Greater water excretion

MBBS Year 2 - Physiology (22 decks)

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