Renal - Loop of Henle Flashcards by Mary Kate Heard

What are the three functionally distinct subsegments of the renal loop?

Thin Descending Limb
Thin Ascending Limb
Thick Ascending Limb

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What is the functionality of the thin descending limb?

No NaCl transport
Water permeable

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What is the functionality of the thin ascending limb?

Passive Na+ reabsorption
Not water permeable

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What is the functionality of the thick ascending limb?

Active Na, Cl, and K+ transport
Not water permeable

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What are the functions of the loops of henle?

Reabsorbtion
create a medullary interstitial solute concentration gradient

essential for concentrating urine and conserving body water

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How does the Na+-K+-2Cl- cotransporter work?

Na+ is cotransported with 2Cl- ions and 1 K+ ion by NKCC2
Some K+ returns to the lumen through K+ ROMK Channels
K+ leak required to replenish luminal K+ so NKCC2 continue to function
Na+ leaves via Na+-K+ pumps
Cl- exits primarily through Cl- channels

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What favors paracellular solute transport?

Positve lumen favors paracellular reabsorption of cations
half of TAL Na+ reabsorption is paracellular
Mg, Ca, K, reabsorbed

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How is Na+ and Cl- reabsorbed in the TAL?

Na-K-2Cl cotransporter
Paracellular solute transport

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How is urea passively recycled between the CD and LoH?

Collecting duct urea transport is oneway out
some renters the descending and ascending limb (one-way in)
some enters vasa recta and returns to systemic circulation

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Define:

Countercurrent

flow of fluid in opposite directions in adjacent structures

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Define

Countercurrent exchange

crossover of some property between two fluids flowing in opposite directions

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Define

Countercurrent multiplication

The result of solute transport occuring in only the outgoing part of a column constantly flowing fluid
Solute transported out in AL continue adding fluid creates an even greater concentration (amplifies) gradient

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What are the two steps of countercurrent multiplication?

The single effect
Fluid Flow

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Define

Single Effect step of Countercurrent Multiplication

Active transport of NaCl out of tubular fluid in the TAL

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What is the result of the single effect step of countercurrent multiplication?

Hyperosmotic interstitial fluid -> water moves passively down its concentration gradient out of the tubular fluid in the descending limb into the interstitial space, until it reaches equilibrium

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Define

Fluid flow step of Countercurrent Multiplication

As urine is continually being produced, new tubular fluid enters the descending limb

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What is the result of the fluid flow step of Countercurrent Multiplication?

Fluid is pushed down the tube at a higher osmolarity and an osmotic gradient begins to develop

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What are the characteristics of the single effect of Countercurrent Multiplication?

What is it permeable to? How/where does it move ions?

Na+-K+-2Cl- transporter moves Na+ and Cl- into the medullary interstitium -> affects concentration of tubular fluid and interstitium
TAL of the LOH lacks aquaporins
Descending limb is H2O permeable

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Single Effect step of Countercurrent Multiplication

How does the Na+-K+-2Cl- transporter affect the tubular fluid and interstitium?

Tubular fluid is hypoosmolar (dilute)
Interstitium has hyperosmolar fluid (more concentrated)

Hyperosmolar fluid is found in the descending limb

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Fluid Flow step of Countercurrent Multiplication

The movement of fluid through the tubules causes…

How does it effect the fluid in the overall loop

the hyperosmotic fluid to move further down the loop

pump - equilibriate - shift

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Fluid Flow step of Countercurrent Multiplication

What is the difference between fluid at the top of the LoH vs at the bottom of the loop?

At the top of LoH fluid is nearly isomolar
At the bottom of the LoH fluis is very concentrated

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Permeabilities of the Descending Limb

Highly permeable to H2O
impermeable to Na+

Permeabilities of Ascending Limb

Actively transports NaCl out
Impermeable to H2O

What are the steps involved in countercurrent multiplication?

Initial state -> equilibrium
Pump out NaCl to interstitium establishing a 200 mosm/l gradient established at each horizontal level (decreases)
H2O diffuses out of descending limb into the interstitium to equilibrate
fluid shifts
200 mosm/l gradient between ascending tubular fluid and interstitial space at each horizontal level
The final vertical osmotic gradient is established and maintained by the ongoing countercurrent multiplication

Pump - equilibriate - shift

How does the osmolarity change throughout the LoH during countercurrent multiplication?

1. equal throughout limbs and with interstitium 2. 200 mosm/l gradient established in the horizontal level of the ascending limb and 400 mosml/gradient in interstitium when NaCl is pumped out 3. 400 mosm/l gradient established in descending limb when water diffuses out to equilibriate 4. osmolarities shift throughout loop 5. 200 mosm/l gradient between ascending limb fluid and interstitial space 6. vertical osmotic gradient established -> low to high in descending limb and interstitium, high to low in ascending limb

What is the purpose of the countercurrent multiplication system in the LoH?

Isotonic fluid enters tubular fluid is concentrated 4x and is then diluted to 1/3 the original concentration

What are the 2 benefits of the countercurrent multiplication system of the LoH?

Gradient is used by collecting ducts to reabsorb H2O (ADH-induced) Creating of a hypotonic fluid enables kidneys to excrete a more dilute urine than normal body fluids

What is the relationship between the vasa recta and LoH?

Vasa recta runs opposite of LoH Blood in vasa rectca removed water leaving LoH

What is an important aspect of the countercurrent exchange with the vasa recta?

Important that the blood circulating through medulla does not disturb the vertical osmotic gradient created by the LoH

How does the blood circulating in the vasa recta avoid disturbing the vertical osmotic gradient of the LoH?

Blood enters and leaves the medulla at the same osmolarity, leaving the medulla nourished but preserving the gradient ## Footnote Blood equilibriates between capilary and ISF at each level on way down and up

What occurs in the Descending Vasa Recta?

Blood from efferent arterial at 300 mosm/l Water diffuses out NaCl diffuses in

What occurs in the Ascending Vasa Recta?

Blood enters renal vein at 300 mosm/l Water diffuses in NaCl diffuses out

What is the role of ADH in the kidney?

Create an opportuity for water to be reabsorbed primary hormonal regulator of renal H2O excretion H2O reabsorption is obligatory in PT (65%) and LoH (15%) In DT and CD it's variable, based on ADH -> impermeable to water

Where is ADH synthesized?

In neuroendocrine cells in SON and PVN of hypothalamus

How is ADH moved throughout the body?

Packaged in vesicles, transported down axon, stored in postary pituitary

Increases in ADH secretion...

Osmolarity of body fluids Volume and pressue in vascular system ADH binds to V2 receptor, increases cAMP Insertion of aquaporin 2

What happens in the DT and CD if no ADH is present?

DT and CD permeability to H2O and urea is low No water reabsorbed Excess H2O eliminated | Dilute

What happens in the DT and CD if ADH is present?

DT and CD are permeable to H2O and urea is High H2O is reabsorbed small volume of concentrated urine | Concentrated

The primary action of diuretics is to...

increase Na+ excretion | Inhibit reabsorption of Na+ ## Footnote Change in ECF Volume

What is the effect of diuretic determined by?

Nephron segment where the diuretic acts Response of the nephron segments not directly affected by the diuretic Volume of the ECF

What is the function of the diuretic furosemide in the TAL?

Inhibition of the Na+-K+-2Cl- symporter

What is the use of the diuretic furosemide in the TAL? ##Footnote What ailments do they treat?

Edematous states (CHF) Pulmonary Edema Hypertension Hypercalcemia

What are the side effects of the diuretic furosemide in the TAL?

Hypokalemia Hypovolemia Alkalosis

# Define Hypercalcemia

Interstitium is neutral Ca2+ remains in filtrate and excreted in urine

# Define: Hypokalemia

Low K+

# Define Hypovolemia

Low volume removes too much fluid

Long term administration of furosemide would do what? A. Inhibit the Na+-Cl- cotransporters in the renal DT B. Inhibit the Na+-K+-Cl-cotransporter in the renal tubules C. Tend to reduce renal concentrating ability D. Tend to cause hyperkalemia E. A and C F. B and C G. B, C, D

F. B and C B. Inhibit the Na+-K+-Cl-cotransporter in the renal tubules C. Tend to reduce renal concentrating ability

What is furosemide?

A "loop" diuretic that inhibits the Na+-K+-Cl- cotransporter in the thick ascending limb of the LoH, thus decreasing urine concentrating ability and increasing Na+, Cl-, and K+ excretion | Tends to cause hypokalemia

What is the osmolarity in Bowman's capsule?

Isotonic (300 mosm/l)

What is the osmolarity at the End of the Proximal tubule?

Isotonic (300 mosm/l)

What is the osmolarity at the tip of LoH in the juxtamedullary nephron (bottom of U hairpin turn)?

Hypertonic (1200 mosm/l)

What is the osmolarity at the end of LoH in the juxtamedullary nephron (before DT)?

Hypotonic (100 mosm/l)

What is the osmolarity at the end of CD?

Varies ranging from hypo to hyper Low - excess water Higher - dehydration