Renal - Loop of Henle Flashcards
What are the three functionally distinct subsegments of the renal loop?
Thin Descending Limb
Thin Ascending Limb
Thick Ascending Limb
What is the functionality of the thin descending limb?
No NaCl transport
Water permeable
What is the functionality of the thin ascending limb?
Passive Na+ reabsorption
Not water permeable
What is the functionality of the thick ascending limb?
Active Na, Cl, and K+ transport
Not water permeable
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
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
What favors paracellular solute transport?
Positve lumen favors paracellular reabsorption of cations
half of TAL Na+ reabsorption is paracellular
Mg, Ca, K, reabsorbed
How is Na+ and Cl- reabsorbed in the TAL?
Na-K-2Cl cotransporter
Paracellular solute transport
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
Define:
Countercurrent
flow of fluid in opposite directions in adjacent structures
Define
Countercurrent exchange
crossover of some property between two fluids flowing in opposite directions
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
What are the two steps of countercurrent multiplication?
The single effect
Fluid Flow
Define
Single Effect step of Countercurrent Multiplication
Active transport of NaCl out of tubular fluid in the TAL
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
Define
Fluid flow step of Countercurrent Multiplication
As urine is continually being produced, new tubular fluid enters the descending limb
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
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
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
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
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
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?
- equal throughout limbs and with interstitium
- 200 mosm/l gradient established in the horizontal level of the ascending limb and 400 mosml/gradient in interstitium when NaCl is pumped out
- 400 mosm/l gradient established in descending limb when water diffuses out to equilibriate
- osmolarities shift throughout loop
- 200 mosm/l gradient between ascending limb fluid and interstitial space
- 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
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+
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?
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
