Loop of Henle Flashcards
What is the function of the proximal tubule?
Major site of reabsorption
65-75% of NaCl and H2O
How much protein (particularly albumin) gets though tubule?
20g/day so 0.5% of total amount presented at glomerulus
Completely reabsorbed by a Tm carrier mechanism in proximal tubule
Describe drugs and pollutants and tubular function
Many are non polar and high lipid soluble so removal of H2O in proximal tubule establishes conc. gradients for their reabsorption
Liver metabolises them polar so reduces their permeability and facilitates the excretion
What is the fluid described as when it leaves the proximal tubule?
Isosmotic with plasma - 300mOmoles/l
Why is the fluid leaving the proximal tubule isosmotic with plasma?
All solute movements are accompanied by equivalent H2O movements so osmotic equilibrium is maintained
What process is attributable to the loops of Henle of juxtamedullary nephrons?
Essential for water balance
Where are the nephrons distal and proximal tubules?
In cortex
All nephrons have common processes for reabsorption and secretion of solutes of filtrate
What does the mechanism of the loop of Henle ensure?
The kidney can produce concentrated urine in times of H2O deficit
What is the max. conc. of urine that can be produced by the human kidney?
1200-1400mOsmoles/l so 4 x more concentrated than plasma as excess of solute over water
What is the minimum obligatory H2O loss and why?
500mls
As this is required to excrete 600mOsmoles of waste products (urea, sulphate and phosphate) and non-waste ions which must be excreted
What happens if no H2O intake?
Functioning kidneys still excrete 500mls so urinate to death
What is the min. conc. of urine?
30-50mOsmoles/l so 10 fold dilution compared with plasma
In conditions of excess H2O
How are kidneys able to produce urine of varying conc.?
Loops of Henle of juxtamedullary nephrons act as counter-current multipliers
What is counter current?
Fluid flows down descending limb and up the ascending limb
What are the critical characteristics that make loops counter-current multipliers?
Ascending limb actively co-transports Na and Cl ions out of tubule lumen into interstitium
Ascending limb impermeable to H2O
Descending limb is freely permeable to H2O but relatively impermeable to NaCl
What happens after loop of Henle is filled with stationary isosmotic fluid (300mOsmoles/l)?
Active removal of NaCl from ascending limb - is put into interstitium so osmolarity in tubule decreases and increases in interstitium
What happens when the descending limb is exposed to greater osmolarity in interstitium?
H2O will move out to equate the osmolarity
H2O does not stay in the interstitium but is reabsorbed by high osmotic and tissue pressure into vasa recta
What happens when fluid is moving in the loop of Henle?
Fluid is entering at proximal and leaving at distal
Concentrated fluid in descending limb rounds the bend and delivers a high conc. to ascending limb - active NaCl removal which further concentrates the interstitium
What does greater conc. of descending (by removal of water) limb mean?
Greater conc. of interstitium by addition of salt from ascending limb
Where in the tubule is the conc. of fluid more and progressively diluted?
More concentrated - as moves down descending limb
Diluted - moves up ascending limb
At horizontal level what is the mOsmol gradient between ascending limb and interstitium?
200mOsmol
As 100 in ascending and 300 in interstitium
What happens when more and more concentrated fluid is delivered to ascending limb?
The interstitium becomes more and more concentrated
What is the vertical gradient in the interstitium?
300 to 1200mOsmol
What is the key step in the loop of Henle?
Active transport of NaCl out of ascending limb
If abolished then (ex. by use of diuretic frusemide) all conc. differences are lost and kidney produces isotonic urine
