Loop of Henle Flashcards
What is the function of the proximal tubule
Major site of reabsorption, 65-75% of all NaCl and H2O all nutritionally important substances.
How does the liver help in excretion of Drugs and pollutants
The liver metabolizes them to polar compounds thus reducing their permeability and facilitating their excretion.
What osmolarity is the filtrate that comes from the proximal tubule heading into the loop of henle?
300 mOsM/L
the same as plasma because all solute movements are accompanied by equivalent H20 movements - osmotic equilibrium is maintained
What is a nephron?
A nephron is the microscopic structural and functional unit of the kidney.
It is composed of a renal corpuscle (glomerulus and capillaries) and a renal tubule.
ALL of the nephrons have their proximal and distal tubules in the Cortex and all nephrons have common processes for the reabsorption and secretion of solutes of the filtrate.
The loops of henle of juxtamedullary nephrons are essential for which important process?
Water balance
How do humans survive without water?
The kidney is able to produce concentrated urine in times of H2O deficit, however, as humans our ability to save water isn’t very good
What is the maximum concentration of urine that can be produced by the kidney?
1200-1400 mOsmoles/L
How many ml of H20 will every person lose in a day no matter what if their kidneys are functioning normally?
500 ml (doesn’t include sweating)
What is the minimum urine concentration in humans?
30-50 mOsmoles/L (very diluted urine)
What is the range of osmolarities that urine can be within in humans?
30-50 to 1200-1400 mOsmoles/l
Characteristics of the ascending limb of the loop of henle?
It actively co-transports Na+ and Cl- ions out of the tubule lumen into the interstitium.
The ascending limb is impermeable to H2O.
Characteristics of the descending limb of the loop of henle?
The descending limb is freely permeable to H2O but relatively impermeable to NaCl.
What happens to the osmolarity inside the tubule and the interstitium when NaCl is actively pumped out of the ascending tubule
The osmolarity decreases inside the tubule but increases in the interstitium
What happens in the descending tubule as a result of active transport of NaCl?
The descending limb is now exposed to greater osmolarity in the interstitium, H2O will move out to equate the osmolarity.
H2O does not stay in the interstitium, but is reabsorbed by the high oncotic and tissue pressures into the vasa recta (Starling’s forces).
What is the vasa recta?
The specialised arrangement of the peritubular capillaries of the juxtamedullary nephrons.
They also participate in the countercurrent mechanism by acting as countercurrent exchangers.
What happens as fluid moves through the loop of henle?
Concentrated fluid in descending limb rounds the bend and delivers a [high] to the ascending limb.
NaCl is actively removed again which further concentrates the interstitium and exposes the descending limb again to a greater osmolarity. This cycle repeats.
So, 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.
At any horizontal level of the loop of henle what is the osmolarity gradient difference between the ascending limb and the interstitium ?
200 mOsmol
What does the vertical gradient in the interstitium go from?
300-1200 mOsmol
The loop of henle is in which part of the kidney?
The medulla
How can the active transport of NaCl be abolished/stopped?
The use of a diuretic e.g furosemide/frusemide
What happens if you take a diuretic like furosemide?
Unable to establish gradient because the diuretic switches off all the active transporters + all the ATP driven processes.
This means that salt (NaCl) is not being reabsorbed so doesn’t move into the interstitium and as a result there is no H20 movement so the filtrate fluid isn’t being concentrated as normal.
The kidney can only produce isotonic urine. Diuretics make you pee more essentially.
How is the fluid ‘diluted’ in the ascending tubule?
By removing NaCl not by adding H20
What osmolarity is the fluid that reaches the distal tubule?
About 100 mOsmole = hypotonic - lower concentration of solutes
What are the key functions of the loop of henle?
To concentrate the medullary interstitium
To deliver hypotonic fluid to the distal tubule
How come the medullary capillaries don’t interfere with the gradient
Due to their structure/arrangement - they are arranged as hairpin loops and therefore do not interfere with the gradient.
As with all capillaries, the vasa recta are freely permeable to H2O and solutes and therefore equilibrate with the medullary interstitial gradient at each level.
The flow rate through the vasa recta is very low (due to length and small diameter) so that there is plenty of time for equilibration to occur with the interstitium, further ensuring that the medullary gradient is not disturbed.
Functions of the vasa recta (2)
Provide O2 for medulla - In providing O2 must not disturb gradient.
Removes volume from the interstitium, up to 36l/day.
In terms of vasa recta H2O out and NaCl in occurs in which limb
Descending
In terms of vasa recta NaCl out of the tubule occurs in which limb?
Ascending - this is most important to get water back into blood.
NaCl moves into the interstitium causing H2O to move out of the descending limb into the interstitium. H2O doesn’t stay in the interstitium but moves into the blood.
What is the site of water regulation?
The collecting duct
