Urinary physiology - loop of Henle Flashcards
How much albumin gets through the glomerulus
30g which is about 0.5% of the amount that is presented to the glomerulus - the albumin is completely reabsorbed by the proximal tubule
What is the effect of drugs being non-polar usually
They are very lipid soluble so the removal of water out of the proximal tubule cells establishes a gradient for their reabsorption so they would not be excreted - the liver therefore breakdowns the drugs to polar compounds which make them able to be excreted
In quick terms describe filtration
Blood to lumen
In quick terms describe reabsorption
Lumen to blood
In quick terms describe secretion
Blood to lumen
In quick terms describe excretion
lumen to external environment
Why is the fluid that leaves the proximal tubule isosmotic
Because every movement of a solute is accompanied by the movement of water
What is the isosmotic plasma concentration and define it
Having the same osmotic pressure as plasma which is 300mOmoles/l
What is the location of the proximal and distal tubules in the nephron
The renal cortex
Where is the loop of Henle in the nephron
Deep within the renal medulla
What is the maximum concentration of urine that can be produced by the kidney
1200-1400 mOsmoles/l (4x plasma concentration)
What is the concentration of solutes alone which must be excreted per day and how much water loss is required
600mOsmoles and requires at least 500mls loss of water
If there is excess water intake - low concentration urine is produced - what is the minimum urine concentration
30-50 mOsmoles/l
Why can the kidneys produce urine of varying concentrations
The loop of Henle of juxtamedullary nephrons acts as a counter-current multiplier
What is a counter-current multiplier
As fluid flows down the descending limb and up the ascending limb, there is exchange between both limbs - The ascending limb actively co transports sodium and chloride ions out of the lumen into the interstitium, the ascending limb is also impermeable to water - the descending limb is freely permeable to water but not sodium chloride
What happens when isosmotic fluid (300mOsmoles) goes up the ascending limb of the loop of Henle
Sodium chloride is pumped out which drops the osmolarity to 200mOsmoles /l - this causes the interstitium osmolarity to rise
What happens when the solution goes to the descending limb after the ascending limb
The interstitium osmolarity is higher then the osmolarity in the descending limb so water moves out to the intersitium to reach equilibrium - the water is then reabsorbed by the vasareacta
How do the ascending and descending limbs of loop of Henle work
descending limb gets rid of water which increases the osmolarity - the cycle causes the reabsorption of both water and sodium chloride while the Ascending reduces osmolarity by getting rid of sodium chloride
What is the function of frusemide
It is a loop diuretic which inhibits the active transport of sodium chloride in the loop of Henle so there is no horizontal osmolarity gradient being produced so the urine will remain isotonic
What is the effect of the countercurrent multiplier on the intersitium
Increased concentration
What concentration is the fluid which reaches the distal tubule
100mOsmoles - more diluted then plasma
What is the vasa recta and how does it work
The specialised arrangement of the peritubular capillaries of the juxtamedullary nephrons which are part of the countercurrent multiplier mechanism
They don’t drain straight through the loop of Henle and interstiium or they would abolish the concentration gradient by removing the sodium chloride and water - Instead they are arranged as hairpin loops which don’t interfere with the gradient
What are the functions of the vasa recta
Provide O2 for the renal medulla
Remove fluid and solutes from the interstitium
Why is the reabsorption favoured at the vasa recta
The high oncotic pressure is high and so it the tissue pressure due to the tight renal capsule which pushes the fluid into capillaries
The flow rate of the vasa recta is low so equilibration can occur without the medullary gradient being disturbed
