Loop of Henley Royal Regatta Flashcards
As humans - we have an obligatory amount of waste products which we always have to excrete
What are these substances and how is this related to water loss?
Urea, sulphate, phosphate (waste products)
+ Some Na+ and K+
Amounts to 600 mOsmol per day excreted
This requires a minimum obligatory loss of 500mls of water per day - just to allow these to be excreted
What is the maximum concentration of urine that is excreted by the kidneys?
1200-1400 mOsmoles/L
ie 4x more concentrated than plasma
How does urine concentration respond to excess H2O intake?
H2O is excreted in excess of solute - meaning urine is diluted so we can get rid of more water
Minimum [urine] in man is 30-50 mOsmoles/l
ie 10 fold dilution compared with plasma
How do juxtamedullary nephrons’ Loops of Henle concentrate urine?
They act as counter-current multipliers
What features of the loop of Henle allow it to be a ‘countercurrent multiplier’
You need to think about it backwards (ie first think about the ascending limb)
Ascending limb:
- Actively transports NaCl out into the interstitium
- Impermeable to H2O
Descending limb:
- Freely permeable to H2O but less so to NaCl
What is the effect of the NaCl active transport which takes place in the Ascending limb of the L.o.H?
NaCl actively transported into the interstitium
This increases the osmolarity in the interstitium and decreases it in the tubule of the ascending limb
Describe how increased interstitial osmolarity between the ascending and descending limb affects the descending limb of the loop of henle
The higher osmolarity of the interstitium means that H2O from the descending limb diffuses into the interstitium to equate the osmolarity
Describe how the osmolarity inside the loop of henle changes as you move through it
As you move down the Descending limb:
- Osmolarity increases as H2O diffuses out
Concentrated fluid goes round the bend and is delivered to ascending limb
As you move up the Ascending limb:
- NaCl is actively removed - which decreases the osmolarity inside the tubule but further increases the osmolarity in the interstitium
Where is the least concentrated and most concentrated (saltiest) part of the INTERSTITIUM surrounding the loop of Henle?
Lowest concentration found at the top - ie start of desc limb and ending of asc limb
What is the osmotic gradient between the ascending limb of the loop of Henle and the interstitium?
200 mOsmole gradient at each horizontal level of the ascending limb of the loop of Henle
Reflects the active pumping of sodium
What would be the effect of stopping the active NaCl transport in the ascending limb?
Transport of NaCl is key step in all this
If stopped - eg by use of the diuretic frusemide, all concentration differences are lost and the kidney can only produce isotonic urine.
What osmolarity is the fluid entering the distal convoluted tubule?
It is Hypo-osmotic - meaning the fluid which enters the distal tubule is more dilute than plasma
Where does the interstitial H2O end up?
Drain into the Vasa Recta - the capillaries following the loop of henle
As they follow the hairpin structure of the Loop - it means that the osmolarity inside the Vasa recta follows the osmolarity of the loop of henle
The Vasa recta removes the salt and water from this area - but does not interfere with the osmotic gradients
What are the functions of the vasa recta?
1) Provide O2 for medulla.
2) Provides O2 without disturbing gradient.
3) Removes volume from the interstitium, up to 36l/day
Loops of henle create the high conc interstitium and low hypotonic distal tubule fluid, what controls the final conc of the urine?
hormones (mainly ADH) control permeability of the collecting duct
E.g. More ADH means more water resorption in the collecting duct –> Conc. urine
