what is osmolality??
Osmolality (mosm/kg): a measure of water concentration.
The higher the solution osmolality the lower the water concentration.
Plasma 285-295 mosm/kg
Urine 50-1400 mosm/kg
What are the units for osmolality and osmolarity?
Osmolality = mosm/kg
Osmolarity = mosm/L
Osmolality in plasma dependent on ??
Plasma sodium concentration 135-145mmol/l.
Freely filtered at renal corpuscle
Plasma Na+ concentration (mmol/l) X GFR (l/min) = amount filtered 140 x 0.125 = 17.5 mmoles/min
AMOUNT FILTERED: 25,200 mmoles/day
dietary salt intake varies 0.05-25g/day.
WHAT SALT IS INGESTED MUST BE EXCRETED
SO: ingest and therefore excrete 100 mmol sodium per day.
Only 0.4% excreted.
where does sodium reabsorption occur?
along the tubule of the nephron
it is an active process so it needs ATP
so we know that it happens where there is alot of mitochondria
what is the sodium reabsorption in the loop of henle?
None in descending limb. Passive in thin ascending limb.
Thin descending limb (thin ascending similar)
Na transport pathways (1) - proximal tubule
65% of filtered load of NaCl reabsorbed
Na transport pathways (2) – thick ascending limb
25% of filtered load of NaCl reabsorbed in thick and thin ascending limb.
Na transport pathways (4) – collecting duct
2 cell types:
1) principal cells (Na+ transport)
2) intercalated cells (H+ transport)
5% of filtered load of NaCl reabsorbed
Na transport pathways (3) – distal tubule
2-5% of filtered load of NaCl reabsorbed
what does water reabsorption depend on ??
Coupling of Water Reabsorption to Sodium Reabsorption ???
sotonic reabsorption– tight junctions have high water permeability.
Also membrane expression of aquaporin-1 (AQP1) water channels.
Filtrate volume reduced but not osmolarity.
How are we going to produce a concentrated urine?
We need to separate Na+ and water reabsorption.
Generate a renal medulla interstitial fluid with high osmolarity to drive water reabsorption.
(both processes occur at the loop of henle)
permeability factors in the ascending limb??
Salt reabsorption via Na+:K+:2Cl- cotransporter.
Water stays in tubule.
permeability in descending limb??
Descending limb picks up salt and loses water
AQP-1 water channels expressed.
Setting up medullary interstital gradient
MULTIPLICATION OF OSMOLARITY BY THE LOOP OF HENLE
special ability of vasa recta??
supply blood without washing the gradient away
Counter-current exchange ?
UREA RECYCLING BY KIDNEY ?
Action of anti-diuretic hormone (ADH) on Collecting Duct
what does concentrated urine depend on ??
Renal medulla interstitial fluid high osmolarity
i) pass through concentrated zone.
ii) water permeable (controllable)
Vasa recta supply blood without washing away gradient and take water away from medulla