Loop Of Henle Flashcards
Urine entering loop of henle
Isotonic
Function of loop of henle
Concentrates urine by creating a region of hypertonicity to extract the water osmotically
More Na+ reabsorption
Urinary dilution
Generation of medullary hyperosmoticity via counter-current multiplication
Descending limb
Water permeable
Impermeable to solutes
Ascending limb
Impermeable to water
Permeable to solutes
Counter-current multiplication
Urinary concentration and generation of hyperosmotic interstitium to aid collecting duct in water reabsorption
Thick ascending limb driving force
Na/K ATPase in basolateral membranes of cells in ascending limb which keep intracellular Na+ concentrations low to allow more reuptake
Which transporter pumps Na+ out of lumen of Thick ascending limb
NKCC2 via secondary active transport
Thick ascending limb - K+
Recycled on apical ,membrane back into lumen through ROMK channels
Thick ascending limb K+channels on apical membrane
ROMK
Thick ascending limb Cl-
Leaves cell through CLCK A channels on basolateral membrane
Where are CLCK B channels found
Inner medulla
Thick ascending limb Ca2+, Mg2+ and Na+
Process of counter current multiplication creates a negatively charged tubule lumen which repels Ca2+, Mg2+ and Na+ and they move paracellularly with the aid of proteins in the tight junctions (paracelin or claudin XVI)
Proteins in tight junctions of Thick ascending limb
Paracelin
Claudin XVI
Function of Thick ascending limb
Creates hyperosmotic interstitium, creates a gradient of 200mOsm/L between lumen and interstitium
Gradient between lumen and interstitium
200 mOsm /L
Thin ascending limb
Salt pumped passively
Descending limb
Only permeable to water which flows out due to osmotic pressure, concentration of interstitium matches concentration in descending limb
As fluid moves down descending limb
Becomes more concentrated- the longer the loop the greater the gradient which is created
Tubule flow means that the concentration gradient starts from a higher baseline than before it
What ions does the ascending limb pump out
Na+
K+
Cl-
Urea involvement
Vasopressin makes collecting duct permeable to urea so it leaks into interstitium- which aids urine concentration in loop of henle
As urea passes through the remainder of the nephron it is reabsorbed, secreted into the tubule and then reabsorbed again
What supplies blood to the loop of henle
Vasa recta
Medullary circulation
Vasa recta prevent elimination of counter current gradient
As blood ,over down it meets an increasingly hypertonic environment drawing water out of the blood vessel into the interstitium (concentrating the blood)- blood has a high oncotic pressure as proteins not filtered
Crossing pathways protect the concentration gradient at each level and bulk flow carries away salts and water reabsorbed
Blood enters the top of the vessel loop and as it flows down into the medulla, Na+ and Cl- flow in and water out
After the bend in the loop the blood ascends and the process is reversed
Advantage of loop structure
Minimises excessive loss of solute from interstitium by diffusion into vasa recta
Volume of blood before and after loop of henle
At least 2 fold higher due to salt and water reabsorption
