Urine formation by kidneys
Histophysiology of urine formation
This is responsible for filtration of urine into the proximal tubules. Fluid
passes at a rate of about 180 l of glomerular filtrate but finally reaches
only 1.5 l of urine.
convoluted tubule physiology
In these tubules the membrane are permeable to water and hence water is lost
from the tubules without Na ions. This also coccurs in the descinding limb
of loop of Henle.
Loop of Henle:
This is the counter-current exchange and multiplier site. There is an active
sodium pump such as the Na+ K+ ATpase system that
actively transports solute out of the loop into the medullary interstitium,
thereby creating a hypertonic environment in the interstitium. The vasa
recta support and maintain the hypertonicity of the interstitium.
Loop of Henle's
In this site the nephron has gone back from medulla (with vasa recta) to
cortex (without vas recta). Here because there is no counter-current
exchange mechanism, sodium pump is active with removal of Na+ and
Cl- but no hypertonic interstitium and hence water is attracted
back into the tubules to cause dilution of urine. Because here the movement
of sodium and chloride occur together it is called NaCl co transporter (NCCT).
Here sodium is exchanged for potassium and hydrogen ions. Na+ is
transported across the epithelial sodium channel called ENaC under the
influence of aldosterone.
Chemical pathology of kidney
filtration of urine
Cross section through the kidney
School of Medicine
Creator: Oluwole Ogunranti