Urine formation by kidneys

 

Histophysiology of urine formation

Glomerulus: 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.


Proximal convoluted tubule physiology
Proximal convoluted tubules: 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 physiology

 

Cortical dilution site: 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).

Distal convoluted tubule: 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
Metabolic acidosis
Metaoilc alkalosis

 

 

 

 

    

Glomerular filtration of urine

 


Cross section through the kidney x40

 


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