title: Tubular fluid
text: # Tubular fluid
  
  Tubular fluid is the fluid in the tubules of the kidney. It starts as a renal ultrafiltrate in the glomerulus, changes composition through the nephron, and ends up as urine leaving through the ureters.
  
  ## Composition table
  
  The composition of tubular fluid changes throughout the nephron, from the proximal tubule to the collecting duct and then as it exits the body, from the ureter.
  
  Concentration (mM) of substances in different segments of nephron and collecting duct system :
  
  | Substance | proximal tubule | proximal tubule | proximal tubule | loop of Henle | loop of Henle | loop of Henle | Distal convoluted tubule | Collecting duct system | Collecting duct system | Collecting duct system | Collecting duct system |
  | - | - | - | - | - | - | - | - | - | - | - | - |
  | Substance | S1 | S2 | S3 | descending limb | thin ascending limb | thick ascending limb | Distal convoluted tubule | connecting tubule | initial collecting tubule | cortical collecting ducts | medullary collecting ducts |
  | $Na^+$ | 142 | | 142 | | | 100 | 70 | | | 40 | |
  