The Kidney

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The Kidney has two main functions

  • Removal of nitrogenous waste from the body
  • Osmoregulation (balancing water and dissolved solutes)


Urea: poisonous chemical made by the liver. Produced when there is an excess of protein, which cannot be stored like lipids and carbs. Amino acids, what happen after protein is broken down, are deaminated in the liver.

The deamination reaction produces ammonia, which is quickly converted to urea as ammonia is highly toxic. Urea is released into the blood until its removal by the kidneys.


Proteins in food --> Amino Acids --> Deamination in the liver --> Ammonia --> Urea--> Kidneys

  • Structure of the Kidney


  • Ureter leads to the bladder.  
  • Renal artery leads to the kidney
  • Renal vein leads away from the kidney
  • Nephrons
  • Kidneys are made up of about a million nephrons. Each nephron is made of four functional parts
    • Bowman's capsule
      • Within each Bowman's capsule is a knot of blood vessels: the glomerulus.
      • A nephron's blood supply begins with the afferent ateriole, which passes through the glomerulus.
      • From the glomerulus, the blood is carried by an efferent ateriole to two other capillary networks; one serving the proximal and distal convoluted tubules, the other running next to the Loop of Henle (this one is known as the vasa recta)
    • Proximal tubule
    • Loop of Henle
    • Distal tubule (leading to a collecting duct)


Ultrafiltration and the Glomerulus

Ultrafiltration: filtration under pressure, separating small, soluble molecules from blood plasma, ie water, glucose, urea and salts. 


  • The capsule surrounding the glomerulus is called the Bowman's Capsule
  • Blood entering the glomerulus is separated from the space inside the capsule by two layers of cells and a basement membrane
  • First Cell Layer: Wall of the capillary. This single layer of cells contains many gaps
  • Second Cell Layer: The wall of the bowman's capsule - the epithelial cells in this layer are called podocytes
  • Basement Membrane: between the two cell layers and acts as a filter.

The basement membrane acts as a sieve, allowing smaller-sized molecules to pass through, like water and sodium, but retains larger molecules like blood cells and proteins in the capillaries.

Selective Reaborsption

This is the process where useful products ie glucose…




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