BY4.6 The Kidneys

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The Kidneys

excretion: removal of metabolic waste from the body

in the humans this includes:

  • CO2
  • urea
  • bile

The production of urea:

  • urea: a poisonous chemical made in the liver
  • when too much protein is present in the diet, it can't be stored and needs to be broken down
  • amino acids that make up the proteins are deaminated in the liver
  • the reaction produces ammonia which is converted into urea
  • urea is released into the blood and travels around the body until it is removed by the kidneys

Human excretory system:

Detail of one kidney:

The Kidneys:

2 main function:

  • removal of nitrogenous emtbaolic waste from the body
  • osmoregualtion

humans have 2 kidneys

each is made up of millions of nephrons

each nephron is made up of 4 parts:

  • bowman's capsule
  • proximal convoluted tubule
  • loop of henle
  • distal convoluted tubule


within is bowman's capsule is a glomerelus

  • blood supply to the nephron starts at the afferent arteriole which serves the glomerelus
  • from glomerelus it does to the efferent arteriole and then to 2 other capillary networks:
    • the capillary network serving the PCT and DCT
    • the capillary network running beside the loop of henle - the vasa recta

3 processes occur in the kidney

  • ultrafiltration
  • selective reabsoprtion
  • secretion

Ultrafiltration: filtration that occurs under pressire

  • separates small soluble molecules from the blood plasma
  • small molecules (H2O, glucose, urea, salts) are filtered from teh glomerelus and into the Bowman's capsule


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