Excretory System

• Purpose of the Excretory System

  To remove by-products of metabolism that may be useful or toxic
• Waste Examples


  • Ammonia
  • Urea
  • Carbon Dioxide
  • Bile
• Ammonia


  By-product of protein metabolism
• Urea


  Product of processing ammonia
• Carbon Dioxide


  By-product of cellular respiration
• Bile


  Produced by the liver
• Urinary System


  • Consists of two kidneys, a bladder, two ureters and a urethra
  • Ureter carries fluid to the bladder
  • Urethra carries fluid through the bladder

  
• The Kidney


  • Main regions are the renal cortex and the renal medulla
  • Renal artery brings blood to the kidney
  • Renal vein drains blood away from the kidney

  
• The Nephron


  • The functional unit of the kidney
  • Glomerulus is a ball made from capillaries
  • Bowman's capsule cups the glomerulus
  • Blood comes into the renal arteriole and fluid gets squeezed into the Bowman's capsule
  • Fluid travels along the proximal convoluted tubule, down the descending arm of the loop of Henle, up the ascending arm, and into the distal convoluted tubules
  • Lastly, it goes down the collecting duct to the bladder
  • The nephron filters by taking everything out and then returning the useful things

  
• Counter current flow in the nephron

  1. Useful things like glucose or water is reabsorbed in the proximal convoluted tubule

  2. In the descending arm of the loop of Henle, water moves out of the tubule into the surrounding tissues

  3. As it goes lower in the loop of Henle, more water is lost

  4. As the fluid goes up the loop, special channel proteins allow ions to leave into the extracellular fluid

  5. Ions continue to leave up the loop while the water left in the descending loop

  6. The water leaves through diffusion, osmosis, and aquaporins
• Other excretory organs


  • Lungs - rid the body of carbon dioxide
  • Liver - detoxifies the blood, breaks down worn red blood cells, converts ammonia to urea
  • Skin - removes excess water and salts
• The excretory system removes excess and unwanted substances from the body to maintain a stable internal environment
• Excretion of ammonia


  1. Excess amino acids are transported from the small intestine to the liver

  2. The liver converts amino acids to ammonia

  3. Ammonia is then broken down to less toxic urea
• Nephron


  The functional unit of the kidney consisting of a glomerulus and tubule system through which filtrate passes and urine is produced

  
• The kidneys are bean-shaped organs located on either side of the spine, just below the ribcage.
• Kidneys filter blood to remove waste products such as urea, creatinine, uric acid, excess salts, and water from the body.
• Collecting ducts collect urine from all the nephrons and carries them to the ureters
• Proximal convoluted tubules reabsorb water and nutrients back into the body
• Antidiuretic hormone (ADH) regulates the amount of water reabsorbed into the bloodstream or lost in urine.
• Urethra transports urine out of the body
• Loop of Henle helps maintain fluid balance by controlling the amount of water that enters and leaves the collecting ducts
• ammonia is a toxic gas that is released from the liver and kidneys
• urea is a waste product of the liver and is excreted in urine