The Excretory System: From Your Heart to the Toilet

Homeostasis: Regulation of a stable internal enviroment no matter where we are or what we are doing.
Kidneys
1. Maintain levels of water and dissolved materials
2. Control blood pressure
3. Filter 180 litres of fluid but only 1.5 litres is peed out
4. Renal Arteries: Blood enters kidneys from heart
Urethra
1. Empties urine outside
Bladder
1. Stores water
Ureter
1. Tubes in which urine flows from kidney to bladder
Osmoregulation: Maintaining the right level of water and absobed substances.
Ammonia: toxic. Converted into urea or uric acid
1. Urea: Combined ammonia and Co2 in liver.
  1. Advantage: Very low toxicity
  2. Extra water must be available to dissolve and get rid of it.
2. Uric Acid: Paste, not a lot of water needed
Nephrons
1. Tiny filtering structures
2. About a million in each kidney
3. !. Glomerulus: Porous capillaries. Starting point. High pressure squeezes out filatre
  1. Filtrate: water, urea and smaller ions and molecules
4. 2. Bowman's Capsule
5. 3. First Tubule:. Osmoregulation takes place. Reabsorb water and materials.
6. 4. Loop of Henle: Reabsorption. Three jobs.
  1. 1. Extracts most of the water that we need from the filtrate.
  2. 2. Pumps out the salts that we want to keep
  3. 3. Makes medula hypertonic
  4. Membrane highly permeable to water
7. 5. Second tube. Regulates levels of potassium, sodium and calcuim
8. 6. Collecting tubes: Channel excess water, urea and other metabolic waste back to the center of the kidney.

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	Created by blythe315 almost 10 years ago

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