The Excretory System: From Your Heart to the Toilet

The Excretory System: From Your Heart to the Toilet

1. Homeostasis: Regulation of a stable internal enviroment no matter where we are or what we are doing.

2. Kidneys

   • Maintain levels of water and dissolved materials
   • Control blood pressure
   • Filter 180 litres of fluid but only 1.5 litres is peed out
   • Renal Arteries: Blood enters kidneys from heart

3. Urethra

   • Empties urine outside

4. Bladder

   • Stores water

5. Ureter

   • Tubes in which urine flows from kidney to bladder

6. Osmoregulation: Maintaining the right level of water and absobed substances.

7. Ammonia: toxic. Converted into urea or uric acid

   • Urea: Combined ammonia and Co2 in liver.
     • Advantage: Very low toxicity
     • Extra water must be available to dissolve and get rid of it.
   • Uric Acid: Paste, not a lot of water needed

8. Nephrons

   • Tiny filtering structures
   • About a million in each kidney
   • !. Glomerulus: Porous capillaries. Starting point. High pressure squeezes out filatre
     • Filtrate: water, urea and smaller ions and molecules
   • 2. Bowman's Capsule
   • 3. First Tubule:. Osmoregulation takes place. Reabsorb water and materials.
   • 4. Loop of Henle: Reabsorption. Three jobs.
     • 1. Extracts most of the water that we need from the filtrate.
     • 2. Pumps out the salts that we want to keep
     • 3. Makes medula hypertonic
     • Membrane highly permeable to water
   • 5. Second tube. Regulates levels of potassium, sodium and calcuim
   • 6. Collecting tubes: Channel excess water, urea and other metabolic waste back to the center of the kidney.