Excretion LoA

  • Created by: Freyae99
  • Created on: 01-12-17 12:14
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  • LoA: The importance of excretion i maintaining metabolism and homeostasis
    • Excretion: the removal of metabolic waste from the body.
      • Carbon dioxide from respiration.
        • Passed from the cells of respiring tissue into the bloodstream where it is taken to the lungs and diffused into the alveoli
      • Nitrogenous compounds e.g urea.
        • Urea is passed into the bloodstream to be taken to the kidneys. Here it is removed from the blood to form urine.
        • The body cant store excess AA but they contain as much energy as carbohydrates so it would be wasteful to just excrete them. Instead they are taken to the liver where deamination can take place. The A group initially forms ammonia which is highly toxic and insoluble. It is converted to urea which is transported to the kidneys. The remaining keto acid can be used to release energy.
          • Deamination: AA + O2 --> keto acid + ammonia.
      • Other products such as bile and faeces.
        • The liver is involved in bile production and the deamination of AA
      • The skin its  involved in excretion but this is not its primary job. Sweat contains salts, urea, water, NH3 and uric acid
    • Metabolic waste: a substance that is produced in excess by the metabolic processes in cells. If it is not removed it may become toxic.
      • If this is not excreted from the body it could be fatal as some metabolic products are toxic e.g. CO2 and NH3. They will interfere with cell processes by altering pH and some will interfere with enzymes.
        • Hydrogen ions (formed when CO2 is transported in the blood as hydrogencarbonate) will affect the pH of the cytoplasm in RBC. Maintaining this pH is essential because if it is changed then this will alter the structure of many proeins found in the blood that help transport substances.
          • If the pH drops below 7.35 it may cause headaches, drowsiness, restlessness, tremor, rapid changed in blood pressure and confusion.
        • They also interact with the bonds formed with haemoglobin, reducing its affinity to bind with oxygen.


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