Excretion notes

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  • Created by: Steff06
  • Created on: 01-03-16 18:43
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  • Excretion
    • The REMOVAL of METABOLIC WASTE from the body. 2 products that are produced in large amounts and must be excreted are CARBON DIOXIDE from respiration and nitrogen-containing compounds such as UREA.
    • Carbon dioxide is passed from the cells of respiring tissue into the bloodstream. It is transported to the lungs where it diffuses into the alveoli to be excreted as we breathe out.
    • Urea is produced by BREAKING  DOWN EXCESS AMINO ACIDS (DEAMINATION). The urea is then passed into the bloodstream to be transported to the kidneys. The urea is removed in the KIDNEYS to become part of URINE.
    • Why does carbon dioxide have to removed?
      • Excess CO2 is TOXIC. High levels of CO2 has 3 main effects.
      • 1. CO2 carried in blood as HYDROGENCARBONATE ions. HYDROGEN ions are also formed under influence of ENZYME CARBONIC ANHYDRASE. Hydrogen ions combine with HAEMOGLOBIN. Too much CO2 will reduce OXYGEN TRANSPORT
      • 2. CO2 combines directly with HAEMOGLOBIN to form CARBAMINOHAEMOGLOBIN which has a LOWER AFFINITY for oxygen.
      • 3. Excess CO2 can also cause respiratory ACIDOSIS where CO2 DISSOLVES in blood PLASMA where it can combine with WATER to produce CARBONIC ACID.
        • CARBONIC acid dissociates to release HYDROGEN. These LOWER the pH, making the blood more ACIDIC. PROTEINS in blood acts as BUFFERS to resist change in pH.
          • Small change in pH = hydrogens detected by MEDULLA OBLONGATA. Causes increase in BREATHING RATE to remove excess CO2.
            • Large change in pH = heaches, drowsiness, confusion, tremor. Respiratory acidosis.
            • Nitrogenous compounds: Body cannot store proteins/amino acids. Amino acids transported to LIVER and TOXIC amino group REMOVED by DEAMINATION.
              • Produces highly SOLUBLE and TOXIC AMMONIA. Converted to LESS toxic and less soluble UREA. Transported to KIDNEYS for EXCRETION.


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