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Excretion - Coggle Diagram
Excretion
Excretion
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CO2: Produced by almost all cells (not RBCs) in aerobic respiration. Excreted by lungs when breathed out (transported in blood - mostly as HCO3- ions in plasma)
- CO2 diffuses from body cells to RBC's
- Enzymes in RBC's combine CO2 and H2O
- Carbonic acid dissociates
- (Hydrogen carbonate ions diffuse out of RBC
- Chloride shift to maintain charge in RBC
- O released to blood plasma)
- Haemoglobinic acid formed
- Oxyhaemoglobin dissociates under influence H+ ions
Problems:
- Low blood pH
- Reduced capacity to carry oxygen
- Reduced affinity of haemoglobin for oxygen
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Cause:
- pH = Reaction with water in plasma to forma carbonic acid that lowers blood pH and so affect enzyme activity
- Reduced capacity = Carbonic acid formed inside RBCs (catalysed by carbonic anhydrase) dissociates to produce H+ that bind to Hb to form Haemoglobinic acid + cause O to dissociate by altering bonds that maintain 3D shape of Hb (Bohr effect)
- Affinity for oxygen = Combines to form carbaminoheamoglobin, which has a lower affinity for oxygen
Urea: Produced by the liver in deamination of excess amino acids and synthesis of urea from ammonia in ornithine cycle. Excreted by the kidneys in urine
Bile pigments: Produced by the liver from the breakdown of Hb. Excreted in bile (stored in the gall bladder + used in small intestine)
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Nitrogenous waste must be removed from the body as the body cannot store excess amino acids so they are transported top the liver and the potentially toxic amine group is removed in deamination. This forms toxic ammonia which raises the blood pH so is converted to the less toxic urea to be transported to the kidneys and excreted in the urine. The remaining keto acids can be used in respiration or converted to carbohydrates or fat for storage.
Structure of hepatocytes
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Glycogen granules: to store glucose that can be mobilised to raise blood glucose levels/for respiration
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Histology of the liver
The structure of the liver ensures blood flows past as many hepatocytes as possible by the liver being divided into many lobules with many sinusoids the carry blood to the central branch of the hepatic vein. The hepatocytes are arranged in long lines that are only a few cells thick. These sinusoids are lined with thin endothelial cells with gaps between the cells to allow hepatocytes to be in direct contact with blood to allow for exchange
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Kupffer cells breakdown and recycle old red blood cells (as they have a limited lifespan - 120 days)
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