Chapter 4 - Excretion

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  • Created on: 21-04-16 10:31
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  • Chapter 4 - Excretion
    • The liver
      • Formation of urea
        • 1. Deamination of excess amino acids - keto acid is respired while ammonia is formed
        • 2. Ammonia is toxic and very soluble, so is combined woth carbon dioxide to form urea, CO(NH2)2, during the ornithine cycle
        • 3. Urea is still toxic, so is removed from the blood by the kidneys
      • Blood supply
        • Hepatic artery brings oxygenated blood
        • Hepatic vein takes deoxygenated blood back to the heart
        • Hepatic portal vein brings blood rich in absorbed nutrients
      • Detoxification of alcohol
        • Ethanol --> Ethanal --> Ethanoate
          • Done by the enzymes ethanol dehydrogenase and aldehyde dehydrogenase
        • Effects of excessive alcohol consumption
          • Fatty liver
          • Cirrhosis
      • Histology
        • Made of lobules
        • Liver cells are called hepatocytes, there are channels that carry blood between these called sinusoids
        • Other channels carry bile (made by some hepatocytes) and are called bile ducts
        • Contains Kupffer cells (special, more efficient, macrophages)
      • Detoxification of other substances
        • Breakdown of hormones
        • Breakdown of medicines
    • The kidney
      • Structure
        • Has a cortex and a medulla, and is made up of thousands of nephrons
      • Nephron structure
        • Starts as a renal (Bowman's) capsule, then proximal convoluted tubule, loop of Henle, distal convoluted tubule and finally a collecting duct, which connects to the ureter
      • Ultrafiltration
        • Filtration on a micro-scale
        • Happens in the renal capsule
        • Happens under high pressure due to the afferent arteriole being larger than the efferent
      • Selective reabsorption
        • PCT
          • Absorbs all glucose and 65% of water
        • Loop of Henle
          • Descending limb
            • Permeable to water so water leaves due to water potential gradient
              • Counter-current system
                • Actively pumps out Na+ and Cl- ions
          • Ascending limb
            • Actively pumps out Na+ and Cl- ions
        • DCT and collecting duct
          • Ions actively pumped so water can be reabsorbed
      • Osmoregulation
        • ADH released when more water is needed to be reabsorbed,isn't released when body has too much water
      • Kidney  failure
        • Dialysis
          • Haemodialysis or peritoneal dialysis
        • Can be acute or chronic
        • Can be treated with a transplant


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