Excretion

Excretion

1. Basics

   • Substances
     • Carbon dioxide
     • Urea
   • Metabolic wate
     • Substances that build up and can become toxic or they are produced in excess and have been inside the organisms cells
     • E.g. Urea, CO2, Water
   • Excretion
     • The removal of metabolic waste from the body
   • The removal of metabolic waste from the body.
     • This process does not use vesicles, requires ATP and is involved in homeostasis
       • The excretory substance is produced in cells during their metabolism, often transported in the blood

2. The liver

   • Structure
     • Many blood supplies
     • • There are cells called Kupfer cells within this and they break down red blood cells
         • This is why any test that involved the blood cannot be carried out over a more than 12 week period, as the cells are replaced
   • Function
   • Reactions
     • Forming urea
     • Deamination
     • Ornithine cycle
     • Alcohol detoxification

3. Kidney

   • Structure
     • Whole
     • Nephron
       • • Bowman's capsule
           • Consists of 3 layers: Endothelium of capillary Basement membrane Podocytes
         • Proximal convoluted tubule
           • The surface of the cells are highly folded to form microvilli, giving a larger surface area for diffusion The membrane is also filled with transport proteins  The membrane on the opposite side of the cell contain sodium potassium pumps These cells are filled with many mitrochonrdia, suggesting that the process requires ATP
         • Loop of henle
         • Distal convoluted tubule
         • Collecting duct
   • Functions/processes
     • Selective reabsorption
       • Wanted substances are reabsorbed via facilitated diffusion/co-transport and active transport
         • Water follows these substances via osmosis
           • This increases the concentrations of remaining substances such as urea
             • This process is aided by the cells having microvilli producing a large surface area and the cell containing many mitochondria for ATP for uptake
     • Ultra filtration
       • Blood flows from the afferent arteriole into the glomerulus
         • The reduced diameter of the lumen increases the pressure within the glomerulus
           • The pressure is higher within the glomerulus than the bowmans capsule, this pushes fluid from the blood into the bowmans capsule
             • The 3 layers that separate the blood and lumen of the bowmans capsule all play a role
               • The epithelial cells of the capillaries have small gaps between them that small enough molecules can pass through
                 • The basement membrane consists of a fine mesh of collagen fibres and glycoproteins that act as a filter, anything smaller than an mr of 69000 can pass
                   • The epithelial cells of the bowmans capsule, podocytes have a specific shape, it has finger like projections called major processes. These ensure that there are gaps between cells
                     • The filtrate can pass through the podocytes
     • Water reabsorption
     • Osmoregulation
   • Kidney failure
     • Solutions
       • Dialysis
         • The use of a partially permeable membrane to filter the blood
         • Haemodialysis
           • Blood taken from a vein and passed through a dialysis machine so diffusion can occur across a dialysis membrane
           • Blood taken from artery and returned into vein
           • An anticoagulant, heparin is used to prevent the blood from clotting while in the machine, and near the end of dialysis no anticoagulant is added to the blood can clot normally when back in the body. Any bubbles are also removed
           • The flow of blood and dialysis fluid are in the opposite direction to maintain the concentration gradient
         • Dialysis membrane
           • A partially permeable membrane that separates blood and dialysis fluid in a dialysis machine. 
         • Dialysis fluid
           • A complex solution that matches the composition of body fluids
         • Peritoneal dialysis
           • Dialysis fluid is pumped into the body cavity so that exchange can occur across the peritoneal membrane
           • Advantages:  patient can move around while it is happening
       • Transplant
   • Fluids
     • Urine
       • Urine tests
     • Filtrate
     • Blood
     • • Fasting before a test
         • It is important that before this test occurs that the patient fasts so that the blood glucose concentration can return to normal concentrations in that time
         • Fasting means food and drink

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