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4.6 Homeostasis

The process by which your body maintains a constant internal environment
1. control systems
  1. Stimuli - Receptors - Coordination centre - Effectors
    1. Receptors; eyes, ears, tongue and nose, skin, brain (blood temperature and concentration of water in the blood), pancreas (concentration of glucose in the blood)
    2. Coordination centres; brain, spinal chord, pancreas
  2. Hormones
    1. Chemicals that control the internal processes
    2. Secreted by glands and are transported to target organs by the blood stream
      1. E.g. pancreas secretes insulin which targets the muscle and liver
Water and ion content
1. water leaves the body via the lungs when we breathe out, skin when we sweat and excess is removed via the kidneys in the urine
  1. if your body doesn't have the right amount of water and ions, your cells could absorb too mych water by osmosis then burst
2. urea and ions are lost via the skin when we sweat. Excess ions are removed via the kidneys in the urine
3. the liver
  1. 1. excess amino acids are deaminated to form ammonia, which is converted into urea for excretion
  2. 2. Poisonous substances are detoxified, and the breakdown of products excreted in the urine via the kidneys
    1. this happens when too much protein is eaten, which is then deaminated to form ammonia, however ammonia is very toxic so it is converted into urea, where it is diluted and excreted into urine. urea s still toxic therefore we have to release it at fairly regular times
  3. 3.old red blood cells are broken down (after approx 3 months) and the iron is stored
4. the kidney
  1. 1. filters blood
  2. 2. reabsorbs glucose
  3. 3. dissolved ions needed by the body are reabsorbed
  4. 4. water needed by the body is reabsorbed
  5. 5. urea, excess ions and water are released as urine
  6. kidney failure
    1. kidney dialysis
      1. it takes over the functions of the kidney (takes blood from the body, filters it and returns it. Mimics the glucose, mineral ion concentration that a normal person would have). It is different in the way that it doesn't excrete urea naturally.
      2. Advantages; keeps the patient alive, if the transplant fails
      3. disadvantages; requires a strict diet (otherwise too much protein/salt could be eaten), only an option for a limited number of years, frequent hospital visits
    2. Kidney transplant
      1. advantages; less hospital visits, allows normal life, allows regular diet
      2. disadvantages; body may reject the organ, risk of infection during operation, requires lifelong immunosuppressant (due to antigens), takes time to find a match, lasts 8 years
5. ADH (anti-diuretic hormone)
  1. if the water content of the blood is too low, the pituitary gland in the brain releases a hormone called ADH. this causes the kidneys to reabsorb more water and results in a more concentrated urine
  2. if the water content is too high, less ADH is released into the blood, less water is reabsorbed by the kidneys, resulting in a more dilute urine
temperature control
1. body temperature is monitored and controlled by the thermoregulatory centre in the brain
2. temperature receptors in the skin send impulses to the thermoregulatory centre
3. if the temperature is too high:
  1. blood vessels supplying skin capillaries dilate so that more blood flows through the capillaries and heat is lost
  2. sweat glands release more sweat, which cools the body as it evaporates
  3. can lead to heatstroke; caused by temperature increasing enzyme rate, heating the body. this can lead to denaturing which is very harmful
4. if the temperature is too low:
  1. blood vessels supplying capillaries constrict to reduce flow
  2. muscles may 'shiver' - their contraction needs respiration, which releases some energy to warm the body
5. behavioural responses also work to control body temperature
blood glucose
1. monitored and controlled by the pancreas
2. much of the glucose in the body is stored as glycogen in the liver and muscles. When the stores are full, excess glucose is stored as lipid (fat), glycogen is the storage carbohydrate in animals
3. if the blood glucose levels are too high:
  1. the pancreas produces insulin, which allows the glucose to move from the blood to the cells. It helps the muscles and liver to take in more glucose
4. if the blood glucose levels are too low:
  1. the pancreas produces a second hormone called glucagon. This converts glycogen back to glucose and released into the blood, raising the levels back up
5. diabetes
  1. type 1: the blood glucose levels are too high because the pancreas does not produce enough insulin.
    1. controlled by a careful diet - it is also more genetically influenced and diagnosed at a younger age
  2. type 2: when the body does not respond to its own insulin.
    1. obesity is often a factor. it can be controlled by drugs that help the cells to respond. Also by regular exercise and a careful diet
  3. untreated, diabetes can cause circulation issues due to the thickening of the bloodbu the glucose, also eyesight issues and kidney damage/faliure

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4.6 Homeostasis

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	Created by Mirabelle Henry almost 8 years ago