Homestasis

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  • Homeostasis
    • Thermoregulation
      • heat gain
        • production of heat by metabolism of food during respiration
        • gain of heat from environment (conduction, convection and radiation)
        • what happens when external temperatures drop?
          • 1-  Drop detected by thermoreceptors in the skin
            • 2- causes electrical impulses to be sent to the thermoregulatory system in the hypothalamus via sensory neurones
              • 3- this will cause the thermoregulatory system to trigger the heat gain system to start.
                • 4- this will cause the smooth muscles in the peripheral arterioles to contract, causing vasoconstriction
                • 4- also causes  erector pili muscles in skin to contract causing hairs on skin to stand up, skeletal muscles rapidly contract and relax to cause shivering and adrenaline is released from adrenaline glands
      • heat loss
        • evaporation of water from skin (sweating)
        • breathing out - water vapour
        • radiation and convection of heat to the atmosphere
        • conduction to the ground
        • urine and faeces
        • what happens if the external temperatures rise?
          • 1- Rise detected by thermoreceptors in the skin
            • 2- causes electrical impulses to be sent to the thermoregulatory system in the hypothalamus via sensory neurones
              • 3- this  will cause the thermoregulatory system to trigger the heat loss system to start.
                • 4-this will cause the smooth muscles in the peripheral arterioles to relax, causing vasodilation.
                  • 4-  also causes sweating caused by sweat glands, erector pili muscles relax and so hairs on the skin's surface lie against the skin
      • Endotherms - mammals and birds. Most heat derived from metabolic activities
      • Ectotherms- Most heat derived from outside sources i.e. environment
      • Negative feedback- means that whenever a change occurs in a system, the change automatically cause a corrective mechanism to start, which reverses the original change and brings the system back to normal
    • oestrus cycle
      • 1. FSH. Produced in pituitary gland and causes a follicle to develop in the ovaries. It also stimulates the production of  oestrogen
        • 2. Oestrogen is secreted from the developing follicle. It cause the thickening of the uterus lining and inhibits FSH at LOW LEVELS
          • Oestrogen at high levels will stimulate the production of FSH (to make sure the follicle is fully developed) and will also stimulate the production of LH
            • 3. LH is produced by the pituitary gland and causes ovulation. It also stimulates the production of progesterone
              • 4. Progesterone is secreted from the corpus luteum. It maintains the lining of the uterus .
                • after a while the corpus luteum degenerates and so progesterone is no longer produced so there is no longer an inhibition on FSH so cycle starts again.
    • maintaining a constant internal environment
    • why is it important?
      • enzymes and proteins are sensitive to change
        • may make respiration less efficient
      • changes to water potential may cause cells to shrink and expand
      • 5 stages in self regulating system
        • 1- set point- desired level at which the system operates. It's monitored by..
        • 2- receptor- detects any deviation from the set point and informs the ..
        • 3-controller- coordinates information from various receptors and sends instructions to the appropriate..
        • 4- effector- brings about changes need to return the system back to normal, brought about by the..
        • 5- feedback loop- informs receptor of the changes to the system brought about by the effector.
    • Insulin and glucagon
      • what happens if blood glucose levels are too high?
        • Beta cells in the islets of langerhans (in the pancreas) release insulin  that will travel in the blood and will bind to cells' receptors (mainly muscle and liver cells)
          • causes cell membranes to become more permeable. This allows more glucose from the blood to move into cells.
            • this can increase the rate of metabolism and respiration
              • lowers blood glucose levels
          • causes glycogenesis  (making glycogen from glucose)
      • made by the pancreas
      • hormones are chemical messengers released by glands and carried in the blood stream to travel to target cells with receptors
      • normal level of blood glucose 90mg/100cm3
    • adrenaline
      • used for fight or flight
      • causes glycogenolysis in the liver and muscle cells to boost glucose concentrations
    • first messenger is the glucagon or the adrenaline binding to their specific receptors
      • this binding activates the enzyme adenyl cyclase
        • this enzyme accelerates the production of cAMP (a small molecule that acts as a second messenger within the cytoplasm)
          • this diffuses through the cytoplasm of the liver where it causes a chain reaction that ends with the breakdown of glycogen to glucose phosphate.
            • this chain reaction produces a a cascade effect that amplifies the response to the hormone (glucagon or adrenaline)
    • diabetes
      • Type 1
        • cause- cells from immune system attack beta cells so body unable to produce insulin
          • treatment- insulin injections, can't be given orally as its a protein so will be digested. Cant't give too much insulin as the body won't get enough glucose
      • type 2
        • cause- receptors less responsive to  insulin. Develops later on in life from eating too many carbohydrates etc.
          • treatment- regulate intake of carbohydrates - get the right balance between their diet and exercise
          • can be diagnosed by finding glucose in the urine as the kidneys can't cope with the high level of glucose.
  • This is positive feedback
  • the stimulation of FSH at high levels is negative feedback

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