A2 Level OCR: Communication & Homeostasis

Hormonal System & Glands
1. Adrenal gland
  1. Cortex (Outer)
    1. Secretes steroid hormones e.g. glucocorticoids
  2. Medulla (Inner)
    1. Secretes catecholamine hormones e.g. adrenaline (when stresed)
  3. Adrenaline
    1. Secreted when blood glucose is low (e.g. when stressed)
    2. Increases blood glucose
      1. Glucose binds to receptors on cell membranes
        Activates adenylate cyclase
        Catalyses production of cyclic AMP inside cells
        Causes cascade of enzymes, that makes glucose more available to cell
    3. Cardiac muscle contracts faster & w/ more force, increasing heart rate
    4. Diaphragm & Intercostals contract w/ more force, increasing rate & depth of breathing
    5. Vasoconstriction at gut & skin, vasodilation at skeletal muscles, heart and lungs
    6. Muscles in broncioles relax, airways widen, deeper breathing
    7. Glycogen to glucose
2. Pancreas
  1. Islets of Langerhans (endocrine)
    1. Control blood glucose
    2. Alpha cells secrete glucagon to increase blood glucose
      1. Glycogenolysis
      2. Gluconeogenesis
        Glycerol + amino acids
      3. Decrease rate of respiration of glucose
    3. Beta cells secrete INSULIN
      1. Glycogenesis
      2. Increase rate of respiration of glucose
      3. 1. Increased glucose = Increased ATP inside cell
      4. 2. Increased ATP causes K+ channels to close
      5. 3. K+ ions build up inside cell membrane. Membrane becomes polarised
      6. 4. Ca2+ channels open, and Ca2+ diffuses into cell
      7. 5. Vesicles fuse with cell membrane, insulin is secreted by exocytosis
  2. Acinar cells (exocrine)
    1. Secrete digestive enzymes into pancreatic duct
      1. e.g. Amylase breaks down starch
      2. Leads to duodenum
Control of body temperaure
1. Ectotherms
  1. Cold blooded animals e.g. lizards
  2. Can't internally control body temperature
  3. Bask in sun to increase heat
  4. Go to shade/underground to decrease heat
  5. Activity level depends on internal temperature (therefore external temperature)
    1. More active at high temperature
  6. Don't generate much heat
  7. Variable metabolic rate
2. Endotherms
  1. Warm blooded animals e.g. humans
  2. Relatively constant, high metabolic rate
  3. Homeostasis used to maintain constant internal temperature
  4. TOO HOT
    1. Hairs lie flat
    2. Vasodilation
      1. More heat lost by radiation as more blood flow to skin surface
    3. Sweating
      1. Heat evaporates off skin
    4. Change behaviour (e.g. strip)
  5. TOO COLD
    1. Shivering
      1. Muscles release more energy from glucose, so heat released
    2. Vasoconstriction
      1. Less heat lost by radiation
    3. Hairs become erect
      1. Forms insulating layer of air above skin
        Air is a poor conductor of heat
    4. Less sweating
    5. Hormones
      1. Adrenaline & thyroxine increase metabolism, therefore more heat energy released
  6. HYPOTHALAMUS
    1. Thermoreceptors in hypothalamus detect internal temp.
    2. Peripheral thermoreceptors detect external temp.
    3. Receives impulses from sensory neurones, sends impulses to effectors via motor neurones
Diabetes
1. Type 1
  1. Likely to be inherited
  2. Auto-immune disease
  3. Immune system attacks Beta cells in pancreas
  4. Insulin not produced by body
  5. Blood glucose remains high after eating
    1. Can cause death if untreated
  6. Treatment
    1. Regular, controlled injections of insulin
    2. Stem cells is a possibilty
2. Type 2
  1. Linked w/ obesity
  2. Body doesn't produce enough insulin, or cells don't react to insulin
    1. Cells don't respond properly to insulin, so cells don't take up glucose
  3. Treatment
    1. Diet
    2. Exercise
    3. If diet & exercise not enough, can take glucose lowering tablets
3. GM Insulin
  1. More effective than pig insulin, and less likely to be rejected by immune system
  2. Cheaper than extracted insulin from pig pancreas
  3. Larger quantities can be produced than pig insulin
  4. Ethical issues
    1. Vegetarians may object to use of animals
    2. Some religions object to use of insulin from pigs
Control of Heart Rate
1. Rate at which SAN fires is unconciously controlled by cardiovascular centre in Medulla Oblongata
2. Internal stimuli
  1. Baroreceptors (in Aorta, vena cava & carotid arteries)
    1. Detect blood pressure
  2. Chemoreceptors (in aorta, carotid arteries, and MOb.
    1. Detect Oxygen level, Carbon dioxide level, & pH
3. High blood pressure
  1. 1. Baroreceptors detect high pressure, send impulses to MOb. via sensory neurones
  2. 2. MOb. secretes ACh
  3. 3. ACh binds to receptors on heart, heart rate DECREASES
4. Low blood Oxygen
  1. 1. Chemoreceptors detect stimuli
  2. 2. MOb. secretes noradrenaline
  3. 3. Noradrenaline binds to receptors on heart, heart rate INCREASES
5. Parasympathetic system
  1. Acetylcholine (ACh)
6. Sympathetic system
  1. Noradrenaline

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A2 Level OCR: Communication & Homeostasis

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