Chemical Control + Homeostasis

Hormones
1. Released by endocrine glands
2. Affect specific target organs with specific receptor proteins in membrane
  1. Specific because of specific tertiary structure which means only complementary shaped hormone can bind to (Receptors have specific binding sites
3. Slow transmission speed
4. Travel to all parts of body via blood
5. Long lasting response
Homeostasis = maintaining a constant internal environment regardless of changes in external
1. Important for: Enzymes (pH and temperature so no denature), Water potential so no osmotic problems and allowing organisms to live in a range of environments
2. Generally works via negative feedback: Deviation from norm -> Receptors detect -> Effectors stimulated -> Norm restored
3. Temperature control
  1. Endotherms: body temperature independent of environment (rely on physiological means)
    1. Heat Gain Centre Stuff
      1. Vasoconstriction = skin arterioles constrict + shunt vessels dilate, so blood goes away from skin so less radiation heat loss
      2. Piloerection = erector pili muscles contract + hairs erect so more insulation
      3. Increased metabolic rate = adrenaline secreted, metabolic rate increased so heat production increased
      4. Shivering = rapid contractions, increasing respiration so more heat released
      5. More Brown fat oxidation = tissue under skin, rapidly oxidising releases heat
    2. Heat Loss Centre Stuff
      1. Vasodilation = Arteriole muscle walls of skin relax + shunt vessels constrict so more heat lost by radiation
      2. Decreased metabolic rate = less adrenaline released so less heat produced
      3. Sweating = vasodilation causes more blood to sweat glands so more sweat released
        Sweat evaporates using heat
      4. Less brown fa is oxidised
  2. Ectotherms: rely on behavioural mechanisms
    1. Behavioural mechanisms
      1. Basking in the Sun to become more active
      2. Shifting between Sun and shade depending on temperature/ retreating to burrow
      3. Changing posture
    2. Ectotherms may also change skin colour to absorb less heat or reduce blood flow to areas
  3. Heat transfer mechanisms
    1. Conduction: Transferring heat between molecules
    2. Convection: Transfer of heat between molecules moving in fluid
    3. Radiation: Heat transfer BC electromagnetic emission
  4. Temperature detected by skin receptors which send impulses to brain which initiates responses
    1. Hypothalimus = Controler
      1. Heat gain centre = generate and conserve heat
      2. Heat loss centre = causing heat to be lost
Positive feedback
1. Normally happens when a breakdown of control
2. When deviation from a norm leads to further deviation
3. Hyperthermia = heat loss mechanisms are overwhelmed causing elevated body temp. Increased body temp causes enzymes to work faster + so metabolic rate increases. This produces more heat so enzymes work even faster until denature
  1. Normally prevented by thermoregulation
  2. Differs from fever BC fever is where norm is just elevated
4. Hypothermia = heat gain system overwhelmed, cold means decreased enzyme activity and so metabolic rate slows, so less heat is produced so enzymes slow further from optimum. This may eventually result in death
Blood Glucose Concentration Control
1. G Words
  1. Glycogenesis = making glycogen
  2. Glycogenolysis = glycogen -> glucose
  3. Gluconeogenesis = Making glucose from non carbs (amino acids)
2. Pancreas: Islets of Langehans
  1. Alpha cells secrete glucagon (For low blood sugar)
    1. So when low blood sugar, detected by Islets of Langerhans which stimulate alpha cells to produce glucagon, which targets mainly liver cells. It binds to specific receptor proteins on cell membrane and increases blood glucose levels by:
      1. Activating glycogenolysis enzymes
      2. Activating glucneogenesis enzymes
      3. Adrenaline is also released which increases blood sugar levels via second messenger model:
        Adrenaline binds to receptor site, activating membrane enzyme. Enzyme converts ATP to cyclic AMP, which activates other enzymes which convert glycogen to glucose
  2. Beta cells secrete insulin (For high blood sugar)
    1. So when high blood sugar, Islets of Langerhans detects and beta sells secrete insulin into blood, going to liver to its target cells, binding to specific glycoprotein receptors Insulin then:
      1. Increases uptake of glucose by cells
        Insulin inserts extra carrier proteins into the membrane from cell's cytoplasm (increasing permeability)
      2. Activates glycogenesis enzymes
      3. Activates glucose -> fat enzymes
      4. Increases respiration rates of cells
3. Diabetes = Inability to control blood glucose levels effectively
  1. Type 1 = body cannot produce insulin (Maybe due to body destroying beta cells)
    1. Treated by insulin injections and monitoring blood glucose levels
  2. Type 2 = loss of responsiveness of target cells to insulin
    1. Treated by monitoring diet
Chemical Mediators
1. Secreted by cells to act locally on themselves and cells near them
2. Inflammatory response
  1. Prostaglandins
    1. Vasodilates arterioles to increase blood flow so more phagocytes to area
    2. Clots blood so no infection
    3. Stimulate histamine production
  2. Histamines (Secreted by mast cells)
    1. Makes capillary walls more permeable so plasma and phagocytes enter damaged tissue
    2. Responsible for allergic reactions
3. Can be secreted by not glands, local response and diffuse quickly to target cells

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Chemical Control + Homeostasis

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