Biology 4.5

• Reflex reactions

  Rapid, automatic protective responses that are quicker than normal responses as they miss out the brain
• Reflex reaction

  1. Receptor organ of the stimulus

  2. Sensory neurone

  3. Relay neurone

  4. Motor neurone

  5. Effector organ
• Homeostasis

  The maintenance of a constant internal environment to keep conditions at an optimum
• Homeostasis

  • Involves hormones and the nervous system
  • Hormones carry chemical messages around the body at low transmission speed
  • Nervous system has electrical messages carried by neurones at high transmission speed
• Regulation of blood glucose

  1. Blood glucose levels are normal

  2. Small intestine absorbs glucose into blood

  3. Pancreas produces insulin

  4. Liver converts excess glucose to glycogen for storage

  5. Pancreas stops insulin production

  6. Glucose used up during exercise

  7. Liver converts glycogen back to glucose
• Diabetes

  Condition where blood glucose levels remain too high
• Types of diabetes

  • Type 1
  • Type 2
• Type 1 diabetes

  Caused by damage to beta cells in pancreas that produce insulin
• Type 2 diabetes

  Caused by body becoming resistant to insulin
• Symptoms of diabetes are weight loss, constant thirst, and passing urine often
• Diagnosis of diabetes is done through urine/blood tests for sugar
• Temperature control


  Chemical reactions in cells are controlled by enzymes, which are affected by temperature
• The skin


  • Has many structures that allow it to regulate body temperature
  • Bodily functions occur best at 37°C
  • Temperatures below 37°C are hypothermia, above 37°C are heat stroke
• When it's hot

  1. Sweat glands produce sweat

  2. Evaporation of sweat draws heat out of skin

  3. Blood vessels near surface dilate to allow more blood flow and heat loss
• When it's cold

  1. Sweat glands produce less sweat

  2. Blood vessels near surface constrict to reduce heat loss

  3. Muscles attached to hair contract to trap air and reduce heat loss

  4. Body shivers to generate heat