Homeostasis and response

• Homeostasis


  Maintenance of a constant internal environment in order to ensure optimum conditions for enzyme and cellular function
• Homeostasis


  • Maintains temperature, glucose concentration, and water levels
• Controls


  • Body temperature
  • Blood glucose concentration
  • Water levels
• Control Systems


  • Receptors
  • Coordination Centres
  • Effectors
• Receptors


  Detect changes in the environment
• Receptors detect changes in

  • Temperature
  • Glucose concentration
  • Water levels
• Coordination Centres


  Brain, pancreas, spinal cord
• Coordination Centre


  1. Obtains information from receptors

  2. Sends instructions to effectors
• Effectors


  Bring about responses to stimuli, e.g. glands, muscles
• Nervous System


  Allows the body to react to its surroundings and coordinate an appropriate response
• How the nervous system works

  1. Stimulus

  2. Receptor

  3. Coordinator

  4. Effector

  5. Response
• Reflex action


  An automatic and rapid response which does not involve any conscious input from the brain
• Reflex actions


  • Important for survival by preventing harm
  • Occur via a reflex arc
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical impulse passes along sensory neurone

  3. Coordination in spinal cord

  4. Impulse passes across synapse to relay neurone

  5. Impulse passes along motor neurone

  6. Effector carries out response
• Conscious pathway


  Coordination centre is in the conscious part of the CNS
• Reflex pathway


  Coordination centre is a relay neurone found in the spinal cord
• Hormone


  A chemical messenger secreted by a gland that travels in the blood to a target organ where it causes a response
• Endocrine System


  The body's coordination system which involves hormones
• Pituitary gland


  The 'master gland' that secretes hormones which stimulate other endocrine glands
• Pituitary gland


  • Secretes human growth hormone
  • Stimulates thyroid gland
  • Stimulates ovulation and production of oestrogens in ovaries
  • Stimulates production of sperm and testosterone in testes
• Thyroid gland


  • Secretes hormone thyroxine which controls metabolism, rate and body temperature
• Pancreas


  • Secretes insulin which controls blood glucose levels
• Adrenal gland


  • Secretes adrenaline which controls the body's fight/flight response
• Ovaries


  • Secrete oestrogen which coordinates the menstrual cycle and development of female secondary sexual characteristics
• Testes


  • Secrete testosterone which coordinates the production of sperm and development of male secondary sexual characteristics
• Blood glucose concentration


  Monitored and controlled by the pancreas
• Pancreas response to high blood glucose

  1. Secretes insulin

  2. Insulin binds to receptors on liver and muscles

  3. Excess glucose converted to glycogen and stored
• Pancreas response to low blood glucose

  1. Secretes glucagon

  2. Glucagon causes liver to release stored glycogen
• Blood glucose concentration control

  Uses negative feedback
• Type 1 diabetes


  Autoimmune disorder where pancreas does not produce sufficient insulin to control blood glucose
• Type 1 diabetes treatment

  • Insulin injections
  • Limiting carbohydrate intake
  • Attempts using pancreas and pancreatic cell transplants
• Type 2 diabetes


  Disorder where body's cells stop responding to insulin, leading to uncontrolled blood glucose concentration
• Type 2 diabetes treatment

  • Carefully controlled diet
  • Regular exercise
  • Weight loss
  • Use of drugs which increase insulin production or effectiveness
• Male reproductive hormones


  • Testosterone produced by testes controls sperm production and development of secondary sexual characteristics
• Female reproductive hormones


  • Oestrogen produced by ovaries is involved in the menstrual cycle and development of secondary sexual characteristics
• Menstrual cycle


  Monthly cycle of physiological changes in females involving the ovaries and uterus
• Events of the menstrual cycle

  1. Uterus lining thickens

  2. Egg matures and is released from ovary (ovulation)

  3. If egg is fertilised, pregnancy may occur

  4. If not, uterus lining is shed (menstruation)
• Ovulation


  Release of a mature egg from the ovaries, occurring approximately every 28 days
• Main hormones involved in menstrual cycle

  • Oestrogen
  • Progesterone
  • Follicle Stimulating Hormone (FSH)
  • Luteinising Hormone (LH)
• Role of FSH


  • Controls maturation of eggs within the ovaries and triggers production of oestrogen