homeostasis and response

• Homeostasis


  The maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular function
• Conditions maintained by homeostasis in the body

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Types of responses used in body control systems

  • Nervous
  • Chemical
• Components of all control systems

  • Receptors
  • Coordination centres
  • Effectors
• Function of a receptor


  Detect changes in the environment (stimuli)
• Function of a coordination centre


  Obtain and process information from receptors
• Function of an effector


  Bring about responses to stimuli
• Nervous system


  Allows the body to react to its surroundings and coordinate an appropriate response
• How a stimulus leads to a response being carried out by the body

  1. Stimulus is converted into an electrical impulse by the receptors

  2. The electrical impulse passes along sensory neurones to the central nervous system (CNS)

  3. The CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response
• Sequence of events describing how the nervous system works

  Stimulus → receptor → coordinator → effector → response
• Reflex action


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


  • Aid survival by preventing harm to the body
• How a reflex action occurs via a reflex arc

  1. The stimulus is detected by a receptor

  2. An electrical impulse passes along a sensory neurone to the spinal cord (part of the CNS)

  3. At a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap and stimulates a new impulse which passes along the relay neurone

  4. The same process occurs at a synapse between a relay neurone and a motor neurone

  5. At the effector, an appropriate response is carried out
• Endocrine system


  The body's coordination system which involves hormones
• Hormone


  A chemical messenger secreted by a gland, that travels in the blood to a target organ and causes a response
• Gland


  An organ that secretes hormones
• Pituitary gland


  The 'master gland' that secretes a wide range of hormones, some of which may stimulate other endocrine glands
• Roles of the pituitary gland

  • Secretes human growth hormone - controls human growth
  • Stimulates the thyroid gland
  • Stimulates ovulation and the production of oestrogen in the ovaries
  • Stimulates the production of sperm and testosterone in the testes
• Reflex pathway


  The coordination centre is a relay neurone found in the spinal cord/unconscious parts of the brain
• Thyroid gland


  Secretes the hormone thyroxine - controls metabolism, heart rate and body temperature
• Conscious pathway


  The coordination centre is in the conscious part of the brain
• Pancreas


  Secretes the hormone insulin - controls blood glucose levels
• Cerebral cortex


  • Controls consciousness, intelligence, memory and language
• Adrenal gland


  Secretes adrenaline - controls the body's 'fight or flight' response
• Ovaries


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


  Secrete testosterone, which coordinates the production of sperm and the development of male secondary sexual characteristics
• Cerebellum


  • Controls muscular coordination
• Pancreas


  Monitors and controls blood glucose concentration
• Pancreas response to high blood glucose

  Secretes the hormone insulin, which binds to receptors on the liver and muscles, causing excess glucose to be converted into glycogen and stored
• Pancreas response to low blood glucose

  Secretes the hormone glucagon, which binds to liver cells, causing glycogen to be converted into glucose and released into the blood
• Medulla


  • Controls unconscious activities eg. breathing, heart rate
• Blood glucose concentration control using negative feedback


  When the blood glucose concentration rises or falls below the optimum, a hormone is secreted by the pancreas. The action of either hormone (insulin or glucagon) helps bring back the concentration to the correct level.
• Type 1 diabetes


  An autoimmune disorder in which the pancreas does not produce sufficient insulin to control the blood glucose concentration, leading to high blood glucose levels, excessive urination, tiredness and weight loss
• Treatment of Type 1 diabetes

  1. Insulin injections before meals - allows glucose to be converted into glycogen

  2. Limiting carbohydrate intake

  3. Attempts using pancreas and pancreatic cell transplants; investigations into genetic engineering of pancreatic cells
• Type 2 diabetes


  A disorder in which the body's cells stop responding to insulin, leading to an uncontrolled blood glucose concentration. Its onset is linked with increasing age and obesity.
• Treatment of Type 2 diabetes

  1. Following a carefully-controlled diet

  2. Doing regular exercise

  3. Losing weight

  4. Use of drugs which increase insulin production and effectiveness
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Investigating and treating the brain

  • The brain is a complex and delicate organ
  • The brain is easily damaged and destroyed
  • Certain membranes prevent drugs from reaching the brain
  • The exact function of each part of the brain is not known
• Ways water is lost from the body

  • During exhalation via the lungs
  • Sweating
  • Urine (some reabsorbed in the kidney)
• Ways ions are lost from the body

  • Sweating
  • Urine (some reabsorbed in the kidney)