Homoeostasis and Response

• Homeostasis


  The maintenance of a constant internal environment
• What homeostasis controls in the human body

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


  • Receptors - cells that detect stimuli
  • Coordination centres - process the information received from the receptors
  • Effectors - bring about responses to bring the conditions in the body back to optimum levels
• Response to a stimulus

  1. Receptor cells convert a stimulus into an electrical impulse

  2. Electrical impulse travels along sensory neurons to the central nervous system

  3. Information is processed and the appropriate response is coordinated

  4. Electrical impulse is sent along motor neurons to effectors

  5. Effectors carry out the response
• Reflex


  Automatic responses which take place before you have time to think
• Reflex arc


  1. Stimulus is detected by receptors

  2. Impulses are sent along a sensory neuron

  3. In the CNS the impulse passes to a relay neuron

  4. Impulses are sent along a motor neuron

  5. The impulse reaches an effector resulting in the appropriate response
• Synapse


  The gaps between two neurons
• Reaction time


  How long it takes you to respond to a stimulus
• Mechanisms to regulate body temperature when it is too high

  • Sweat is produced from sweat glands
  • Vasodilation - more blood flows closer to the surface of the skin
• Mechanisms to regulate body temperature when it is too low

  • Sweating stops
  • Skeletal muscles contract rapidly (shivering) to generate heat from respiration
  • Hairs stand on end to create an insulating layer, trapping warm air
  • Vasoconstriction - blood does not flow so close to the surface, resulting in less heat lost
• Endocrine system


  Communication system that sends hormones (chemical messengers) around the body
• Glands that make up the endocrine system

  • Pituitary gland
  • Pancreas
  • Thyroid
  • Adrenal gland
  • Ovary
  • Testes
• Comparison of nervous and endocrine systems

  Endocrine system is much slower but acts for longer compared to the nervous system
• The concentration of glucose in your blood needs to be kept within a certain limit because glucose is needed by cells for respiration
• Pituitary gland


  Secretes anti-diuretic hormone (ADH)
• Adrenal gland


  • Secretes adrenaline
  • Involved in the 'fight or flight' response (the body's response to stressful situations)
• Ovary


  • Secretes oestrogen
  • Involved in the menstrual cycle and the development of female secondary sexual characteristics
• Testes


  • Secretes testosterone
  • Involved in the production of sperm and the development of male secondary sexual characteristics
• The blood transports the hormone to a target organ or tissue where it has an effect
• Compared to the nervous system, the hormonal system is much slower but it acts for longer
• Control of Blood Glucose Concentration

  1. Eating foods that contain carbohydrates increases the glucose levels in the blood

  2. If the glucose levels are too high, the pancreas produces the hormone insulin

  3. Insulin binds to cell in target organs (muscles and liver) causing glucose to move from the blood into muscle cells for respiration and excess glucose to be converted into glycogen which is stored in the liver

  4. The blood glucose concentration is reduced

  5. If glucose levels decrease, the pancreas produces the hormone glucagon

  6. Glucagon binds to to the liver cells causing glycogen to be broken down into glucose

  7. Glucose is released into the blood, increasing the blood glucose concentration
• When blood glucose levels increase/decrease


  A hormone is secreted to oppose the change
• When you have diabetes you cannot control your blood glucose level
• Type 1 diabetes


  The pancreas cannot produce enough insulin
• Type 2 diabetes


  The body cells no longer respond to insulin
• Osmosis


  The process by which water molecules move from a place where they are in high concentration to a place where they are in low concentration
• The Kidneys


  1. Filtering out the waste products

  2. Selectively reabsorbing useful substances such as glucose, ions and water
• Waste products processed at the kidney

  • Water
  • Ions
  • Urea
• Anti-diuretic hormone (ADH)


  A hormone involved in the control of the loss of water as urine
• Dialysis


  1. Blood moves between partially permeable membranes surrounded by dialysis fluid (has the same concentrations of ions and glucose as healthy blood)

  2. Useful ions and glucose are not lost from the blood but urea, excess ions and water diffuse across the membrane
• Kidney transplants


  Providing the individual with a healthy kidney
• Testosterone


  The main male reproductive hormone
• Oestrogen


  The main female reproductive hormone
• Menstrual cycle


  1. The lining of the uterus breaks down, and the woman has her period

  2. The layer then builds up again, until ovulation (day 14) occurs- an egg is released from the ovary and moves to the uterus via the fallopian tube

  3. If a fertilised egg has not been embedded in the lining after 28 days, it begins to break down and the cycle continues
• Hormones controlling the menstrual cycle

  • Follicle stimulating hormone (FSH)
  • Oestrogen
  • Luteinising hormone (LH)
  • Progesterone
• Contraceptive pill


  The mixed pill contains oestrogen and progesterone, which means the oestrogen levels are constantly high, inhibiting FSH so no eggs mature, and the lining also stops developing and the mucus in the cervix becomes thick so sperm cannot move through
• Oestrogen


  Hormone produced in the ovaries, secreted as a result of FSH, stimulates the production of LH and inhibits the secretion of more FSH
• Luteinising hormone (LH)


  Produced in the pituitary gland, produced as a result of the hormone oestrogen, its release results in ovulation
• Progesterone


  Produced in the ovaries and secreted from the egg follicle, maintains the lining of the uterus and supports a pregnancy if the egg is fertilised, inhibits the release of both FSH and LH
• Hormonal methods of contraception

  • The mixed pill (contains oestrogen and progesterone)
  • The progesterone only pill
  • The contraceptive patch (contains oestrogen and progesterone)
  • The contraceptive implant (releases progesterone)
  • The contraceptive injection (made up of progesterone)
  • The plastic intrauterine device (IUD) (releases progesterone)