homeostasis and response (aqa trilogy gcse bio p2)

• definition of Homeostasis


  the maintenance of a constant internal environment
• homeostasis controls:

  blood glucose concentration, body temperature and water levels
• receptors:


  cells that detect stimuli. Are in (Skin, eyes and ears)
• coordination centres:


  process the information received from the receptors. (Spine and brain)
• effectors:


  bring out responses to bring the conditions in the body back to optimum levels. (muscles or glands)
• reflex arc: stimulus -> receptors-> sensory neuron-> CNS->relay neuron -> motor neuron -> effectors
• synapses:


  gaps between neurons. Chemical is released, it diffuses across and triggers impulse for next neuron.
• reaction time:


  how long it takes you to respond to a stimulus.
• endocrine system


  complex network of glands and organs
• thyroid:


  secretes thyroxine, controls metabolic/ heart rate and temperature
• testes:


  secretes testosterone
• ovary


  secretes oestrogen
• pituitary gland


  the master gland, secretes hormones into the blood to either have an effect on the body or act on other glands to stimulate them to produce different hormones.
• pancreas


  secretes insulin, controls blood glucose levels
• the concentration of glucose in your blood needs to be kept within a certain limit because glucose is needed by cells for respiration. Controlled by the pancreas.
• high glucose levels:


  pancreas produces the hormone insulin, binds to target organs and causes glucose to move from blood to muscle cells for respiration, excess glucose converted to glycogen which is stored in the liver, the concentration is reduced.
• glucose levels decrease:


  the pancreas produces glucagon, binds to liver cells, broken down into glucose, released into blood, increases conc
• FSH


  causes the maturation of an egg in the ovary, in follicle. produced in pituitary gland, stimulates ovaries to produce oestrogen.
• oestrogen


  causes the lining of the uterus to grow again, (ovaries, result of FSH), stimulates the production of LH and inhibits the secretion of more FSH.
• LH:


  (pituitary gland, result of oestrogen) results in ovulation (egg maturing)
• Progesterone:


  (ovaries, from egg follicle), maintains the lining of the uterus, supports pregnancy if egg is fertilised. Inhibits the release of FSH + LH
• hormonal contraception:

  • the pill: oestrogen and progesterone -> stops eggs from maturing
  • patch, implant, injection, IUD
• non-hormonal contraception:

  • copper intrauterine device
  • spermicides
  • barrier methods: condoms and diaphragms
  • surgical methods
• Fertility drugs + IVF:

  FSH + LH (stimulate the maturation and release of egg)
• negative feedback:


  body responds to an increase/decrease in a factor by returning it back to its original level
• adrenal gland:

  • secretes adrenaline, ('flight or fight response)
  • released by the adrenal glands (kidneys)
  • effects include:
  • increases heart + breathing rate delivering more oxygen + glucose to brain and muscles for respiration.
  • (to increase body temp -> shivering)
• describe how the hormones given to women during IVF treatment interact with other hormones to prepare the body for pregnancy.

  • FSH + LH -> cause and increase progesterone + oestrogen: maintain the lining of the uterus, lining ready for egg to be planted
• 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
• Endocrine system


  • Sends hormones (chemical messengers) around the body
  • Hormones have an effect when they reach a target tissue
• Glands in the endocrine system

  • Pituitary gland
  • Pancreas
  • Thyroid
  • Adrenal gland
  • Ovary
  • Testes
• 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
• The concentration of glucose in your blood needs to be kept within a certain limit because glucose is needed by cells for respiration