Homeostasis + Response - aqa gcse

• Homeostasis


  The regulation of the internal conditions of a cell or organism in response to external and internal changes
• Why is it important?

  It keeps the conditions at a constant level for enzyme action and cell functions
• What does it control?

  Blood glucose conc.

  Body temp.

  Water and ion levels
• Control systems may involve

  Response using nerves

  Chemical responses using hormones
• Control systems


  Cells called receptors

  Coordination centres

  Effectors
• What is a receptor?


  They detect stimuli
• Stimuli


  Changes in the environment
• What is a coordination centre?


  They receive and process info. from receptors

  Such as the brain/spinal cord/pancreas
• What is an effector?


  They bring about responses that restore optimum levels.

  Such as muscles/glands
• Negative feedback:


  A receptor detects a change in a stimulus

  The coordinating centre compares the stimulus to a set point

  An effector then produces a response to correct any difference from the set point

  THIS IS A CONTINUOUS PROCESS
• What is the nervous system?


  Enables humans to react to their surroundings and coordinate their behaviour.
• Where does the info. from receptors pass to?

  (Which 2 structures make the CNS)

  Central nervous system

  (the brain and spinal cord)
• What does the CNS coordinate?

  The response of effectors.

  Such as muscles contracting/glands secreting hormones
• What are reflex actions?

  Automatic and rapid so they can protect the body.
• They don't involve the conscious part of the brain:

  The pain stimulus is detected by receptors

  Impulses from the receptor pass along a sensory neurone to the CNS

  An impulse then passes through a relay neurone

  A motor neurone carries an impulse to the effector.

  The effector (usually a muscle) responds

  Such as to withdraw a limb away from the source of pain.
• Neurones


  They aren't directly connected to eachother
• How do neurones communicate with each other?

  Through synapses
• What is a synapse?

  Gaps between neurones
• What happens when an electrical impulse reaches a synapse?

  A chemical is released that diffuses across the gap between the 2 neurones.

  This causes an electrical impulse to be generated in the second neurone.
• What is the endocrine system?

  It is made up of glands that secrete hormones directly into the bloodstream.
• What is a hormone?


  A chemical messenger that is carried in the blood to a target organ where they produce an effect.
• Compare the effects of the nervous system and the endocrine system

  The effects of the hormones in the E.S are slower and act for longer

  Whereas in the CNS the effects are quicker and last for less time.
• What is the pituitary gland?

  'Master gland'

  It secretes several hormones in response to body conditions
• Why do some hormones they act on other glands?

  To stimulate other hormones to be released to be released and bring about effects.
• What are the main glands that produce hormones in the human body?

  Pituitary gland

  Thyroid gland

  Adrenal gland

  Testis

  Ovary

  Pancreas
• Where is adrenaline produced?


  Adrenal glands (in fear or stressful times)
• What is the effect of adrenaline to the body?

  Increases heart rate

  Boosting the delivery of oxygen and glucose to the brain and muscles

  Prepares for 'flight or fight'-In times of stress such as in a car accident
• Where is thyroxine produced?

  Thyroid gland
• What is the effect of thyroxine to the body?

  Increases the metabolic rate

  Controls the growth and development in young animals
• How is thyroxine controlled?

  By negative feedback
• How is blood glucose concentration controlled?

  By the pancreas
• What happens if the blood glucose conc. is too high?

  The pancreas releases more of the insulin

  Insulin causes glucose to move from the blood into the cells

  In the liver and muscle cells all the excess glucose is converted to glycogen for storage.
• What is insulin?


  A hormone produced in the pancreas that moves glucose out of the blood into the cells
• What happens if the blood glucose conc. is too low?

  The pancreas releases glucagon

  Glucagon stimulates glycogen to be converted into glucose and released into the blood.

  (AN EXAMPLE OF NEGATIVE FEEDBACK)
• Type 1 diabetes


  Caused by the pancreas failing to produce sufficient insulin
• What is the effect of type 1 to the body's blood glucose levels?

  Makes the body's blood glucose levels uncontrollably high
• How is type 1 treated?

  Insulin injections
• Type 2 diabetes


  Caused by the body cells no longer responding to insulin
• What is a risk factor of type 2 diabetes?

  Obesity
• How can type 2 be treated?

  Carbohydrate controlled diet and regular exercise