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HOMEOSTASIS AND RESPONSE (HOMEOSTASIS AND BODY TEMPERATURE (the importance…

- - - - blood glucose concentration
      - body temperature
      - water and ion levels
    - - nervous responses
      - chemical responses
  - - - monitors and controls body temperature
      - has receptors that monitor the temperature of the blood flowing through the brain
      - receives information (impulses) from temperature receptors in the skin
    - - blood vessels widen (dilate), directing more blood to the surface of the skin (vasodilation)
      - sweat produced from the sweat glands and evaporates
      - causes a transfer of heat energy to the environment
    - - blood vessels narrow (constrict), directing blood away from the surface of the skin (vasoconstriction)
      - sweating stops and skeletal muscles uncontrollably contract and relax quickly (shiver)
      - causes a transfer of heat energy to the blood
- - - - controls complex behaviour
      - made of billions of interconnected neurones and has different regions that carry out different functions
      - cerebral cortex
        
        controls conscious thought, intelligence, personality, and high-level functions, such as language and verbal memory
      - cerebellum
        
        controls balance, co-ordination of movement and muscular activity
      - medulla
        
        controls unconscious actions, such as heart rate and breathing rate
      - Neuroscientists have been able to map the regions of the brain to particular functions by:
        
        studying patients with brain damage
        
        electrically stimulating different parts of the brain
        
        using MRI scanning techniques
      - The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
    - - sense organ containing receptors sensitive to light intensity and colour
      - retina
        
        contains receptor cells that are sensitive to the brightness and colour of light
      - optic nerve
        
        carries impulses from the retina to the brain
      - sclera
        
        tough outer layer of the eye
      - cornea
        
        refracts light
      - iris
        
        controls the size of the pupil and the amount of light reaching the retina
      - ciliary muscles and suspensory ligaments
        
        change the shape of the lens to focus light onto the retina
      - accommodation: the process of changing the shape of the lens to focus on near or distant objects
      - focus on a near object
        
        ciliary muscles contract
        
        suspensory ligaments loosen
        
        lens becomes thicker and strongly refracts light rays
      - focus on a distant object
        
        ciliary muscles relax
        
        suspensory ligaments are pulled tight
        
        lens is pulled thin and only slightly refracts light rays
      - two common defects of the eyes occur when rays of light do not focus on the retina: myopia (short sightedness) and hyperopia (long sightedness)
      - defects are often treated with spectacle lenses, which refract light rays so that they focus on the retina
      - new technologies include contact lenses, laser surgery to change the shape of the cornea, and replacement eye lenses
- - - - located in the brain
      - 'master gland'
      - secretes several hormones in response to body conditions, some of these hormones act on other glands to stimulate different hormones to be released and bring about effects
    - - produced by adrenal glands
      - increases the heart rate
      - increases the rate of oxygen and glucose to the brain and muscles
      - prepares the body for 'flight or fight'
    - - produced by the thyroid gland
      - increases the metabolic rate
      - controls growth and development
      - controlled by negative feedback
  - - - pancreas releases more of the hormone insulin
      - insulin causes glucose to move from the blood into the cells
      - in liver and muscle cells, excess glucose is converted to glycogen for storage
    - - pancreas releases glucagon
      - glucagon stimulates glycogen to be converted into glucose and released into the blood
    - - caused by the pancreas failing to produce sufficient insulin
      - results in uncontrolled high blood glucose levels
      - normally treated with insulin injections
    - - caused by the body cells no longer responding to insulin
      - has obesity as a risk factor
      - normally treated with a carbohydrate-controlled diet and regular exercise
  - - - regulate the balance of water and ions in the body
      - excrete urea, a waste product produced by the liver from the breakdown of proteins and contains nitrogen
      - urine is produced in millions of small tubes in the kidneys called tubules
      - produce urine through filtering the blood, selective reabsorption of useful substances (such as glucose, ions and water), leaving urea and excess water and ions to form urine
    - - hormone which controls the water level in the body
      - released by the pituitary gland when the blood is too concentrated
      - passes in the blood to the kidney tubules
      - causes more water to be reabsorbed back into the blood
    - - kidney transplant
      - kidney dialysis
        
        used to remove waste products from the blood, three times a week