coordination and response

• Eye


  A sense organ containing receptor cells that are sensitive to light (rod cells) and colour (cone cells)
• Blind spot


  • At the point where the optic nerve joins the retina, there are no light-sensitive rod and cone cells on that part of the retina
  • Light falling onto that part of the retina will not result in an image being detected
  • The brain 'fills in' from surrounding light so we don't see a black hole where no light has fallen
• Pupil reflex


  1. In dim light, the pupil dilates (becomes larger) to allow more light to enter the eye to improve vision

  2. In bright light, the pupil constricts (gets smaller) to allow less light to enter the eye to protect the retina from damage
• Pupil reflex


  A reflex action carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light
• Pupil reflex


  • Antagonistic muscle action between radial muscles and circular muscles of the eye
  • When one set of muscles contracts, the other relaxes
• Accommodation

  1. The function of the eye in focusing on near and distant objects

  2. The lens becomes fatter when the ciliary muscles contract and the suspensory ligaments loosen

  3. The lens becomes thinner when the ciliary muscles relax and the suspensory ligaments tighten
• Rod cells


  Sensitive to dim light
• Cone cells


  • Distinguish between different colours in bright light
  • There are 3 types sensitive to red, blue and green light
• Fovea


  • An area on the retina where almost all of the cone cells are found
• Blind spot


  • There are no light-sensitive cells at all in the area where the optic nerve attaches to the retina
• Night vision is black and white because the low light intensity isn't enough to stimulate cone cells, so only rod cells are stimulated
• Dim stars disappear when looked at directly but reappear when looked at slightly to the side, because the light falls on the fovea with fewer rods when looked at directly
• Hormone


  A chemical substance produced by a gland and carried by the blood. The hormone alters the activity of one or more specific target organs.
• Endocrine system


  The glands that produce hormones in animals
• Endocrine glands


  • Have a good blood supply as they need to get hormones into the bloodstream as soon as possible so they can travel around the body to the target organs
  • Hormones only affect cells with target receptors that the hormone can bind to, either on the cell membrane or inside cells
• Liver


  Regulates levels of hormones in the blood; transforming or breaking down any that are in excess
• Insulin


  A hormone produced when blood glucose rises, which stimulates liver and muscle cells to convert excess glucose into glycogen to be stored
• Glucagon


  A hormone produced when blood glucose falls, which stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood
• Blood glucose levels are controlled by a negative feedback mechanism involving the production of insulin and glucagon


  Both hormones control blood glucose concentration
• Adrenaline


  The 'fight or flight' hormone, produced in situations where the body may be in danger
• Effects of adrenaline


  • Increasing blood glucose concentration
  • Increasing pulse rate and breathing rate
  • Diverting blood flow towards muscles and away from non-essential parts of the body
  • Dilating pupils
• Homeostasis is defined as the maintenance of a constant internal environment
• Homeostasis


  The maintenance of a constant internal environment within the body (such as temperature, blood pressure, water concentration, glucose concentration etc) in order to ensure that reactions in body cells can function and therefore the organism as a whole can live
• When one of these internal conditions deviates far away from the normal if not brought back within set limits the body will not function properly and the eventual consequence without medical intervention will be death
• Role of Insulin


  Insulin is secreted into the blood at times when blood glucose levels are high, usually directly after a meal. Insulin temporarily converts excess glucose into glycogen in the liver and muscles, decreasing blood glucose concentration. The glycogen is converted back to glucose several hours later when blood glucose levels have dipped due to respiration in all tissues.
• The kidneys can only cope with a certain level of glucose in the blood. If the level gets too high, glucose gets excreted and is lost in the urine.
• Negative feedback


  Occurs when conditions change from the ideal or set point and returns conditions to this set point
• Negative feedback mechanism


  1. If the level of something rises, control systems are switched on to reduce it again

  2. If the level of something falls, control systems are switched on to raise it again

  3. Negative feedback mechanisms are usually a continuous cycle of bringing levels down and then bringing them back up so that overall, they stay within a narrow range of what is considered 'normal'
• Blood glucose control


  Controlled by a negative feedback mechanism involving the production of two hormones - insulin and glucagon
• Insulin


  Produced when blood glucose rises and stimulates liver and muscle cells to convert excess glucose into glycogen to be stored
• Glucagon


  Produced when blood glucose falls and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood
• The terms glucagon and glycogen are very often mixed up by students as they sound similar
• Glucagon


  The hormone
• Glycogen


  The polysaccharide glucose is stored as
• Type 1 diabetes


  A condition where the blood glucose levels are not able to be regulated as the insulin-secreting cells in the pancreas are not able to produce insulin
• Treatment for Type 1 diabetes


  Injecting insulin, which causes the liver to convert glucose into glycogen, reducing the blood glucose level
• Symptoms of diabetes


  • Extreme thirst
  • Weakness or tiredness
  • Blurred vision
  • Weight loss
  • Loss of consciousness in extreme cases
• People with Type 1 diabetes


  • Have to monitor their blood glucose levels throughout the day as their levels of physical activity and their diet affect the amount of insulin needed
  • Can help to control their blood glucose level by being careful with their diet - eating foods that will not cause large increases in blood glucose level, and by exercising, which can lower blood glucose levels due to increased respiration in the muscles
• Homeostasis


  The maintenance of a constant internal environment
• Homeostasis


  • Internal conditions within your body (such as temperature, blood pressure, water concentration, glucose concentration etc) need to be kept within set limits in order to ensure that reactions in body cells can function and therefore the body can survive