homeostasis (5)

• Homeostasis

  The maintenance of constant internal conditions
• Internal conditions maintained by homeostasis

  • Body temperature (37 degrees)
  • Blood glucose
  • Water content (osmoregulation)
• Receptor

  Cell type that detects stimuli in the internal or external environment
• Coordination centre

  Part of the nervous system that processes information from stimuli
• Effector

  Part of the nervous system that brings about a response to a stimulus
• It is important to maintain a constant internal environment to provide an optimum body temperature for enzymes in the body (If temperature was too high, enzymes would be denatured)
• Types of response in automatic control systems

  • Voluntary (Conscious)
  • Involuntary (Reflex)
• Central nervous system

  Made up of the brain and spinal cord
• How the nervous system helps respond to changes in the environment

  1. Receptors – detect stimuli

  2. Coordination centre – receives and processes information

  3. Effectors – produce a response
• Neurone

  Carries electrical impulses around the body
• Sensory neurone

  Carries impulses to the central nervous system
• Motor neurone

  Carries impulses away from the central nervous system
• Neurone

  • Has a long structure called the axon
• Synapse

  • The gap between two neurones
• Relay neurone

  Found in the spinal cord in a reflex arc
• Types of effectors

  • Muscles
  • Glands (e.g. to release a hormone)
• Reflex actions

  Rapid, automatic response that doesn't involve the conscious part of the brain
• Main structures in the brain

  • Cerebral cortex – used for balance, coordination, movement
  • Cerebellum
  • Medulla – regulates heartrate, breathing (unconscious activities)
• It is difficult to investigate the brain because it is complex and very delicate, with a high risk of causing further damage
• Ways to study different regions of the brain

  • Electrical stimulation
  • MRI brain scans
  • Studying the brain after accidents / pathological specimens
• Accommodation of the eye

  When the lens changes shape to focus light on to the retina
• What the eye does to focus on near objects

  1. Ciliary muscles contract

  2. Lens becomes 'fatter'

  3. Light is refracted more on to the retina
• Eye changes when light intensity is low

  The pupil dilates to allow more light to enter the pupil
• Lens used to correct myopia and hyperopia

  • Myopia (short sightedness) is corrected with a concave lens
  • Hyperopia (long sightedness) is corrected with a convex lens
• Part of the eye responsible for detecting light

  The retina (specifically cone cells)
• Centre in the brain that monitors and controls body temperature

  The 'thermoregulatory' centre in the hypothalamus
• Organ that detects changes in temperature

  Skin (receptors in the skin)
• What happens if body temperature is too high

  1. Sweating – sweat evaporates from the skin

  2. Vasodilation – blood vessels dilate
• What happens if body temperature is too low

  1. Vasoconstriction – blood vessels become more narrow

  2. Shivering – muscle contraction that releases energy (exothermic)
• Function of glands

  A gland releases a hormone
• Master gland

  The pituitary gland, located in the brain
• Role of the master gland

  The master gland stimulates other glands to release hormones
• Hormones released by the pancreas

  Insulin and glucagon
• Gland that releases adrenaline

  Adrenal gland
• What happens in the body if blood glucose concentration is too high

  1. Pancreas detects high blood glucose and insulin is released

  2. Insulin causes glucose to move into cells and converts glucose to be stored as glycogen

  3. This lowers the blood glucose level
• Cause of type 1 diabetes

  Pancreas produces little or no insulin
• Cause of type 2 diabetes

  The cells in the body no longer respond to insulin
• Treatment for type 2 diabetes

  Carbohydrate controlled diet and regular exercise
• What happens in the body if blood glucose concentration is too low

  1. Pancreas detects low blood glucose and glucagon is released

  2. Glucagon causes glycogen to be broken down into glucose

  3. Blood glucose level increases
• If blood water content is too high


  Too much water could move into cells by osmosis, causing animal cells to burst