homeostasis

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• Enzymes and cells require very stable conditions in order to work
• The body has systems in place to keep the internal conditions optimum for the cells to function
• Internal conditions maintained by homeostasis

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Automatic control systems in the human body

  • Can involve the nervous system or hormones
• Automatic control system


  1. Receptor cells detect changes in the environment

  2. Receptor cells pass information to a Coordination Center

  3. Coordination Center receives and processes the information

  4. Coordination Center sends instructions to the effector

  5. Effector carries out the response
• Stimulus

  A change to the environment detected by receptor cells
• Effector

  A muscle or gland that carries out the response
• The homeostasis topic will cover a range of different systems, each with a stimulus, receptor, Coordination Center, and effector
• Nervous system


  Consists of two parts: central nervous system (brain and spinal cord) and other nerves running to and from the central nervous system
• Homeostasis


  1. Stimulus

  2. Receptor

  3. Coordination Center

  4. Effector

  5. Response
• Neuron


  Nerve cell
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical impulse passed along sensory neuron to central nervous system

  3. Electrical impulse passed along relay neuron in central nervous system

  4. Electrical impulse passed along motor neuron to effector

  5. Effector (muscle) contracts, response occurs
• In reflexes, there is no decision-making by the conscious part of the brain, making reflexes automatic and rapid
• Reflexes help to protect us from danger
• Measuring a person's reaction time

  1. Person 1 sits on a stool with good upright posture

  2. Person 1 places the forearm of their dominant arm across the table with hand overhanging the edge

  3. Person 2 holds a ruler vertically with the 0 cm mark between Person 1's thumb and first finger

  4. Person 2 tells Person 1 to prepare to catch the ruler

  5. Person 2 drops the ruler at a random time

  6. Person 1 catches the ruler with thumb and first finger as quickly as possible

  7. Person 2 records the measurement on the ruler level with Person 1's thumb

  8. Repeat the test several times and calculate the mean
• Reaction time


  The time taken for a person to respond to a stimulus
• The two people then switch places with Person 1 testing the reaction time of Person 2
• Independent variable


  The variable that is changed in an experiment
• Dependent variable


  The variable that is measured for each change in the independent variable
• Control variables


  • Variables that are kept constant to avoid affecting the dependent variable
  • Examples: distance between thumb and first finger, measuring at top of thumb, room conditions
• Practicing catching the ruler

  Reaction time becomes shorter
• Using dominant hand vs non-dominant hand


  Reaction time is shorter with dominant hand
• Consuming caffeine before the test


  Reaction time may change
• Need to check for any medical issues that could be affected by caffeine
• The test should be carried out in a lab where hazardous chemicals are not normally used
• Endocrine system


  The system in the body that is controlled by chemicals called hormones
• Endocrine system


  • Consists of a number of glands that secrete hormones directly into the bloodstream
  • Hormones are carried in the bloodstream and act on specific target organs
• Key endocrine glands


  • Pancreas
  • Ovaries
  • Testes
  • Thyroid
  • Adrenal
  • Pituitary
• Pancreas


  Releases hormones involved in controlling glucose concentration in blood
• Ovaries and Testes


  Release hormones involved in puberty and reproduction
• Thyroid gland


  Produces hormones involved in growth and regulating basal metabolic rate
• Adrenal glands


  Release hormone adrenaline produced in times of fear or stress
• Pituitary gland


  Located in the brain, releases hormones that act on other glands to trigger a range of effects in the body, considered the 'master gland'
• The pituitary gland is extremely important in the endocrine system
• Insulin


  Hormone used to control the blood glucose concentration
• How insulin controls blood glucose concentration

  1. Pancreas senses rise in blood glucose after meal

  2. Pancreas produces insulin

  3. Insulin triggers body cells to take up glucose from blood

  4. Insulin triggers liver and muscle cells to store excess glucose as glycogen

  5. Blood glucose concentration returns to normal
• Type 1 diabetes


  Pancreas does not produce enough insulin
• Symptoms of type 1 diabetes

  • Blood glucose concentration rises and stays high
• Treatment for type 1 diabetes

  Monitor blood glucose, inject insulin