Homeostasis

• Definition

  1. Homeo means similar
  2. Stasis means standing still
  3. Homeostasis is the ability to maintain a stable/constant internal environment (keeping things within an appropriate range)
• How does homeostasis work?

  
  

  An organism's body always monitors its internal conditions such as:

  Body temperature

  Blood pH

  Blood sugar

  Water level/balance

  Ion balance

  
  

  Their bodies respond to stimuli (cues) in their external environment and adjust their internal environment accordingly to ensure that they don't fall ill.
• Blood Temperature in Homeostasis

  • Stays around 37°C
  • Heat gained must be equal to the heat lost
• Blood pH in Homeostasis

  • (% hydronium) must be optimum.
  • If blood is too acidic or too alkaline, normal functioning cannot happen (7.35 – 7.45)
• Blood sugar in Homeostasis

  • amount of glucose in blood 70 – 100 mg/dL (milligrams (mg) per decilitre (dL))
  • When eating food, your blood sugar levels are high. To maintain the blood sugar levels, hormones like insulin and glucagon are released. When problems occur, it results in conditions such as diabetes.
• Water level/balance in Homeostasis

  • approximately 60% water (can vary between 45-75%)
• Ion Balance


  • Concentration of dissolved substances (ions such as Na, Cl, K,)
• Interdependence of Body Systems

  • All body systems rely on each other to function properly
  • If one system fails, it will affect the other systems
  • Example: The circulatory, respiratory, and integumentary systems work together to ensure your cells receive enough oxygen when exercising. Your breathing rate increases (respiratory), your heart rate increases (circulatory), and you start to sweat (integumentary system)
• Body Systems

  1. Nervous
  2. Endocrine (hormonal)
  3. Respiratory
  4. Circulatory
  5. Digestive
  6. Excretory
  7. Integumentary (skin)
• Why homeostasis is important

  • Our bodies work best under certain (optimal) conditions.
  • Our body temperature, blood pressure, water concentration and other factors need to be within certain ranges for us to function properly.
  • If they fall outside these ranges, they can become very sick, or even die.
  • People get hypothermia because the water is too cold for the body to maintain a stable internal temperature.
  • A failure to maintain homeostasis is a common trait of many diseases/medical conditions (e.g. type 1 diabetes, hypo/hyperthermia, hypertension, dehydration)
• What can you/your body do to maintain a stable body temperature when it's too cold?

  • Blood vessels constrict
  • Muscle contraction (shivering and goosebumps)
  • Wear more clothing
  • Decrease surface area
  • Heater
  • Exercise/move
  • HR/BP increase
• What can you/your body do to maintain a stable body temperature when it's too hot?

  • Sweat (blood vessels dilate)
  • Wear less clothing
  • Increase surface area
  • Aircon/fan
  • Don’t move much
  • HR/BP decrease
• Example of Maintaining Homeostasis

  • Heat gain is always equal to heat loss

  Heat Input:

  • The heat from body processes (metabolism) especially respiration of liver and muscle cells
  • Heat is gained from surroundings such by radiation and conduction

  Heat Output:

  • Heat is lost through radiation, conduction and convection to surroundings
  • Evaporation of water from skin and lungs; warm air breathed out; warm urine and feces
• Negative feedback loop

  • Reduces the response to keep within a stable/normal range
  • Control centres in the brain and other parts of the body monitor and react when the body deviates from optimum ranges
  • REVERSES a deviation
  • Maintains body parameters within normal ranges
  • Occurs all the time (continuously).
• Negative feedback loop: Example

  Stimulus: Body temperature exceeds 37°C

  Sensor: Sensors like nerve cells with endings in the skin

  Control: Temperature regulatory centre in the brain

  Effector: Sweat glands throughout body