Homeostasis

• Homeostasis


  The control or regulation of the internal conditions of a cell or organism
• Examples of internal conditions regulated by homeostasis


  • Water content
  • Temperature
  • pH
  • Blood pressure
  • Blood glucose concentration
• It is important for an organism to keep these internal conditions within set limits to ensure they stay healthy and to maintain optimum conditions to allow the organism to function in response to internal and external changes
• If these limits are exceeded, the organism may die
• Homeostasis maintains optimal conditions for enzyme action and all cell functions
• This ensures that reactions in body cells can function and therefore the organism as a whole can live
• Examples of homeostasis in humans


  • Control of body temperature
  • Control of body water content
• Control of body temperature in humans


  • Core body temperature kept close to 37 °C
  • Change in core body temperature of more than 2 °C can be fatal
  • Reason: would stop essential enzymes from functioning optimally
• Control of body temperature in humans


  1. Body temperature monitored by thermoregulatory centre in base of brain

  2. Skin contains temperature receptors that send impulses to thermoregulatory centre

  3. Brain coordinates cooling or heating response
• Control of body water content in humans


  1. Water loss via lungs or skin cannot be controlled

  2. Volume of water lost in urine production can be controlled by kidneys

  3. Nephrons contain tubules where water can be reabsorbed

  4. If blood water content too high, less water reabsorbed

  5. If blood water content too low, more water reabsorbed
• ADH (antidiuretic hormone)


  Hormone released by pituitary gland that affects permeability of collecting ducts to water
• Regulation of blood water content by ADH


  1. If blood water content falls below certain level, receptors detect this and stimulate pituitary to release more ADH

  2. This causes collecting ducts to become more permeable, more water reabsorbed, less urine produced

  3. If blood water content rises above certain level, receptors detect this and stimulate pituitary to release less ADH

  4. This causes collecting ducts to become less permeable, less water reabsorbed, more urine produced
• The endocrine system also plays a role in homeostasis through hormones that regulate various bodily functions.
• Negative feedback is used to maintain stability within biological systems.
• Examples of hormones include insulin, which regulates glucose levels, thyroid hormones, which control metabolism, and sex hormones, such as testosterone and estrogen, which play a role in reproduction.
• Positive feedback is used when rapid change is required but not sustained over time.
• Heat loss occurs primarily through radiation, convection, conduction, and evaporation.