Homeostasis

• Physiology


  Branch of biology concerned with functions of living organisms i.e. what they do to keep alive
• Physiology


  How living organisms adjust to the adversities of the environment. How they obtain enough water & food to live, how they escape extremes in temperature, move about to find suitable surroundings, food and mates and how it obtains information about its environment through its senses
• Physiology


  The regulation of all these functions - how they are correlated and integrated into a smooth functioning organism. Not only a description of function; it also asks why and how these different processes occur
• Categories of response when an animal is confronted with changes in its environment


  • Conformity
  • Regulation
  • Avoidance (spatial or temporal)
• Conformity and Regulation


  Maintenance of a constant internal environment can be achieved more cheaply by avoidance & behavioral tricks. It may not need to be achieved at all - i.e. animals adopt a conforming lifestyle - involves much less energy & resource expenditure
• Control and Integration


  Physiological processes must be controlled & not allowed to run wild. Regulate: to adjust an amount, a concentration, a rate, or some other variable, usually in order to maintain it at some desired level (e.g. rate of O2 used in respiration). Integrate: putting parts together. To control all functional components so that they merge into a smoothly operating organism where no single process is allowed to proceed at its own independent rate
• Homeostasis


  The co-ordinated physiological processes which maintain most of the steady states in living organisms, i.e. the way in which the various organ systems are integrated to maintain the constancy of the internal environment of the body
• Control & Control Theory


  Control mechanisms are responsible for maintenance of steady states in living organisms. In engineering, control systems are so important that control theory and design constitute an independent branch with its own terminology & theoretical approach. Control theory has resulted in: More precise definition of components of physiological control mechanisms, Better understanding of the relations between the component parts
• Homeostasis


  1. Receptors detect stimulus

  2. Integrator compares input to set point

  3. Effectors trigger widespread adjustments

  4. Response to maintain steady state
• Homeostasis


  The co-ordinated physiological processes which maintain most of the steady states in living organisms
• Components of homeostasis


  • Receptor (e.g. nerve ending)
  • Integrator (e.g. brain)
  • Effector (e.g. muscle, gland)
• Homeostatic response to overheating in a husky


  1. Receptors in skin detect temperature rise

  2. Integrator (hypothalamus) compares to set point

  3. Effectors (pituitary, thyroid, muscles, blood vessels, salivary glands, adrenal glands) trigger adjustments

  4. Response lowers body temperature
• Negative feedback


  Regulation of input to a system by some part of the output, to stabilize the input and maintain the system at a given level
• Positive feedback


  A deviation leads to an ever-increasing augmentation of the deviation, rather than stabilization
• Production of trypsin


  1. Pancreas releases inactive trypsinogen

  2. Trypsin activates more trypsinogen (autocatalytic activation)

  3. Trypsin inhibitor limits activation
• Physiological traits


  • Environmentally determined
  • Genetically determined
  • Combination of both
• Physiological responses on different timescales


  • Evolutionary (irreversible changes in genotype and phenotype)
  • Within individuals: Short-term/acute (no gene expression change), Long-term/chronic (physiology adapts to environment)
• Acclimatization


  Physiological, biochemical, or anatomic change within an individual animal during its life (change in gene expression, but reversible)
• Acclimation


  Same process as acclimatization, but in response to experimentally imposed changes in conditions