AP week two

• William B. Cannon coined the term 'homeostasis' in 1929, which means 'similar standing', and further developed the concept in his book 'The Wisdom of the Body' in 1932
• Claude Bernard in 1859 wrote that 'constancy of the internal environment is a requirement of free-living animals'
• Homeostasis is the control or stabilization of the internal environment, where the internal environment of a multicellular animal is regulated within close tolerances for critical factors
• Conformers are more 'primitive' organisms restricted to constant environments, while regulators can control their internal environment and exploit physiologically hostile and variable environments
• The internal environment includes about 60% of body weight as body water, with approximately 67% being intracellular fluid (ICF) and 33% extracellular fluid (ECF), which represents the internal environment
• Intracellular fluid (ICF), interstitial fluid, plasma, and extracellular fluid (ECF) collectively make up the internal environment, with changes in ECF driving changes in ICF due to osmotic activity
• Factors like O2, CO2, Na+, K+, Ca2+, glucose, blood pH, and temperature are maintained within specific normal ranges in the internal environment for proper functioning
• Changes to the internal environment due to regulatory system failures can lead to ill health and threaten survival, as seen in cases like blockage of blood supply causing cell death within seconds
• Examples of homeostasis mechanisms include the buffering function of hemoglobin, respiratory control of CO2, maintenance of electrolytes, blood sugar regulation, acid-base balance, blood pressure regulation, and temperature regulation
• Homeostasis is maintained by feedback systems, with negative feedback being the predominant mechanism where an effector system opposes the initiating stimuli
• Negative feedback systems in homeostasis are characterized by a set point, a sensor to monitor the regulated variable, a comparator to detect errors, and an effector to bring about compensatory changes
• Examples of negative feedback systems in homeostasis include blood pressure regulation, temperature regulation, and blood sugar (glucose) homeostasis
• Homeostasis is defined as the control or stabilization of the internal environment, and it is maintained by feedback systems, primarily negative feedback mechanisms
• The vast majority of physiological systems use negative feedback because positive feedback can lead to an unstable, increasing stimulus-response cycle that can be dangerous and even lethal
• Components of the internal environment in homeostasis include extracellular fluid (ECF), intracellular fluid (ICF), plasma, and interstitial fluid (ISF)
• Illness is often due to a disruption of homeostasis, and physiological feedback systems play a crucial role in maintaining stability in the internal environment