PRINSIP HOMEOSTASISRAHMATINA B. HERMANFakultas Kedokteran Universitas Andalas

The Good HealthThe good health was somehow associated with a balance among the multiple life-giving forces (humours) in the bodyPhysiologistFrom the earliest (at least the time of Aristotle)

The Good HealthWhat is being balanced ?How the balanced can be achieved

Living tissue is composed of trillions of small cellsPackaged in such a way to permit movement of certain substances across the cell membraneThe advent of modern tools of science including ordinary microscope:

The bodys internal environment is the extracellular fluid surrounding cells (interstitial fluid)Most cells are in contact with the interstitial fluidThe interstitial fluid was found to be state of flux, with chemicals, gases and water traversing it in two directions back and forth between the cell interiors and the blood in nearby vessels (capillaries)Over the course of the 19th and 20th century,it became clear that:

Plasma(3 L,20% ofECFInterstitial fluid(11 L, 80% of ECFIntracellular fluid(28 L, 2/3 TBW)Extracellular fluid (ECF)(Internal environment)(14 L, 1/3 TBW)Total body water (TBW)(42 L, 60% body weight)

Healthy organisms: most of the common physiological variables found in normalBlood pressure, body temperature, blood-borne factors (ex: oxygen, glucose, natrium) are maintained at relatively steady statesDespite external environmental conditions being far from constantFurther determined by careful observation:

The Good HealthA constant internal milieu is a prerequisite for good healthClaude BernardFrench Physician and Physiologist

The Good HealthHomeostasis !!!Walter CannonAmerican Physiologist

HomeostasisGreekHomeo - = same, similar, unchanging- stasis = maintaining a constant levelHomeostasis = a tendency to equilibrium or stability in the normal physiological state of the organism

Compensatory mechanismNegative feedback mechanismMost physiological variables cannot be absolutely constant over long periods of timeNormal range

Homeostasis is a dynamic process !!!Homeostasis relatively constantTime-averaged meanHomeostasis must be described differently for each variable

One variable/system becomes out of balance Other variables/systems in the body become non-homeostaticJust one non-homeostatic variable, can have life-threatening consequences!!!!!!!triggering

The Good HealthAll the major organ systems are operating in homeostatic manner

When homeostasis is maintained it is referred tophysiologyWhen homeostasis is not maintained it is referred topathophysiology

How quantify homeostasis?Determine time-averaged meansRely on values obtained from large populations of healthy subjectsDistibuted according to age, sex, weight, and other characteristic

Processes related to homeostasisAdaptation and acclimatizationBiological rhythms: circadian rhythmsRegulated cell death: apoptosisBalance in the homeostasis of chemicals

FoodAirGI tractLungsSynthesis in bodyStorage depotsPOOLReversibleIncorporationInto othermoleculesMetabolismExcretion from bodyVia lungs, GI tract,Kidneys, skin,Menstrual flowBalance diagram for a chemical substanceNet gain to bodyDistribution within bodyNet lossfrom body

SUMMARYThe bodys internal environment is the extracellular fluid surrounding cellsThe function of organ systems is to maintain the internal environment relatively constant homeostasisNumerous variables within the body must be maintained homeostaticallyWhen homeostasis is lost for one variable, it may trigger a series of changes in other variables.