What is the difference between positive and negative feedback? (Use the article attached) CLINICALSYSTEMS OF LIFEHomeostasiS Part 1: anatomy and physiologyAUTHORS Brendan Doherty, MSc, PGCE, RN, isExtracellularfluidArteryPlasmanurse patient access manager, Prince of WalesHospital, Sydney, Australia; Colette Foudy, RN,GradDip, is clinical care coordinator, intensive careunit, St George Private Hospital, Sydney, Australia.This article, the first in a series of four, looks at theanatomy and physiology of homeostasis.Homeostasis comprises the dynamic processes thatenable optimum conditions to be maintained forcells, in spite of continual changes taking placeinternally and externally (Clancy and McVicar, 1995).ArterioleCellAll the systems of the human body are involved,with particular contributions by the endocrine,Venulecapillarynervous, respiratory and renal systems. Whenever animbalance occurs, regulatory systems become activeto restore optimum conditions, usually by a processknown as negative feedback in which a deviationfrom the normal level is detected and initiatesCapillaryFIG 1. EXTRACELLULARFLUID AND BLOOD VESSELSVeinchanges that bring the level back to where it shouldbe (Clancy and McVicar, 1995). These systems have toendure for survival and adapt to modifications of theBrainEarPineal gland-Hypothalamusenvironment so must therefore evolve.EyesTaste and smell -Spinal cordThyroid-- PituitaryAnatomy and physiologyMany factors affect the suitability of body fluids tosustain life. These will be explored later in this series.They include:• Oxygen (0,) and carbon dioxide (Co,)sensors- ThymusAndrenalsconcentrations;• The pH of the internal environment;• Concentrations of nutrients and waste products;• Concentration of salt and other electrolytes(osmoregulation);• Volume and pressure of extracellular fluid;• Body temperature;• Blood glucose level.As these properties affect the chemical reactions thatsustain life, there are built-in physiological mechanismsto maintain them at desirable levels. The body needshomeostasis to maintain stability and survive byensuring that the internal environment remainsrelatively constant (Tortora and Anagnostakos, 2003).To enable cells to survive, the composition of thePancreasOvariesSkinTestessensorsNervesintracellular and extracellular fluids must beaccurately maintained at all times. Intracellular fluidaccounts for two-thirds of total water content (Tortoraand Anagnostakos, 2003). Extracellular fluid includesgases, nutrients, plasma (in blood vessels) and ions,all of which are necessary for maintaining life(Tortora and Anagnostakos, 2003) (Fig 1).Extracellular fluid circulates constantly withinNERVOUS SYSTEMENDOCRINE SYSTEMFIG 2. THE ENDOCRINE AND CENTRAL NERVOUS SYSTEMS KEYWORDS Anatomy and physiology Homeostatic controlNegative feedbackHomeostasis is constantly disturbed by externalfactors, which can be described as a form of stresson the internal environment (Tortora andAnagnostakos, 2003). These stresses can be:• Internal: occurring within the body, for example inpain, or as a result of high or low blood pressure;• External: occurring outside the body, for example asa result of heat, cold or loud noises.the blood and lymphatic system and is known as'the body's internal environment' (Tortora andAnagnostakos, 2003).The body is said to be in homeostasis when itsREFERENCESBodyguide (2005) EndocrineSystem. www.besthealth.com/bestheolth/bodyguide/reftext/html/endo sys_fin.htmlshomeostatic.internal environment contains:• Optimum levels of gases, ions, water and nutrients;• Is at optimal temperature;• Has optimal pressure for the health of cells.A disturbance in these optimum conditions causesfailure of the organs and may lead to death (Tortoraand Anagnostakos, 2003).Clancy, J., McVicar, A. (1995)Physiology and Anatomy:A Homeostatic Approach.Since these stresses affect the chemical reactionsLondon: Edward Arnold Publishers.sustaining life, there are built-in physiologicalmechanisms to maintain or return them toDocherty, B. (2005) Thearteriovenous system: part one, theanatomy. Nursing Times; 101: 34,28-29.Homeostatic controlThe endocrine and central nervous systems arethe major control systems for regulating homeostasis(Tortora and Anagnostakos, 2003) (Fig 2). Theendocrine system consists of a series of glandsthat secrete chemical regulators (hormones). Thenervous system can detect deviation from thebody's normal equilibrium (state of homeostasis)and sends messages to the affected organ tocounteract this disturbance. Over a relativelyshort time it restores the required balance. Bothdesirable levels.Each organ or structure has its own intrinsic wayof keeping the internal environment within normallimits. When homeostasis is altered there are twopossible responses:• In negative feedback the system respondsto reverse the direction of change. As this tendsto keep things constant, it allows the maintenanceof homeostasis. For example, if there is a fallin calcium in the blood, the parathyroid glandssense the decrease and secrete more parathyroidhormone, thereby increasing calcium release fromthe bones;• Positive feedback increases the variable in theDocherty, B. (2002)Cardiorespiratory physicalassessment for the acutely ill: partone. British Journal of Nursing;11: 11, 750-758.systems act mostly automatically but there is somevoluntary control over the nervous systemSherwood, L. (1997) HumanPhysiology: From Cells to Systems.Pacific Grove, CA: West Publishing.(Sherwood, 1997).The control and maintenance of blood sugar levelsis an example of homeostatic regulation by thesame direction, a destabilising effect that doesnot result in homeostasis. Positive feedback is usedwhen rapid change is needed. For example inchildbirth the hormone oxytocin is produced toTortora, G.J., Anagnostakos, N.P.(2003) Principles of Anatomy andPhysiology. New York, NY: JohnWiley and Sons.endocrine system. Blood sugar is maintained by twohormones secreted by the pancreas: insulin andglucagon. Blood sugar rises after digestion of food. In stimulate and enhance labour contractionsresponse, pancreas cells are stimulated to secreteinsulin, which enables sugar uptake by cells and thestorage of sugar in the liver and muscles. In effect,insulin decreases blood sugar levels to normal(Tortora and Anagnostakos, 2003).The respiratory system provides an exampleof homeostatic regulation by the nervous system.In normal breathing there is a state of homeostasis.During exercise the respiratory system must workfaster to keep the 0, in the extracellular fluid andin the cells within normal limits, preventing excessivebuild-up of CO, and disturbance to the blood pHthrough the accumulation of acid (Tortora andAnagnostakos, 2003). Because muscles requiremore 0, during exercise, more CO, is released andtherefore also needs to be excreted (Tortora andAnagnostakos, 2003).These chemical changes are detected in certainnerve cells, which send this message to the cardio-respiratory centre in the medulla oblongata inthe base of the brain (Docherty, 2002). The brainsends a message to the heart to increase its pumpingaction (heart rate) to take on more 0, and enablethe blood to give up excess CO,. Respiratory musclesalso receive instructions from the brain to contractfaster, enabling a rise in both 0, delivery andCo, exhalation.(Bodyguide, 2005).Components of homeostasisA system requires three components for homeostasis:A receptor;A control centre;An effector.These components do specific jobs that allowregulation of the internal environment.A receptor detects external changes that couldinfluence the internal environment. For example,the following are involved in the regulation ofblood pressure:• Receptors are in the baroreceptor system;• The control centre is the medulla oblongata;• The effector is the cardiovascular system.When there is an increase in heart rate more bloodis pumped into the arteries resulting in an increase inblood pressure (Docherty, 2005). This is detected bythe baroreceptors, which are located in the walls ofcertain arteries.These receptors send impulses to the controlcentre (the medulla oblongata), which interpretsthe message and sends impulses to the effectors(the cardiovascular system). These slow thepulse, decreasing blood pressure (Tortora andAnagnostakos, 2003). mThis article has been double-blindpeer-reviewed.For related articles on this subjectand links to relevant websites seewww.nursingtimes.net

Question

Accepted Answer

The stable state of internal circumstances that living organisms maintain is known as homeostasis.