Homeostasis & Feedback Loops

• Anatomy is the study of the structure of body parts and their relationship to one another
• Physiology is the study of the function of body parts; how they work to carry out life-sustaining activities
• The principle of complementarity of structure and function states that function always reflects structure
• Homeostasis is the maintenance of relatively stable internal conditions despite continuous changes in the environment
• Homeostasis is a dynamic state of equilibrium, always readjusting as needed
• It is maintained by contributions of all organ systems
• Variables are factors that can change (e.g., blood sugar, body temperature)
• Negative feedback mechanisms reduce or shut off the original stimulus
• Negative feedback is the most-used feedback mechanism in the body
• Examples of negative feedback include the regulation of body temperature and blood glucose by insulin
• Positive feedback mechanisms enhance the original stimulus
• Positive feedback usually controls infrequent events that do not require continuous adjustment
• Examples of positive feedback include enhancement of labor contractions by oxytocin and platelet plug formation and blood clotting
• Body temperature is regulated by a negative feedback mechanism
• When body temperature rises, the response includes shivering and vasoconstriction to reduce the temperature
• When body temperature falls, the response includes evaporation of sweat and vasodilation to increase the temperature
• Positive feedback mechanism in the delivery of a baby
• Stimulus: labor contractions
• Receptor: stretch receptors in the cervix
• Afferent pathway: nerve impulses to the brain
• Control Center: hypothalamus in the brain
• Efferent pathway: nerve impulses to the uterus
• Effector: uterine muscles
• Response: increased contractions leading to childbirth
• The positive feedback loop eventually stops when the baby is delivered