Maintaining Life

Survival Needs  Nutrients Consumed chemical substances that are used for energy and cell building

Survival Needs cont.  Oxygen Required by the chemical reactions that release energy from foods

Survival Needs cont.  Water The most abundant chemical substance in the body Provides an environment for chemical reactions Fluid medium for secretions of the body to occur at the proper rate.

Survival Needs cont  Normal Body Temperature Required for the chemical reactions of the body to occur at the proper rate

Survival Needs cont  Atmospheric Pressure Must be within an appropriate range so that proper gas exchange occurs in the lungs

Homeostasis  Homeostasis: All body systems working together to maintain a stable internal environment  Failure to function within a normal range results in disease

Mechanisms of Regulation  Autoregulation (intrinsic): automatic response in a cell, tissue, or organ  Extrinsic regulation: responses controlled by nervous and endocrine systems

Homeostatic Control Mechanisms  Receptor: receives the stimulus (monitors changes in the environment & sends information to the control center)  Control center: processes the signal and sends instructions (determines the set point, analyzes input, & coordinates response)  Effector: carries out instructions (directed by control center)

Maintaining Normal Limits

Negative Feedback Mechanisms  The response of the effector negates the stimulus (causes the variable to change in a way that opposes the initial change)  Most homeostatic control mechanisms are negative feedback

Negative Feedback Mechanisms cont.  Both the nervous system & the endocrine system are important to the maintenance of homeostasis  Goal of negative feedback is to prevent sudden, severe changes in the body

Positive Feedback Mechanisms  The response of the effector reinforces the stimulus

Positive Feedback Mechanisms cont.  A positive feedback mechanism causes the variable to change in the same direction as the original change, resulting in a greater deviation from the set point  Typically activate events that are self- perpetuating  Most positive feedback mechanisms are not related to the maintenance of homeostasis

Working Together

 Systems integration: systems work together to maintain homeostasis

KEY CONCEPT  Homeostasis is a state of equilibrium: opposing forces are in balance  Physiological systems work to restore balance  Failure results in disease or death