Unit 1 – Homeostasis Introduction

Homeostasis Defined: The body’s ability to maintain a relatively stable internal environment Homeo = same Stasis = stand, stay

Control of Homeostasis ALL body systems work together to maintain homeostasis! The majority of homeostatic mechanisms are controlled by 2 systems: NERVOUS SYSTEM Sends nerve impulses to organs; usually messages from the brain * FASTER changes ENDOCRINE SYSTEM Secretes molecules called hormones into the blood *when released work more slowly

Homeostatic Feedback Mechanisms cycle of events through which the body’s internal conditions are monitored, reevaluated, and changed STIMULUS  any disruption in the body that causes a response (change in the human body condition) Stimuli may be external and come from outside the body or they are internal changes that occur from within

3 Basic Components of a Feedback Mechanism 1) RECEPTOR  body structure that monitors changes in the body and sends INPUT to the control center The INPUT are messages either in the form of nerve impulses or chemical signals

3 Basic Components of a Feedback Mechanism 2) CONTROL CENTER  body structure that evaluates the INPUT that it receives from receptors and generates OUTPUT as needed to be sent to the effector(s) The OUTPUT are messages either in the form of nerve impulses or chemical signals

3 Basic Components of a Feedback Mechanism 3) EFFECTOR  body structure that receives OUTPUT from the control center and produces a response (effect) that changes the condition This leads to a return to HOMEOSTASIS when the response brings the condition back to normal 

NEGATIVE VS. POSITIVE FEEDBACK Negative Feedback  REVERSES the condition to bring the body back to its normal state Positive Feedback  REINFORCES the condition *Eventually negative feedback will kick in; if the positive feedback mechanism cannot be stopped it can produce life threatening changes in the body

NEGATIVE VS. POSITIVE FEEDBACK Negative Feedback Examples  regulation of body temperature or blood pressure changes * NEGATIVE feedback is the mechanism in action in MOST instances!! Positive Feedback Examples  childbirth, blood clotting Many diseases produce positive feedback loops that overwhelm the normal negative feedback loops that maintain homeostasis