HOMEOSTASIS AND FEEDBACK CONTROL pp 1041-1042

HOMEOSTASIS REVIEW Homeostasis: maintaining stable internal environment Bringing body back to normal

FEEDBACK MECHANISMS Process that uses the conditions of one component to regulate the function of the other Part of a chain of cause-and-effect that forms a circuit or loop

Four Parts to A Feedback Loop Stimulus: A change to the baseline condition (set point) Receptor: an organ or structure that monitors a specific condition Control Center: An organ that process the change or information from the receptor and determines next action. Effector: Receives directions from the control center and produces a response that changes condition.

POSITIVE FEEDBACK The product stimulates production (amplify) of the initial stimulating substance or action until the stimulus or change is gone (i.e. contractions during labor)

Negative feedback: the product (response) stops production of the initial stimulus to bring back to normal NEGATIVE FEEDBACK

At the Molecule Level In a series of enzyme mediated reactions, the last product (molecule) made will inhibit the activity of the first enzyme

At the Organ System Level Many organs, chemical signals, and tissues work together to slow or stop the initial stimulus or change to the body QUESTION: What does your body do when you are hot? When you are cold?

Integumentary system The subcutaneous layer (fat cells) and body hair provide insulation against heat loss The dermis (inner layer) contains blood vessels, nerves, hair follicles, oil glands, and sweat glands (for cooling) Melanocytes in the epidermis produce melanin for protection from the sun

Muscular system Shivering is the uncontrollable activity of muscles contracting When the myosin “heads” walk along the actin ATP is required to walk and to release along the action Using ATP generates heat

Figure 40.8 A nonliving example of temperature regulation: control of room temperature. 14

NEGATIVE FEEDBACK cont Most of the systems use negative feedback to bring the body back to the set point Negative feedback consists of two loops to form a “figure 8”. This addresses both extremes away from a set point (ie. Thermoregulation, urine production) NEGATIVE FEEDBACK cont