Homeostasis Maintenance of a stable internal environment.

b b Homeostasis is a state of equilibrium b b Maintains the conditions necessary to support life

Levels of Organization in the Body b Molecular b Cellular b Tissues b Organs b Systems

b b There are hundreds of monitored events in the body that must be maintained in order for the body to function efficiently. b b These conditions are maintained by feedback mechanisms

Negative Feedback b b A negative feedback mechanism tells the body to stop doing what is was doing when a monitored event goes outside of its acceptable range.

Example b b When under stress, the heart pumps harder and faster, causing blood pressure to increase. b b Baroreceptors monitor the increased blood pressure that results from the increased force and frequency of the heartbeat. b b The negative feedback mechanism stimulates the heart to decrease the force and slow the frequency of the heartbeats. b b Thus, blood pressure is restored to normal.

Positive Feedback b b A positive feedback mechanism tells the body to continue doing what it has been doing.

b b Example: When contractions begin to push the baby into the birth canal, the pressure of the baby in the birth canal stimulates increased strength of contractions. b b The forceful contractions continue until the pressure of the baby in the birth canal is removed by the baby being born.

Nervous and Endocrine Systems b b Nervous and Endocrine Systems work together or independently, deliver the signals, electrical or chemical, respectively, that cause corrective measures to occur. a. Blood sugar levels, electrolyte balance, blood pressure, internal and skin temperature, blood oxygenation levels are all examples of monitored events that are controlled by feedback mechanisms.

Methods of Gaining Heat b Metabolism b Environmental changes

Methods to Gain Heat b b 1. Internal heat production (thermogenesis) b b a. Muscle contraction b b b. Other metabolic activities such as digestion b b 2. Environmental changes-turning on heat, put on sweater

Methods of Losing Heat b Evaporation - converts liquid water to vapor b Conduction - direct contact between objects b Convection - conduction where one object is in motion b Radiation - loss of heat to environment due to a temperature gradient

Methods for Body Cooling b Sweating b Dermal blood vessel dilation

Methods for Body Warming b Shivering b Dermal blood vessel constriction