Homeostasis Balancing the internal environment

External vs. Internal Environment What is the difference?

External environment: Your surroundings. The factors that cause your body to change in order to stay in homeostasis. (Cold outside, working out, bacteria)

Internal Environment Conditions within the fluid surrounding its body cells Comprised of self-regulating control systems – homeostatic mechanisms

Feeling Feverish?

Homeostatic Mechanisms Have three common components: Receptors – Set point – Effectors - provides information about specific conditions tells what a particular value should be Cause the response that alter conditions in the internal environment.

Response – Change Corrected Receptor Set Point Control Center Effectors Stimulus – change in external environment Homeostatic Mechanism

Negative vs. Positive feedback mechanisms

Negative Feedback Systems There is a change from the set point and negative feedback corrects this change or brings it back to normal. This correction reduces the action of the effectors until the body is back in homeostasis.

Hyperthermia Heat receptors in the skin Hypothalamus Stress Sensors Control Center Increased activity of sweat glands Increased blood flow to the skin Effectors Perspiration evaporates cooling the skin Effect Stress is reduced shutting down mechanism Homeostatic Regulation of Body Temperature through Negative Feedback

Homeostasis Using a Neural Pathway Control center Many homeostatic mechanisms use a nerve pathway in which to produce their effects. These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors.

Positive Feedback Systems Change that occurs is in the same direction as the initial disturbance. Deviation from the set point is accelerated No correction to the action of the effectors Body will shut down, however some positive feedback systems work in favor of the body – ie. Childbirth.

Positive Feedback Mechanisms Typical Positive Feedback Process Effector Intensifies Control Center Sensor Stress

Homeostatic Regulation of Child Birth through Positive Feedback Pressure of Fetus on the Uterine Wall Nerve endings in the uterine wall carry afferent messages to the Hypothalamus Production and Release of Oxytocin into the Blood Increasing strength of uterine contractions Intensifies The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

Harmful Effects of Positive Feedback Positive feedback can be harmful. A specific example of these harmful outcomes would be: Positive feedback is frequently a normal way of producing rapid change. However, positive feedback can be harmful to the body. For example, if the body temperature rises above 108 o F a dangerous positive feedback loop may be created. This high temperature will increase the metabolic rate, thus producing heat faster than the body can get rid of it. Thus, temperature rises still further, increasing metabolic rate and heat production still more. This becomes fatal at approximately 113 o F.

Some examples of what your body can regulate: Body temperature Blood pressure Oxygen needed or Respiration Heart Rate (or blood delivered to heart) Glucose level or blood sugar level.