Homeostasis

Homeostasis Maintenance of a relatively stable internal, fluid environment (internal milieu) despite a changing external environment Temperature 37oC (98.6oF) Blood pH 7.35 Blood sugar level 0.1%

Homeostatic Control Systems 3 main components A monitor -> senses state of system A coordinating centre -> receives incoming info about system and decides what the next steps should be A regulator or effector -> carries out the appropriate next step to keep system at homeostasis Monitor sales and stock of stores and report to factory manager. Based on stocks, factory manager instructs more or less of something to be made. Works increase or decrease production of certain items.

Feedback loops Positive feedback - a mechanism by which an output is enhanced Contractions in childbirth: contractions stimulate oxytocin which stimulates more muscle contractions Negative feedback mechanism consists of reducing the output or activity of any organ or system back to it's normal range of functioning. Blood vessels can sense resistance of blood flow against the walls when blood pressure increases. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both are the effectors. The heart rate would decrease as the blood vessels increase in diameter. This change would result in the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases.

Negative feedback - a mechanism by which an output is diminished Any change from normal range of function is resisted in negative feedback. The change initiates responses that bring the function of the organ back to its normal range. Negative feedback loops require a Receptor, A Control Center, and Effectors.

Negative Feedback Loop

Blood vessels have receptors which can measure the resistance of blood flow against vessel walls The brain (control center) receives info about change in body’s internal conditions, sends out signals via nerves Effectors - the muscles, organs, and other structures that receive signals from the control center and respond to correct the deviation.

Example of Negative feedback: Blood Pressure Regulation Negative feedback mechanism consists of reducing the output or activity of any organ or system back to it's normal range of functioning. Blood vessels can sense resistance of blood flow against the walls when blood pressure increases. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both are the effectors. The heart rate would decrease as the blood vessels increase in diameter. This change would result in the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases.

Thermoregulation (see next presentation)

Positive Feedback In a positive feedback system, the output enhances the original stimulus. For example, during labor, a hormone called oxytocin is released that intensifies and speeds up contractions. The increase in contractions causes more oxytocin to be released and the cycle goes on until the baby is born. The birth ends the release of oxytocin and ends the positive feedback mechanism.

Positive Feedback Another good example of a positive feedback mechanism is blood clotting. Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed.