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

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 - 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

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.