Human Body Systems and Homeostasis Chapter 8 1

Human Body Systems and Homeostasis Chapter 8. 1 Mc. Graw-Hill Ryerson Biology 12 (2011)

Homeostasis • Maintenance of a relatively stable internal, fluid environment (internal milieu) despite a changing external environment • Temperature 37 o. C (98. 6 o. F) Blood p. H 7. 35 Blood sugar level 0. 1% http: //www. lionden. com/homeostasis. htm • Critical for survival since proteins, enzymes, etc, require optimal conditions for operation

Homeostasis Example: • Blood glucose levels rise after a meal thus endocrine system works to lower it to normal • Blood glucose levels fall during a fast thus endocrine system works to raise it to normal by resorting to glycogen supply in the liver

Homeostatic Control Systems • Homeostasis relies on a feedback system: cycle of events in which a variable* is monitored assessed and adjusted • 3 main components of feedback system – A sensor -> senses state of system – A control 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 *Variable can be tempearture, blood p. H, blood glucose level, etc.

Positive Feedback System • A mechanism by which an output is enhanced – Contractions in childbirth: contractions stimulate oxytocin which stimulates more muscle contractions

Positive Feedback System • What positive feedback actually does is push the variable even further away from the normal – The system is pushed to the extreme until the ordeal is over – Positive feedback is not very commonly seen – Negative feedback systems are much more common in organisms

Negative Feedback System • a mechanism by which an output is diminished – The system resists change thus will initiate a response to bring it back to normal range – Negative feedback loops require a Receptor, A Control Center, and Effectors

Negative Feedback System

Negative Feedback System E. g. – 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. Sweating when hot Shivering when cold

Homework • Pg. 348 #1, 2, 7, 8, 9