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Western University
Physiology 2130

Physiology 2130 Module 1 Online Notes (Sec 1.1 to 1.11) Introduction to Physiology Introduction What is “Physiology”?  Physiology is the study of function in living organisms  It explores the mechanisms by which organisms control their internal environment despite what is occurring in the external environment  Physiology also attempts to explain the physical and chemical factors responsible for normal function and disease (pathology) Homeostasis – the maintenance of relatively stable conditions within the internal environment regardless of what is happening in the external environment  The internal environment is the fluid in which the cells of the body are bathed and consists of the interstitial fluid and blood plasma  The external environment is the region outside the body including the space and contents of the digestive, respiratory and urogenital tracts.  The body maintains homeostasis using negative and positive feedback control mechanism. Positive and Negative Feedback Control Systems Negative Control Systems:  Found throughout the body and perform different functions, from maintaining body temperature to maintaining body fluid volumes.  All negative feedback control systems operate in a similar manner to maintain homeostasis, which includes a set point, a control center (integrator), an effector, a controlled variable, and a sensor (receptor) Example:  The heating system in a house is negative feedback controlled  The set point would be the temperature to which the room is set (23°C)  The Sensor/Control Center (combined in this example, not combined in the body) are the thermostat  The effector is the furnace and the controlled variable is heat  The negative feedback loop begins when the temperature drops below 23°C (set point)  The sensor in the thermostat detects this change and sends a signal to the furnace (effector)  The furnace raises the temperature by producing heat (controlled variable)  When the temperature reaches the set point, the thermostat stops signaling and the furnace stops producing heat  This cycle repeats itself whenever the temperature falls below set point How does Negative Feedback control body temperature?  Set point for body temperature is 37°C (98.6°F), this is the temperature you want your body to maintain o Your actual body temperature may be different, for example, on a cold day it may drop to 35°C o This actual body temperature would be detected by sensors in the nervous system, which would signal a control center in the hypothalamus o This control center would realize that there is a difference between the pre determined set point (37°C) and the actual value (35°C) and would activate organs and systems (effector) to generate heat (controlled variable) by shivering and conserving heat by decreasing blood flow o Once the temperature goes back to 37°C the control center would st
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