BIO 461 Principles of Physiology 1
1.1.2
Homeostatic Control Systems
In order to explain how homeostasis works, let us revisit changes that occur to maintain body
temperature. How does the body know when to shiver or sweat? The body first needs to detect a
temperature change. In the body, this function is attributed to a receptor, which is a type of sensor
that monitors the environment and detects changes in variables. When conditions cause a change in a
variable, we call those conditions stimuli. Once a receptor detects a change, it then communicates
this change to a control center. Control centers are located throughout the body, often in the brain,
and are responsible for determining the set point and the appropriate course of action to correct
deviations from the set point. Control centers dictate a course of action by communicating
with effectors. An effector provides the means to correct the deviation. In terms of temperature
regulation, the control center is located in the hypothalamus, a small region in the brain, and the
effectors would include skeletal muscles (shivering), sweat glands (sweating), and blood vessels
(constriction and dilation). It is also interesting that the human body can change a set point for a
particular variable. This change is generally temporary and beneficial. For example, the set point for
body temperature can change to a higher value in response to infections, called a fever. This increase
in temperature aids the immune system in eliminating the pathogen. Consider this critical thinking
question: does the set point change observed during a fever represent a negative or positive feedback
response? The answer is negative, but why?
An essential component of homeostasis is communication. Communication in the body occurs
primarily through two systems: the nervous system and the endocrine system. Regardless of the
system used, if communication flows toward the control center from the receptor, it is termed an
afferent pathway. If information flows from the control center to the effector, it is termed
an efferent pathway. Collectively, the receptor, afferent pathway, control center, efferent pathway,
and effector comprise a homeostatic control system. Essentially, all organs and tissues of the body
are part of homeostatic control systems and perform functions that help maintain the body's internal
environment.
