Aging is process that begins at maturity and ends with death.  While all adults are aging, the initial affects of aging for a person is their 20s are typically minimal.  Culturally we have defined 40 years of age to be significant and in fact biologically speaking this is also when aging tend to become noticeable.  By definition individuals above the age of 60 are elderly, but individual organs age at different rates and any specific organ does not age at the same rate in different individuals.  Consequently individuals of the same chronological age may have vastly different physiological ages, which is a measure of functional capacity.  An individual’s aging process will be determined by a combination of his genetic makeup and environmental factors.

Each body system will be studied in depth throughout this course and in general each system’s capacity to function is reduced as an individual ages.  Additionally, while the decreased functionality of body systems is a normal part of the aging process and does not by itself cause disease the relationship between aging and disease is well known.  The older one gets the more likely one is to die from a major disease.  This is largely due to the fact that as the body ages it has a reduced capacity tolerate physiological stress and maintain homeostasis.

Maintaining homeostasis requires that the body continuously monitor its internal conditions. From body temperature to blood pressure to levels of certain nutrients, each physiological condition has a particular set point. A set point is the physiological value around which the normal range fluctuates. A normal range is the restricted set of values that is optimally healthful and stable. For example, the set point for normal human body temperature is approximately 37°C (98.6°F) Physiological parameters, such as body temperature and blood pressure, tend to fluctuate within a normal range a few degrees above and below that point. Control centers in the brain play roles in regulating physiological parameters and keeping them within the normal range. As the body works to maintain homeostasis, any significant deviation from the normal range will be resisted and homeostasis restored through a process called negative feedback. Negative feedback is a mechanism that prevents a physiological response from going beyond the normal range by reversing the action once the normal range is exceeded. The maintenance of homeostasis by negative feedback goes on throughout the body at all times.