Integration of Biological Processes

The 19th-century French physiologist, Claude Bernard (1813–1878), first recognized that all higher organisms actively and constantly strive to prevent the external environment from upsetting the conditions necessary for life within the organism.

Claude Bernard - Wikipedia

Thus, the temperature, oxygen concentration, pH, ionic composition, osmolarity, and many other important variables of our internal environment are closely controlled

. This process of maintaining a stable internal environment.is homeostasis. ¹

The stability of the body's internal environment is maintained by several physiologic controlled variables within narrow normal ranges by the presence of negative feedback control mechanisms.

The purpose of homeostasis is to provide an optimal fluid environment for cellular function

5. Homeostasis and response - THOMAS TALLIS SCIENCE

Negative Feedback Control

Negative feedback counter deviations of a controlled variable from its normal range.

It is the major control process used to maintain a stable internal environment.

A negative feedback control system has the following elements:

A set point value, which is at the center of the normal range and is treated by the control system as the target value.
Sensors that monitor the controlled variable.
A comparator, which interprets input from the sensors to determine when deviations from the set point have occurred. The comparator initiates a counter response.
Effectors are the mechanisms that restore the set point.

Using the control of blood pressure as an example:
1. The controlled variable is mean arterial blood pressure (MAP).
2. The normal set point for MAP is approximately 95 mm Hg.
3. Pressure sensors are located in the carotid sinus and relay information to a comparator located in the central nervous system.
4. If MAP suddenly changes, the activity of effectors (e.g., cardiac contractility, vascular tone, and urinary fluid excretion) is altered to restore normal blood pressure.]