BIO 264 Homeostasis Definitions

Afferent Pathway

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.

Homeostatic Control System

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.

Effectors

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 muscle (shivering), sweat glands (sweating) and blood vessels. 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, call a fever. This increase in temperature aids the immune system in eliminating the pathogen.

Homeostasis

Homeostasis then, by definition, is the ability of the body to maintain relatively stable internal conditions (internal environment) even though the outside world (external environment) is changing. The internal environment is defined as the fluid that surrounds the cells. An inability to maintain homeostasis may lead to death or diseases such as: diabetes, dehydration, hyperthermia, and even allergic reactions.

Efferent Pathway

If information flows from the control center to the effector, it is termed an efferent pathway.

Receptor

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.

Control Center

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.

Set Point

One of the defining features of warm blooded animals like humans is the ability to maintain a core body temperature that is different from the environmental temperature. The average human body temperature is 98.6°F (37°C), and the body exerts a fair amount of energy ensuring that this temperature stays relatively constant; we call this the set point for body temperature. Different set points for different systems are found throughout the body. For instance, the set point for glucose (blood sugar) is 85 mg/dl and the set point for sodium is 142 mmol/L.

Variables & Normal Range

The body uses a variety of organs and organ systems to help ensure that certain variables remain as close to their set point value as possible, or at least within a normal range. For example, without the assistance of clothing the human body has a remarkable capacity for keeping the variable of body temperature between 98°F and 100°F even when placed in environmental conditions that range from 68°F to 130°F. How does the body stay warm at 68°F and cool at 130°F?

Stimuli

When conditions cause a change in a variable, we call them stimuli.