Homeostasis is the ability of the body to maintain relative stability and function even though drastic changes may take place in the external environment or in one portion of the body. A series of control mechanisms, some functioning at the organ or tissue level and other centrally controlled, maintain homeostasis. The major central homeostatic controls are the nervous and endocrine systems.
Physical and mental stresses, injury, and disease continually challenge us and any of them can interfere with homeostasis. When the body loses its homeostasis, it may plunge out of control, into dysfunction, illness, and even death. Homeostasis at the tissue, organ, organ system, and organism levels reflects the combined and coordinated actions of many cells. Each cell contributes to maintaining homeostasis.
To maintain homeostasis, the body reacts to an abnormal change (induced by a toxic substance, biological organism, or other stress) and makes certain adjustments to counter the change (a defense mechanism). The primary components responsible for the maintenance of homeostasis include:
An example of a homeostatic mechanism can be illustrated by the body's reaction to a toxin that causes anemia and hypoxia (low tissue oxygen) (Figure 1). The production of red blood cells (erythropoiesis) is controlled primarily by the hormone, erythropoietin. When the body goes into a state of hypoxia (the stimulus), it prompts the heme protein (the receptor) that signals the kidney to produce erythropoietin (the effector). This, in turn, stimulates the bone marrow to increase red blood cells and hemoglobin, raising the ability of the blood to transport oxygen and thus raises the tissue oxygen levels in the blood and other tissues. This rise in tissue oxygen levels serves to suppress further erythropoietin synthesis (feedback mechanism). In this example, cells and chemicals interact to produce changes that can either disturb homeostasis or restore homeostasis. Toxic substances that damage the kidney can interfere with the production of erythropoietin or toxic substances that damage the bone marrow can prevent the production of red blood cells. This interferes with the homeostatic mechanism described resulting in anemia.
Figure 1. Homeostatic mechanism to restore levels of red blood cells
(Image Source: NLM)