HOMEOSTASIS
Figure 1 - 10 Homeostasis of blood glucose. Range over which a given value, such as blood glucose concentration, is maintained through homeostasis. Note that the concentration of glucose fluctuates above and below a normal value (90 mg/ml) within normal range (80 to mg/ml).
Claude Bernard (1813-1878), a famous French biologist, made a startling observation more than a century ago. Only when the temperature, pressure, and chemical composition of their fluid environment remained roughly consistent could body cells stay healthy. The interior environment of cells, or milieu interieur, is what he termed it. Although many aspects of the exterior world in which we live are constantly changing, Bernard discovered that essential aspects of the interior environment, such as body temperature, are relatively consistent. A tourist flying from Alaska to Florida in January, for example, will experience substantial temperature fluctuations. Fortunately, regardless of temperature fluctuations in the external environment, a healthy person's body temperature will remain at or around the normal of 37° C (98.6° F).
The fluid environment around each bodily cell is prone to change, just as the external environment surrounding the body as a whole does. Hundreds of different chemicals are found in the specialised fluid that bathes each cell. The right and consistent amount of each chemical in the blood and other bodily fluids is essential for good health, and indeed life itself. The internal environment's exact and consistent chemical composition must be kept within very restricted limitations ("normal ranges"), or disease and death would ensue.
Walter B. Cannon, a well-known American physiologist, coined the term "homeostasis" (ho-me-o-STA sis) to describe the body's largely consistent states in 1932. In contemporary physiology, the term "homeostasis" is used often. It is made up of two Greek words (homoios, "the same", and stasis, "standing"). The literal meaning of homeostasis is "standing or remaining the same." Cannon established one of the most unifying and essential concepts of physiology in his famous book The Wisdom of the Body. He said that the body's regulatory mechanisms were all designed to keep the body's internal environment in a state of homeostasis, or consistency. However, as Cannon pointed out, homeostasis does not imply that anything is fixed and immovable and remains the same all of the time. "A situation that may change, yet is largely consistent," he defines homeostasis as. Homeostasis is defined as the preservation of generally consistent internal circumstances despite changes in the external environment. For example, even if external temperatures change, body temperature homeostasis means that it stays generally constant at around 37° C, even if it varies slightly above or below that threshold and remains "normal."
The fasting blood glucose concentration, an essential nutrient, can also change somewhat while being within acceptable ranges (Figure 1-10). Depending on food consumption and meal time, a value of 80 to 100 mg per 100 ml of blood is normal. Although oxygen and carbon dioxide levels vary with respiratory rate, these chemicals, like body temperature and blood glucose levels, must be kept within extremely strict limitations. Adjusting bodily systems to preserve homeostasis is the responsibility of certain regulatory processes. The body's capacity to "self-regulate," or "return to normal," in order to preserve homeostasis, is a crucial notion in modern physiology, and it also serves as a foundation for understanding disease processes.
In order to maintain homeostasis, each cell of the body, each tissue, and each organ system must work together. Homeostasis will be explained as a function of each of the several regulatory systems described in later chapters of the work. You'll discover how particular regulatory tasks like temperature management and carbon dioxide removal are carried out. Furthermore, knowing the link between homeostasis and healthy survival will help to explain why such processes are required.
