In spite of the variations in the external environment, the intensity of these substances in body fluid stays unaffected. (Homeostasis {hohm-ee-oh-stay"-sis}).

             For the existence of a cell, homeostasis is necessary and each cell provides as part of body system to homeostasis. (Topic: Concepts and Themes of Human Physiology) Homeostasis relies on the body's incessantly working of many actions. Its main activities or functions are reacting to variation in the body"s environment, exchanging materials between the environment and cells, metabolizing foods, and incorporating all of the body"s miscellaneous activities. Over the years, the capacity of the body to do many of its functions changes slowly. Generally, the body performs its duties perfectly at both ends of life – in infancy and old age. At childhood, body works effectively and efficiently. At late maturity and old age the reverse is true. Slowly they become less and less able and operational. They usually work with utmost efficiency and effectiveness at young adulthood. (Body Functions and Life Process) Homeostasis of Some Body Parameters is essential for Life. Homeostasis is the perseverance of body conditions in a stable steady state and the cells of the body need specific conditions to live and function. Some of the body parameters kept in a steady state: Body temperature is controlled close to 37 deg C and Blood pH is kept at 7.4. Arterial blood pressure is retained around 120/80 mm Hg. (Lecture 21: Control of Physiological Functions: Homeostasis) .

             In human beings, many organs check homeostasis in the blood that gives fluid for all tissues. The kidney controls urea, pH and water concentration. The lungs control oxygen and carbon dioxide. The liver and the skin control temperature. The liver and the pancreas control the glucose levels in the blood. Body cells must be in ambiance where the conditions do not vary much and never reach tremendous that are harmful to them.