stable and balanced environment of a living organism. It includes all physiological processes and conditions that ensure the normal functioning of cells, tissues and organs. It is a set of vital and dynamic interactions that occur in the body to maintain homeostasis, which is the stability of vital factors such as temperature, fluid levels, salt balance, blood pressure, and oxygen and carbon dioxide levels. The internal environment serves as the “internal biosphere”, providing the necessary conditions for the effective functioning of cells and protecting them from sudden changes in the external environment. For example, when the body experiences a rise or decrease in temperature, its systems, such as the nervous, circulatory, and endocrine systems, adjust their functions to maintain the blood temperature within normal limits.