The body structure is composed of systems that are made up
of tissues that are also made up of cells (approximately 40 billions for
an adult body). These components work in harmony for the proper functioning of
the body.
Cells
A cell is the basic structural unit of living organisms. All
living cells arise from other cells, either by division of one cell to make two,
as in MITOSIS and MEIOSIS, or by fusion of two cells to make one, as in the
union of the sperm and ovum to make the zygote in sexual reproduction.
Tissues
A tissue is a group or layer of similarly specialized cells that
together perform certain special functions. The body consists of several
tissues classified according to its organ, e.g. connective tissue, epithelial
tissue, fibrous tissue, etc.
Organs
An organ is made-up of tissues and an independent body part
that performs specific function or functions. The body is composed of different
organs like the heart, brain, liver, pancreas, lungs, kidney, etc.
Systems
A system is a set or series of interconnected or interdependent
parts or entities that act together in a common purpose or produce results
impossible by action of one alone.
