Human body is a self sustaining, living machine composed of over 10 trillion cells which are its structural and functional units. Human body is not always a 10 trillion celled structure. It finds its origin from a single cell- the zygote. Zygote periodically divide and differentiate as per the necessity.Cells are structurally and functionally different at different parts of our body. A group of structurally and functionally similar cells form a tissue. A tissue performs a particular function in our body.For eg: adipose tissue stores fat, areolar tissue helps in packeging etc. When tissues having similar functions combine they form an organ. Different organs co-operate in order to give a system. Human body has altogether 9 systems viz.circulatory, nervous, respiratory, digestive, urinery, reproductive, endocrine, musculoskeletal and integumentary system. A system has its specific function in our body. For eg: digestive system has its function of ingestion, digestion, absorption of nutrients and egestion of unused food. The human body what we see is a sum total of all cells working together in harmony. If this harmony is broken and chaos is created within than it is a state of deforfmity or disease.