Stem cells, one of the most fascinating areas of biology, are cells which are not terminally differentiated. They produce cells of other types that can grow to specific tissues or organs. There are two types of stem cells: embryonic stem cell, and adult (somatic) cell. Embryonic stem cells are s primitive type of cell that can be developed into most or all of the 220 types of  cells found in the human body. They are further diveded into three categories: totipotent, pluripotent and multipotent. A singke totipotent stem cell can grow into an entire organism, pluripotent stem cells to any organ in the body and multipotent stem cells to only a particular types of cells. Adult stem cells bearing some similarities to embyonic stem cells are originated from bone marrow and skin cell.

Stem cell are used in the treatment and cure of many human diseases and disorders including Alzheimer's, diabetes, cancer, etc. The stemcell research holds great promise of improving human health by control of degenerative diseases and restoration of damage to organs by varios injuries; but at the same time it also raises several ethical and social issues such as destruction of humahn embryos to create human embryonic stem (HES) cell lines, potentialfor introducing commodification in human tissues and organ with inherent barriers of access to socio-economically deprived  and possible of technology for germ- line engineering and reproductive cloning. The  research in this field, therefore, needs to be regulated to strike a balance. There are no appoved treatments or human trials using embryonic stem cell. Neverthless, some are of the opinion that the differentiation potential of embryonic stem cell is broader than modt ault stem cells.

Stem cells provide huge potential for finding treatments and cures to a vast array of diseases including, different cancers, diabetes, spinal cord injuries, Alzheimers, MS, Huntingtones, Parkinsons and more.

Pros and cons :

Every technology has its own advantages and disadvantages. \but benefits always outweighs risk, so is the case with stem cell research. The excitement about stem cell research is primarily due to the medical benefits in areas of regenerative medicine and therapeutic cloning. There is endless potential for scientists to learn about human groeth and cell development from studyin stem cells. Use of adult-derived stem cells, from blood, skin and other tissues, has been demonstrated to be effective for treating different diseases in animal models. Some trials in human are also in progress and proved effective. Blood from the placenta and unbilical cord of new-born babies is a useful source of adult stem cells. Since 1988 these 'cord blood' stem cells have been  used to treat Gunther's disease, Hunter syndrome, Hurler syndrome, acute lympocytic leukemia and many more problems mostly in children.

But some disadvanteges or shortcomings including short-life of embryonic cell lines and vast money invested are not technically considered individual living beings by pro-life advocates. Further, the use of embryonic stem cells from research involves the destruction of blastocytes formed from laboratory-fertilized human eggs. For those who believe that life begins at conception, the blastocyst is a human life and to destroy it is unacceptable and immoral. This seems to the only controversial issue standingin the way of stem cell research . Many countries ban research on stem cell  and cloning or they are  tightly regulated.