Stem Cells: Types, Characteristics, and Applications

Stem cells (or stem cells) are cells that have not completed their differentiation, either by being part of an embryo a few days old, or by being part of nature's reserves of immature cells in the adult organism.

Characteristics of Stem Cells

The key characteristics of stem cells are:

1. Self-renewal: The ability to produce more stem cells.
2. Differentiation: The origination of daughter cells of various types, which are converted by differentiation into specialized cell types.

Different Types of Stem Cells

Stem cells can be classified into the following types:

Totipotent Cells

There are about two hundred types of specialized cells, and all of them originate from unspecialized stem cells or differentiated cells. The first cell of every living thing, the egg or zygote, is totipotent because it generates the embryo and therefore the entire body. This potential can be maintained artificially in some of the cells that come from the first four divisions (morula).

Pluripotent Cells

Five days after fertilization, the blastocyst is obtained. There is already a first specialization, with the emergence of a superficial layer that gives rise to the trophoblast, which forms the placenta, and a nearly empty cavity (filled with fluid) which is the inner cell mass. The cells of the inner cell mass are pluripotent because they give rise to the complete fetus with all tissues and cell types in the adult.

Although the cells of the inner cell mass of the blastocyst are pluripotent, they are not themselves embryonic stem cells because they do not remain as such indefinitely in vivo, but differentiate into different cell types during the stage of development in the womb. When extracted from the embryo and cultured in vitro, under certain conditions, stem cells become endowed with two properties: self-renewal and differentiation capacity.

Multipotent Cells

In differentiated adult tissues, multipotent stem cells exist that can produce cells of one or more types of tissues. They are found in the red bone marrow and skin, and their existence has been discovered in all tissues. They are reserves that nature has left for the repair of tissues. In bone marrow, there is also a pluripotent cell type. Therefore, stem cells can be of two types:

Embryonic Stem Cells

These are undifferentiated cells from the inner cell mass of the blastocyst, which remain as such in laboratory culture, and under certain stimuli can lead to populations of differentiated cells.

Adult Stem Cells

These are undifferentiated cells found in differentiated tissue, and whose specific function remains in the body as a reserve for the repair of tissues and organs. The adult stem cell can renew itself and, with certain limitations, differentiate to give rise to cells of the same or other types of tissue from which it comes.