Cell, stem: An ancestral cell, the most primitive type of cell.
Stem cells are relatively unspecialized (undifferentiated) cells that are characteristically of the same family type (lineage). They retain the ability to divide throughout life and give rise to cells that can become highly specialized and take the place of cells that die or are lost.
Stem cells thus contribute to the body’s ability to renew and repair its tissues. Unlike mature cells, which are permanently committed to their fate, stem cells can both renew themselves as well as create new cells of whatever tissue they belong to (and other tissues).
Bone marrow stem cells, for example, are the most primitive cells in the marrow. From them all the various types of blood cells are descended. Bone marrow stem-cell transfusions (or transplants) were originally given to replace various types of blood cells.
Stem cells from bone marrow can also, quite remarkably, give rise to non-marrow cells. In a 1999 report in the journal Nature, scientists from Boston led by Dr. Louis M. Kunkel reported that they gave bone marrow transplants from normal mice to dystrophic mice. Some 12 weeks later about 10% of the muscle fibers in the diseased animals were making the correct form of dystrophin, the protein that is defective in Duchenne muscular dystrophy. This work suggests that bone marrow stem cells may offer new ways of treating muscular dystrophy (and other non-blood diseases).
- Cell, T-4
Cell, T-4: A type of T cell that has CD4 markers on its surface and participates in the immune response by recognizing foreign antigens and secreting substances called cytokines that activate T and B cells. T-helper cells fall into two main classes: those that activate other T cells to achieve cellular inflammatory responses; and those […]
- Cell, totipotent
Cell, totipotent: A cell with the capacity to form an entire organism. Human development begins when a sperm fertilizes an egg and creates a single totipotent cell. In the first hours after fertilization, this cell divides into identical totipotent cells. Approximately four days after fertilization and after several cycles of cell division, these totipotent cells […]
- Cells, germ
Cells, germ: The eggs and sperm are the germ cells: the reproductive cells. Each mature germ cell is haploid in that it has a single set of 23 chromosomes containing half the usual amount of DNA and half the usual number of genes. Except for the eggs and sperm, each cell in the human body […]
- Cells, reproductive
Cells, reproductive: The eggs and sperm are the reproductive cells. Each mature reproductive cell is haploid in that it has a single set of 23 chromosomes containing half the usual DNA amount. Except for the eggs and sperm, each cell in the human body — there are 100 trillion cells in each of us — […]
- Human genome
Human genome: All the genetic information in a person. The human genome is made up of the DNA in chromosomes as well as the DNA in mitochondria.