Cell, rod: A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provides side vision and the ability to see objects in dim light (night vision).
By contrast, the cones are the retinal photoreceptors that provide color vision and sharp central vision.
- Cell, stem
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 […]
- 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 — […]