You scrape your knee so deeply that it bleeds. Later a scab forms over the wound. When the scab falls off, you have new skin underneath. Where did the new skin come from?
When you fall and scrape your knee, blood seeps through the surface of your injury; antibodies, clotting proteins and blood cells rush to the rescue for a quick self-repair (as long as you haven’t been injured too badly). A blood clot forms in the tissue, and begins to form a protective shield over your scrape as it hardens, that will remain throughout the duration of the healing process. Underneath this, your skin cells will begin dividing in order to allow growth within the individual cells that have split. For this to happen, your body must send signals within and throughout the cells that tell which cells to divide. Chemical signaling is also how your cells know when you’re all healed and they can stop dividing. Before a cell divides, it’s nucleus must divide and DNA must be copied; this process is called the interphase. In DNA replication, a chromosome splits, and after this division the cell contains two identical double helix DNA strands.
The duplication of somatic (body) cells is called Mitosis. The first step of mitosis technically happens before the mitotic phase actually begins, but it is called the prophase. During the prophase, the cell prepares for mitosis by making chromatids (both of the threadlike strands which a chromosome divides into) more dense, and protein structures start to move into place as the nuclear envelope begins to dissolve. Next comes the metaphase; this is when the chromatids line up at the “equator” (middle) of the cell, and a spindle-like figure is formed. This leads us to the anaphase, where your chromatids begin to separate and all your free chromosomes move to opposite ends of the cell. Lastly, you undergo the telophase. In this phase, two nuclei are formed and cell “cleanup begins”. Your cells are now beginning to divide! Cytokinesis is what it’s called when mitosis is finally complete, and the cell moves apart to become two identical cells. This will continue until all your cells are surrounded with other healthy cells and they will receive the chemical signal to stop reproducing. Your scab will fall off (or be picked off) and new healthy skin will be visible again.