According to Science NetLinks, cells convert energy for your body and continually divide to make more cells for growth and repair. The body has about 200 different types of cells, and specific cells have assorted jobs to do. The various shapes of body cells depends on each cell's job.
Cells that do the same job combine together to form body tissue, such as muscle, skin or bone tissue. Groups of different types of cells make up the organs in your body, such as your heart, liver or lungs. Red blood cells contain the protein haemoglobin, which carries oxygen around your body, and white blood cells defend the body against infection and disease. Brain cells communicate by sending tiny electric signals to each other; the more signals that are sent, the more electricity the brain will produce. Regular exercise does not help you gain more muscle cells; instead it makes each cell grow bigger and stronger. Smooth muscle cells function to maintain organ dimensions and regulate the diameter of the arteries, and they also have the ability to rhythmically contract, allowing them to propel substances such as foods through the digestive system, blood through the vessels and air through the bronchial tubes. As is the case with any living thing, body cells do die. Your body is constantly replacing old cells with new ones at the rate of millions per second.