The organs such as the brain, skin, liver and kidneys have specific functions in the body. Organs are made up of tissues: tissues that are supportive and tissues carry out specific functions. These tissues in turn are made up of cells, of which billions may be found working together in the body, with their own specific functions.
Information Processing
The cells interpret internal and external information. Internal information is encoded in DNA, which tells the cell how to build proteins. According to the University of Utah, the proteins carry out chemical reactions and support the cells' specific functions. The needs of the body and the local environment around the cell change constantly, though, requiring the cell to be able to respond appropriately. The cell gathers information from many possible sources. These may include nerves, similar cells nearby, cells and chemicals of the immune system, and chemicals in the blood.
Signalling
In addition to processing information, many cells are able to send out signals, so the flow of information works in both directions. Cells of the endocrine, or hormonal, system release hormones that travel in the blood to tell distant cells how to function. A cell infected with a virus signals the immune system for help. Nerves signal muscle cells to contract. Every cell has the ability to communicate with other cells.
Mechanical Support
While all cells provide informational support, some function more toward providing mechanical support. The functional cells of the liver filter and cleanse the blood by making chemical alterations to drugs, foods and other ingested chemicals. The structural cells of the liver provide support to these cells. As another example, some cells make the hard calcium that supports bones. And a final example: The cells of skeletal muscles support the structures to which they are attached and can change length to move parts of the body.
Protection
Cells protect themselves, each other and the body. This is facilitated by their ability to interpret and send out information and at times even by mechanical support. The skin, for instance, provides a physical barrier to the outside world that protects against environmental insults such as germs, heat, and cold. Cells of the immune system also offer protection to the body by attacking invading organisms and cancerous cells.
Reproduction
Reproduction does not necessarily refer only to the sperm and eggs. Many cells are able to replicate in the process of mitosis. The cells of the bone marrow make blood cells, actively reproducing to replenish old blood cells. The cells of the intestine frequently divide to replace those that are sloughed off in the process of digestion. Other cells, such as many of the nerve cells in the brain, rarely if ever reproduce.
Energy Transfer
All of these functions and others would not be able to take place without a source of energy. The more active a cell is, whether a contracting skeletal muscle or a hormonal cell that is signaling distant cells, the more energy it needs. Cells make energy from oxygen and glucose in the blood. The energy is converted into chemicals that are easier for the cell to store and use at its discretion, mostly in a molecule called adenosine triphosphate, or ATP.
References
- The University of Utah: The Inside Story of Cell Communication
- Kimball's Biology Pages: Muscles
- Essortment: Liver Structure and Function
- National Institutes of Health: National Institute of Allergy and Infectious Disease: Immune Cells and Their Products
- University of Maryland: College of Chemical and Life Sciences: Mitosis
