Cells are the biological units of life, and all living organisms are composed of one or more cells. Some organisms, like bacteria, are made up of a single cell responsible for all the functions performed by the organism. More complicated living creatures, however, including animals, are multicellular. In organisms such us these, cells specialize. While individual cells become part of different organ systems and tissue types, however, all cells perform one of more valuable functions that support and maintain life.
Transport
Some cells are responsible for transporting materials from one place in the body to another. In humans, for instance, cells lining the small intestine transport the molecular products of digestion from the inside of the gut to the bloodstream. Glucose, for instance, which is also called blood sugar, is transported by specialized cells that move glucose molecules out of the intestine together with sodium ions, note biochemists Mary Campbell, Ph.D., and Shawn Farrell, Ph.D., in their text, “Biochemistry.” In this way, both glucose and sodium—also important to the function of the human body—are absorbed from food.
Storage
Some cells specialize in storage. Adipose cells, for instance, serve the purpose of storing large quantities of triacylglyceride, or fat, explain Drs. Campbell and Farrell. While most body cells can burn sugar, protein or fat for energy, fat provides far more energy per gram of weight, so it’s most efficient as a stored fuel. While adipose cells don’t engage in many other functions—they’re not particularly active with regard to anything else the body does—they do serve the valuable role of providing for the rest of the body’s energy needs when food is scarce.
Communication
In order to keep a multicellular organism running efficiently, there must be cell-to-cell communication. While neighboring cells can communicate with one another without significant difficulty, things become a bit more complicated when, for instance, a gland in the brain needs to send a message to the gonads. Specialized cells, therefore, secrete communication molecules, called hormones, into the blood stream. The anterior pituitary gland in the brain, for instance, secretes a hormone that travels throughout the body, but only cells on the gonads respond to the hormone, notes Lauralee Sherwood in her text “Human Physiology.” In women, the gonads—ovaries, in this case—ripen an egg in preparation for ovulation in response to the pituitary hormone. In men, the testes produce sperm. Neurons are also communication cells. Instead of sending chemical messages via the bloodstream, however, they communicate directly with one another and with neighboring cells by using electrical impulses.
Movement
Yet another specialized function a cell can perform is to produce movement. Muscle cells, notes Dr. Sherwood, are filled with strands of special proteins. In response to stimulation by neighboring communication cells, these protein strands slide past one another, shortening the muscle cell. As muscle cells shorten, muscles contract, producing movement. Every movement an animal makes is coordinated by communication cells causing muscle cells to shorten in the right order, to result in flexion and extension of specific joints for meaningful locomotion.
References
- “Biochemistry”; Mary Campbell, Ph.D., Shawn Farrell, Ph.D.; 2005
- “Human Physiology”; Lauralee Sherwood, Ph.D.; 2004
