Specialized Cell Types

Cells can be defined as the building blocks of life. All cells are composed of cytoplasm and DNA and are contained by a cell membrane. Some cells have additional structures called organelles that perform specific functions, much like the organs in the human body. Cells themselves are also specialized. There are hundreds of specialized cell types within the human body alone, but all cells that make up human tissue can be classified in four categories.

Epithelial Cells

• Epithelial cells line the body cavities and organs and make up some glands. Examples of epithelial cells include the other layer of skin and lining of the mouth. Epithelial cells provide protection, absorb nutrients, filter waste and, in some cases, secrete hormones. The cells are packed tightly together for protection and usually have good regenerative capabilities. All epithelial tissues have a basement membrane that they adhere to in order to grow and regenerate. Tissues composed of epithelial cells usually contain a lot of nerves but do not have blood vessels and have to rely on blood diffusion from the underlying tissues.

Connective Tissue Cells

• Connective tissues do exactly what their name states --- they connect. Examples of connective tissue are tendons, bone, cartilage and blood. Functions of connective tissue cells include storing nutrients, supporting and protecting organs and protecting joints. Cells of this type tend be less loosely packed than epithelial cells. Connective tissue cells also survive within a matrix composed of nonliving material that is essential for nourishing the cells.

Muscle Cells

• Muscles move food, blood and waste through the body as well as moving the body itself. There are three distinct types of muscles in the human body and, therefore, three types of muscle cells. All muscle cells contain contractile fibers that are used to change the shape of the cell and cause muscle contractions. In addition, muscle cells have more than one nucleus. This enables the muscle cells to contract quickly.

Nerve Cells

• The brain, spinal cord and nerves are the only parts of the body made up of nervous cells. There are two types of cells in the nervous system--neurons and glial cells. Glial cells act as a support system, providing nutrition, maintaining homeostasis and participating in signal transmission. Neurons are responsible for processing and transmitting information via electrical and chemical signaling and are the only cells that communicate with other cells via synapses. A variety of different types of neurons exist to perform specific functions within the human body.