Cells, Tissues, & Membranes

This section details the structure and function of cells, the four basic types of tissues of the human body, and the different types of cell membranes found in the body.

The skin membrane is a multilayered membrane composed of epithelium and connective tissue. The upper surface of the membrane is exposed to the external environment and covered with dead keratinocytes to help protect the body from dry pathogens. Skin is an example of skin membrane. Aggregation of human cells can be classified into four types of tissues, epithelial cells, connective tissue cells, muscle cells and nerve cells. Epithelial tissue functions as a cover to control the movement of the material on its surface. Connective tissue combines various parts of the body to provide support and protection. Muscle tissue allows the body to move, nerve tissue plays a role in communication

The epithelial membrane consists of a continuous cell sheet of one or more layers bonded to the underlying connective tissue via the basement membrane. Cells are linked together in specific areas called intercellular junctions. The important thing to remember is that epithelial cells do not contain blood vessels. Nutrients and oxygen reach epithelial cell membranes by diffusion from blood vessels in connective tissue located under the basement membrane. - A simple cylindrical shape with a single layer of tall, cylindrical cells. This type of epithelium usually contains absorptive cells interspersed with secretory cells. For example, in the small intestine, there are secretory cells called goblet cells that secrete mucus. On the other hand, absorbable cells have microvilli on the surface of their cavities and promote absorption of nutrients. Generally, these microvilli produce a visible fringe boundary in an optical microscope.