Cells are organized into four basic types of tissues that perform specific functions.

• Epithelial (ep-i-THE-le-al) tissue covers and protects body structures and lines organs, vessels, and cavities.

• Connective tissue supports and binds body structures. It contains fibers and other nonliving material between the cells. Included are adipose (fat) tissue, cartilage, bone, and blood.

• Muscle tissue (root my/o) contracts to produce movement. There are three types of muscle tissue:

• Skeletal or voluntary muscle moves the skeleton. 

• Cardiac muscle forms the heart. It functions without conscious control and is described as involuntary.

• Smooth, or visceral, muscle forms the walls of the abdominal organs; it is also involuntary.

• Nervous tissue (root neur/o) makes up the brain, spinal cord, and nerves. It coordinates and controls body responses by the transmission of electrical impulses.

The simplest tissues are membranes. Mucous membranes secrete mucus, a thick fluid that lubricates surfaces and protects underlying tissue. Serous membranes, which secrete a thin, watery fluid, line body cavities and cover organs.

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