Connective tissue, such as blood and bone, binds and supports other tissues; epithelial tissue, such as skin, covers internal and external body surfaces; muscle tissue creates movement and force; and nervous tissue is the body's means of signaling from one part to another. These four tissue types combine to form organs and other body structures.
Loose connective tissue is made up of various types of fibers, such as reticular fibers, elastic fibers and collagenous fibers. Fibrous connective tissue includes tendons and ligaments. Other types of connective tissue include adipose tissue, which stores fat, and cartilage, which supports structures such as the nose and ears.
Epithelial tissue includes not only the outer skin but also internal barriers that protect organs and cavities. These tissues guard organs from microorganisms, injury and loss of fluids, and regulate absorption and secretion.
Muscle tissue is contractile in response to stimulation. It includes cardiac muscle, which is responsible for the heartbeat, skeletal muscle, which creates the body's voluntary movements, and visceral muscle, the smooth muscle in the bladder, digestive tract and arteries.
The basic unit of nervous tissue is the neuron. Neural tissue includes the central nervous system, comprising the brain and spinal cord, and the peripheral nervous system, which transmits signals by means of the cranial nerves and the spinal nerves.