Body Tissues

A TISSUE is a group of similar cells that work together to carry out a specific function.

BODY TISSUES can be classified into four basic tupes according to their function and strcture: Epithelial tissue, connective tissue, muscular tissue and nervous tissue.

EPITHELIAL TISSUE consists of tightly packed cells that form a continous layer. It can be classified into covering and lining epithelium and glandular epithelium. Its functions include protection, filtration, secretion, absoption, and excretion.

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CONNECTIVE TISSUE consists of cells that are widely separated by a matrix and contains fibers. Its functions include binding organs together, providing support and protection, filling spaces, producing blood cells, and storing fat.

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 MUSCULAR TISSUE 

consists of elongated cells called muscle fibers. Its functions include producing body movements, maintaining posture and generating heat. Depending on its location in the body, muscular tissue can be divided into skeletal muscle, smoth muscle, and cardiac muscle.

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NERVOUS TISSUE consists of two types of cells, neurons and neuroglia, which are found in the brain, spinal cord, and nerves. The neurons are made up of the cell body, dendrites, and axons that are usually covered with a myelin sheath. The functions of nervous tissue are sensory input, integration of data, and motor output.

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SKELETAL MUSCLE TISSUE is attached to bones of the skeleton. It is considered to be voluntary because it can be made to contract or relax by conscious control, and it consists of skeletal muscle fibers that are cylindrical in shape with several nuclei located in the periphery of the cell. The skeletal muscle fibers have striations, which are alternating light and dark bands visible under a microscope. The muscle fibers found within a whole muscle are parallel to one another

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CARDIAC MUSCLE TISSUE is found in the wall of the heart, and like skeletal muscle, it is striated, but unlike skeletal muscle, it is involuntary. Cardiac muscle fibers are branched and usually have a central nucleus. These cardiac muscle fibers are attached to each other, end to end, by transverse thickenings of the plasma membrane called intercalated discs, which hold the fibers together during vigorous contractions and provide a route for quick conduction of muscle action potentials throughout the heart.OLYMPUS DIGITAL CAMERA

SMOOTH MUSCLE TISSUE is found in the walls of hollow internal structures such as blood vessels, airways to the lungs, the stomach, intestines, gallbladder, and urinary bladder. It contraction helps constrict or narrow the lumen of blood vessels, breakdown and move food along the digestive track, move fluids though the body and eliminate wastes. Smooth muscle fibers are spindle-shaped with a central nucleus, involuntary and nonstriated.

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The AXON is a long, singular process that conducts nerve impulses away from the cell body. It is the output part of the neuron conducting nerve impulses toward another neuron or to some other tissue. Long axons are covered by a myelin sheath, which is a white fatty substance that increases the speed of nerve impulses. The term fiber is used here to refer to an axon with its myelin sheath. Outside the brain and spinal cord, fibers bound by connective tissue form nerves. The function of nervous tissue includes sensory input, integration of data, and motor output

NEUROGLIA are the other cell type found in nervous tissue, outnumbering the neurons nine to one and taking up more than half the volume of the brain. Even though they do not generate or conduct nerve impulses, these cells have many important supportive functions. The four types of neuroglia in the brain are microglia, astrocytes, oligodendrocytes, and ependymal cells.

MICROGLIA, support neurons and engulf bacteria and cellular debris. Astrocytes provide nutrients to neurons and produce a hormone known as glia-derived growth factor, which has potential as a treatment for Parkinson disease and other diseases caused by neuron degeneration. Oligodendrocytes form myelin sheaths. Ependymal cells line the fluid-filled spaces of the brain and spinal cord

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