UNIT 5 STRUCTURE AND FUNCTION IN LIVING THINGSFigure 15.20: The four types of
tissues work together in the stomach.epithelial tissue - made up of
closely packed cells in one or
more layers. Lines the internal and
external body surfaces.
connective tissue - provides
strength, support, and protection
to soft body parts.Vertebrate organs are made of four types of tissues
Four types of
tissuesAn organ is a group of tissues that function together. Vertebrate
organs are made of four types of tissues: epithelial, connective,
muscle, and nerve. Figure 15.20 shows some organs where each
tissue is found.Epithelial tissue Epithelial tissue is made up of closely-packed cells in one or more
layers. It forms the covering or lining of all internal and external
body surfaces. Epithelial tissue protects the body and organs from
dehydration, damage, and invasion by bacteria.Connective
tissueConnective tissue provides strength, support, and protection
to the soft parts of the body. The cells of connective tissue are
embedded in a large amount of extracellular material. This
material, secreted by the cells, is made up of protein fibers.
Cartilage and bone are both made of connective tissue. Another
type of connective tissue is the binding material for organs.
Muscles are surrounded by a layer of connective tissue.Nerve tissue Nerve tissue transmits signals
throughout the body. It is
made of specialized cells called
neurons. Each neuron (shown
right) consists of a cell body
which contains the nucleus,
dendrites, and a single long fiber called the axon. The nerve signal,
called an impulse, is conducted along the axon.Muscle tissue Three kinds of muscle tissue are found in vertebrates. Skeletal
muscle is made of long fibers in bundles and causes bones to move.
Smooth muscle lines the walls of organs and blood vessels.
Contractions of smooth muscle help organs like the stomach and
intestines to function. The heart is made of cardiac muscle.