The
major types of connective tissue are: 1) loose connective tissue; 2) adipose
tissue; 3) blood; 4) collagen, sometimes called fibrous or dense connective tissue;
5) cartilage; and 6) bone. Loose
connective tissue, also called areolar tissue (from the
Latin areola, meaning “open place”), is a mass of widely scattered cells
whose matrix is a loose weave of fibers. Many of the fibers are strong protein
fibers called collagen. Loose connective tissue is found beneath the skin and
between organs. It is a binding and packing material whose main purpose is to
provide support to hold other tissues and organs in place. Adipose tissue consists of adipose cells in loose connective tissue. Each
adipose cell stores a large droplet of fat that swells when fat is stored and
shrinks when fat is used to provide energy. Adipose tissue provides padding,
absorbs shocks, and insulates the body to slow heat loss. Blood is a loose connective tissue whose matrix is a liquid called
plasma. Blood consists of red blood cells (erythrocytes), white blood cells
(leukocytes), and platelets (thrombocytes), which are tiny pieces of bone
marrow cell. Plasma also contains water, salts, sugars, lipids, and amino
acids. Blood is approximately 55 percent plasma and 45 percent formed elements.
Blood transports substances from one part of the body to another and plays an
important role in the immune system.
Collagen (from the Greek kola,
meaning “glue,” and genos, meaning “descent”) is a dense connective tissue, also known
as fibrous connective tissue. It has a matrix of densely packed collagen
fibers. There are two types of collagen: regular and irregular. The collagen
fibers of regular dense connective tissue are lined up in parallel. Tendons,
which bind muscle to bone, and ligaments, which join bones together, are
examples of dense regular connective tissue. The strong covering of various
organs, such as kidneys and muscle, is dense irregular connective tissue. Cartilage (from the Latin, meaning “gristle”) is a connective tissue
with an abundant number of collagen fibers in a rubbery matrix. It is both
strong and flexible. Cartilage provides support and cushioning. It is found
between the discs of the vertebrae in the spine, surrounding the ends of joints
such as knees, and in the nose and ears. Bone
is a rigid connective tissue that has a
matrix of collagen fibers embedded in calcium salts. It is the hardest tissue
in the body, although it is not brittle. Most of the skeletal system is
comprised of bone, which provides support for muscle
attachment
and protects the internal organs.
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