98
in the production of heparin (an anticoagulant) and
histamine (an inflammatory substance produced in
response to allergies). Areolar tissue is the basic sup-port
tissue around organs, muscles, blood vessels, and nerves
-(Figure 5-5). It forms the delicate membranes around the
spinal cord and brain. It attaches the skin to its -underlying
tissues.
Adipose tissue is the second type of loose connec-tive
tissue (Figure 5-6). It is loaded with fat cells. Fat cells are
so full of stored fat that their nuclei and cytoplasm are
pushed up against the cell membrane. In a histologic
section under a microscope, they look like large soap
bubbles and are very easy to recognize. Adipose tissue acts
as a firm, protective packing around and between organs,
bundles of muscle fibers, and nerves, and it sup-ports blood
vessels. The kidneys have a surrounding layer of adipose
tissue to protect them from hard blows or jolts. In addition,
because fat is a poor conductor of heat, adipose tissue acts
as insulation for the body, pro-tecting us from excessive
heat losses or excessive heat increases in temperature.
Think of the animals in the Arctic and Antarctic. They can
live there because of their layers of blubber, which is
adipose tissue. The camel’s hump is not a water storage
organ but a thick hump of fat containing adipose tissue to
protect the animal’s internal organs from the heat of the
desert.
Chapter 5Reticular tissue is the third type of loose connective
tissue. It consists of a fine network of fibers that form the
framework of the liver, bone marrow, and lymphoid organs
such as the spleen and lymph nodes.Dense Connective Tissue
Again as the name implies, dense connective tissue is
composed of tightly packed protein fibers. It is further
divided into two subgroups based on how the fibers are
arranged and the proportions of the tough collagen and the
flexible elastin fibers. Examples of dense connective tissue
having a regular arrangement of fibers are tendons,
which attach muscle to bone; ligaments, which attach
bone to bone; and aponeuroses (ap-oh-noo-ROH-seas),
which are wide flat tendons (Figure 5-7). Tendons have a
majority of tough collagen fibers, whereas ligaments (e.g.,
the vocal cords) have a combination of tough col-lagen and
elastic elastin fibers.
Examples of dense connective tissue having an
irregular- arrangement of these fibers are muscle sheaths,
the dermis layer of the skin, and the outer coverings of
body tubes like arteries. Capsules that are part of a joint
structure also have dense irregular connective tissue as do
fascia (FASH-ee-ah), the connective tissue covering a
whole muscle.Function Characteristics and Location Morphology (^)
(^) Mast cell (^)
Areolar (loose) connective It is composed of a large, (^) Reticular fibers (^)
This tissue surrounds various semifluid matrix, with many (^) Collagen fibers (^)
organs and supports both different types of cells and fibers (^) Fibroblast cell (^)
nerve cells and blood embedded in it. These include (^) Plasma cell
vessels, which transport nutrient fibroblasts (fibrocytes), plasma
Elastic fiber
material (to cells) and wastes cells, macrophages, mast cells, (^)
(away from cells). Areolar tissue and various white blood cells. (^) Matrix (^)
also (temporarily) stores The fibers are bundles of strong, (^) Macrophage cell (^)
glucose, salts, and water. flexible white fibrous protein (^) (A) (^)
called collagen, and elastic^
single fibers of elastin. It is^
found in the epidermis of the^
skin and in the subcutaneous^
layer with adipose cells. (^)
(B)
SourceAssociates/Science Biophoto ©(B) Photo(^) ,
® Learning
Cengage
© (A)
Figure 5- 5 Views of areolar or loose connective