156
UNIT ONE
Reticular f
bers
are thin collagenous f
bers. They are
highly branched and Form delicate supporting networks in
a variety oF tissues, including those oF the spleen.
Table 5.6
summarizes the components oF connective tissue.
PRACTICE
11
What are the general characteristics of connective tissue?
12
What are the major types of cells in connective tissue?
13
What is the primary function of F
broblasts?
14
What are the characteristics of collagen and elastin?
Categories oF Connective Tissues
Connective tissue is divided into two major categories.
Connective tissue proper
includes loose connective tissue
(areolar, adipose, reticular) and dense connective tissue
(dense regular, dense irregular, elastic). The
specialized
con-
nective tissues
include cartilage, bone, and blood. The Fol-
lowing sections describe each type oF connective tissue.
Areolar Tissue
Areolar
(ah-re
o-lar)
tissue,
Forms delicate, thin membranes
throughout the body. The cells oF this tissue, mainly f bro-
blasts, are located some distance apart and are separated by
a gel-like ground substance that contains many collagenous
and elastic f bers that f
broblasts secrete
(f g. 5.18)
.
Areolar tissue binds the skin to the underlying organs
and f lls spaces between muscles. It underlies most layers
oF epithelium, where its many blood vessels nourish nearby
epithelial cells.
Adipose Tissue
Adipose
(ad
ı˘-po
¯s)
tissue,
or Fat, develops when certain cells
(adipocytes) store Fat in droplets in their cytoplasm. At f rst,
these cells resemble f broblasts, but as they accumulate Fat,
they enlarge, and their nuclei are pushed to one side
(Fig.
5.19)
. When adipocytes become so abundant that they crowd
out other cell types, they Form adipose tissue. This tissue lies
beneath the skin, in spaces between muscles, around the kid-
neys, behind the eyeballs, in certain abdominal membranes,
FIGURE 5.17
Scanning electron micrograph of collagenous F
bers
(shades of white to gray) and elastic F
bers (yellow) (4,100×).
Collagenous
fiber
Elastic
fiber
TABLE
5.6
|
Components of Connective Tissue
Component
Characteristic
Function
±ibroblasts
Widely distributed, large, star-shaped cells
Secrete proteins that become F
bers
Macrophages
Motile cells sometimes attached to F
bers
Clear foreign particles from tissues by phagocytosis
Mast cells
Large cells, usually located near blood vessels
Release substances that may help prevent
blood clotting
and promote in²
ammation
Collagenous F
bers (white F
bers)
Thick, threadlike F
bers of collagen with great tensile strength
Hold structures together
Elastic F
bers (yellow F
bers)
Bundles of microF
brils embedded in elastin
Provide elastic quality to parts that stretch
Reticular F
bers
Thin F
bers of collagen
±orm supportive networks within tissues
FIGURE 5.16
Scanning electron micrograph of a mast cell (6,600×).
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