136
UNIT 1
Organization of the Body
4
(i)
Cartilage: fibrocartilage
Description:
Matrix similar to but less firm
than that in hyaline cartilage; thick collagen
fibers predominate.
Function:
Tensile strength allows it to
absorb compressive shock.
Location:
Intervertebral discs; pubic
symphysis; discs of knee joint.
Photomicrograph:
Fibrocartilage of an intervertebral
disc (125
m
). Special staining produced the blue color seen.
Intervertebral
discs
Chondrocytes
in lacunae
Collagen
fiber
Figure 4.8
(continued)
Connective tissues. (i)
Cartilage. (For a related image, see
A Brief
Atlas of the Human Body
, Plate 19.)
Bone (Osseous Tissue)
Because of its rocklike hardness,
bone
, or
osseous tissue
(os
9
e-
us), has an exceptional ability to support and protect body
structures. Bones of the skeleton also provide cavities for stor-
ing fat and synthesizing blood cells. Bone matrix is similar to
that of cartilage but is harder and more rigid because, in addi-
tion to its more abundant collagen fibers, bone has an added
matrix element—inorganic calcium salts (bone salts).
Osteoblasts
produce the organic portion of the matrix, and
then bone salts are deposited on and between the fibers. Mature
bone cells, or
osteocytes
, reside in the lacunae within the ma-
trix they have made (Figure 4.8j). A cross section of bone tissue
reveals closely packed structural units called
osteons
formed of
concentric rings of bony matrix (lamellae) surrounding central
canals containing the blood vessels and nerves serving the bone.
Unlike cartilage, the next firmest connective tissue, bone is well
supplied by invading blood vessels.
Blood
Blood
, the fluid within blood vessels, is the most atypical
connective tissue. It does
not
connect things or give mechan-
ical support. It is classified as a connective tissue because
it develops from mesenchyme and consists of
blood cells
,
surrounded by a nonliving fluid matrix called
blood plasma
(Figure 4.8k).
Te vast majority of blood cells are red blood cells, or eryth-
rocytes, but scattered white blood cells and platelets (needed for
blood clotting) are also seen. Te “fibers” of blood are soluble pro-
tein molecules that precipitate, forming visible fiberlike structures
during blood clotting. Blood functions as the transport vehicle for
the cardiovascular system, carrying nutrients, wastes, respiratory
gases, and many other substances throughout the body.
Check Your Understanding
13.
Which connective tissue has a soft weblike matrix capable of
serving as a fluid reservoir?
14.
What type of connective tissue is damaged when you cut
your index finger tendon?
15.
John wants to become a professional basketball player.
Unfortunately he is short for his age and his epiphyseal
plates have already fused. What type of connective tissue
forms the epiphyseal plates?
For answers, see Appendix H.
Muscle Tissue
Compare and contrast the structures and body locations of
the three types of muscle tissue.
Muscle tissues
are highly cellular, well-vascularized tissues that
are responsible for most types of body movement. Muscle cells
possess
myofilaments
, elaborate versions of the
actin
and
my-
osin
filaments that bring about movement or contraction in all
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