HUMAN BIOLOGY

tIssUes, orGans, and orGan systeMs 71

What is connective tissue?

• Connective tissue binds together and supports other body
  tissues and organs.


• The differing types of fibrous connective tissues have different
  amounts and arrangements of collagen and elastin fibers in their
  matrix.


• Cartilage, bone, blood, and adipose tissue are specialized
  connective tissues. Cartilage and bone are structural materials.
  Blood transports substances. Adipose tissue stores energy.

taKe-hoMe Message

adipose tissue Tissue that

stores fat in adipose (fat)

cells.

bone tissue Hard tissue

in bones, mineralized with

calcium salts.

cartilage Pliable tissue with

a matrix of collagen and

elastin fibers in a rubbery

ground substance.

connective tissue Tissue

that connects and supports

body parts; consists of cells

and fibers in a matrix.

fibrous connective

tissue Connective tissue

having a matrix that makes

it strong and stretchy;

varying characteristics of

the matrix result in loose,

dense, and elastic forms.

matrix Blend of cells,

fibers, and ground sub-

stance that gives each type

of connective tissue its spe-

cialized properties.

such as in the flaps of your ears.

Sturdy fibrocartilage is packed with

thick bundles of collagen fibers. It

can withstand a lot of pressure, and

it forms the cartilage “cushions” in

joints such as the knee and in the

disks between the vertebrae in the

spinal column.

Bone tissue is the main tissue in

bones. It is hard because its matrix

includes not only collagen fibers and

ground substance but also calcium

salts (Figure 4.3E). Bones serve the

body in ways described in Chapter 5.

Adipose tissue stores fat—the

way the body deals with carbohy-

drates and proteins that are not

immediately used for metabolism.

It is mostly cells packed with fat

droplets, with just a little matrix

between them (Figure 4.3F). Most

of our adipose tissue is located just

beneath the skin, where it provides

insulation and cushioning.

Blood is classified as connective tissue even though it

does not “connect” or bind other body parts. Instead blood’s

role is transport. Its matrix is the fluid plasma, which

contains proteins (blood’s “fibers”) as well as a variety of

blood cells and cell fragments called platelets (Figure 4.4).

Chapter 8 discusses this complex tissue.

Figure 4.4 Blood is an unusual connective tissue that

transports substances. Here you see some components of

human blood. This tissue’s liquid matrix (plasma) is mostly

water in which various substances are dissolved.

Type Bone tissue

Description Collagen

fibers, matrix

hardened with calcium

Common Locations Bones

of skeleton

Function Movement,

support, protection

E

Type Adipose tissue

Description Large, tightly

packed fat cells occupying

most of matrix

Common Locations Under

skin, around heart, kidneys

Function Energy reserves,

insulation, padding

F

bone cell

(osteocyte)

compact

bone tissue

cell bulging

with fat

droplet

nucleus

blood vessel

platelet

white blood cell

red blood cell

Science Source

Another version of this tissue has bundles of collagen
fibers aligned in the same plane (Figure 4.3C). It is found
in tendons, which attach many skeletal muscles to bones,
and in ligaments, which attach bones to one another. The
tissue’s structure allows a tendon to resist being torn, and
in ligaments the tissue’s elastic fibers allow the ligament to
stretch so bones can move at joints such as the knee.
Elastic connective tissue is a form of dense connective tis-
sue in which most of the fibers are the protein elastin. As a
result, this tissue is elastic and is found in organs that must
stretch, such as the lungs, which expand and recoil as air
moves in and out.

special connective tissues include cartilage,
bone, adipose tissue, and blood

Like rubber, cartilage is solid, pliable, and not easily com-
pressed. Its matrix is a blend of collagen and elastin fibers
in a rubbery ground substance. The result is a tissue that
can withstand considerable physical stress. The collagen-
producing cells are trapped inside small cavities in the
matrix (Figure 4.3D). If you have ever torn a cartilage, you
know that injured cartilage heals slowly. This is because
cartilage lacks blood vessels.
Most cartilage in the body is whitish, glistening hyaline
cartilage (hyalin = “glassy”). Hyaline cartilage at the ends of
bones reduces friction in movable joints. It also makes up
parts of your nose, wind pipe (trachea), and ribs. An early
embryo’s skeleton consists of hyaline cartilage.
Elastic cartilage has both collagen and elastin fibers. It
occurs where a flexible yet rigid structure is required,

E: Ed Reschke; F: © University of Cincinnati, Raymond Walters College, Biology

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