Chapter 7
Skeletal Tissues
Types of Bones
• Four types of bones:
a. Long bones
b. Short bones
c. Irregular bones
d. Flat bones
• Bones serve various needs, and their
size, shape, and appearance will vary to
meet those needs
Types of Bones
• Bones vary in their
proportions of compact
and cancellous (spongy)
bone
 compact
bone: dense
and solid in
appearance
 cancellous
bone
(spongy): open space
partially filled with
needle-like structures
Parts of a Long Bone

Epiphysis (head)
• Both ends of a long bone, made of
cancellous bone filled with marrow
• Bulbous shape
• Function is to provide attachments for
muscles and give stability to joints

Diaphysis (shaft)
• Main shaft of long bone
• Hollow, compact bone
• Function is to provide strong support
Parts of a Long Bone

Periosteum
• Dense, white, fibrous membrane that covers bone
• Attaches tendons firmly to bones
• Contains cells that form and destroy bone
• Contains blood vessels important in growth and repair

Medullary (or marrow) cavity
• Tubelike, hollow space in diaphysis
• Filled with yellow marrow in adult
Types of Bones
• Short, flat, and irregular bones

Inner portion is cancellous bone, covered on the
outside with compact bone

Spaces inside cancellous bone of a few irregular
and flat bones are filled with red marrow
Bone Tissue
• Extracellular components are
hard and calcified
• Rigidity of bone allows it to
serve its supportive and
protective functions
• Tensile strength is nearly equal
to cast iron at less than one
third the weight
Bone Tissue
• Composition of bone matrix

Inorganic salts
• Slender, needle-like crystals
are oriented to most
effectively resist stress and
mechanical deformation

Organic matrix
• Composite of collagenous
fibers and ground substance

Ground substance is
secreted by connective
tissue cells
• Adds to the strength of bone
Microscopic Structure of the Bone
• Compact bone

Types of structures make up each osteon:
• Lamella—concentric, cylinder-shaped layers of calcified
matrix
• Lacunae— “little lakes”- small spaces containing tissue
fluid in which bone
cells are located
between hard
layers of the lamella
Microscopic Structure of the Bone
• Blood supply
 Bone
cells are metabolically active and
need a blood supply, which comes from the
bone marrow in the internal medullary
cavity of cancellous bone
 Compact
bone, in addition to bone marrow
and blood vessels from the periosteum,
connects with vessels
Structure of the Bone
• Cancellous bone (spongy)

Trabeculae
• Needle-like bony spicules
• Arranged along lines of stress and differ in different
bones
Microscopic Structure of the Bone
• Types of bone cells

Osteoblasts
• Bone-forming cells found in all bone surfaces
• Small cells synthesize and secrete osteoid,
an important part of the ground substance
• Blasts = building
Structure of the Bone
• Types of bone cells

Osteoclasts
• Giant multinucleate cells
• Responsible for the active erosion
of bone minerals
• Contain large numbers of
mitochondria and lysosomes
• Clasts = Cut
Osteoclast vs. Osteoblast
• Note the large
multinucleate
osteoclast cell
(Oc) resorbing
bone on the
upper surface of
a developing
bony spicule
while smaller
osteoblast cells
(Ob) on the
under surface of
the spicule are
secreting new
osteoid.
Structure of the Bone

Types of bone cells
• Osteocytes— mature, non-dividing osteoblast
surrounded by matrix, lying within lacunae
Bone Marrow
• Site for the production of blood cells
• Found in medullary cavities of long bones and in the
spaces of spongy bone
• Two types:
 Red
Marrow
 Yellow
Marrow
Bone Marrow
• Two types of marrow are present during a person’s lifetime:

Red marrow
• Found in virtually all bones in an infant’s or child’s body
• Functions to produce red blood cells

Yellow marrow
• As an individual ages, red marrow is replaced by yellow
marrow
• Marrow cells become saturated with fat and are no
longer active in blood cell production

Fatty degeneration is completed around 21 years old
Bone Marrow
• The main bones in an adult that still
contain red marrow include the:

ribs

bodies of the vertebrae

humerus

pelvis

femur
• Yellow marrow can alter to red marrow
during times of decreased blood supply,
such as with anemia, exposure to
radiation, and certain diseases
Functions of Bone
• Support— bones form the framework of the body
• Protection— protect the delicate structures they enclose
• Movement— bones with their joints are levers that move as
muscles contract
• Mineral storage— bones are the major reservoir for calcium
• Hematopoiesis— blood cell formation is carried out in bone
Regulation of Blood Calcium Levels
• Skeletal system serves as a storehouse for about
98% of body calcium reserves
 Helps
maintain constancy of blood calcium
levels
Maintaining a constant environment is called
________?
Regulation of Blood Calcium Levels
 Homeostasis
of calcium ion concentration
essential for the following:
• Bone formation, remodeling, and repair
• Blood clotting
• Transmission of nerve impulses
• Maintenance of skeletal and cardiac muscle
contraction
Development of Bone
• Osteogenesis— development of bone from small cartilage
model to an adult bone

Ossification: process where connective tissue forms bone tissue
• Two types:

Endochondral ossification

Intramembranous ossification
• Occurs within embryonic connective tissue
• Forms Flat bones
Development of Bone
•
Endochondral ossification
1.
Most bones begin as cartilage,
with bone formation spreading
from the center to the ends
2.
Periosteum develops and
enlarges, producing a collar of
bone
3.
Primary ossification center
forms
4.
Blood vessel enters the
cartilage model at the midpoint
of the diaphysis
Development of Bone
• Survey photograph of a
specially prepared fetal
hand specimen showing
primary ossification centers
in the bones of the hand
(metacarpals) and fingers
(phalanges). Note that none
of the wrist (carpal) bones
show any evidence of
ossification.
toddler
school-age child
young adolescent
• Radiographs showing increasing numbers of ossification
centers becoming visible in the wrist with increasing age.
Cartilage
• Characteristics

Avascular connective tissue

Fibers of cartilage are embedded in a firm gel

Has the flexibility of firm plastic

No canal system or blood vessels

Chondrocytes receive oxygen and nutrients by diffusion

Perichondrium—fibrous covering of the cartilage

Cartilage types differ because of the amount of matrix
present and the amounts of elastic and collagenous fibers
Cartilage
• Histophysiology of cartilage

Gristle-like nature permits cartilage to sustain
great weight or serve as a shock absorber

Strong yet pliable support structure

Permits growth in length of long bones
Cartilage
• Growth of cartilage

Interstitial or endogenous growth
• Seen during childhood and early adolescence
while cartilage is still soft
• Cells within tissue mass divide
Cartilage
• Growth of cartilage

Appositional or exogenous growth
• Chondrocytes in the deep layer of the perichondrium
divide and secrete matrix
• New matrix is deposited on the surface, increasing its
size
• Unusual in early childhood but, once initiated, continues
throughout life
Growth from the
perichondrium is
appositional growth.
Cycle of Life: Skeletal Tissues
• Skeleton fully ossified by mid-twenties

Soft tissue may continue to grow— ossifies more slowly
• Adults— changes occur from specific conditions

Increased density and strength from exercise
• Stresses of exercise  more collagen fibers and salts in bone
matrix

Decreased density and strength from pregnancy, nutritional
deficiencies, and illness
• Advanced adulthood— apparent degeneration

Hard bone matrix replaced by softer connective tissue

Exercise can counteract degeneration

Osteoporosis- loss of bone mineral density