There are two types of bone tissue: compact bone which is dense and forms the outer layer, and spongy bone which is less dense and found in low stress areas. Bones are composed of osteocytes embedded in bone matrix, as well as osteoblasts which build bone, osteoclasts which resorb bone, and osteogenic cells which develop into osteoblasts. A long bone has a central shaft made of compact bone surrounding marrow, expanded ends made of inner spongy and outer compact bone lined with marrow, and growth plates between the shaft and ends.

1. The Skeletal System
LT4.2: Bone Anatomy & Function
Anatomy & Physiology
Mrs. DeFord

2. There are two types of bone tissue:
1. Compact Bone
• Dense, weight-bearing bone
• Ivory appearance
• Thickest at the center of the shaft
• Forms the outer, protective layer of all bones
2. Spongy (Cancellous) Bone
• Location of blood cell formation (hematopeiosis)
• Honeycomb appearance (trabeculae)
• Found in low stress areas, thickest on the ends of bones
• Forms the inner layer of all bones, less dense than compact bone
Histology of Bone

3. • Osteocytes are found within the
bone matrix of compact bone,
in tiny cavities called lacunae,
which are arranged in
concentric circles (lamella)
around Haversian canals.
• Spongy bone is composed of
small needlelike pieces of bone
called trabeculae and lots of
“open” space filled by marrow,
vessels, and nerves.
Histology of Bone

4. Microscopic Anatomy of the Bone
There are four types of cells present in bone tissue:
1. Osteogenic Cells
• Undergo cell division; the resulting cells develop into
osteoblasts
2. Osteoblasts
• Bone-building cells; synthesize extracellular matrix of
bone tissue
3. Osteocytes
• Mature bone cells, maintains bone tissues
• Exchange nutrients and wastes with the blood
4. Osteoclasts
• Bone-chewing cells; release enzymes that digest the
mineral components of bone matrix (resorption)
• Regulate blood calcium and phosphate levels

5. Gross Anatomy of the Long Bone
– The structure of a long bone allows for the best
visualization of all of the parts of a bone.
– The outer surface of the bone is covered by a fibrous
membrane called the periosteum, which isolates the
bone from surrounding tissues, provides a route for
circulatory and nervous supply, and actively
participates in bone growth and repair. Tendons and
ligaments also attach here.
– Within the bone, a cellular endosteum lines the
marrow cavity and other inner surfaces. The
endosteum is active during bone growth and
whenever repair or remodeling is under way.

6. Typical Bone Structure
There are 3 main regions of structure in the long
bone:
• Diaphysis
– The central shaft, or length, of the long bone
(excluding the epiphyses); composed of
compact bone.
– Surrounds a central medullary cavity
containing yellow bone marrow.
» Yellow bone marrow is involved in the
storage of fats.

7. Typical Bone Structure
There are 3 main regions of structure in the long
bone:
• Epiphyses
– The expanded ends of the long bone
consisting of outer compact and inner
spongy bone lined with red bone marrow.
» Red bone marrow is involved in blood cell
formation.
– The epiphysis of adjacent bones articulate
with each other and are covered by articular
cartilages, which facilitate joint movement.

8. Typical Bone Structure
There are 3 main regions of structure in the long
bone:
• Metaphyses
– Also called epiphyseal plate; the cartilage
between the diaphysis and epiphysis.
– It is this part of the bone that grows during
childhood; as it grows it ossifies at the
junctions between the diaphysis and
epiphysis.