Dr. Noura El Tahawy
Assistance in movement
Blood cell production
Functions of bones
1. Bones form the skeleton which is the framework of the body.
2. The skeleton supports the softer tissues and provides points of attachment
for most skeletal muscles.
3. The skeleton provides mechanical protection for many of the body's
internal organs, reducing risk of injury to them. It forms boundaries of
cranial, thoracic and pelvic cavities. Thus it protects the brain, lungs, heart
4. Bones permit movement of the body as a whole or part of the body, by
formation of joints, which are moved by muscles.
5. Bone tissues store several minerals, including calcium and phosphorus.
When required, bone releases minerals into the blood facilitating and
maintaining the balance of minerals in the body.
6. Bone contains red bone marrow in which blood cells develop.
7. Bone acts as an important chemical reserve. With advancing age, some
bone marrow changes from red bone marrow to yellow bone marrow
which consists mainly of adipose cells and a few blood cells.
Bone Growth & Remodeling
Appositional Growth = widening of bone
Bone tissue added on surface by osteoblasts of the periosteum
Medullary cavity maintained by osteoclasts
Lengthening of Bone
Epiphyseal plates enlarge by chondroblasts
Matrix calcifies (chondrocytes die and disintegrate)
Bone tissue replaces cartilage on diaphysis side
Endochondral ossification is the gradual replacement of
cartilage by bone during development. This is responsible
for formation of most of the skeleton. Osteoblasts arise in
regions of cartilage called ossification centers. They
develop into osteocytes, which are mature bone cells,
embedded in the calcified (hardened) part of the bone
known as the matrix.
Intramembranous ossification is the transformation of the
mesenchyme, embryonic cells, into bone. During early
development, the embryo consists of three primary cell layers,
ectoderm on the outside, mesoderm in the middle and
endoderm on the inside. Mesenchyme cells constitute part of
the embryo's mesoderm and develop into connective tissue
such as bone and blood. The bones of the skull derive directly
from mesenchyme cells by intramembranous ossification.
Most bones arise from a combination of intramembranous
and endochondral ossification. Mesenchyme cells develop
into chondroblasts and increase in number by cell division.
Chondroblasts enlarge and excrete a matrix which hardens due
to presence of inorganic minerals. Chambers form within the
matrix and osteoblasts and blood-forming cells enter these
chambers. The osteoblasts then secret minerals to form the