1. OSTEOLOGY-2
STRUCTURE AND FUNCTIONS OF
SKELETAL SYSTEM

2. Gross structureof an adult long
bone
• Gross examination of the longitudinal and
transverse section of the long bone shows the
following features.
• 1. Shaft: From without inwards it is composed
of periosteum, cortex and medullary cavity.
• (a) Periosteum is a thick fibrocellular
membrane covering the surface of the bone.It
is madeup of an outer fibrous and inner
cellular layer. The inner cellular layer is
osteogenic in nature. Periosteum is united to

3. • The underlying bone by collagen fibers, called
sharpey’s fibres. This union is particularly
strong over the attachments of tendons and
ligaments. At the articular margins the
periosteum is continuous with the capsule of
the joint. The periosteal arteries nourish the
outer part of the underlying cortex also.
Periosteum has a very rich sensery innervation
which makes it the most sensitive part of the

4. • Bone.
• (b) Cortex is made up of compact bone which
gives it the desired strength to withstand all
possible mechanical strains.
• (Medullary cavity is filled with red or yellow
bone marrow. At birth the marrow is red
everywhere with widespread active
hemopoiesis. As the age advances, the red
marrow at many places atrophies and is
replaced by yellow, fatty marrow with no

5. • Power of hemopoiesis. The red marrow
persists in cancellous ends of long bones. In
the sternum,ribs iliac crest, vertabrae and
skull bones the red marrow is found through
life.
• 2. The two ends of the long bones are made
up of the cancellous bone covered with
hyaline cartilage.

6. Parts of a growing long bone
• A typical long bone ossifies in three parts, the
two ends from secondary centres, and the
intervening shaft from a primary centre.
Before ossification is complete the following
parts of a bone can be defined.
• 1. Epiphysis
• The ends and tips of a bone which ossify from
secondary centre are called epiphysis. These
are of the following types.

7. Types of epiphysis
• (a) Pressure epiphysis: pressure epiphysis
develops at the articular ends of long bones.
These epiphysis take part in transmission of
weight and develop due to pressure of an
adjascent articulating bone. Examples are
head of the femur, lower end of radius, etc.
• (b) Traction epiphysis: Traction epiphysis is
nonarticular and does not take part in
transmission of weight. It always provides
attachment to one or more tendons which

8. • Exert a traction on the epiphysis. The traction
epiphysis ossify later than the pressure
epiphysis. Examples: trochanters of femur and
tubercles of humerus.
• Atavistic epiphysis: atavistic epiphysis is
phylogenetically a separate bone which in
man becomes fused to another bone.
Examples: coracoid process of scapula and os
trigonum or lateral tubercle of talus.

9. • Abberant epiphysis: these are unusually
present,e.g; epiphysis of the head of the first
metacarpal and the base of other metacarpal
bones.
• Composite epiphysis: Some parts of bones are
formed from multiple secondary centres;one
of them is pressure epiphysis while others are
traction epiphysis. All these centres coalesce
before uniting with the primary centre, e.g;
upper ends of humerus, femur ,ribs and

10. Functions of skeletal system
1. Support. The skeleton serves as the structural framework for the body by supporting
soft tissues and providing attachment points for the tendons of most skeletal
muscles.
2. Protection. The skeleton protects the most important internal organs from injury. For
example, cranial bones protect the brain, vertebrae (backbones) protect the spinal
cord, and the rib cage protects the heart and lungs.
3. Assistance in movement. Most skeletal muscles attach to bones; when they contract,
they pull on bones to produce movement.
4. Mineral homeostasis (storage and release). Bone tissue stores several minerals,
especially calcium and phosphorus, which contribute to the strength of bone. Bone
tissue stores about 99% of the body’s calcium. On demand, bone releases minerals
into the blood to maintain critical mineral balances (homeostasis) and to distribute
the minerals to other parts of the body.
5. Blood cell production. Within certain bones, a connective tissue called red bone
marrow produces red blood cells, white blood cells, and platelets, a process called
hemopoiesis. Red bone marrow consists of developing blood cells, adipocytes,
fibroblasts, and macrophages within a network of reticular fibers. It is present in
developing bones of the fetus and in some adult bones, such as the hip bones, ribs,
breastbone, vertebrae (backbones), skull, and ends of the bones of the arm and
thigh.
6. Triglyceride storage. Yellow bone marrow consists mainly of adipose cells, which
store triglycerides. The stored triglycerides are a potential chemical energy reserve.
In a newborn, all bone marrow is red and is involved in hemopoiesis. With increasing
age, much of the bone marrow changes from red to yellow.

11. 7. Respiration and sound transmission: ribs have some protective function for the
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8.
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thoracic viscera, but respiration would have been tedious if not impossible without
ribs.
Muscle attached to skull are mandatory for chewing.
Ossicles small bones inside the middle ear cavity are important factor for sound
transmission from external ear to internal ear.
Speech, a hallmark of human race is impossible without skeletal element to which
speech muscle s are attached.
Body defense WBC are important to combat bacterial infections and prepare
antibodies against various antigens. These cells are also produced in the bone
marrow.
Reticulo-endothelial system consist of wide spread phagocytic cells incorporated
in the walls of the capillaries in many organs e.g. liver spleen, etc. and bone
marrow possesses sizeable part such cells in its sinusoids thus contributing to first
defense line of the body

12. Uses made of dead bones
1. Height Determination
2. Age determination
3. Sex determination
4. Race determination
5. Anthropometery
6. Dating of human Fossils
a) Carbon Dating
b) Potassium Dating

13. STRUCTURE OF BONE
:
2. The diaphysis is the bone’s shaft or body—the long, cylindrical, main
portion of the bone.The diaphysis ossifies in a primary
centre.Microscopically, the diaphysis differs from the shaft of adult
long bones in having no true haversian system and its surface
presents collagenous bundles of fibres which are continuous with
periosteum. Thus microscopically it is a fibrous bone.
3. The metaphyses are the regions between the diaphysis and the
epiphyses.In a growing bone, each metaphysis contains an epiphyseal
(growth) plate, a layer of hyaline cartilage that allows the diaphysis of
the bone to grow in length. When a bone ceases to grow in length at
about ages 18–21, the cartilage in the epiphyseal plate is replaced by
bone; the resulting bony structure is known as the epiphyseal line.
4. The articular cartilage is a thin layer of hyaline cartilage covering the
part of the epiphysis where the bone forms an articulation (joint) with
another bone. Articular cartilage reduces friction and absorbs shock
at freely movable joints.

14. IMPORTANCE OF METAPHYSIS
• 1.Growth activities are predominantly marked
in this area.
• 2.Most of the muscles of the joint are inserted
in this area.
• 3.This is the most highly vascular area of the
long bone

17. STRUCTURE OF BONE
contd
5. The periosteum surrounds the external bone surface wherever it is
not covered by articular cartilage. It is composed of an outer fibrous
layer of dense irregular connective tissue and an inner osteogenic
layer that consists of cells. Some of the cells of the periosteum
enable bone to grow in thickness, but not in length. The periosteum
also protects the bone, assists in fracture repair, helps nourish bone
tissue, and serves as an attachment point for ligaments and
tendons. It is attached to the underlying bone through perforating
(Sharpey’s) fibers, thick bundles of collagen fibers that extend from
the periosteum into the extracellular bone matrix.
6. The medullary cavity or marrow cavity is a hollow, cylindrical space
within the diaphysis that contains fatty yellow bone marrow in
adults.
7. The endosteum is a thin membrane that lines the internal bone
surface facing the medullary cavity. It contains a single layer of cells
and a small amount of connective tissue.

20. COMPOSITION OF BONE
Like other connective tissues, bone, or osseous
tissue, contains an abundant extracellular
matrix that surrounds widely separated cells.
The extracellular matrix is about 25% water,
25% collagen fibers, and 50% crystallized
mineral salts. The most abundant mineral salt
is calcium phosphate [Ca3(PO4)2]. It combines
with another mineral salt, calcium hydroxide
[Ca(OH)2], to form crystals of hydroxyapatite
[Ca10(PO4)6 (OH)2].

21. • As the crystals form, they combine with still other mineral
salts, such as calcium carbonate (CaCO3), and ions such as
magnesium, fluoride, potassium, and sulfate. As these
mineral salts are deposited in the framework formed by
the collagen fibers of the extracellular matrix, they
crystallize and the tissue hardens. This process, called
calcification, is initiated by bone-building cells called
osteoblasts (described shortly).
• The process requires the presence of collagen fibers.
Mineral salts first begin to crystallize in the microscopic
spaces between collagen fibers. After the spaces are filled,
mineral crystals accumulate around the collagen fibers.

22. Cells of Bone tissue
Four types of cells are present in bone tissue:
• Osteogenic cells,
• Osteoblasts,
• Osteocytes, and
• Osteoclasts

23. • 1. Osteogenic cells are unspecialized stem
cells derived from mesenchyme, the tissue
from which almost all connective tissues are
formed. They are the only bone cells to
undergo cell division; the resulting cells
develop into osteoblasts. Osteogenic cells are
found along the inner portion of the
periosteum, in the endosteum, and in the
canals within bone that contain blood vessels.

24. • 2. Osteoblasts are bone-building cells. They
synthesize and secrete collagen fibers and other
organic components needed to build the
extracellular matrix of bone tissue, and they
initiate calcification. As osteoblasts surround
themselves with extracellular matrix, they
become trapped in their secretions and become
osteocytes. (Note: The ending -blast in the name
of a bone cell or any other connective tissue cell
means that the cell secretes extracellular matrix.)

25. 3. Osteocytes mature bone cells, are the main
cells in bone tissue and maintain its daily
metabolism, such as the exchange of nutrients
and wastes with the blood. Like osteoblasts,
osteocytes do not undergo cell division.

26. • 4. Osteoclasts are huge cells derived from the fusion of as
many as 50 granulocytes-macrophage precursor cells. they
are concentrated in the endosteum. On the side of the cell
that faces the bone surface, the osteoclast’s plasma
membrane is deeply folded into a ruffled border. Here the
cell releases powerful lysosomal enzymes and acids that
digest the protein and mineral components of the
underlying bone matrix. This breakdown of bone
extracellular matrix, termed resorption is part of the
normal development, maintenance, and repair of bone. In
response to certain hormones, osteoclasts help regulate
blood calcium level. They are also target cells for drug
therapy used to treat osteoporosis.

27. • Bone is not completely solid but has many small
spaces between its cells and extracellular matrix
components. Some spaces serve as channels for
blood vessels that supply bone cells with
nutrients. Other spaces act as storage areas for
red bone marrow. Depending on the size and
distribution of the spaces, the regions of a bone
may be categorized as compact or spongy.
Overall, about 80% of the skeleton is compact
bone and 20% is spongy bone.