BONE HISTOLOGY TUTORIAL
By the end of this tutorial students should know:
1. Basic classification of bone, based on its gross and
2. Haversian system and its structure
3. Difference between spongy and compact bone, and
woven and lamellar bone.
4. Types of bone cells.
• Bone is a variety of connective tissue characterized by
deposition of mainly salts of calcium phosphate with
collagenous fibers and a large amount of water in its matrix.
• The three basic components of connective tissue i.e., cells,
fibers and ground substance form the organic part of bone.
• Calcium is the inorganic part of ground substance.
• Bone is hard, its hardness is due to the inorganic minerals.
Bone serves as a storage site for calcium and phosphate.
TYPES OF BONE
There are three kinds of mature bone:
; Compact bone: also called dense bone or cortical
; Spongy bone: also called cancellous bone,
trabecular bone or medullary bone.
; Woven Bone.
STRUCTURE OF A BONE
A long bone e.g.., the femur consists of:
• Centre piece, the shaft (diaphysis) and a thickened head
(epiphysis) at each end.
• Bone is covered with a tough, strong membrane, the
periosteum which is richly supplied with blood vessels. • Beneath the periosteum is a layer of compact bone which is
thicker in the shaft than in the two heads.
• The shaft encloses a hollow, the marrow cavity, which is
lined with a thin soft membrane known as the endosteum.
• The marrow cavity contains a soft tissue richly supplied with
fat cells and blood corpuscles, the yellow marrow.
• The epiphysis of a long bone consist of spongy (or cancellous)
bone covered with a thin layer of compact bone. • This is made up of bony bars (or trabeculae) arranged in such
a way that they are able to resist any force which is applied
upon the bone.
• Between the bars are many tiny cavities filled with a red
marrow which contains numerous red blood corpuscles in
different stages of development
• The matrix is the major constituent of bone, surrounding the
• It has inorganic and organic parts.
INORGANIC PART OF BONE MATRIX
• The inorganic matter is mainly crystalline mineral salts and
calcium, present in the form of Hydroxyapatite.
• The matrix is initially laid down as unmineralized osteoid
(manufactured by osteoblasts).
• Mineralisation involves osteoblasts secreting Vesicles.
ORGANIC PART OF BONE MATRIX
• The organic part of matrix is mainly Type I collagen.
• Other factors present include:
• glycosaminoglycains, osteocalcin and osteonectin.
One of the main things that distinguishes the matrix of a bone from
that of another cell is that the matrix in bone is hard.
MICROSCOPIC STRUCTURE OF COMPACT BONE
• Under the microscope dense, compact bone shows a definite
and a characteristic pattern of arrangement.
• The ground substance of bone is arranged in concentrated
layers (lamellae) round the small canals.
• The canals called Haversian canals run parallel to the long
axis (shaft) of the bone.
• Haversian canals of different osteons are interconnected with
one another and the marrow cavity via Volkmann's canals
and contain a blood vessel, a nerve and a lymph vessel.
• Volkmann's canals provide major route of blood vessels
from marrow cavity to the Haversian canals.
• Each Haversian canal is surrounded by concentric layers of
bone matrix (called lamallae) and concentric rings of bone
forming cells (osteoblasts).
• Once bone cells have been completely surrounded by the
hard bone matrix, they are called osteocytes.
• The osteocytes are embedded in fluid-filled cavities within
the concentric lamellae.
• These cavities are known as lacunae and occur at regular
intervals in these concentric layers of bone tissue. • The lacunae are connected to one another and to the
Haversian canals by a system of interconnecting canals
known as canaliculi.
• Each Haversian canal, its concentric lamellae, lacunae with
osteocytes and canaliculi forms a long cylinder and is called
a Haversian system or osteon, the structural & functional
unit of bones.
LOCATION OF BONES
• Compact bone and spongy bone are found in specific
• In long bones, most of the thickness of the diaphysis is made
of compact bone, with a small amount of spongy bone facing
the marrow cavity.
• The ends (epiphyses) of long bones, however, consist
mostly of spongy bone covered with a shell of compact bone. • The flat bones of the skull have a middle layer of spongy
bone sandwiched between two relatively thick layers of
STRUCTURES OF LONG BONE
• The marrow surface of compact bone, and the spicules of
spongy bone, are lined by an (often single) layer of cells
called the endosteum (endosteal cells).
• Like the periosteal cells, these endosteal cells are also
osteoprogenitor cells, capable of becoming osteoblasts. (The
two names periosteal cells and endosteal cells refer to their
different locations, both function as osteoprogenitor cells).
• Spongy bone is composed of bone spicules, also called
trabeculae, of varying shapes and sizes.
• The spaces between the spicules are filled with marrow. • The composition of spongy bone (cells and matrix) is the
same as that of compact bone.
• In spongy bone, however, the lamellae of collagen are not
arranged concentrically around a central canal, but run
parallel to one another.
• Osteocytes sit in lacunae between lamellae.
WOVEN AND LAMELLAR BONE
• Bone can also be either woven or lamellar (layered).
• Woven bone is weak, with a small number of randomly
oriented collagen fibers, during periods of repair or
• After a break, woven bone quickly forms and is
gradually replaced by slow-growing lamellar bone on
pre-existing calcified Hyaline Cartilage through a
process known as "bony substitution”.
• Non-lamellar form of bone is normally found in rapidly
growing areas of embryonic or developing bone, and in
• Most woven bone is replaced by lamellar bone during
• The process of bone remodeling occurs continually in
the embryo, fetus and the adult.
TYPE OF BONE CELLS
• Osteoblasts secrete the collagen fibres and ground substance (matrix) of bone and are responsible for the calcification of the matrix.
• When an osteoblast is completely surrounded by matrix, it is called an osteocyte.
• Osteocytes are responsible for maintaining the matrix, and can both secrete and resorb matrix.
• Another type of cell called the osteoclast is responsible
for the resorption of bone.
• These large, multinucleated cells arise from monocytes.
They help to break down bone matrix.