This document provides an overview of bone histology. It defines bone as a mineralized connective tissue composed of bone matrix and three cell types: osteoblasts, osteocytes, and osteoclasts. It describes the microscopic structure of compact and spongy bone, including osteons, central canals, lamellae, and trabeculae. It explains the functions of osteoblasts in bone formation, osteoclasts in bone resorption, and osteocytes in bone maintenance. Finally, it discusses the periosteum and endosteum, which cover the external and internal bone surfaces and provide nutrition and new osteoblasts.

1. Histology of the Bone
By:
Dr Mohammed Faez

2. Objective of The Lecture
• To know about definition of the bone.
• To master the basic structure of the
bone.
• To know about bone matrix and bone
cells.
• Illustrate and differentiate the three
type of bone cells.
• To know about the periosteum &
endosteum.

3. Bone
• Bone is a dense,
semirigid, porous,
calcified connective
tissue forming the
major portion of the
skeleton.
• It consists of a dense
organic matrix and an
inorganic, mineral
component.

4. Bone
• Bone is a specialized
connective tissue composed
of intercellular calcified
material, the bone matrix,
and three cell types:
osteocytes, osteoblasts and
osteoclasts
• All bones are lined on both
internal and external
surfaces by layers of tissue
containing osteogenic cells
endosteum on the internal
surface and periosteum on
the external surface.

5. Bone Functions
• Protects vital organs
• Supports soft tissue
• Movement
• Mineral storage
• Blood cell production

6. Microscopic structure
of compact bone
• The structural unit of
Compact bone is the
osteon,or haversian
system.
Each osteon
• Is an elongated cylinder
• Oriented parallel to the
• Long axis of the bone.

7. Microscopic structure
of compact bone
Osteon System:
• A central (Haversian)
canal with concentric
rings (lamellae) of bone
matrix running
lengthwise.
• Very strong!

8. Microscopic structure
of compact bone
• Central, or haversian
canal carries blood
vessels and nerves to all
areas of the bone.
• Canaliculi tiny canals that
radiate outward from the
central canals to each
lacunae space.
• Volkmann’s Canals:
canals that run at right
angles to the central
canals and perforate the
shaft of the bone.

9. Microscopic structure
of compact bone

10. Osteon
Central Canal
w/ blood vessels,
nerves
Lacunae w/
bone cells

11. Compact bone structure

12. Compact bone structure

13. Spongy Bone
• Spongy bone contains
trabeculae and spicules
giving it a honeycomb
appearance.
• Trabeculae: are
irregularly arranged and
contain lamellae and
osteocytes, but contain
no osteons as they
receive nutrients from
the marrow tissue.

14. Spongy bone histology

15. Bone Matrix
• 25% Water
• 25% Protein or organic
matrix
– 95% Collagen Fibers
– 5% Chondroitin Sulfate
• 50% Crystalized Mineral
Salts Hydroxyapatite
(Calcium Phosphate) Other
substances: Lead, Gold,
Strontium, Plutonium, etc.
• Combination provides
strength and rigidity
– Laid down by osteoblasts

16. Bone Matrix
• If mineral removed, bone is too bendable
• If collagen removed, bone is too brittle

17. Bone Cells
1. Osteoblasts: Bone
generating cells
“B” means building
2. Osteocytes: Mature
bone cells, spider
shaped and maintain
bone tissue
3. Osteoclasts: Bone
destroying cells
“C” means chewing

18. Osteoblasts
• Osteoblasts are
responsible for the
synthesis of the organic
components of bone
matrix (type I collagen,
proteoglycans, and
glycoproteins).
• Osteoblasts depends on
deposition of the
inorganic components
of bone.

19. Osteoblasts
• Osteoblasts are exclusively
located at the surfaces of
bone tissue, side by side, in
a way that resembles simple
epithelium.
• When they are actively
engaged in matrix synthesis,
osteoblasts have a cuboidal
to columnar shape and
basophilic cytoplasm.
• When their synthesizing
activity declines, they
flatten, and cytoplasmic
basophilia declines.

20. Osteoblasts

21. Osteocytes
• Osteocytes, which
derive from osteoblasts,
lie in the lacunae
situated between
lamellae of matrix.
• Only one osteocyte is
found in each lacuna.
• Lacunae: spaces
occupied by osteocyte
cell body

22. Osteocytes

23. Osteocytes

24. Osteoclasts
• Osteoclasts are very large
and branched motile
cells.
• Dilated portions of the
cell body contain from 5
to 50 (or more) nuclei.
• Osteoclasts are derived
from the mononucleated
cells; (engulf bony
material).
• Active osteoblasts
stimulate osteoclast
activity.

25. Osteoclasts
Resorption of bone
• Ruffled border: where
cell membrane borders
bone and resorption is
taking place.
• H ions pumped across
membrane, acid forms,
eats away bone.
• Release enzymes that
digest the bone.

26. Osteoclasts

29. Bone Resorption

30. Periosteum
• It consists of an outer
layer of collagen fibers
and fibroblasts.
• Bundles of periosteal
collagen fibers, called
Sharpey's fibers,
penetrate the bone
matrix, binding the
periosteum to bone.

31. Periosteum

32. Endosteum
• It lines all internal cavities
within the bone and is
composed of a single
layer of flattened
osteoprogenitor cells and
a very small amount of
connective tissue.
• The endosteum is
therefore considerably
thinner than the
periosteum.

33. Periosteum & Endosteum
• The principal functions
of periosteum and
endosteum are
nutrition of osseous
tissue and provision of a
continuous supply of
new osteoblasts for
repair or growth of
bone.

34. Periosteum & Endosteum