This document describes the structure and formation of bone. It discusses the microscopic and macroscopic structure of both compact and cancellous bone, including the cells involved like osteoblasts and osteoclasts. It explains the two types of ossification - endochondral, where bone forms from cartilage, and intramembranous, where bone forms directly from mesenchymal tissue. Key structures of bone are also summarized such as the Haversian system, periosteum, and differences between long, flat, and irregular bones.

1. BONES and OSSIFICATION

2.  Bone or osseous tissue is a rigid form of
connective tissue comprising most of
the skeleton of higher vertebrates.
 Consists of cells, fibers(collagenous)
and ground substance/matrix
(calcified).
 Extracellular components are calcified
making it hard and brittle.

3.  Ca3(PO4)2 . Ca(OH)2 makes up the
major portion of salts present in bone.
 PO4 resemble the structure of
hydroxyapatite.

4. FUNCTIONS
1. Provides for the internal support of
the body attachment of muscles and
tendons for locomotion.
2. Encloses the blood forming elements
of bone marrow and protects vital
organs of the cranial and thoracic
cavities.

5. 3. Metabolic function as site for the
storage of Ca in blood and other body
fluids.

6. MACROSCOPIC STRUCTURE of
BONE
2 Forms of bones based on their structure
1. Cancellous or spongy (substantia
spongiosa)
2. Compact (substantia compacta)
CANCELLOUS BONE- consists of a 3
dimensional lattice of branching bony
spicules or trabeculae enclosing a
system of intercommunicating spaces
that are occupied by bone marrow.

7. CANCELLOUS BONE
 No haversian
sysytems
 Trabeculae are lined
by a delicate layer of
tissue called
ENDOSTEUM which
contains
osteoprogenitor
cells,
osteoblasts,osteocla
sts.

8. COMPACT BONE- appears as a solid
continuous mass containing spaces
seen only with the aid of microscope.
LONG BONE
a. EPIPHYSES- are the two spongy ends
of the long bones.
b. DIAPHYSES- the thick walled hollow
cylinder.

9. COMPACT BONE

10. c. MEDULLARY CAVITY- central cavity of
the shaft.
d. EPIPHYSEAL PLATE is the cartilaginous
plate separating the epiphyses from the
diaphyses. It is the usual ossification
center in cartilaginous type of bone
formation. It is the place where growth
takes place.

11. e. METAPHYSES are columns of spongy
bone found at the transition between
the epiphyseal plate and the diaphyses.
f. PERIOSTEUM- a layer of connective
tissue that covers the surface of the
bones.
g. ENDOSTEUM is a thin cellular layer
that lines the bone marrow cavity. Both
the periosteum
and the endosteum are endowed with
osteogenic properties.

12. LONG BONE

13. EPIPHYSIS
 center of ossification
in the epiphyseal
cartilage SC
 D diaphysis
 C compact bone
 GP growth plate

14.  Pericranium is the periosteum that
covers the skull.
 All portions of the bone not covered
with articular cartilage is covered with
periosteum.
 The periosteum consists of an outer
layer of dense fibrous connective tissue
which contains larger blood vessels.

15.  Middle layer of the periosteum is dense
elastic tissue which is adherent to the
bone.
 The third layer of the periosteum
contains osteoblasts, especially in
growing bones.
 PERFORATING FIBERS OF SHARPEY are
coarse bundles of collagenous fibers
from the outer layer of the periosteum
that penetrate the outer circumferen-

16. tial lamellae and interstitial system of
the bone.
FLAT BONES
- Substancia compacta forms on both
surface, inner and outer tables.
- Layer of spongy bone varying thickness
between these tables constitute the
diploe.

17. MICROSCOPIC STRUCTURE
OF BONES
 Structure of Bone in General
1. Matrix is composed of calcified subs-
tance made up of organic and
inorganic elements deposited in
lamellae or layers.
2. Collagenous fibers are embedded in
an amorphous ground substance
consists of inorganic elements Ca, Mg,

18. Na.
3. Osteocytes are found in cavities called
lacunae.
CANALICULI- are extensions of lacunae
where cytoplasmic processes of cells
lodge.It serves as continous system of
intercommunication for th epasssage of
metabolites and nutritive materials.

19. A Single Haversian System
 C canaliculi
 L lacuna

20. BONE CELLS
 Osteoprogenitor cells
 Osteoblasts
 Osteocytes
 osteoclasts

21. OSTEOPROGENITOR CELLS
 Relatively undifferentiated cells having
the capacity for mitosis and for further
structural and functional specialization.
 Pale staining oval or elongated nuclei.
 Found in free bony surfaces,
endosteum, periosteum, lining the
haversian canals and at the epiphyseal
plate of growing bones.

22.  Active during normal growth of bones
and in adult life.
 Activated during healing of fractures or
repair of other forms of injury.
 Undergo division, transforming into
osteoblasts or unite giving rise to
osteoclasts.

23. OSTEOBLASTS
 Responsible for the formation of bone
matrix and found on the surfaces of
developing bones.
 Nucleus located often at the end of the
cell farthest from the bony surface.
 Elongated mitochondria are fairly
numerous: the golgi apparatus is well
developed, owing to its large content

24. RNA, the cytoplasm appears intensely
basophilic.

25. OSTEOBLASTS AND OSTEOID

26. OSTEOCYTES
 Principal cells of fully formed bone residing in
lacunae.
 Processes of neighboring osteocytes are in
contact at their ends.
 Their apposed membranes form gap junctions
or nexuses at their site of contact.
 Play an active role in the release of Ca from
bone to blood, thus, it participate in the
homoeostatic regulation of its concentration
in the body fluids.

27.  OSTEOLYSIS- it is a physiological
process where bony matrix immediately
surrounding the osteocytes in modified
and bone salt is resorbed.

28. OSTEOCLASTS
 Giant multinucleated cells about 20-100
um. In diameter, that are closely
associated with areas of bone
resorption.
 Active agents in bone resorption.
 Frequently found in shallow concavities
in the surface of the bone called
LACUNAE OF HOWSHIP.

29. OSTEOCLASTS
 Specimen with low
serum Ca level.
 H howship’s lacunae
 O osteoclasts
 Os osteoid (organic
matrix before
mineralization)

30. A. SPONGY OR CANCELLOUS
BONE
 Found in diploe of flat bones of the skull
and face; in the middle or inner portion
of all other bones.
 Found only as a thin portion inside the
diaphysis of long bone but, constitutes
a greater part of the epiphyses.

31.  Simple in structure, consists of
irregular, branching bony spicules or
trabeculae (lamellae) that form a
network.
 Spicules are made up of layers
consisting organic and inorganic
elements.

32.  Cells are embedded in the trabeculae or
spicules.
 Cells are small, ovoid in shape with fine
cytoplasmic projections extensding to
the canaliculi.
 Trabeculae are thin usually not
penetrated by blood vessels.
 Absence of haversian system.

33.  Bone cells are nourished by diffusion from the
surface thru the minute bony canaliculi that
interconnect lacunae and extend to the
surface.
 Marrow cavities or intertrabecular spaces are
lined by a cellular membrane called
ENDOSTEUM which is composed of flattened
cells that are potential bone and blood
forming cells.

34. B. COMPACT BONE
 Found on the outer surface of all bones.
 Shaft of diaphyses of long bone, spongy
bone found with in is very thin.

35. COMPACT BONE
1 haversian canal
2 interstitial lamellae

36. 1 haversian canal

37. 1 haversian canal
2 interstitial lamellae
3 outer circumferential
lamellae
4 volkmann’s canal

38.  A cross section and
longitudinal section
thru an osteon
showing the bone
lacunae and bone
canaliculi.

39.  The osteocytes with
their extensions.

40. PERIOSTEUM
 A dense, fibrous membrane covers all
portions of the compact bone except
those covered by articular cartilages.
 Outer layer is dense connective tissue
containing blood vessels.
 Inner layer is made up of loose
fibroelastic ct containing flattened cells
which are potential osteoblasts or bone
forming cells.

41.  Flattened fibroblasts has osteogenic
properties in case of bone injury where
they form new bone.
 Immediately beneath the periosteum at
the external surface of the bone are
several lamellae that extend uninterrup-
tedly around the circumference of the
shaft.Constitute the PERIOSTEAL OR
EXTERNAL OR BASIC
CIRCUMFERENTIAL LAMELLAE.

42.  Surrounding the central medullary
cavity are several lamellae constituting
the ENDOSTEAL OR INNER
CIRCUMFERENTIAL LAMELLAE.
 Between these external and internal
circumferential lamellae are located the
haversian systems.

43. PERIOSTEUM
 Haversian systems
(H)
 Irregularly interstitial
system (I)
 Cortical bone (C)
 Periosteum (P)
 Osteocytes (O)

44. ACTIVE PERIOSTEUM

45. MATURE PERIOSTEUM

46. HAVERSIAN SYSTEM
 Is the structural and functional unit of
the bone tissue. It consists of the
following:
1. LACUNAE- are the bone spaces that
are arranged concentrically around the
haversian canal.
2. Each lacuna contain the different bone
cells or osteocytes.

47. 3. The lacunae are arranged in layers
called LAMELLAE.
a. inner circumferential lamellae- are
the layers of lacunae that surround the
haversian canal.
b. outer circumferential lamellae are
the layers of lacunae that are found on
the outskirts of the haversian system.

48. c. Interstitial lamellae are the lacunae
found in between the Haversian
systems.
4. Canaliculi are the minute canals that
connect the lacunae.
5. Haversian canal is the big passage at
the center of the Haversian system.
Each canal contains artery and vein and
nerve fibers.

49. 6. Volkmann’s canal is the canal that
serve as the communication between
the Haversian canals.

51. OSSIFICATION
 The term used for bone formation.
There are two types:
A. ENDOCHONDRAL- is a type where
bone develops from cartilages.
B. MEMBRANOUS- is a type where the
bone develops from membranes.

52.  In both types the following steps
occur:
1. First, there is proliferation of
mesenchymal cells at the site of
ossification.
2. In the endochondral type these cells
differentiate into cartilage cells.

53. 3. The cartilage cells will become the
young bone cells, called osteoblasts.
4. The osteoblasts mature to form
osteocytes which are the bone cells.
5. The bone cells which are matured will
die and form osteoclasts.
6. The osteoclasts will undergo resorption

54. and calcification will take place
leaving a hard substance.
c. The intramembranous type of
ossification occurs in the bones of the
skull.
1. In the area where bone develops are
occupied first by mesenchymal cells.

55. 2. Clusters of mesenchymal cells
differentiate into osteoblasts. These are
taking place in centers of ossification.
3. After their appearance the osteoblasts
secrete the organic matrix of the bone.
4. Osteogenic cells also develop in this
area and this will serve as the source of
the rest of the osteoblasts.

56. 5. Trabeculae develop. This are spicules
that radiate out from the ossification
centers. This result in the formation of
the cancellous bones.

58. ENDOCHONDRAL
OSSIFICATION
 Metaphysis
 Blue stained spicules
of calcified cartilage
matrix surrounded
by osteoblasts.
 Newly formed
woven bone stained
pink.

59. INTRAMEMBRANOUS
 B spicules of woven
bone
 M primitive
mesenchyme