SKELETAL SYSTEM PART 1 IS AN INTRODUCTION CLASS ABOUT BONE ANATOMY , DEVELOPMENT & OSSIFICATION PROCESS. BONE & CARTILAGE NORMAL HISTOLOGY & OSSIFICATION PROCESS ARE DISCUSSED IN DETAIL. HREST OF THE BONE PATHOLOGY WILL BE DISCUSSED IN OTHER SECTIONS.

1. Skeletal system part 1
INTRODUCTION
DR MEENU E V
MBBS MD DNB

3. BONE ANATOMY
Diaphysis : long shaft of bone
Epiphysis : ends of bone
Epiphyseal plate : growth plate
Metaphysis : b/w epiphysis & diaphysis
Articular cartilage : covers epiphysis
Periosteum : bone covering (pain
sensitive)
Sharpey’s fibers : periosteum attaches to
underlying bone
Medullary cavity: Hollow chamber in
bone
- red marrow produces blood cells
- yellow marrow is adipose
Endosteum: thin layer lining the
medullary cavity

5. Cells of Bone Tissue

6. • Osteoprogenitor cells:
- unspecialized stem cells
- undergo mitosis and
develop into osteoblasts
- found on inner surface of
periosteum and endosteum.
 Osteoclasts
- bone resorbing cells
- bone surface
- growth, maintenance
and bone repair

7. • Osteoblasts:
- bone forming cells
- found on surface of bone (arrow)
- no ability to mitotically divide
- collagen secretors
• Osteocytes:
- mature bone cells
- derived form osteoblasts
- do not secrete matrix material
- cellular duties include exchange of
nutrients and waste with blood.

8. BONE
Compact Bone – dense outer layer
Spongy Bone – (cancellous bone)
- honeycomb of trabeculae
(needle-like or flat pieces)
filled with bone
marrow

9. COMPACT BONE
 called lamellar bone
Central (Haversian) canals run longitudinally
- around canals are concentric lamella
- osteocytes occupy lacunae which are b/w the lamella
- radiating from lacunea r channels called canaliculi
 bvs and nerves penetrate
periosteum through horizontal
openings called perforating
(Volkmann’s) canals.
Osteon contains: central canal +
surrounding lamellae +
lacunae + osteocytes +

10. SPONGY BONE (CANCELLOUS BONE)
 trabecular bone tissue (haphazard arrangement).
filled with red and yellow bone marrow
 osteocytes get nutrients directly from circulating blood.
short, flat and irregular bone is made up of mostly
spongy bone

11. SKELETAL CARTILAGE
• Chondroblast : give rise to
chondrocytes & pd matrix
• Chondrocytes : cartilage
cells.
• Lacunae : small cavities
where the chondrocytes are
encased.
• Extracellular matrix :
jellylike ground substance.
• Perichondrium : layer of
dense irregular connective
tissue that surrounds the
cartilage.
• No blood vessels or nerves

12. BONE FORMATION
• The process of bone formation is called
ossification
• Bone formation occurs in four situations:
• 1) Formation of bone in an embryo
• 2) Growth of bones until adulthood
• 3) Remodeling of bone
• 4) Repair of fractures

13. TWO PATTERNS
• Intramembranous ossification
• Flat bones of the skull and mandible are formed in this
way
• Endochondral ossification
• The replacement of cartilage by bone
• Most bones of the body are formed in this way
including long bones

14. INTRAMEMBRANEOUS OSSIFICATION
• An ossification center
appears in the fibrous
connective tissue
membrane
• Osteoblasts secrete bone
matrix within the fibrous
membrane
• Osteoblasts mature into
osteocytes

15. Endochondral Ossification
Enlarging
chondrocytes within
calcifying matrix
Chondrocytes at
the center of the
growing cartilage
model enlarge
and then die as
the matrix
calicifies.
Newly derived
osteoblasts cover
the shaft of the
cartilage in a thin
layer of bone.
Blood vessels
penetrate the
cartilage. New
osteoblasts form a
primary ossification
center.
The bone of the
shaft thickens,
and the cartilage
near each
epiphysis is
replaced by shafts
of bone.
Blood vessels invade the
epiphyses and osteo-
blasts form secondary
centers of ossification.
Cartilage
model
Bone
formation
Epiphysis
Diaphysis Marrow
cavity
Primary
ossification
center
Blood
vessel
Marrow
cavity
Blood
vessel
Secondary
ossification
center
Epiphyseal
cartilage
Articular
cartilage
Replacement of hyaline cartilage with bone
Most bones are formed this way (i.e. long bones).