BASIC ANATOMY OF BONE AND ITS TYPES OSSIFICATION IS ALSO EXPLAINED BENEFICIAL FOR MEDICAL EXAMS

1. Dr. Ayshah Hashimi

2. Introduction
Bone or osseous tissue is a specialized type of structural and supportive connective tissue that makes up the
body's skeleton
Functions
• Shape & Support- Form the framework and shape of the body
• Lipid & Mineral storage- It is a reservoir holding adipose tissue within the bone marrow and calcium within
the hydroxyapatite crystals
• Hematopoiesis- provides the medium—marrow—for the development and storage of blood cells
• Protection- surrounds the major organs of the body (Brain, Lungs, Heart)

3. Epiphysis
Gross anatomy of Bone
A long bone has 3 parts
• Epiphysis (The wider section at each end of the bone)
• Metaphysis (the transitional zone at which the diaphysis and epiphysis
of a bone come together)
• Diaphysis/ Shaft (mid-section of the bone is hollow)
There are 3 types of bone tissue
• Cortical or Compact bone tissue
• Spongy or Cancellous bone tissue
• Subchondral tissue
Epiphysis
Metaphysis
Metaphysis
Diaphysis
Epiphyseal Line

4. Epiphysis
Epiphysis
Epiphysis
Epiphysis
Metaphysis
Metaphysis
Metaphysis
Metaphysis
Diaphysis
Diaphysis
Epiphysis consists of-
• Articular cartilage
• Compact bone tissue
• Spongy bone tissue
• No periosteum

5. Epiphysis
Epiphysis
Epiphysis
Epiphysis
Metaphysis
Metaphysis
Metaphysis
Metaphysis
Diaphysis
Diaphysis
Metaphysis consists of-
• Compact bone tissue
• Spongy bone tissue
• Periosteum

6. Epiphysis
Epiphysis
Epiphysis
Epiphysis
Metaphysis
Metaphysis
Metaphysis
Metaphysis
Diaphysis
Diaphysis
Diaphysis consists of-
• Periosteum
• Compact bone tissue
• Spongy bone tissue
• Endosteum
• Medullary cavity

7. • Epiphysis has major spongy bone tissue and less compact
bone tissue with articular cartilage in place of periosteum
• Diaphysis has major compact bone tissue lined by thick
periosteum and less compact spongy tissue with medullary
cavity in center lined by endosteum
• Metaphysis has major spongy bone tissue and less compact
bone tissue with thin periosteum

8. Compact Bone
Spongy Bone

9. Microscopic structure of Bone
• Osteocyte are arranged in a concentric pattern with the help of projections that connect each other is called
as Lamella and multiple lamella are arranged in vertical cylindrical form (5-20 in number)
• Osteoblasts secretes collagen fiber in between these concentric lamella
• Within these collagen fibers a hard inorganic hydroxyl-apatite is deposited
• Hydroxylapatite forms a hollow space around the osteocytes called as lacuna and space around the
projection is called as canaliculi
• Collagen fibers forms the organic part while this hard deposition constitute inorganic part of the bone
• Central hollow tube like structure is called as central canal or Haversian canal (vessels and nerves passes
through it )
Lamella
Osteocyte

10. • Osteod is organic portion of the bone (bone without mineralization)
• Perforating canals/Volkmann’s canal are branching canals that pierce the lamella and connects different
central canal through which small blood vessels runs and supplies the osteocytes
• Multiple concentric lamella with central canal and perforating canal is called as OSTEON or Haversian
system (Structural and functional unit of bone)
• Between these concentric lamella is interstitial lamella
• Inner circumpherential lamella is found in the center
• Outer circumpherential lamella is found on the inner side of the periosteum
Osteod Osteon
Volkmann’s canal
Interstitial Lamella
Outer Circumferential
Lamella
Inner Circumferential
Lamella
Haversianl Canal

11. Periosteum
• An outer covering of a bone that protects and provide site for attachment of muscles, tendon and ligaments
• It assists in repairing fracture as it contains progenitors stem cell
• Provides nutrition to bone tissue as it contains tiny blood vessels
• It consists of 2 layers outer is fibrous layer and inner osteogenic layer
• Fibrous layer has fibrocytes
• Osteogenic layer has osteo-progenitor cells
• Osteo-progenitor cells converts or modified into chondroblasts or osteoblasts cells
• Connected to bone tissue by collagen fibers called as Sharpey’s fibers
Fibrous layer
Bone tissue
Osteogenic layer
Endosteum
Periosteum
Osteoblasts, Fibrocytes And Osteoclasts Cells

12. Endosteum
• Endosteum layer lines the medullary cavity
• It consists of 2 type of cells
 Osteoblasts cells
 Osteoclasts cells
 Fibrocytes
 Osteo-progenitor cells
• Osteoblasts cells forms type I collagen protein and non-collagen protein (0steo-Nectin and osteo-Calcin)
Mineralization
Ca, P and H2O in blood are present on the form of Ca(OH)2 + H3(PO4) needed for bone mineralization
Ca10(PO4)6(OH)2 Hydroxyl-Apatite is solid crystal like
Calcification is deposition and stabilization (osteo-Calcin stabilizes Ca⁺ ⁺ ion while osteo-Nectin connects it with
collagen fibers) of Hydroxyl apatite in the bone

13. Cells of Bone
• Mesenchymal cells (present in bone marrow and form almost all type of connective tissue e.g. blood cells,
muscle, tendon, bone tissue etc.)
• Osteo-progenitor cells (arises from mesenchymal cells)
• Location- Periosteum, Endosteum, Haversian and Volkmann's canal
• Undifferentiated and unspecialized cells
• Multiply rapidly
• Converts into osteoblasts cells
• Osteoblast secretes collagen and deposit hydroxyl apatite
• Entrapped osteoblast within its own secretion modifies and stops multiplying and are called as osteocytes
cells
• Osteocytes monitors the health of the bone tissue, incase of any damage, osteocyte signals Osteo-
proginators for production of osteoblasts cells

14. Osteoclasts Cells
• Not derived from Osteo-progenitor cells
• Multinucleated cells
• Arises from aggregation of approx. 2-50 monocytes in bone
• Function as removal of bone
• Possess mineral degrading substance (H⁺) and organic degrading substance (Collagenase and Cathepsin K)

15. Classification of Bone Type
• Bones make up the skeletal system of the human body and are responsible for somatic rigidity, storage of
different micronutrients, and housing bone marrow. The bones are essential for the bipedal posture
• There are 300 bones at birth which becomes 206 by adulthood, not including teeth and sesamoid bones
(small bones found within cartilage)
• There are 80 axial bones (head, facial, hyoid, auditory, trunk, ribs, and sternum) and 126 appendicular bones
(arms, shoulders, wrists, hands, legs, hips, ankles, and feet)
• According to shape there are five types of bone
 Long bone
 Short bone
 Flat bone
 Irregular bone
 Sesamoid bone
• According to ossification there are two types
 Endochondral Ossification
 Membranous Ossification

16. Endochondral ossification
• A process in which the hyaline cartilage plate is slowly replaced by bony tissue
• All bones ossify through endochondral ossification except flat bones of skull, mandible and clavicle
• There are six steps of endochondral ossification
Step 1. Formation of cartilage model
 Mesenchymal cells multiplies rapidly
 Comes closer and arrange in a shape of bone
 Mesenchymal cells modifies into chondroblast cells
 Chondroblast cells forms hyaline cartilage
 Perichondrium is formed on the surface

17. Step 2. Growth of cartilage model
 As chondroblast forms extracellular matrix and gets embedded, it transform into Chondrocyte
 Chondrocytes grow in both directions and increases in size of the bone
 The vertical growth in chondrocytes is called as interstitial or endogenous growth, it increases the length of
the bone
 Osteogenic layer of perichondrium modifies into osteoblast cells and transform into periosteum
 Osteoblast cells multiply and forms collagen fiber and deposits hydroxyl-apatite
 The growth in osteoblast is side to side thus this growth is called as exogenous or appositional growth

18. Step 3. Development of primary ossification center
• In the middle of the bone, chondrocytes undergoes hypertrophy with deposition of calcium salts
• Upon calcification, the middle portion is devoid of nutrients because blood cannot pass through
the hard calcified region resulting in death of chondrocytes
• Nutrient foramen is formed to supply nutrients to this region
• Appositional growth transforms perichondrium into periosteum
• Osteocytes are formed calcification occurs and result in formation of primary centre

19. Step 4 & 5. Development of medullary cavity and Secondary Ossification Center
• Primary ossification center grows towards both the ends and the bone formed is spongy bone
• Osteoclast cells present in the periphery starts to break the trabeculae and because of this a
cavity is formed in the center called as Medullary cavity
• Epiphyseal artery enters at the end and secondary ossification center develops and forms
permanent spongy bony tissue
• In the middle, the spongy bone tissue is converted into a compact bone tissue

20. Step 6. Formation of epiphyseal plate
• Secondary ossification leaves the chondrocytes at
the periphery
• The hyaline cartilage covers the ends of the bone
for articulation
• Between epiphysis and diaphysis the left over
chondrocytes remains active and is responsible for
the length of the bone and thereby the height and is
called as epiphyseal plate
• In adulthood, this metaphysis region is also ossified
and appears as epiphyseal line

21. • Membranous ossification
 Bones develop directly from sheet of mesenchyme connective tissue
 Example of membranous ossification is Flat bones of skull, clavicle, mandible etc.
 There are four steps of intramembranous ossification
 Mesenchymal cells group into clusters and ossification center forms
 osteoblast secretes osteoid thereby entrapping osteoblast within that transforms into osteocyte
 Osteoid secreted around the capillaries result in trabecular matrix and osteoblast present on the
surface of the spongy bone becomes periosteum. The trabecular bone crowds and condense into
red marrow
 Compact bone develops superficial to the trabecular bone

22. Long Bones
• Develop from endochondral ossification
• Has 2 ends (Epiphysis) and a shaft (Diaphysis)
• Epiphysis is mainly spongy while diaphysis is made up of compact bone tissue
• E.g. Humerus, Ulna, Radius, Femur, Tibia, Fibula, Metacarpals, Phalanges etc.
Short Bones
• Thin compact bone covers vast spongy bone
• Cuboidal in shape
• E.g. Carpals and Tarsals
Flat Bones
• 2 layers of compact bone covers the spongy bone
• E.g. Skull bones, Ribs, Sternum, Scapula, Clavicle, Mandible

23. Irregular Bones
• Thin compact covers the most spongy bone
• E.g. Vertebras, Facial bones (Hyoid, Ethmoid, Sphenoid, Vomer)
Sesamoid Bone
• bones embedded within tendons
• Found in the end of long bones
• E.g. patella etc.