Bone Tissue
Dr. Amam Ali Amam
PhD: Periodontal Disease
Skeletal Tissues
Cartilage
1- Hyaline.
2- Fibrous.
3- Elastic.
Bone
1- Compact.
2- Cancellous
( Spongy ) .
Bone tissue
1. It is a specialized connective tissue.
2. Highly vascularized.
3. Metabolically very active.
Bone tissue
4 forms of Bone:
1- Long Bone: femur.
2- Short Bone: carpal bones.
3- Flat Bone: costae, scapula (shoulder).
4- Irregular Bone: sacrum.
Bone
is composed of
1- Cells
2- Extracellular matrix
1- osteoblasts.
2- osteocytes
3- osteoclast.
1- Fibers
2- Ground substance
Fibers
• Fibres :Type I collagen.
spaces within this three- dimensional structure,
are the initial site of mineral deposition.
• alkaline phosphatase
• calcium homeostasis
Ground substance contain:
I- proteoglycan .
II- several specific
structural glycoproteins.
1- organic matrix
2- inorganic salts
Ground substance contain:
1- 30% organic matrix: proteoglycans and a group
of non-collagen molecules
osteocalcin, osteonectin, sialoproteins
2- 70% inorganic salts: Calcium and Phosphate
( hydroxyapatite crystals ) Magnesium carbonate, sodium
and potassium ions , Hydroxyapatite crystals Ca10(PO4)6(OH)2
Bone matrix
• Bone glycoproteins may be responsible for promoting
calcification of bone matrix.
• The association of minerals with collagen fibers is
responsible for the hardness and resistance of bone
tissue.
• Because of the removal of the organic part of the
matrix , it becomes fragile, breaking and crumbling
easily when handled.
Bone Cells
1- osteoblasts: synthesize the organic components of the matrix
2- osteocytes:
found in cavities ( Lacunae) within the matrix
3- osteoclast: multinucleated gaint cells involved in the resorption
& remodeling of bone tissue
Osteoblasts ,1 .
Function: the synthesis of the organic components of
bone matrix (type I collagen, proteoglycans, glycoproteins).
Location: at the surfaces of bone tissue , side by side
(resembles simple epithelium).
Receptors: for parathyroid hormone, when activated
produced a cytokine called osteoclast stimulating factor.
Lacuna: some osteoblasts are gradually surrounded by
newly formed matrix and become osteocytes.
Osteoblasts, 2.
Shape: cuboidal to columnar, flatten, when their
synthesizing activity declines.
Cytoplasm: basophilic.
Cells: Polarized.
osteoblasts.
osteocytes.
Derive from osteoblasts.
Lie in the lacunae, situated between lamella of matrix .
Function: synthesize the organic components of the matrix.
Shape: flat, almond-shaped
Chromatin: condensed nuclear chromatin
Golgi complex.
Long–living cells.
Osteocytes
Osteoclast, 1
Size: very larg. from osteoblasts.
Cells: branched motile.
Nuclei: dilated portions of the cell body contain
5-50 Nuclei.
Lie: in areas of bone undergoing resorption
(Hownship's lacunae).
Derived: from the fusion of bone marrow-derived
mononucleated cells.
Osteoclast, 2
Function:
Secretes collagenase and other enzymes and
pumps protons into subcellular pocket
Promoting the localized digestion of collagen.
Dissolving calcium salt crystals.
Activity: controlled by cytokines & hormones.
Receptors: for calcitonin & a thyroid hormone.
osteoclast.
osteoclast.
Special structures,1
1- Canalculi:
the exchanges between osteocytes & blood
capillaries depend on communication through
Canalculi, which are thin, cylindrical spaces
that perforate the matrix.
2- Endosteum: A layer of tissue containing
osteogenic cells and covering internal surfaces
of all bones.
Special structures,2
3- Periosteum: A layer of tissue containing
osteogenic cells and covering external
surfaces of all bones.
4- Hownship’s lacunae: depressions in the
matrix where oseoclasts lie.
5- Clear zone: area surrounding the ruffed
border & rich in action filaments.
Bone tissue functions
1- mechanical.
2- metabolic.
1. Supports muscles, fleshy tissue.
2. Protects vital (important) organs.
3. Harbors the bone marrow where blood cells
are formed.
4. It is reservoir of body calcium, phosphate
and other ions (salts).
5. Multiple skeletal muscles function .
6. Contain haemopoietic bone marrow
7. Organism movement
Types of Bone tissue
Microscopic
examination
1 Compact
1bone
2- Cancellous
(spongy)
bone
1- Woven
bone.
2- Lamellar.
Compact
Bone
Cancellous
(spongy) Bone
The Body of long bone
The Epiphyses of long bone
The surfaces of short &
Flatted bone
a haversian system
The Body of short & Flatted
bone
No a haversian system
1- Compact bone: dense areas without cavities.
2- Cancellous (spongy) bone:
areas with numerous interconnecting cavities.
Epiphyses: is composed of spongy bone covered by
a thin layer of compact bone.
Located: long bones
Diaphysis: is almost totally composed of compact
bone with a small component of spongy bone on its
inner surface around the bone completely surrounded
by compact bone.
Located: short bones, calvarias.
Microscopic examination,1
1- Woven bone: (primary, immature)
is the first bone tissue to appear in embryonic
development and in fracture repair and other
repair processes.
Characterized : by random diposition of
fine collagen fibers.
Location: (near the sutures of the flat bones of
the skull, in tooth sockets, and in the insertions
of some tendons) its replaced in adult by
Secondary bone tissue
Microscopic examination, 2
2- Lamellar bone: (secondary, mature)
usually in adults.
Characterized: by collagen fibers arranged in
lamellae, surrounding a haversian system:
( a canal containing blood vessels, nerves and
loose connective tissue).
Types of Bone tissue
Histogenesis
Bone can be formed in 2 ways:
1- Intramembranous ossification: direct mineralization of
matrix secreted by osteoblasts.
2- Endochondral ossification: deposition of bone matrix on
a preexisting cartilage matrix
Woven bone: Primary bone is a temporary tissue
and is soon replaced by the definitive lamellar
or secondary bone.
Histogenesis
During bone growth: areas of primary bone,
areas of resorption &
areas of secondary bone
appear side by side.
This combination of bone synthesis & removal (remodeling)
occurs not only in growing bones but also throughout
adult life, although its rate of change in adults is considerably
slower
Intramembranous ossification
Bone growth and remodeling.
Bone growth is generally associated with partial
resorption of preformed tissue and the simultaneous
laying down of new bone (exceeding the rate of bone loss).
Bone remodeling (bone turnover) is very active in young
children, it can be 200 times faster than the rate in adults
Metabolic role of bone tissue.
The skeleton contains 99% of the total calcium
of the body and acts as a reservoir of calcium
and phosphate ions.
The concentration of calcium ions in the blood
and tissues in stable because
of a continuous interchange between Blood
Calcium and bone calcium.
Bone apposition - histogenesis
1- intramambrane ossification
Bone apposition - histogenesis
2- endochondral ossification
Resting zone.
Proliferating zone.
Hypertrophic zone.
Calcified cartilage zone.
Ossification zone.