Bone lecture
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Transcript of Bone lecture
1- Is the highest differentiation of CT
2-Form the skeleton
3-sites for attachment of the muscles and
tendons essential for locomotion.
4-Supports and protects vital organs
5- Harbors bone marrow, fat store
6- Acts as a reservoir of Calcium & Phosphate
BoneBone
Gross anatomy of bones
Compact bone Spongy
(trabecular) bone
Blood vessels Medullary
cavity Membranes
PeriosteumEndosteum
Cartilage BoneWater content: ~70%Collagen II: ~40% of organic content.
Grows interstitially and by apposition.
Avascular
Water content: 25% Collagen I: 90% of organic
content.
Other Ground Substance
Osteonectin: anchor collagen to bone mineral.
Osteocalcin: Calcium binding protein involved in bone calcification.
Osteopontin: Binding of osteoblasts and osteoclasts to bone.
Grows only by apposition.
Highly vascular
Types of BoneTypes of Bone(Flat, long, short and irregular bones)(Flat, long, short and irregular bones)
Long bones
Diaphysis= shaft Epiphyses at the ends: covered with “articular”
(=joint) cartilage Epiphyseal line in adults
Kids: epiphyseal growth plate (disc of hyaline cartilage that grows to lengthen the bone)
Blood vessels Nutrient arteries and veins through nutrient foramen
Cells Fibers
Matrix1. Osteogenic cells2. Osteoblasts3. Osteocytes4. Osteoclasts
Type 1 Collagen (90%)
Structure of bone
Organic1.GAGs: Hyaluronan, Chondroitin & Keratan Sulfate2.Proteoglycans
InorganicHydroxyapatite crystals
[Ca10(PO4)6(OH)2]Calcium phosphate
1. Osteogenic or osteoprogenitor cells:
- stem cells derived from mesenchyme. - They are spindle-shaped with elongated nuclei.- present in:
• inner layer of periosteum • endosteum • lining the vascular canals of compact bone.
Function: differentiation into osteoblast cells.
Cells of Bone
2. Osteoblasts: - young bone cells, located at the surfaces .- known as bone-forming cells.- cuboidal cells with short, slender processes.- has a large nucleus + prominent nucleolus.- The cytoplasm: basophilic, well-developed Golgi
apparatus, mitochondria.- can not divide. Functions: synthesis of the organic component and
deposition of inorganic components of bone matrix.
3. OsteocytesOnce the osteoblast cells surrounded by matrix:1. The cytoplasmic processes become more evident. 2. The cells become flattened.3. lacunae and canaliculi appear
osteoblasts are referred to as Osteocytes. - Processes make contact via gap junctions (?????)- can not divide.- faint basophilic cytoplasm.- Dark nucleus.- Few RER & Golgi. Function:maintenance of the bony matrix.
4. Osteoclasts:- Bone-eating cells. - found in depressions known as Howship’s lacunae.- derived from the fusion of blood monocytes.- very large cells (20 – 100 µm).- multinucleated (5 –50).- acidophilic cytoplasm. -The surface facing the bone matrix is irregular.- contain a well-developed Golgi + great number of
lysosomes.Function:secrete acid collagenase, and proteolytic enzymes that
attack the bone matrix and liberate the calcified ground substance.
Compact (dense) and Spongy (cancellous) Bone
cancellous bone
Compact bone
• found in diaphysis (shaft) of long bones.
• dense, hard, with no cavities.
• found in epiphyses (bulbous ends) of long bones, flat (Skull) & irregular (vertebrae) bone
• with cavities.
.
1.Compact boneCompact bone is a solid mass composed of:
1. Haversian system.2. Circumferential lamellae.3. Interstitial lamellae (O&I). 4. Periostem 5. Endosteum
1. Haversian system (osteon):the structural unit of compact bone, composed of:1. Haversian canal: it runs parallel to the long axis of bone. It
contains loose connective tissue rich in blood vessels and nerves and lined with osteogenic cells.
2. Bone lamellae: they are calcified osteoid tissue arranged in concentric layers (4-20 layers).
3. Osteocytes: they are present in their lacunae between the bone lamellae.
2. Circumferential lamellae:bone lamellae under the periosteum (outer circumferential lamellae)
or adjacent to the endosteum (inner circumferential lamellae).3. Interstitial lamellae: lamellae between Haversian system
Volkmann`s canal: transverse or oblique canals that connect haversian canals together.
Haversian system (osteon), Haversian canal (HC) and Volkmann’s canal (VC)
Transverse section Longitudinal section
Osteon
VC
HC
VC
HC
•Nutrients diffuse from vessels in central canal•Alternating direction of collagen fibers
increases resistance to twisting forces
Isolated osteon:
• Canaliculi
• Tiny canals
• Radiate from the central canal to lacunae
• Form a transport system
Figure 5.3
Dark spots are called ‘lacunae’ and would contain osteocytes in living bone
Central canal containing an artery, vein, lymph vessel and nerves.
Periosteum: Connective tissue membrane Covers entire outer surface of bone except at epiphyses Two sublayers
1. Outer fibrous layer 2. Inner (deep) cellular osteogenic layer (Osteoblasts: bone
depositing cells, also osteoclasts: bone destroying cells) Secured to bone by perforating fibers (Sharpey’s fibers)
Endosteum: Lines the internal surfaces of bones - one cell thick Is also osteogenic
• Important roles of the periosteum and endosteum: 1. nutrition 2. histogenesis and repair.
Cancellous Bone
1- NO Haversian system.2- Irregularly arranged bone. 3- Irregular marrow spaces.4- Periostem and endosteum.