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The Skeletal System-Osseous Tissue & Skeletal Structure
The Skeletal System-Osseous Tissue & Skeletal Structure
• The skeletal system includes:– Bones– Cartilage– Joints– Ligaments– Other connective tissues
• Functions of the Skeletal System– Support against gravity
– Protection of soft internal organs
– Movement (Leverage)
– Storage• Minerals (calcium, phosphorous) – within the
matrix of bone tissue• Energy reserve (adipose) – within the yellow
marrow of long bones
– Blood cell production – within red marrow of spongy bone tissue
Bone tissue
• Anatomy of a bone
• Structure of bone tissue
• Formation and growth of bone
• Fracture and repair
• Effects of physiological processes on bone
Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones
Sutural bones
Anatomical Classification of Bones
Bones are classified by their basic shape
The parts of a long bone
• Diaphysis-shaft• Epiphyses- ends• Come together at
metaphyses• Articular cartilage
protects epiphyses• Periosteum covers bone • Medullary cavity contains
marrow; is lined by endosteum
Bone cells
Organization of bone tissue
compact
spongy
Compact vs. spongy bone
• Compact bone– External layer– Arranged in osteons– Lamellae are found
around periphery and between osteons
– Central canals connected to each other by perforating canals
• Spongy bone– No osteons– Arranged in trabeculae– Major type of tisse in
short, flat, irregular bones
– Much lighter than compact bone
– Supports red bone marrow
Blood and nerve supply to bone
• Abundant supply of blood
• May have several nutrient arteries
• Nerves accompany blood vessels
Ossification (osteogenesis)
• Bone forms within mesenchyme in layers (intramembranous)– Flat bones of skull and
mandible– Osteocytes secrete
calcium– Compact and spongy
bone form
Bone remodeling replaces old tissue
• Resorption by osteoclasts, deposition by osteoblasts
• Strengthens bone
• Repairs damaged bone
The Structure of a Typical Bone
• All bones have a combination of spongy (cancellous) & compact (dense) bone tissue
The Histological Features of Compact Bone
• Osteon/Haversian system - basic functional unit of compact bone
Concentric lamellae (layers) of matrix surrounding central (Haversian) canal
Osteocytes located within lacunae
Canaliculi branch out radially from lacunae
Central canals (containing BVs) run vertically down the length of the bone
Perforating (Volkmann’s) canals (containing BVs) run horizontally across the width
Bone Cells• In addition to Osteocytes, the mature bone
cells found within the matrix of bone tissue, there are three other cells that are associated with bones– Osteoprogenitor cells– Osteoblasts– Osteoclasts
Bone Cells
• Osteoprogenitor cells– Derived from mesenchymal cells– Can undergo mitosis– Mature into osteoblasts
Bone Cells
• Osteoblasts– Responsible for osteogenesis – create bone
tissue– Mature into osteocytes
Bone Cells
• Osteoclasts– Derived from embryological WBCs– Secrete enzymes for osteolysis –
resorb/break down bone tissue– Necessary for calcium homeostasis
Structure of a Typical Long Bone
diaphysis (compact bone)
The Structure of a Long Bone
diaphysis
epiphysis (spongy bone)
epiphysis
The Structure of a Long Bone
diaphysis
epiphysis
epiphysis
articular cartilage
articular cartilage
The Structure of a Long Bone
epiphysis
epiphysis
metaphysis – location of
• epiphyseal plate – in children
• epiphyseal line – in adults
diaphysis
metaphysis
articular cartilage
The Structure of a Long Bone
medullary cavity
• filled with yellow marrow in adults
• lined with endosteum
The Structure of a Long Bone
periosteum
Outer fibrous layer of dense irregular CT for attachment of tendons& ligaments; provides route for blood vessels & nerves; separates bone tissue from surrounding tissues
Double layered membrane surrounding bone except at articular cartilage
Inner cellular layer contains osteoprogenitor cells, osteoblasts, osteoclasts; therefore functions in bone growth & repair
Bone Formation and Growth• Ossification - Process of converting other
tissues to bone; begins around week 6-8 of embryological development
Two types of ossification processes occur during embryological formation:
• Intramembranous
•Endochondral
An Overview of the Skeleton
Skeletal Divisions• Axial skeleton (80 bones)
– Skull– Thoracic cage and sternum– Vertebral column
• Appendicular skeleton (126 bones)– Upper, lower limbs– Pectoral girdle– Pelvic girdle
There are 206 bones in the adult human body
Types of fracture
Stress fracture is not visible;Overuse or degeneration
Process of fracture repair
Bone grows slowly; blood supply may be affected
Life processes and bone formation
• Why is exercise good for bones?• How does aging affect bones?
– Loss of bone mass due to calcium loss– Decreased production of collagen
Treatment of osteoporosis
• Prevention
• Steroid hormone replacement (stimulates osteoblast activity)
• Evista has estrogen-like effects on bone formation
• Fosamax blocks bone resorption
Summary
• Bone is a complex tissue• It is constantly being remodeled• Bones consist of compact and spongy bone, lots
of blood vessels and nerves• Functions of bone:
– Support and protection– Movement– Calcium levels– Blood cell formation– Fat storage