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

Anatomical Classification of Bones Bones are classified by their basic shape Flat bones Sutural bones Irregular bones Long bones Short bones Sesamoid bones

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 Spongy 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 articular cartilage

The Structure of a Long Bone epiphysis metaphysis – location of epiphyseal plate – in children epiphyseal line – in adults diaphysis metaphysis epiphysis 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 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 periosteum

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 There are 206 bones in the adult human body Skeletal Divisions Axial skeleton (80 bones) Skull Thoracic cage and sternum Vertebral column Appendicular skeleton (126 bones) Upper, lower limbs Pectoral girdle Pelvic girdle

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