Bone Tissue

Functions of Bone Support Protection Assists in movement Mineral homeostasis—calcium & phosphorus Site of blood cell production—red bone marrow Storage of energy—yellow bone marrow— adipose (fat) cells

Four Types of Bones Long bones – femur, humerus, radius, tibia, etc. Short bones – carpals and tarsals – sesamoid bones—form in a tendon Flat bones – most skull bones, scapulae, ribs, sternum Irregular bones – vertebral bones, facial bones, pelvic bones

Figure 6.2

Sesamoid bones in area of big toe

Parts of a Long Bone Diaphysis – shaft, mostly compact bone, hollow Epiphyses – ends of the bone, spongy bone Articular cartilage – thin layer of cartilage covering epiphyses at joint to reduces friction Periosteum – membrane around surface of bone

Figure 6.3a

Figure 6.3

Parts of Periosteum

Figure 6.3c

Figure 6.3b

Electron Micrograph of Spongy Bone

Spongy Bone--trabeculae

Figure 6.4

Three Types of Bone Cells Osteoblasts – secretes collagen and forms bone Osteocytes – mature bone cells derived from osteoblasts – As osteoblasts surround themselves with bone they become trapped and become osteocytes – Osteocytes maintain bone tissue Osteoclasts – Huge multi-nuclei cells that settle on surface of bone and destroy bone – Needed for repair, growth, and release of calcium into blood

Figure 6.6b

Osteoclast

Spongy Bone Compact Bone

Compact Bone Tissue Concentric ring structure Osteon—each central canal, with its surrounding lamellae, lacunae, osteocytes and Canaliculi. Two Types of Canals: 1)Volkmann’s canals – run parallel to ground 2)Haversian canals – run up and down bone

Figure 6.6c

Spongy Bone Compact Bone

Spongy Bone Tissue Doesn’t contain osteons Trabeculae – irregular latticework of thin plates of bone – Spaces between are filled with red marrow. Found in short, flat, and irregularly shaped bones, and most of the epiphyses of long bones

Endosteum with Plump Osteoblasts

Osteoblasts

Osteoclasts

Osteoclast

Osteoclasts

Growth of Bone Length – Rate of growth is regulated by growth hormones and sex hormones – When the chondrocytes stop dividing, the growth stops and the epiphyseal plate becomes the epiphyseal line – Injury to the epiphyseal plate will stop growth in bone – Steroids close epiphyseal plate and thus long term steroid users are shorter than normal height

Figure 6.10

Epiphyseal Plate

Epiphyseal Plates

Bone Growth in Diameter Osteoclasts destroy bone inside medullary cavity to enlarge marrow cavity At the same time, osteoblasts from periosteum add new bone to the outer surface

Figure 6.10

Animation Bone Growth in Width

Remodeling of Bone The ongoing replacement of old bone by new bone Osteoclasts remove bone and osteoblasts lay down new bone If too much mineral is deposited, the surplus may form spurs A loss of too much calcium weakens the bone to cause osteoporosis

Figure 6.14 Osteoporosis

Animation Osteoporosis

Steps to Repair a Bone Fracture As a result of the fracture, blood vessels are broken Forms a clot around the fracture called a fracture hematoma – Loss of blood causes the bone cells to die – Swelling and inflammation occur after the hematoma

Fibroblasts produce collagen fibers—helps connects broken ends of bone together. This creates a callus - mass of repair tissue that bridges the broken ends of the bone Lasts for 3 weeks Steps to Repair a Bone Fracture

In areas more vascularized, osteoblasts begin to produce spongy bone The trabeculae join living and dead portions of the original bone fragments This is now called a bony callus Lasts for 3-4 months Steps to Repair a Bone Fracture

Remodeling - dead portions of the original fragments are gradually reabsorbed by osteoclasts Compact bone replaces spongy bone Sometimes, healing is so complete that the fracture line is undetectable even on X-ray Thickened area on the surface of the bone remains as evidence of a healed fracture site Steps to Repair a Bone Fracture

Figure 6.13