chapter 5/6

study of bone structure & the treatment of bone disorders

• 1. Support
• 2. Protection
• 3. Assist in movement
• 4. Mineral storage & release
• 5. Site of blood cell production
• 6. Storage of energy

• 1. Diaphysis - Shaft of the bone
• 2. Epiphyses - Extremities of the bone
• 3. Metaphyses - Region where the diaphysis & epiphyses meet. In growing bone, the metaphyses contain the epiphyseal plates, a layer of hyaline cartilage that allow the bone to grow lengthwise.
• 4. Articular cartilage - covers the epiphyses, reducing friction & absorbing shock at freely movable joints
• 5. Periosteum - covers the diaphysis. It is composed of:
• A) Fibrous (outer) layer made of dense irregular CT, blood vessels, & nerves
• B) Osteogenic (inner) layer composed of elastic fibers, blood vessels, & bone cells
• 6. Medullary (marrow) cavity - space within the diaphysis containing fatty yellow marrow
• 7. Endosteum - membrane, containing osteoprogenitor cells & osteoclasts, which lines the medullary cavity

shaft of bone

extremities of the bone

Region where the diaphysis & epiphyses meet. In growing bone, the metaphyses contain the epiphyseal plates, a layer of hyaline cartilage that allow the bone to grow lengthwise

covers the epiphyses, reducing friction & absorbing shock at freely movable joints

covers the diaphysis

contains fibrous and osteogenic layers

space within the diaphysis containing fatty yellow marrow

membrane, containing osteoprogenitor cells & osteoclasts, which lines the medullary cavity

matrix and cells

• 1. 25% water
• 2. 25% protein fibers - collagen
• 3. 50% mineral salts - hydroxyapatite (tricalcium phosphate) & calcium carbonate
• The collagen fibers form the framework of bone & give bone its tensile strength, while the mineralization or calcification of the mineral salts give bone its hardness.
• Without the collagen fibers bone would be brittle
• Bone is not completely solid but contains spaces (lacunae) & channels (canaliculi) within

• osteogenic cells
• osteoblasts cells
• osteocytes cells
• osteoclasts cells

Forms the external layer of all bones of the body & the bulk of the diaphyses of long bones

found in the osteogenic layer of the (central & perforating) containing blood vessels periosteum, the endosteum, & in the bone canals

• form bone
• secrete collagen

• mature bone cells
• maintain daily metabolic activities

• monocytes and reabsorb bone
• important for development, growth, and repair

- Basic Structural Unit = Haversian System

conduit system for blood vessel and nerves

concentric rings of hard, calcified matrix - collagen & mineral salts

spaces that contain osteocytes

mature blood cells

canals connecting the lacunae with each other & the central canals - conduit system for nutrient & waste transport

• interstitial lamellae
• perforating canal

areas between osteons; they are fragments of older osteons that have been partially destroyed during bone rebuilding or growth

canal allowing blood vessels, nerves, & lymphatics of the periosteum to connect to the central canals & ultimately the medullary cavity

• 1. No osteons, no Haversian canal
• 2. Lamellae layers are formed into columns called trabeculae, which possess lacunae with osteocytes inside
• 3. Spaces between the trabeculae are filled with red bone marrow - blood cell production
• 4. Osteocytes obtain their nutrients directly from the blood vessels penetrating into the medullary cavity.

formation of bone directly on or within fibrous CT

convert bones into tissues

1. Cells in the mesenchyme come together & develop into osteoprogenitor cells & then into osteoblasts. This is the center of ossification. Osteoblasts secrete matrix, surrounding themselves

1. Secretion stops. Osteoblasts are now encapsulated osteocytes. The osteocytes maintain communication via the canaliculi. Matrix calcifies.

• The bone matrix develop into trabeculae that fuse together into spongy bone. On the outside of the bone the mesenchyme condenses

1. mesenchyme develops into the periosteum

replacement of cartilage by bone

Mesenchymal cells come together to form the shape of the bone, and then differentiate into cartilage producing cells = cartilage model

membrane called the perichondrium develops around the cartilage

Chondrocytes in the mid-region trigger calcification

other chondrocytes die due to a lack of nutrients = formation of cavities

nutrient artery penetrates the bone which stimulates the osteoprogenitor cells in the perichondrium to develop into osteoblasts. These cells produce compact bone under the perichondrium which is now properly called the periosteum

Capillaries grow into the disintegrating cartilage, & stimulate the development of a primary ossification center. Osteoblasts will replace the calcified matrix with spongy bone, extending toward the ends (epiphyses)

Osteoclasts break down the spongy bone, creating the medullary cavity, which fills with red bone marrow

diaphysis is now composed of compact bone surrounding the medullary cavity

When blood vessels enter the epiphyses, secondary ossification centers will develop, spongy bone is formed but not destroyed.Hyaline remains covering the epiphyses as well as at the epiphyseal plate.

• 1. Zone of resting cartilage - chondrocytes that
• anchor the epiphyseal plate to the epiphysis; starting area
• 2. Zone of proliferating cartilage - dividing (mitotically active) chondrocytes that will eventually replace those that die at the diaphyseal side
• 3. Zone of hypertrophic (maturing) cartilage - chondrocytes grow; mitosis is halted
• 4. Zone of calcified cartilage - dead chondrocytes in calcified matrix, allowing osteoblasts & blood vessels from the diaphysis to invade it & replace it with bone.

chondrocytes that anchor the epiphyseal plate to the epiphysis; starting area

dividing (mitotically active) chondrocytes that will eventually replace those that die at the diaphyseal side

chondrocytes grow; mitosis is halted

dead chondrocytes in calcified matrix, allowing osteoblasts & blood vessels from the diaphysis to invade it & replace it with bone

• 1. Bone lining the medullary cavity is destroyed by osteoclasts
• 2. Osteoblasts from the periosteum add new bone to the outer surface
• 3. Spongy bone is initially produced & is reorganized into compact bone

any break in bone

• 1) Development of a fracture hematoma - develops in 6 – 8 hours from broken blood vessels in the periosteum, osteons, & medullary cavity. Serves as the focus for cellular invasion. Osteoclasts remove the dead & dying tissue for the next several weeks
• 2) Blood capillaries grow into the fracture hematoma helping the fracture organize itself into a procallus, which is actively growing connective tissue
• 3) Fibroblasts & osteoprogenitor cells invade the procallus. Fibroblasts produce collagen to unite the ends of the broken bone. Osteoprogenitor cells develop into chondroblasts in areas of the break that are avascular, which produce fibrocartilage, transforming the procallus into a fibrocartilaginous (soft) callus
• 4) Osteoprogenitor cells in vascular regions develop into osteoblasts which will produce spongy bone trabeculae. They will also eventually replace fibrocartilage, resulting in a bony (hard) callus
• 5) Remodeling is the final phase in which: A) remaining original fragments are removed by osteoclasts, and B) compact bone replaces spongy bone around the periphery of the fracture

• reduction
• closed reduction
• open reduction

fractured ends must be aligned

fractured ends of the bone are brought into alignment manually & the skin remains intact

fractured ends of the bone are brought into alignment by a surgical procedure in which internal fixation devices are used

• partial
• complete
• closed
• open
• comminuted
• greenstick
• stress

break across the bone is incomplete

• break is complete
• leaving one or more pieces

bone doesn't break through skin

• ends of bone go through skin
• yuck

bone has splintered at the site of impact, and smaller fragments of the bone lie between the two main fragments

partial fracture in which one side of the bone is broken & the other side bends; occurs only in children

Microscopic fractures resulting from the inability to withstand repeated stressful impact