Bone Physio PDF

BONE PHYSIO Types of cartilage growth  Types of cartilage growth appositional Interstitial growth growth chondrocytes Chondroblasts in within the tissue the perichondrium divide and...

BONE PHYSIO Types of cartilage growth  Types of cartilage growth appositional Interstitial growth growth chondrocytes Chondroblasts in within the tissue the perichondrium divide and add add new cartilage to the outside edge more matrix of the existing between the cartilage. existing cells The chondroblasts No increase in size lay down new matrix and add new chondrocytes to the outside of the tissue The bone matrix is composed by weight of the following 35% organic 65% inorganic organic material inorganic material consists primarily consists primarily of collagen and of a calcium proteoglycans phosphate crystal called hydroxyapatite The collagen and mineral components are responsible for the major functional characteristics of bone  Types of Bone Cells Osteocytes · Mature bone cells · Osteoblasts · Bone-forming cells · Produce collagen and proteoglycans · Release matrix vesicles that concentrate Ca 2+ and 3− PO and form needlelike hydroxyapatite crystals 4 · Osteoclasts · Bone-destroying cells · Break down bone matrix for remodeling and release of calcium · Bone remodeling is a process by both osteoblasts and osteoclasts Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Compact vs Spongy  Spongy bone consists of interconnecting rods or plates of bone called trabeculae Each osteocyte is associated with other osteocytes through the canaliculi The surfaces of trabeculae are covered with a single layer of cells consisting of osteoblasts with a few osteoclasts Trabeculae are oriented along the lines of stress within a bone  Compact bone denser and has fewer spaces Concentric lamellae are circular layers of bone matrix that surround the central canal. The outer surfaces of compact bone are formed by circumferential lamellae Figure 6.3 Figure 6.3b Figure 6.4 Figure 6.4b Young vs Mature Figure 6.2a Figure 6.2b Figure 6.2c  Intramembranous vs Endochondral Ossification Intramembranous Endochondral begins at approximately the approximately the eighth week of eighth week of embryonic embryonic development until as development and is late as 18–20 years of completed by approximately 2 years age. of age base of the skull, part skull bones, part of the of the mandible, the mandible and the epiphyses of the diaphyses of the clavicles, and most of clavicles the remaining skeletal system The steps in intramembranous ossification Intramembranous ossification begins when some of the mesenchymal cells in the membrane become osteochondral progenitor cells, which specialize to become osteoblasts. The osteoblasts produce bone matrix that surrounds the collagen fibers of the connective tissue membrane, and the osteoblasts become osteocytes. As a result of this process, many tiny trabeculae of woven bone develop The steps in intramembranous ossification Additional osteoblasts gather on the surfaces of the trabeculae and produce more bone, thereby causing the trabeculae to become larger and longer. Spongy bone forms as the trabeculae join together, resulting in an interconnected network of trabeculae separated by spaces The steps in intramembranous ossification Cells within the spaces of the spongy bone specialize to form red bone marrow, and cells surrounding the developing bone specialize to form the periosteum. Osteoblasts from the periosteum lay down bone matrix to form an outer surface of compact bone  The steps in endochondral ossification mesenchymal cells aggregate in regions of future bone formation. The mesenchymal cells become osteochondral progenitor cells that become chondroblasts. The chondroblasts produce a hyaline cartilage model having the approximate shape of the bone that will later be formed. As the chondroblasts are surrounded by cartilage matrix, they become chondrocytes. The cartilage model is surrounded by perichondrium, except where a joint will form connecting one bone to another bone. The perichondrium is continuous with tissue that will become the joint capsule later in development.  The steps in endochondral ossification When blood vessels invade the perichondrium surrounding the cartilage model, osteochondral progenitor cells within the perichondrium become osteoblasts. The perichondrium becomes the periosteum when the osteoblasts begin to produce bone. The osteoblasts produce compact bone on the surface of the cartilage model, forming a bone collar. Two other events occur at the same time that the bone collar is forming. First, the cartilage model increases in size as a result of interstitial and appositional cartilage growth.  The steps in endochondral ossification Second, the chondrocytes in the center of the cartilage model absorb some of the cartilage matrix and hypertrophy or enlarge. The chondrocytes also release matrix vesicles, which initiate the formation of hydroxyapatite crystals in the cartilage matrix. At this point, the cartilage is called calcified cartilage. The chondrocytes in this calcified area eventually die, leaving enlarged lacunae with thin walls of calcified matrix.  The steps in endochondral ossification Blood vessels grow into the enlarged lacunae of the calcified cartilage. Osteoblasts and osteoclasts migrate into the calcified cartilage area from the periosteum by way of the connective tissue surrounding the outside of the blood vessels. The osteoblasts produce bone on the surface of the calcified cartilage, forming bone trabeculae, which changes the calcified cartilage of the diaphysis into spongy bone. This area of bone formation is called the primary ossification center.  The steps in endochondral ossification As bone development proceeds, the cartilage model continues to grow, more perichondrium becomes periosteum, and the bone collar thickens and extends farther along the diaphysis. Additional cartilage within both the diaphysis and the epiphysis is calcified. Remodeling converts woven bone to lamellar bone and contributes to the final shape of the bone. Osteoclasts remove bone from the center of the diaphysis to form the medullary cavity, and cells within the medullary cavity specialize to form red bone marrow.  The steps in endochondral ossification In long bones, the diaphysis is the primary ossification center, and additional sites of ossification, called secondary ossification centers, appear in the epiphyses. The events occurring at the secondary ossification centers are the same as those at the primary ossification centers, except that the spaces in the epiphyses do not enlarge to form a medullary cavity as in the diaphysis. Primary ossification centers appear during early fetal development, whereas secondary ossification centers appear in the proximal epiphysis of the femur, humerus, and tibia about 1 month before birth. A baby is considered full-term if one of these three ossification centers can be seen on radiographs at the time of birth.  The steps in endochondral ossification At about18–20 years of age, the last secondary ossification center appears in the medial epiphysis of the clavicle Replacement of cartilage by bone continues in the cartilage model until all the cartilage, except that in the epiphyseal plate and on articular surfaces, has been replaced by bone. The epiphyseal plate, which exists during the time a person’s bones are actively growing, and the articular cartilage, which is a permanent structure, are derived from the original embryonic cartilage model.  The steps in endochondral ossification After a person’s bones have stopped growing, the epiphyseal plate regresses into a “scar,” called the epiphyseal line In mature bone, spongy and compact bone are fully developed, and the epiphyseal plate has become the epiphyseal line. The only cartilage present is the articular cartilage at the ends of the bone. All the original perichondrium that surrounded the cartilage model has become periosteum. Figure 6.6 Figure 6.6a Figure 6.6b Figure 6.6c Figure 6.6d Figure 6.7 Figure 6.7a Figure 6.7c  Bone Fractures · A break in a bone · Types of bone fractures · Closed (simple) fracture – break that does not penetrate the skin · Open (compound) fracture – broken bone penetrates through the skin · Greenstick- frays, hard to repair, breaks like a green twig · Bone fractures are treated by reduction and immobilization · Realignment of the bone Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Clinical Focus 6B Clinical Focus 6Ba Clinical Focus 6Bb Clinical Focus 6Bc Clinical Focus 6Bd Figure 6.8 Figure 6.8a Figure 6.8b Figure 6.8c Figure 6.8d END