12. Be familiar with the possible skin grafts a person might receive if burns ar
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12. Be familiar with the possible skin grafts a person might receive if burns are severe enough: autograf, allograft and xenograft. (See also clinical focus in chapter 5, where it mentions skin production at pharmaceutical companies). Ch. 6 Introduction to the Skeletal System 1. Be able to identify examples of specific bones based on the four classifications of Bones. 2. Kn ow the bone. functions of bones and list the cell types responsible for the development of Describe factors that affect bone development and growth able to explain how a bone develops by endochondral ossification(figure 6.10) Describe at least three specific types of fractures and the difference between a stress fracture and a pathological fracture. 3. Be 4. 5. Know the structure of a long bone and the function of each structure 6. Be familiar with the steps in the healing of a fracture(Fig. 6.16)Explanation / Answer
1.there are five types of bone
Flat Bones Protect Internal Organs There are flat bones in the skull (occipital, parietal, frontal, nasal, lacrimal, and vomer), the thoracic cage (sternum and ribs), and the pelvis (ilium, ischium, and pubis). The function of flat bones is to protect internal organs such as the brain, heart, and pelvic organs. Flat bones are somewhat flattened, and can provide protection, like a shield; flat bones can also provide large areas of attachment for muscles.
Long Bones Support Weight and Facilitate Movement
The long bones, longer than they are wide, include the femur (the longest bone in the body) as well as relatively small bones in the fingers. Long bones function to support the weight of the body and facilitate movement. Long bones are mostly located in the appendicular skeleton and include bones in the lower limbs (the tibia, fibula, femur, metatarsals, and phalanges) and bones in the upper limbs (the humerus, radius, ulna, metacarpals, and phalanges).
Short Bones Are Cube-shaped
Short bones are about as long as they are wide. Located in the wrist and ankle joints, short bones provide stability and some movement. The carpals in the wrist (scaphoid, lunate, triquetral, hamate, pisiform, capitate, trapezoid, and trapezium) and the tarsals in the ankles (calcaneus, talus, navicular, cuboid, lateral cuneiform, intermediate cuneiform, and medial cuneiform) are examples of short bones.
Irregular Bones Have Complex Shapes
Irregular bones vary in shape and structure and therefore do not fit into any other category (flat, short, long, or sesamoid). They often have a fairly complex shape, which helps protect internal organs. For example, the vertebrae, irregular bones of the vertebral column, protect the spinal cord. The irregular bones of the pelvis (pubis, ilium, and ischium) protect organs in the pelvic cavity.
Sesamoid Bones Reinforce Tendons
Sesamoid bones are bones embedded in tendons. These small, round bones are commonly found in the tendons of the hands, knees, and feet. Sesamoid bones function to protect tendons from stress and wear. The patella, commonly referred to as the kneecap, is an example of a sesamoid bone.
2. The terms osteogenesis and ossification are often used synonymously to indicate the process of bone formation. Parts of the skeleton form during the first few weeks after conception. By the end of the eighth week after conception, the skeletal pattern is formed in cartilage and connective tissue membranes and ossification begins.
Bone development continues throughout adulthood. Even after adult stature is attained, bone development continues for repair of fractures and for remodeling to meet changing lifestyles. Osteoblasts, osteocytes and osteoclasts are the three cell types involved in the development, growth and remodeling of bones. Osteoblasts are bone-forming cells, osteocytes are mature bone cells and osteoclasts break down and reabsorb bone.
3. Endochondral ossification involves the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed in this manner. These bones are called endochondral bones. In this process, the future bones are first formed as hyaline cartilage models. During the third month after conception, the perichondrium that surrounds the hyaline cartilage "models" becomes infiltrated with blood vessels and osteoblasts and changes into a periosteum. The osteoblasts form a collar of compact bone around the diaphysis. At the same time, the cartilage in the center of the diaphysis begins to disintegrate. Osteoblasts penetrate the disintegrating cartilage and replace it with spongy bone. This forms a primary ossification center. Ossification continues from this center toward the ends of the bones. After spongy bone is formed in the diaphysis, osteoclasts break down the newly formed bone to open up the medullary cavity.
The cartilage in the epiphyses continues to grow so the developing bone increases in length. Later, usually after birth, secondary ossification centers form in the epiphyses. Ossification in the epiphyses is similar to that in the diaphysis except that the spongy bone is retained instead of being broken down to form a medullary cavity. When secondary ossification is complete, the hyaline cartilage is totally replaced by bone except in two areas. A region of hyaline cartilage remains over the surface of the epiphysis as the articular cartilage and another area of cartilage remains between the epiphysis and diaphysis. This is the epiphyseal plate or growth region.
4. tree specific types of facture :
5 . long bone consists of two parts
epiphysis : it consists of
epiphyseal line :
(1) the vascular reserve zone cartilage, which is responsible for growth of the epiphysis toward the joint,
(2) the epiphyseal plate, which is responsible for growth in bone length.
spongy bone:
Cancellous bone is made up of spongy, porous,bone tissue that is filled with red bone marrow. It is not as strong as cortical bone, which is found in the long bones, but it is very important for producing blood cells. It is found in the ends of long bones and in the bones of the pelvis, ribs, vertebrae, and skull.
diaphysis :
medullary cavity : it consisThe medullary cavity (medulla, innermost part) is the central cavityof bone shafts where red bone marrow and/or yellow bone marrow (adipose tissue) is stored; hence, the medullary cavity is also known as the marrow cavity
nutrient foramen :
larger or smaller foramina (openings) for the entrance of blood-vessels; these are known as the nutrient foramina, and are particularly large in the shafts of the larger long bones, where they lead into a nutrient canal, which extends into the medullary cavity.
Endosteum: The outer surface of a bone is lined by a thin layer of connective tissue that is very similar in morphology and function to endosteum. It is called the periosteum, or the periosteal surface. During bone growth, the width of the bone increases as osteoblasts lay new bone tissue at the periosteum.
Periosteum: It serves as protection as well as a channel for the blood supply and nutrients for bone tissue.
6.
Fracture healing can be divided into two types:
The former occurs only with absolute stability and is a biological process of osteonal bone remodeling. The latter occurs with relative stability (flexible fixation methods). It is very similar to the process of embryological bone development and includes both intramembraneous and endochondral bone formation. In diaphyseal fractures, it is characterized by the formation of callus.
Bone healing can be divided into four stages:
Inflammation
After fracture, the inflammatory process starts rapidly and lasts until fi brous tissue, cartilage, or bone formation begins (1–7 days postfracture). Initially, there is hematoma formation and inflammatory exudation from ruptured blood vessels. Bone necrosis is seen at the ends of the fracture fragments. Injury to the soft tissues and degranulation of platelets results in the release of powerful cytokines that produce a typical inflammatory response, ie, vasodilatation and hyperemia, migration and proliferation of polymorphonuclear neutrophils, macrophages, etc. Within the hematoma, there is a network of fibrin and reticulin fibrils; collagen fibrils are also present. The fracture hematoma is gradually replaced by granulation tissue. Osteoclasts in this environment remove necrotic bone at the fragment ends.
Soft callus formation
Eventually, pain and swelling decrease and soft callus is formed. This corresponds roughly to the time when the fragments are no longer moving freely, approximately 2–3 weeks postfracture.The soft callus stage is characterized by the growth of callus. The progenitor cells in the cambial layer of the periosteum and endosteum are stimulated to become osteoblasts. Intramembraneous, appositional bone growth starts on these surfaces away from the fracture gap, forming a cuff of woven bone periosteally, and filling the intramedullary canal. Ingrowth of capillaries into the callus and increased vascularity follows. Closer to the fracture gap, mesenchymal progenitor cells proliferate and migrate through the callus, differentiating into fibroblasts or chondrocytes, each producing their characteristic extracellular matrix and slowly replacing the hematoma
Hard callus formation
When the fracture ends are linked together by soft callus, the hard callus stage starts and lasts until the fragments are firmly united by new bone (3–4 months). As intramembraneous bone formation continues, the soft tissue within the gap undergoes endochondral ossification and the callus is converted into rigid calcified tissue (woven bone). Bone callus growth begins at the periphery of the fracture site, where the strain is lowest. The production of this bone reduces the strain more centrally, which in turn forms bony callus. Thus, hard callus formation starts peripherally and progressively moves towards the center of the fracture and the fracture gap. The initial bony bridge is formed externally or within the medullary canal, away from the original cortex. Then, by endochondral ossification, the soft tissue in the gap is replaced by woven bone that eventually joins the original cortex.
remodeling
The remodeling stage begins once the fracture has solidly united with woven bone. The woven bone is then slowly replaced by lamellar bone through surface erosion and osteonal remodeling. This process may take anything from a few months to several years. It lasts until the bone has completely returned to its original morphology, including restoration of the medullary canal.
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