Bone development begins with the replacement of collagenous mesenchymal tissue by bone. This results in the formation of woven bone, a primitive form of bone with randomly organized collagen fibers that is further remodeled into mature lamellar bone, which possesses regular parallel rings of collagen.
Lamellar bone is then constantly remodeled by osteoclasts and osteoblasts. There are two different methods by which bone is produced from mesenchymal tissue:. In adults, after growth has ceased, bone is formed by the osteoblasts only where it was previously resorbed by the osteoclasts.
This follows a specific sequence of events, and takes about three months in total to complete:. Answer: Haversian canals are central channels in bone that contain nerves, vessels, and lymphatics. They all run parallel to each other but are connected perpendicularly by Volkmann's canals. Canaliculi are tiny extensions of the osteocytes through the bone matrix. They allow these isolated cells to communicate with one another. Answer: Endochondral ossification involves the conversion of cartilage to bone.
This occurs in most long bones of the body. Intramembranous ossification does not involve a cartilage precursor. It takes place in the bones of the skull.
Answer: Activation, resorption, reversal, formation. See pre-lab for more details. The instructor will provide you with a plastic model of enlarged bone tissue. Find all the following items in the model and be prepared to point out any three to the instructor on their request.
Figure The model of enlarged bone tissue you will use to identify the histological features listed above. Skip to main content. Search for:. Figure 6. The structural features of compact bone. Lab 6 Exercises 6. Licenses and Attributions.
CC licensed content, Original. The weight of the body pushes it down near the joint, but the vertical diaphysis of the femur pushes it up at the other end. The neck of the femur must be strong enough to transfer the downward force of the body weight horizontally to the vertical shaft of the femur Figure 2. Bone consists of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells.
Osteoblasts are bone cells that are responsible for bone formation. Osteoblasts synthesize and secrete the organic part and inorganic part of the extracellular matrix of bone tissue, and collagen fibers. Osteoblasts become trapped in these secretions and differentiate into less active osteocytes.
Osteoclasts are large bone cells with up to 50 nuclei. They remove bone structure by releasing lysosomal enzymes and acids that dissolve the bony matrix. These minerals, released from bones into the blood, help regulate calcium concentrations in body fluids.
Bone may also be resorbed for remodeling, if the applied stresses have changed. Osteocytes are mature bone cells and are the main cells in bony connective tissue; these cells cannot divide.
Osteocytes maintain normal bone structure by recycling the mineral salts in the bony matrix. Osteoprogenitor cells are squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts. Osteoprogenitor cells are important in the repair of fractures. Compact bone tissue is composed of osteons and forms the external layer of all bones.
Spongy bone tissue is composed of trabeculae and forms the inner part of all bones. Secondary bone is further classified as two types: trabecular bone also called cancellous or spongy bone and compact bone also called dense or cortical bone. Slide 70 Developing bone. Primary bone or woven bone is characterized by the irregular arrangement of collagen fibers , large cell number, and reduced mineral content.
Note the primary bone is deposited on hyaline cartilage. Primary bone is acidophilic while the hyaline cartilage is basophilic.
Slide 69 Bone, femur. The trabecular bone present in this slide is found mostly within the epiphysis and some in the bone marrow cavity. Osteoblasts are located immediately above the osteoid newly formed bone matrix. Osteocytes are found within lacunae. Giant multinucleated osteoclasts , which break down bone, are occasionally found in lacunae termed Howship's lacunae. These are readily found in the ossification zone of the growth plate.
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