Matrix extracellular vesicles contain a nucleational core that is composed of proteins and a complex of acidic phospholipids, calcium, and inorganic phosphate that is sufficient to precipitate hydroxyapatite crystals. First, it provides a consistent way to compare different tissues. Which cells do not originate from osteogenic cells? All bones are formed from two types of bone structure. Yellow marrow is found in the medullary cavity, the hollow interior of the middle portion of long bones. Examples of short bones are the Carpals and Tarsals - the wrist and foot bones. Crystal enlargement occurs both by crystal growth and by aggregation.
The second system forms curved paths from the outer side of the shaft and intersects the first system at right angles. Finally, concepts regarding bone remodeling, osteoclast and osteoblast function, extracellular matrix, matrix mineralization, and osteocyte function are synthesized in a summary of the currently understood functional determinants of bone strength. In the upper section of the femur, the cancellous bone is composed of two distinct systems of trabeculae. Sesamoid bones are unique because of their sesame seed shape and the fact that they form inside muscle tendons. The articular cartilage, which is composed of , covers the articular surface of each epiphysis. Compact bone is dense so that it can withstand compressive forces, while spongy cancellous bone has open spaces and supports shifts in weight distribution. Cortical bone is dense and solid and surrounds the marrow space, whereas trabecular bone is composed of a honeycomb-like network of trabecular plates and rods interspersed in the bone marrow compartment.
The hollow region in the diaphysis is called the medullary cavity, which is filled with yellow marrow. Serum osteocalcin synthesized by osteoblasts was previously thought to function as a promoter or initiator of calcium deposition at the nidus between the ends of collagen fibrils and therefore regarded as a marker of bone formation. The osteoblasts fill up the tunnel in staggered amounts creating lamellae which exist at the 2 nd level of structure. Trabecular bone is more compliant than cortical bone and it is believe to distribute and dissipate the energy from articular contact loads. Hierarchical Structure of Cortical Bone As with all biological tissues, cortical bone has a hierarchical structure.
In addition to the blood vessels, nerves follow the same paths into the bone where they tend to concentrate in the more metabolically active regions of the bone. They are found on bone surfaces, are multinucleated, and originate from monocytes and macrophages, two types of white blood cells, not from osteogenic cells. Which of the following occurs in the spongy bone of the epiphysis? Medullary Cavity Long bones all have a long cavity inside the diaphysis called the medullary cavity. Collagen is the main fibrous protein in the body. There is no evidence that noncrystalline calcium phosphate clusters amorphous calcium phosphate forms in bone before it is converted to hydroxyapatite. This section will examine the gross anatomy of bone first and then move on to its histology. Long bones contain yellow bone marrow and red bone marrow, which produce blood cells.
These are the attachment points for tendons and ligaments. Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal plate growth plate , a layer of hyaline transparent cartilage in a growing bone. The walls of the diaphysis are composed of dense and hard compact bone. In other epiphyses of the limbs, the spaces between trabeculae are filled with yellow bone marrow, which is composed of adipose tissue. They are usually somewhat curved for strength. The osteoclast itself has also been proposed to play a role during reversal.
The diaphysis is hollow but its walls are made of compact bone less holes, sturdier. Long bones: have greater length than width and consist of a shaft and a variable number of endings extremities. Ligaments and tendons attach to the periosteum. Because of the nature of the packing, the orientation of the collagen fibrils will determine the orientation of the mineral crystals. Irregular bones include the vertebrae, sacrum, coccyx, and hyoid bone.
This is because it becomes more difficult to measure both bone structure and mechanics at increasingly small levels. Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal plate growth plate , a layer of hyaline transparent cartilage in a growing bone. The vertebra is composed of cortical to trabecular bone in a ratio of 25:75. Remodeling sites may develop randomly but also are targeted to areas that require repair ,. Covering the ends of bones, where they form a joint with another bone, is a layer of hyaline cartilage. Examples include femur, tibia, fibula, humerus, ulna and radius.
Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and calcium salts. Remodeling begins before birth and continues until death. These two types are classified as on the basis of porosity and the unit microstructure. Osteoblasts are responsible for making the collagen-rich substance osteoid, which is key in building bone. Because serum osteocalcin is derived from both matrix release by osteoclast activity and osteoblast synthesis, it is currently regarded as a marker of bone turnover rather than a specific marker of bone formation. Call 911 for all medical emergencies. Micrograph provided by the Regents of University of Michigan Medical School © 2012 The microscopic structural unit of compact bone is called an osteon, or Haversian system.