Where is cancellous bone found in the body

The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to bones at the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints Figure.

In this region, the epiphyses are covered with articular cartilage , a thin layer of cartilage that reduces friction and acts as a shock absorber.

The two layers of compact bone and the interior spongy bone work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer. Bone Markings The surface features of bones vary considerably, depending on the function and location in the body.

Figure describes the bone markings, which are illustrated in Figure. There are three general classes of bone markings: 1 articulations, 2 projections, and 3 holes. These surfaces tend to conform to one another, such as one being rounded and the other cupped, to facilitate the function of the articulation. A projection is an area of a bone that projects above the surface of the bone. These are the attachment points for tendons and ligaments.

In general, their size and shape is an indication of the forces exerted through the attachment to the bone. A hole is an opening or groove in the bone that allows blood vessels and nerves to enter the bone. As with the other markings, their size and shape reflect the size of the vessels and nerves that penetrate the bone at these points.

Bone Cells and Tissue Bone contains a relatively small number of cells entrenched in a matrix of collagen fibers that provide a surface for inorganic salt crystals to adhere. These salt crystals form when calcium phosphate and calcium carbonate combine to create hydroxyapatite, which incorporates other inorganic salts like magnesium hydroxide, fluoride, and sulfate as it crystallizes, or calcifies, on the collagen fibers.

The hydroxyapatite crystals give bones their hardness and strength, while the collagen fibers give them flexibility so that they are not brittle. Although bone cells compose a small amount of the bone volume, they are crucial to the function of bones.

Four types of cells are found within bone tissue: osteoblasts, osteocytes, osteogenic cells, and osteoclasts Figure. The osteoblast is the bone cell responsible for forming new bone and is found in the growing portions of bone, including the periosteum and endosteum. Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and calcium salts.

As the secreted matrix surrounding the osteoblast calcifies, the osteoblast become trapped within it; as a result, it changes in structure and becomes an osteocyte , the primary cell of mature bone and the most common type of bone cell.

Each osteocyte is located in a space called a lacuna and is surrounded by bone tissue. Osteocytes maintain the mineral concentration of the matrix via the secretion of enzymes. Like osteoblasts, osteocytes lack mitotic activity. If osteoblasts and osteocytes are incapable of mitosis, then how are they replenished when old ones die?

The answer lies in the properties of a third category of bone cells—the osteogenic cell. These osteogenic cells are undifferentiated with high mitotic activity and they are the only bone cells that divide.

Immature osteogenic cells are found in the deep layers of the periosteum and the marrow. They differentiate and develop into osteoblasts. The dynamic nature of bone means that new tissue is constantly formed, and old, injured, or unnecessary bone is dissolved for repair or for calcium release. The cell responsible for bone resorption, or breakdown, is the osteoclast. They are found on bone surfaces, are multinucleated, and originate from monocytes and macrophages, two types of white blood cells, not from osteogenic cells.

Osteoclasts are continually breaking down old bone while osteoblasts are continually forming new bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone.

Figure reviews the bone cells, their functions, and locations. The differences between compact and spongy bone are best explored via their histology. Compact bone is dense so that it can withstand compressive forces, while spongy cancellous bone has open spaces and supports shifts in weight distribution.

Compact bone is the denser, stronger of the two types of bone tissue Figure. It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection. The microscopic structural unit of compact bone is called an osteon , or Haversian system. Running down the center of each osteon is the central canal , or Haversian canal, which contains blood vessels, nerves, and lymphatic vessels. As described earlier, canaliculi connect with the canaliculi of other lacunae and eventually with the central canal.

This system allows nutrients to be transported to the osteocytes and wastes to be removed from them. Like compact bone, spongy bone , also known as cancellous bone, contains osteocytes housed in lacunae, but they are not arranged in concentric circles. Muscles, ligaments, and tendons may attach to the periosteum. Bones are classified by their shape. They may be long like the femur and forearm , short like the wrist and ankle , flat like the skull , or irregular like the spine.

Primarily, they are referred to as long or short. There are bones in the human skeleton. The bones include:. This includes the head, facial, hyoid, auditory, trunk, ribs, and sternum. This includes arms, shoulders, wrists, hands, legs, hips, ankles, and feet. Bones give shape and support for the body. They give protection to some organs. Bone also serves as a storage site for minerals. And soft bone marrow in the center of certain bones is where blood cells are formed and stored.

This type of blood cell is within the bone. These trabeculae follow the lines of maximum tensile stress, and in general are lighter in structure than those of the compressive system.

The thickness of the trabeculae varies with the magnitude of the stresses at any point, and by following the paths of the principal compressive and tensile stresses they carry these stresses economically.

The greatest strength is therefore achieved with the minimum of material. The distribution of the compact bone in the shaft is also due to the requirement to resist the bending moment stresses. To resist these stresses, the material should be as far from the neutral axis as possible.

A hollow cylinder is the most efficient structure, again achieving the greatest strength with the minimum of material. Diagram showing computed lines of constant stress from the analysis of various transverse sections. Structure of Bone and Implant Materials Aims Before you start Introduction Structure and composition of bone Formation and remodelling of bone Mechanical properties of bone Bone replacement An introduction to hip replacements Selecting implant materials Materials selection of femoral stem component Materials selection of femoral head and acetabular cup components Summary Questions Going further.

Previous Next Structure and composition of bone Long bones such as the femur contain two distinct morphological types of bone: Cortical compact bone Cancellous or Trabecular spongy bone These are shown in the figure below.