![]() Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and calcium salts. 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. Osteoclasts develop from monocytes and macrophages and differ in appearance from other bone cells. When osteoblasts get trapped within the calcified matrix, their structure and function changes, and they become osteocytes. Osteogenic cells are undifferentiated and develop into osteoblasts. Four types of cells are found within bone tissue. Bone Markings (Table 2)įoramen (holes through which blood vessels can pass through)įigure 5. As with the other markings, their size and shape reflect the size of the vessels and nerves that penetrate the bone at these points. A hole is an opening or groove in the bone that allows blood vessels and nerves to enter the bone. In general, their size and shape is an indication of the forces exerted through the attachment to the bone. These are the attachment points for tendons and ligaments. A projection is an area of a bone that projects above the surface of the bone. These surfaces tend to conform to one another, such as one being rounded and the other cupped, to facilitate the function of the articulation. As the name implies, an articulation is where two bone surfaces come together (articulus = “joint”). There are three general classes of bone markings: (1) articulations, (2) projections, and (3) holes. Table 2 describes the bone markings, which are illustrated in ( Figure 4). The surface features of bones vary considerably, depending on the function and location in the body. This cross-section of a flat bone shows the spongy bone (diploë) lined on either side by a layer of compact bone. ![]() In this region, the epiphyses are covered with articular cartilage, a thin layer of cartilage that reduces friction and acts as a shock absorber.įigure 3. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints ( Figure 2). Tendons and ligaments also attach to bones at the periosteum. The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. The outer surface of the bone is covered with a fibrous membrane called the periosteum (peri – = “around” or “surrounding”). The medullary cavity has a delicate membranous lining called the endosteum (end- = “inside” oste- = “bone”), where bone growth, repair, and remodeling occur. When the bone stops growing in early adulthood (approximately 18–21 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line. 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. Red marrow fills the spaces in the spongy bone. The wider section at each end of the bone is called the epiphysis (plural = epiphyses), which is filled with spongy bone. A typical long bone shows the gross anatomical characteristics of bone. The walls of the diaphysis are composed of dense and hard compact bone.įigure 1. The hollow region in the diaphysis is called the medullary cavity, which is filled with yellow marrow. The diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone. A long bone has two parts: the diaphysis and the epiphysis. The structure of a long bone allows for the best visualization of all of the parts of a bone ( Figure 1). This section will examine the gross anatomy of bone first and then move on to its histology. Later discussions in this chapter will show that bone is also dynamic in that its shape adjusts to accommodate stresses. Bone is hard and many of its functions depend on that characteristic hardness. Compare the composition and function of compact bone versus spongy boneīone tissue (osseous tissue) differs greatly from other tissues in the body. ![]()
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