Bone, or osseous tissue, is a connective tproblem that constitutes the endoskeleton. It consists of specialized cells and a matrix of mineral salts and collagen fibers.

You are watching: At what age are nearly all bones completely ossified?

The mineral salts primarily encompass hydroxyapatite, a mineral created from calcium phosphate. Calcification is the procedure of deposition of mineral salts on the collagen fiber matrix that crystallizes and hardens the tissue. The process of calcification only occurs in the existence of collagen fibers.

The bones of the humale skeleton are classified by their shape: long bones, short bones, flat bones, sutural bones, sesamoid bones, and irregular bones (Figure 19.16).

Figure 19.16. Shown are different forms of bones: level, ircontinual, long, short, and sesamoid.

Long bones are longer than they are wide and also have a shaft and also two ends. The diaphysis, or main shaft, includes bone marrow in a marrow cavity. The rounded ends, the epiphyses, are extended with articular cartilage and are filled via red bone marrowhead, which produces blood cells (Figure 19.17). Most of the limb bones are long bones—for example, the femur, tibia, ulna, and radius. Exceptions to this incorporate the patella and the bones of the wrist and also ankle.

Figure 19.17. The lengthy bone is covered by articular cartilage at either end and also consists of bone marrowhead (presented in yellow in this illustration) in the marrowhead cavity.

Brief bones, or cuboidal bones, are bones that are the exact same width and also size, giving them a cube-choose shape. For example, the bones of the wrist (carpals) and ankle (tarsals) are brief bones (Figure 19.16).

Flat bones are thin and relatively wide bones that are uncovered where comprehensive defense of organs is required or wbelow wide surencounters of muscle attachment are required. Instances of flat bones are the sternum (breast bone), ribs, scapulae (shoulder blades), and the roof of the skull (Figure 19.16).

Irconstant bones are bones via complex forms. These bones may have short, flat, notched, or ridged surencounters. Instances of irregular bones are the vertebrae, hip bones, and numerous skull bones.

Sesamoid bones are little, level bones and also are shaped similarly to a seexact same seed. The patellae are sesamoid bones (Figure 19.18). Sesamoid bones build inside tendons and might be uncovered close to joints at the knees, hands, and also feet.

Figure 19.18. The patella of the knee is an instance of a sesamoid bone.
Figure 19.19. Compact bone tconcern consists of osteons that are aligned parallel to the long axis of the bone, and also the Haversian canal that has the bone’s blood vessels and nerve fibers. The inner layer of bones consists of spongy bone tproblem. The little dark ovals in the osteon represent the living osteocytes. (credit: alteration of work by NCI, NIH)

Whereas compact bone tproblem creates the outer layer of all bones, spongy bone or cancellous bone creates the inner layer of all bones. Spongy bone tconcern does not contain osteons that constitute compact bone tissue. Instead, it is composed of trabeculae, which are lamellae that are arranged as rods or plates. Red bone marrow is uncovered in between the trabuculae. Blood vessels within this tworry supply nutrients to osteocytes and also rerelocate waste. The red bone marrowhead of the femur and the internal of other big bones, such as the ileum, forms blood cells.

Spongy bone reduces the density of bone and also allows the ends of lengthy bones to compress as the outcome of stresses applied to the bone. Spongy bone is significant in areas of bones that are not heavily stressed or wbelow stresses arrive from many type of directions. The epiphyses of bones, such as the neck of the femur, are subject to anxiety from many type of directions. Imagine laying a heavy framed photo level on the floor. You could hold up one side of the photo via a toothpick if the toothpick was perpendicular to the floor and the photo. Now drill a hole and stick the toothpick right into the wall to hang up the picture. In this situation, the function of the toothpick is to transmit the downward press of the photo to the wall. The force on the picture is right dvery own to the floor, however the force on the toothpick is both the image wire pulling dvery own and also the bottom of the hole in the wall pushing up. The toothpick will break off right at the wall.

The neck of the femur is horizontal choose the toothpick in the wall. The weight of the body pushes it dvery own near the joint, yet the vertical diaphysis of the femur pushes it up at the various other end. The neck of the femur have to be strong enough to transport the downward pressure of the body weight horizontally to the vertical shaft of the femur (Figure 19.20).

See more: Reading: The _________ Is A Global System Of Linked, Hypertext Documents.

Figure 19.20. Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the various other withstands compression.