The Skeletal System

1. The Skeletal System Bones Lecture 1

2. Functions of Bones • To serve as a firm framework for the entire body • To protect the brain and spinal cord • To serve as levers, working with attached muscles to produce movement • To serve as a storehouse for calcium salts, which may be reabsorbed into the blood if there is not enough calcium in the diet • To produce blood cells

3. Bone Structure • Bones consists of several shapes • Flat bones are found in the skull and ribs • Cube shaped bones are found in the wrist and ankle • Irregularly shaped bones are found in the face and vertebrae • Long bones make up most of the arms and legs • Long bones have a long narrow shaft called the diaphysis, which had a central marrow cavity, and two irregular ends, called the epiphyses.

4. Bone Tissue • There are two types of bone or osseous tissue • Compact bone is hard and dense • It makes up the main shaft of a long bone and the outer layer of other bones • The osteocytes (bone cells) are located in rings of osseous tissue around a central haversian canal containing nerves and blood vessels • Spongy bone has more air spaces than compact bone • It is made of a meshwork of small, bony plates filled with red marrow and is found at the ends of long bones and at the center of other bones • Spongy bone is much stronger than compact bone

5. Bone Tissues

6. Bone Marrow • Red marrow is found at the ends of long bones and at the center of other bones. • It manufactures blood cells. • Yellow marrow is found chiefly in the central cavities of the long bones. • It is composed mainly of fat.

7. Bone Membranes • Bones are covered with a membrane called the periosteum. The only regions that lack the periosteum are where the joints are found. • The inner layer of the periosteum contains osteoblasts, which are essential in bone formation during growth and during the repair of fractures. • It also contains blood and lymph vessels that play an important role in the nourishment of osseous tissue. • The periosteum also contains nerve fibers. • The inner membrane, the endosteum, lines the marrow cavity of a bone; it also contains cells that aid in the growth and repair of bone tissue.

8. Bone Growth and Repair • Development • In the embryo, most of the skeletal system is composed of cartilage. • Bone formation, ossification, begins during the second and third months of life. During this time osteoblasts become active. • Osteoblasts first begin to manufacture the matrix. This intercellular substance contains large quantities of collagen. • With the help of enzymes, calcium compounds are deposited within the matrix. Once this material has hardened around the cells they are known as osteocytes. • Osteocytes are still living and continue to maintain the bone, but they do not produce new bone tissue. • Osteoclasts are responsible for the process of resorption, or the breakdown of bone, which is necessary for remodeling and repair. • Several hormones, including vitamin D, regulate the formation and resorption of bone tissue.

9. Formation of a Long Bone • The transformation of cartilage into bone begins at the center of the shaft. • Later, secondary bone-forming centers develop across the ends of the bones. • The long bones continue to grow in length at these centers through childhood and into the late teens. • Finally, the bones stop growing in length. Each bone-forming region hardens and can be seen in x-ray films as a thin line across the end of the bone. • As the bone grows in length, the shaft is remodeled so that it grows wider as the central marrow cavity increases in size. Alternations in the shape of the bone are a result of the addition of bone tissue to some surfaces and its resorption from others.

10. Bones of Children and the Elderly • The bones of small children are relatively pliable because they contain a larger proportion of cartilage and are undergoing active bone formation. • In the elderly, there is a slowing of the processes that continually renew bone tissue. • As a result, the bones are weaker and more fragile. • Elderly people also have a decreased ability to form the protein framework on which calcium salts are deposited. • Fractures heal more slowly because of these decreases in bone metabolism.

11. Bone Markings • Bone markings are distinguishable features that include raised areas and depressions that help to form joints orserve as points of attachment for muscles. • Bone markings also include various holes that allow the passage of nerves and blood vessels.

12. Types of Bone Markings • Projections • Head: a rounded, knoblike end separated from the rest of the bone by a slender region, the neck • Process: a large projection of a bone, such as the upper part of the ulna in the forearm that creates the elbow • Crest: a distinct border or ridge, often rough, such as over the top of the hip bone • Spine: a sharp projection from the surface of a bone, such as the spine of the scapula

13. Depressions or Holes • Foramen: a hole that allows a vessel or a nerve to pass through or between bones. The pleural is foramina. • Sinus: an air space found in some skull bones • Fossa: a depression on a bone surface. The pleural is fossae. • Meatus: a short channel or passageway, such as the channel in the temporal bone of the skull that leads to the inner ear.