Anatomy & Physiology Ms. Figueroa Fall 2011

 Objectives: 1. Name 5 functions of the skeletal system 2. Describe the anatomy of a long bone 3. Describe the growth & development of bones.

1. The average human adult skeleton has 206 bones. 2. The skeletal system consists of the bones and joints, along with the cartilage and ligaments found at the joints. 3. During development, a fetus has approximately 300 bones. These bones are made up of cartilage. 4. In an adult, the skeleton comprises 30-40% of the total body weight. Half of this weight is water.

1. Supports the body 2. Protects soft body parts 3. Produces blood cells 4. Stores minerals and fat 5. Permits flexible body movement, along with the muscles

 Bones are classified according to their shape.  There are 5 classifications: 1. Long bones 2. Short bones: cube shaped; their lengths and widths are about equal 3. Flat bones: plate-like with broad surfaces 4. Irregular bones: varied shapes with many places for connections with other bones 5. Sesamoid (round) bones: circular

1. Bones have the ability to grow and repair damaged tissue. 2. There are several different types of cells that are involved in both bone growth and repair. 3. Osteoprogenitor cells: unspecialized cells 4. Osteoblasts: bone-forming cells responsible for secreting the matrix characteristic of bone.

5. Osteocytes: mature bone cells derived from osteoblasts. 6. Osteoclasts: believed to be a type of white blood cell, they perform bone reabsorbtion– break down bone and assist in depositing calcium and phosphate into the blood.

1. Long bones are used to illustrate the principles of bone anatomy. 2. Bone is enclosed in a tough, fibrous connective tissue called the periosteum. 3. The periosteum contains blood vessels that enter bone and service the cells. 4. Both ends of the bone are called the epiphysis. 5. The shaft is called the diaphysis.

The epiphyses are covered by articular cartilage (form of hyaline cartilage). This cartilage is located where the bones articulate or join together with other bones.

a. Known as dense bone b. Contains many cylinder shaped units called osteons. c. Osteocytes are found in tiny chambers called lacunae. d. Lacunae occur between concentric layers of matrix called lamellae. e. The matrix contains collagenous protein fibers and mineral deposits (calcium and phosphorus salts).

6. The diaphysis has a medullary cavity, which contains yellow marrow. 7. Yellow marrow contains large amounts of fat. 8. The cavity is bounded at the sides by compact bone. 9. The epiphyses contain spongy bone.

f. In each osteon, the lemellae and lacunae surround a single central canal. g. Blood vessels and nerves enter the canal from the periosteum. h. Osteocytes are connected to one another by passageways called canaliculi.

a. Known as cancellous bone b. Contains numerous bars and plates called trabeculae c. Lighter than compact bone but designed for strength d. The trabeculae are designed like support braces and follow lines of distress. e. Site for hematopoiesis- formation of red blood cells (in adults)

f. Hematopoiesis occurs in the following bones: sternum (breastbone), skull, ribs, vertebrae, and at the end of long bones.

 Ossification means bone growth.  Bones form during embryonic development in one of two ways: intramembranous ossification and endochondral ossification.

a. Bone develops between sheets of fibrous connective tissue b. Osteoblasts form a matrix similar to the trabeculae of spongy bone. c. Other osteoblasts lay down compact bone over the spongy bone. d. The osteoblasts become osteocytes when they become surrounded by a matrix. e. Your skull develops this way.

a. Most of the bones in the skeleton develop this way. b. Basically hyaline cartilage in the fetus is replaced by bone as development continues. c. Cartilage begins to break down in the center of the diaphysis, which is covered by periosteum. d. Osteoblasts start to lay down spongy bone in what is referred to as “the primary ossification center”.

e. Other osteoblasts lay down compact bone under the periosteum. f. As the compact bone thickens, the spongy bone layer is destroyed by osteclasts, and the medullary cavity is formed. g. After birth, the epiphyses still continue to grow. h. Spongy bone forms in the epiphyses (secondary ossification center) and is not broken down.

i. A band of cartilage remains called the epiphyseal plate. j. Bones keep increasing in length and width so long as the plate is present. k. When the plate becomes ossified, bones stop growing. l. The rate of growth is controlled by hormones (growth and sex). m. Boys can grow until age 21, girls can grow until age 19.