Function of the Skeletal System

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Function of the Skeletal System
1. Support
2. Movement: The bones of the upper and lower limbs pull and push, with the help of muscles.
3 storage as a mineral store. 97% of the body's calcium is stored in bone. Here it is easily available and turns over fast. In pregnancy the demands of the fetus for calcium require a suitable diet and after menopause hormonal control of calcium levels may be impaired: calcium leaches out leaving brittle osteoporotic bones.

4. Protective. Skull for the brain and rib for the heart and lungs.

5. Blood cell production: as a marrow holder.

Structure of Bone
1.Diaphysis: shaft of the bone and it is composed primarily compact bone
2.Epiphysis: End of bone consists primarily of cancellous or spongy bone.
3.Epiphyseal plate: Hyaline cartilage is located between the epiphysis and
diaphysis. Growing in the bone length occurs at the epiphyseal plate. But,
when a bone stops growing in length the epiphyseal plate become ossified
and is called the epiphyseal line
4. Medullary cavity: The diaphysis of a long bone has a large space called
the medullary cavity. The cavities of cancellous bone and the medullary
cavity are filled with marrow. Red marrow is the site of blood cell
formation and yellow marrow is most adipose tissue
5. Periosteum: double-layered connective tissue membrane covering the outer surface of bone except where articular cartilage exist; ligaments and tendons attach to bone through the periosteum; blood vessels and nerves from the periosteum supply the bone; the periosteum is the site of bone growth in diameter.

6. Endosteum: Thin connective tissue membrane lining the inner cavities of bone
7. Particular cartilage: Thin layer of hyaline cartilage covering a bone where it forms a joint with another bone.
8. Red marrow: Connective tissue in the spaces of cancellous bone or in the medullary cavity; the site of blood cell production.
9. Yellow marrow: Fat stored within the medullary cavity or in the spaces of cancellous bone.

*Periosteum is essential for bone growth, repair, and nutrition; and also serves as a point of attachment for ligaments and tendons.

*Chondroblast - a cartilage forming cell.
*Chondroclast - a cartilage destroying cell.
*Chondrocyte - a mature cartilage cell.

History of Bone
The matrix contains 65% mineral salts and 35% organic matter; it is the mineral salts which accounts for the hardness of bone tissue. The organic component is composed of collagen fibers with predominately type I collagen (95%) and amorphous material, including proteinglycans. Inorganic matter composed of abundant calcium and phosphorus crystal known as hydroxyapatite crystals.

1. Osteoblasts: are very active cells at the surface of bone tissue. Their function is to secrete organic substance (collagen fiber) add to the matrix, form osteoid tissue for the deposition of mineral salts thus forming bonetissue. Sites: centers of ossification, [immature bone], deep layers of periosteum, fractures.

2. Osteocytes: are formed from osteoblasts, but is less active and no longer form new bone tissue. Osteocytes become isolated in lacunae [small spaces] within the matrix. Nutrition is via fluid in the canaliculi, which are part of the Haversian system. Their function is thought to be moving calcium between bone and blood.

Sites: within the Haversian system.

3. Osteoclasts: are large active cells situated at the surface of growing tissue. A brush [cilia] like border on one surface is directed towards the matrix, the function is the resorption of bone. To achieve this function osteoclasts secrete substances to break down minerals salts and collagen fibers and destroy the remains [this process is phagocytosis]. Particularly important in intracartilaginous bone development.

Sites: under periosteum, during growth, walls of medullary canal.

The balance between number of osteoblasts and
osteocytes and their related activity is important
in maintaining...
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