Skeletal System

• Function of Skeletal System

  1. Support
  2. Protection
  3. Movement
  4. Mineral Storage (reservoir for minerals and adipose tissue)
  5. Hematopoiesis (blood production)
• Bone cells

  1. Osteoblasts - bone builders, bone calcification, found in the endosteum lining the periosteum. Produce new bone called "osteoid". Control mineral deposition
• Bone cell

  1. Osteocytes - formed when osteoblasts becomes embedded in matrix. Mature bone cells. Inside the bone.
• Bone cells

  1. Osteoclasts - bone eaters(dissolves bone). Bone resorption. Come from bone marrow.
• Bone resorption - osteoclasts break down bone tissue, releasing minerals such as calcium and phosphate into the bloodstream.

  Summary

  1. Osteoclasts form bone resorption
  2. Osteoblasts - bone formation thru matrix deposition
  3. Osteoblasts turn into osteocytes

  
• Bone Anatomy (Longitudinal)

  1. Compact bone - called cortical bones. Made up of osteons. Fill the outer layer of most bones. Forms the shaft or diaphysis of long bones. In adult, yellow bone (medullary cavity) marrow is found.
• Bone Anatomy (Longitudinal)

  1. Spongy bone - called cancellous bones. Made up of trabeculae. Fill the inner layer of most bones. Forms the ends or epiphyses of long bones. Found red bone marrow (produce RBC)
• Bone Classification

  1. Long bones - tubular shaft (diaphysis), ends of long bone are called epiphyses. The joint of epiphyses is covered with articular cartilage.

  -Joint of epiphyses is covered by double-layered membrane known as periosteum

  -Internal surface are covered with delicate connective tissue membrane known as endosteum. (contains both osteoblasts and osteoclasts)
• Bone Classification

  2. Short, Irregular, and Flat - consists of thin plates of spongy bone covered by compact bone.

  -No diaphysis or epiphyses since they are not cylindrical.

  -Contain bone marrow between their trabeculae, but no marrow cavity.

  3. Flat - internal spongy bone layer is called diploe and arrangement is a stiffened sandwich.
• Two Types of Ossification

  1. Intramembranous Ossification - making bones between connective tissue membranes
  2. Endochondral Ossification - making bones within cartilage
• Intramembranous Ossification

  1. Formation of the ossification center - Mesenchymal cells cluster and differentiate into osteoblasts forming the ossification center (ossification begins)
  2. Bone Matrix Secretion - Osteoblasts secrete osteoid which becomes calcified and forms the bone matrix
  3. Trabeculae & Periosteum Formation - Formation of the network of trabeculae and periosteum by the condensation of the mesenchyme.
  4. Compact Bone Formation - Trabeculae thicken and fuse together. Vascular tissue becomes red bone marrow.
• Endochondral Ossification

  1. Matrix Calcification - Enlargement of chondrocytes. Calcification of the matrix.
  2. Bone Formation - Osteoblasts covering the cartilage.
  3. Ossification Center Formation - Penetration of blood vessels into the cartilage. Formation of the ossification center.
  4. Bone Shaft Formation - Thickening of the bone shaft. Replacement of the cartilages near the epiphyses to bone shaft.
  5. Formation of Secondary Centers of Ossification - Secondary centers of ossification are formed by the osteoblasts. Blood vessels invade the epiphyses
• Bone Growth

  1. Appositional Growth - Formation of new bone on the surface of existing bone. Increase in bone diameter.
  2. Endochondral Growth - Formation of new bone on the epiphyseal ends of existing bone. Increase in bone length.