Chapter 06 - Skeletal

• Skeletal System


  Components: Bones, Cartilages, Tendons, Ligaments
• Bones of the Skeletal System


  • Figure 6.11
• Skeletal System Functions


  • Support
  • Protect
  • Movement
  • Storage
  • Blood cell production
• Extracellular Matrix


  Composition: Collagen, ground substance, other organic molecules, water, minerals
• Collagen


  Tough, ropelike protein
• Proteoglycans


  Large molecules consisting of many polysaccharides attaching to and encircling core proteins
• Extracellular Matrix of Tendons and Ligaments

  Contains large amounts of collagen fibers, making these structures very tough, like ropes or cables
• Extracellular Matrix of Cartilage

  Contains collagen and proteoglycans. Collagen makes cartilage tough, whereas the water-filled proteoglycans make it smooth and resilient.
• Extracellular Matrix of Bone

  Contains collagen and minerals, including calcium and phosphate. The ropelike collagen fibers lend flexible strength to the bone, and the mineral component gives bone compression (weight-bearing) strength.
• Bone Shape Classifications


  • Long
  • Short
  • Flat
  • Irregular
• Long Bones


  Longer than they are wide, examples are upper and lower limb bones
• Short Bones


  Approximately as wide as they are long, examples are the bones of the wrist and ankle
• Flat Bones


  Have a relatively thin, flattened shape, examples are bones of the skull and sternum
• Irregular Bones


  Include the vertebrae and facial bones, which have shapes that do not fit readily into the other three categories
• Long Bone Structures


  • Diaphysis: Shaft, compact bone tissue (on outside)
  • Epiphysis: ends, spongy bone tissue
  • Articular cartilage: covers epiphyses, reduces friction
• Long Bone Structures


  • Epiphyseal plate: site of growth between diaphysis and epiphysis
  • Medullary cavity: center of diaphysis, red or yellow marrow
• Long Bone Structures


  • Periosteum: membrane around bone's outer surface
  • Endosteum: membrane that lines medullary cavity
• Figure 6.2 shows the structure of a long bone
• Bone Marrow


  Soft tissue filling the cavities in bones, including the medullary cavity in the diaphysis and smaller cavities in the epiphyses
• Red Marrow


  Location of blood forming cells
• Yellow Marrow


  Mostly fat
• In newborns most bones have blood making red bone marrow, but in adults red marrow in the diaphysis is replaced by yellow bone marrow
• In adults most red bone marrow is in the flat bones and the long bones of the femur and humerus
• Compact Bone Tissue


  • Located in the outer part of the diaphysis (long bones) and thinner surfaces of other bones
  • Osteon: structural unit, includes lamella, lacunae, canaliculus, central canal, osteocytes
• Lamella


  Rings of bone matrix
• Lacunae


  Spaces between lamella
• Canaliculus


  Tiny canals that transport nutrients and remove waste
• Central Canal


  Center of osteon, contains blood vessels
• Figure 6.3 shows the structure of bone tissue
• Spongy (Cancellous) Bone Tissue

  • Located at the epiphyses of long bones and center of other bones
  • Has trabeculae, which are interconnecting rods, and spaces that contain marrow
  • Has no osteons
• Figure 6.4 shows spongy bone tissue
• Bone Cells


  • Osteoblasts: responsible for bone formation, repair and remodeling
  • Osteocytes: maintain bone matrix and form from osteoblasts
  • Osteoclasts: contribute to bone repair and remodeling by removing existing bone
• Ossification


  1. Bone formation by osteoblasts

  2. Intramembranous ossification: bone formation within connective tissue membranes

  3. Endochondral ossification: bone formation inside hyaline cartilage
• Intramembranous Ossification


  1. Osteoblasts produce bone within connective tissue

  2. Occurs primarily in the bones of the skull

  3. Osteoblasts line up on connective tissue fibers and deposit bone matrix to form trabeculae

  4. Trabeculae radiate out from ossification centers
• Figure 6.5 shows bone formation in the fetus
• Endochondral Ossification


  1. Bone formation within a cartilage model

  2. Cartilage model is replaced by bone

  3. Primary ossification center forms in diaphysis

  4. Secondary ossification center forms in epiphysis
• Figure 6.6 shows endochondral ossification of a long bone
• Bone Growth in Width

  Osteoblasts deposit new bone matrix on the surface of bones between the periosteum and the existing bone matrix, increasing the bone's width or diameter
• Bone Growth in Length

  1. Occurs in the epiphyseal plate through endochondral ossification

  2. Chondrocytes increase in number on the epiphyseal side of the epiphyseal plate

  3. Chondrocytes enlarge and die, cartilage matrix becomes calcified, cartilage is removed by osteoclasts, and osteoblasts deposit new bone
• Figure 6.7 shows endochondral bone growth