skeletal system

• Components of Skeletal System

  • Bones
  • Cartilages
  • Tendons
  • Ligaments

  
• Skeletal System Functions


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


  Composition of connective tissues like bone, cartilage, tendons, and ligaments
• Extracellular Matrix


  • Contains collagen, ground substance, and other organic molecules, as well as water and minerals
• Collagen


  A 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
  • Epiphysis
  • Articular cartilage
  • Epiphyseal plate
  • Medullary cavity
  • Periosteum
  • Endosteum

  
• Diaphysis


  Shaft of long bone, contains compact bone tissue on the outside

  
• Epiphysis


  Ends of long bone, contain spongy bone tissue

  
• Articular Cartilage


  Covers epiphyses, reduces friction
• Epiphyseal Plate


  Site of growth between diaphysis and epiphysis
• Medullary Cavity


  Center of diaphysis, contains red or yellow marrow
• Periosteum


  Membrane around bone's outer surface

  
• Endosteum


  Membrane that lines medullary cavity
• Bone Marrow Types


  • Red marrow
  • Yellow marrow
• Red Marrow


  Location of blood forming cells
• Yellow Marrow


  Mostly fat
• In newborns most bones have blood making red bone marrow
• 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 Characteristics

  • Location: outer part of diaphysis (long bones) and thinner surfaces of other bones
  • Osteon: structural unit including lamella, lacunae, canaliculus, central canal, osteocytes
  • Lamella: rings of bone matrix
  • Lacunae: spaces between lamella
  • Canaliculus: tiny canals transport nutrients and remove waste
  • Central canal: center of osteon, contains blood vessels

  
• Spongy bone has trabeculae, which are interconnecting rods, and spaces that contain marrow

  
• Spongy bone has no osteons

  
• Bone Cells


  • Osteoblasts
  • Osteocytes
  • Osteoclasts

  
• Osteoblasts


  Responsible for the formation of bone and the repair and remodeling of bone

  
• Osteocytes


  Cells that maintain bone matrix and form from osteoblast after bone matrix has surrounded it

  
• Osteoclasts


  Contribute to bone repair and remodeling by removing existing bone, called bone reabsorption

  
• Bone Formation Types


  • Intramembranous ossification
  • Endochondral ossification

  
• Intramembranous Ossification


  Bone formation that occurs within connective tissue membranes

  
• Endochondral Ossification


  Bone formation that occurs inside hyaline cartilage

  
• Intramembranous Ossification


  1. Osteoblasts line up on the surface of connective tissue fibers and begin depositing bone matrix to form trabeculae

  2. The process begins in areas called ossification centers and the trabeculae radiate out from the centers

  3. Usually, two or more ossification centers exist in each flat skull bone and mature skull bones result from fusion of these centers as they enlarge

  4. The trabeculae are constantly remodeled and they may enlarge or be replaced by compact bone

  
• Endochondral Ossification


  1. Cartilage model is replaced by bone

  2. Initially formed is a primary ossification center, which is bone formation in the diaphysis of a long bone

  3. A secondary ossification center is bone formation in the epiphysis

  4. Chondroblasts build a cartilage model, the chondroblasts become chondrocytes

  5. Cartilage model calcifies (hardens)

  6. Osteoblasts invade calcified cartilage and a primary ossification center forms diaphysis

  7. Secondary ossification centers form epiphysis

  8. Original cartilage model is almost completely ossified and remaining cartilage is articular cartilage