skeletal

• Skeletal system


  Composed of bones, cartilages, tendons and ligaments
• Functions of skeletal system

  • Body support
  • Organ protection
  • Body movement
  • Mineral storage
  • Blood cell production
• Bone tissue


  Connective tissue containing collagen, ground substance, organic molecules, water and minerals
• Collagen


  Fibrous protein that provides flexibility and resistance to pulling or compression
• Ground substance


  Contains proteoglycans which are water-trapping, hydrophilic proteins
• Hydroxyapatite


  Calcium phosphate crystal that makes bone hard and resistant to decomposition
• Bone cells


  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteoblasts


  Responsible for bone formation, repair and remodelling by producing collagen and hydroxyapatite
• Osteocytes


  Mature bone cells that maintain the bone matrix, located inside spaces called lacunae
• Osteoclasts


  Bone-destroying cells that break down bone tissue to release calcium into the blood
• Spongy bone


  Has less bone matrix and more spaces filled with red bone marrow for blood cell production
• Compact/cortical bone


  Solid outer layer of bones, with a structural unit called an osteon containing concentric rings of matrix
• Canaliculi


  Tiny canals that interconnect osteocytes to transport nutrients and remove waste
• Long bone structure


  • Shaft/diaphysis (compact bone)
  • Ends/epiphysis (spongy bone)
  • Epiphyseal plate (cartilage growth plate in young bones)
• In young bones, the epiphyseal plate is a thick layer of hyaline cartilage that allows for longitudinal growth of the long bones
• In adult bones, the epiphyseal plate is replaced by a thin epiphyseal line
• Diaphysis


  The shaft of a bone
• Epiphysis


  The ends of a bone
• The epiphysis is covered with a layer of cartilage called articular cartilage, which is made of hyaline cartilage
• Epiphyseal plate


  A thick plate of cartilage in young bones, which is where growth in length of long bones occurs
• As a person reaches adulthood

  The epiphyseal plate is replaced by a thin epiphyseal line as the cartilage is turned into bone tissue
• 1. rays can clearly show the epiphyseal plates in young, growing bones
• Red bone marrow


  Found in the cavities of spongy bone, responsible for the formation of new blood cells
• Yellow bone marrow


  Found in the medullary cavity, mainly composed of fat for storage
• Ossification


  1. The process of bone formation

  2. Occurs in two forms: intramembranous ossification and endochondral ossification
• Intramembranous ossification


  Bone formation within embryonic connective tissue membranes
• Endochondral ossification


  Bone formation within a cartilage model
• Both intramembranous and endochondral ossification result in the formation of compact and spongy bone tissue
• Intramembranous ossification


  1. Osteoblasts begin to produce bone within connective tissue

  2. Ossification centers form, with bone formation radiating outwards

  3. Edges of flat bones meet and fuse to form a closed vault
• Endochondral ossification


  1. Chondroblasts form a cartilage model

  2. Cartilage model hardens through calcification

  3. Osteoblasts invade the calcified cartilage, forming a primary ossification center in the diaphysis

  4. A secondary ossification center forms in the epiphysis

  5. Epiphyseal plate of cartilage remains between the epiphysis and diaphysis, allowing for bone growth in length

  6. Epiphyseal plate is eventually replaced by bone as growth stops
• Oppositional growth


  The process by which bones grow in width and diameter, with new bone being deposited between the periosteum and existing bone
• Bone remodeling


  1. The continuous process of bone removal by osteoclasts and deposition of new bone by osteoblasts

  2. Responsible for changes in bone shape, bone repair, and calcium regulation
• Fracture healing


  1. Hematoma formation

  2. Callus formation

  3. Callus ossification

  4. Bone remodeling
• Fractured bones are realigned through reduction, either by internal fixation with plates and screws or by external casting
• Calcium homeostasis


  The balance of calcium levels between the blood and bone, maintained by parathyroid hormone and calcitonin
• Low calcium intake


  Stimulates parathyroid hormone secretion, which activates osteoclasts to break down bone and release calcium into the blood
• High calcium intake


  Stimulates calcitonin secretion, which inhibits osteoclast activity and promotes calcium storage in bone