Chapter 6- Bones Flashcards
Name 6 functions of bones:
- Support
- Movement
- Protection
- Mineral storage
- Blood cell formation and energy storage
- Energy metabolism
Canaliculi of osteon:
Run thru matrix connecting neighboring lacunae to another and to nearest capillaries.
Lamella of osteon:
Layer of bone matrix where collagen fibers and mineral crystals align. Run in single direction.
Haversion (central) canal:
Core of each osteon. Lined internally with endosteum.
Compact bone:
Made up of osteons. Heavier and tougher.
Central canal contains its own blood vessels which supply nutrients to bone cells.
Spongy bone:
Made of trabeculae. Lighter bones.
Do not contain osteons or blood vessels. They are made of lamella and osteocytes. The osteocytes get nutrients from capillaries in the endosteum via canaliculi.
Intramembranous ossification phase 1:
(1) During week 8 of embryonic development, mesenchymal cells cluster within the connective tissue membrane and become bone forming osteoblasts.
Intramembranous ossification phase 2:
Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. Osteoblasts become osteocytes.
Intramembranous ossification phase 3:
Woven bone and periosteum form. Vascularized mesenchyme condenses on external face of woven bone and become periosteum.
Intramembranous ossification phase 4:
Trabeculae at periphery grows thicker until plates of compact bone are present in both surfaces. Trabeculae remain distinct in the center of membranous bone, which become spongy bone. Final pattern is that of flat bone.
Endochondral ossification phase 1:
Perichondrium surrounding diaphysis is invaded by blood vessels and become a bone forming periosteum. Osteoblasts lay down a collar of bone tissue around diaphysis.
Endochondral ossification phase 2:
Cartilage in center of diaphysis calcifies and then develops cavities.
Endochondral ossification phase 3:
The periosteal bud invades the internal cavities and spongy bone forms.
Endochondral ossification phase 4:
The diaphysis elongates, and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses
Endochondral ossification phase 5:
The epiphyses ossify. When completed hyaline cartilage remains only in the epiphyseal plates and articular cartilage.
Why are bones considered organs?
Because they contain several different tissues
Describe postnatal lengthening of endochondral bones:
Bones lengthen by growth of epiphyseal plates. Cartilage is replaced with bone tissue on diaphysis side as soon as it grows, so epiphyseal plate remains a constant thickness. At the end of adolescence, chondroblasts divide less often and plates become thinner. Cartilage stops growing and is replaced by bone tissue. Long bones stop lengthening when the epiphyses and diaphysis fuse.
Describe postnatal widening of endochondral bones:
Osteoblasts in the iatrogenic layer of the periosteum add bone tissue in circumferential lamellae to the external face of the diaphysis as osteoclasts in the endosteum remove bone from within the diaphysis wall.
Microscopic anatomy of epiphyseal plates (top to bottom):
Resting zone Proliferation zone Hypertrophic zone Calcification zone Ossification zone
Resting zone:
The cartilage cells nearest epiphysis are small and inactive.
Proliferation zone:
Tall columns formed by cartilage cells. Chondroblasts divide quickly, pushing epiphysis away from diaphysis.
Hypertrophic zone:
Older chondrocytes enlarge and signal the surrounding matrix to calcify.
Calcification zone:
Matrix become calcified; cartilage cells die; matrix begins deteriorating.
Ossification zone:
New bones forming.
