Bones

Question 1

Components of bone

Answer 1

Extracellular matrix - majority of bone mass; consists of fibers and ground substances (mineralized)
Cells
Periosteum that lines the external surface of bones
Endosteum that lines the central cavity of bones

Question 2

Periosteum

Answer 2

Found on external surface of bones; well vascularized. Meant to maintain the bone and functions in remodeling and repair of bone. Helps to anchor tissues and ligaments
Outer layer has dense collagenous connective tissue with collagen fibers, blood vessels, and fibroblasts
Inner cellular layer has osteoprogenitor cells and osteoblasts

Question 3

Osteocytes

Answer 3

Found in lacunae in the extracellular matrix. Mature bone cells

Question 4

Canaliculi

Answer 4

Narrow channels in the bone matrix radiating from the lacunae of osteocytes
Contain cytoplasmic processes that extend from osteocytes and make contact via gap junctions

Question 5

Osteoclasts

Answer 5

Large multinucleated cells with acidophilic cytoplasm
Resorb bone
Occupy small depressions in the bone surface (resorption bays)

Question 6

Osteoprogenitor cells

Answer 6

found in inner cellular layer of periosteum. Produce osteoblasts

Question 7

Osteoblasts

Answer 7

Found on bone surfaces. Produce the organic matrix (osteoid). When surrounded by extracellular matrix, become osteocytes
Active osteoblasts are cuboidal or columnar with basophilic cytoplasm
Inactive osteoblasts are flattened with reduced basophilic staining of their cytoplasm

Question 8

Endosteum

Answer 8

Thin layer of cells lining the internal surface of bone. Contains osteoprogenitor cells, osteoblasts, and “bone lining cells” (flattened, quiescent osteoblasts)

Question 9

Two types of bone

Answer 9

Compact bone - very dense
Trabecular bone - consists of trabeculae and spicules

Question 10

Compact bone

Answer 10

Basic structures are osteons/Haversian canal systems
Composed of concentric lamellae and osteonal (Haversian or central) canals

Question 11

Concentric lamellae of compact bone

Answer 11

In a circular arrangement of bone around a central canal. Contain osteocytes

Question 12

Osteonal (Haversian or central) canals of compact bone

Answer 12

Spaces in the center of osteons. Lined by endosteum, contain blood vessels and nerves

Question 13

Interstitial lamellae

Answer 13

Irregular pieces of lamellae scattered among the intact osteons. Contains transverse canals which are vascular channels connecting adjacent central canals of osteons

Question 14

Two types of bone formation during embryonic development

Answer 14

Intramembranous and endochondral

Question 15

Intramembranous bone formation

Answer 15

Mesenchymal cells are stimulated to differentiate into osteoblasts that secrete bone matrix
Bone replacing mesenchyme
Most flat bones are formed this way

Question 16

Endochondral bone

Answer 16

Requires presence of hyaline cartilage template model that is replaced by bone
Most long and short bones are formed this way

Question 17

5 zones of the epiphysial plate

Answer 17

1) zone of reserve cartilage - chondrocytes are randomly oriented and mitotically active
2) zone of proliferation - chondrocytes rapidly divide and line up in isogenous rows paralleling the direction of bone growth
3) zone of maturation and hypertrophy - chondrocytes mature and hypertrophy; interterritorial matrix gets thin
4) zone of calcification - hypertrophied chondrocytes die, cartilage matrix becomes calcified using calcium provided by invading blood vessels
5) zone of ossification - osteoprogenitor cells invade and differentiate into osteoblasts that form bone matrix

Question 18

Megakaryocytes

Answer 18

Large cells found in bone marrow
Mononucleated
Extend cytoplasmic processes into the sinusoids and break off pieces that become platelets