Structure of a Flat Bone
The parietal bone of the skull
Resembles a sandwich of spongy bone
Between two layers of compact bone
Within the cranium, the layer of spongy bone between the compact bone is called the diplo�
Bone (Osseous) Tissue
Dense, supportive connective tissue
Contains specialized cells
Produces solid matrix of calcium salt deposits
Around collagen fibers
Characteristics of Bone Tissue
Dense matrix, containing:
Deposits of calcium salts
Osteocytes (bone cells) within lacunae organized around blood vessels
Canaliculi
Form pathways for blood vessels
Exchange nutrients and wastes
Bone Matrix
Mature bone by weight consists of 35% organic and 65% inorganic material.
Minerals
Two thirds of bone matrix is calcium phosphate, Ca3(PO4)2
Reacts with calcium hydroxide, Ca(OH)2
To form crystals of hydroxyapatite, Ca10(PO4)6(OH)2
Which incorporates othe
Organic Material
Consists of Collagen and Proteoglycans
Inorganic Material
Consists of a Calcium Phosphate crystal called Hydroxyapatite.
Periosteum
Covers outer surfaces of bones
Consists of outer fibrous and inner cellular layers
on the outside
Covers all bones except parts enclosed in joint capsules
Made up of an outer, fibrous layer and an inner, cellular layer
Perforating fibers: collagen fibers
Functions of Periosteum
1. Isolates bone from surrounding tissues
2. Provides a route for circulatory and nervous supply
3. Participates in bone growth and repair
Bone Cells
Make up only 2% of bone mass
Bone contains four types of cells
Osteocytes
Osteoblasts
Osteoprogenitor cells
Osteoclasts
Osteoblasts
Are associated with bone formation.
Have extensive endoplasmic reticulum and numerous ribosomes.
Ossification or Osteogenesis - Is the formation of bone by osteoblast
Immature bone cells that secrete matrix compounds (osteogenesis)
Osteoid � matrix produc
Osteoclasts
Secrete acids and protein-digesting enzymes
Giant, multinucleate cells
Contain numerous lysosomes
Dissolve bone matrix and release stored minerals (osteolysis)
Derived from stem cells that produce macrophages
Develop from circulating monocytes (one type o
Osteocytes
Are mature bone cells.
Are the principal cells of bone tissue.
Lacunea - Are spaces occupied by the osteocyte cell bodies.
Canaliculi (little canals) - Are spaces occupied by the osteocyte cell processes.
Mature bone cells that maintain the bone matrix
Li
Osteoprogenitor Cells
Mesenchymal stem cells that divide to produce osteoblasts
Located in endosteum, the inner cellular layer of periosteum
Assist in fracture repair
Are stem cells that have the ability to become osteoblasts and chondrioblasts.
Note: Osteoblasts are derived f
Origin of Bone Cells
Connective tissue develops embroyologically from mesenchymal cells.
Stem Cells
Have the ability to replicate and give rise to more specialized cell types.
Homeostasis
Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance
More breakdown than building, bones become weak
Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone
Woven and Lamellar Bone
According to the organization of collagen fibers within the bone matrix, bone tissue is classified as (a) Woven bone or (b) Lamellar bone.
Woven bone
Collagen fibers are randomly oriented in many direction.
Lamellar bone
Is mature bone that is organized into thin sheets or layers called lamellae.
Cancellous and Compact Bone
Bone woven or lamellar are classified according to the amount of bone matrix relative to the amount of space present within the bone.
Cancellous bone has less matrix and more space while Compact bone has more matrix and less space.
Cancellous Bones
Consists of interconnecting rods or plates of bones called trabeculae.
Between the trabeculae are spaces that in life are filled with bone marrow and blood vessels.
Note: Cancellous bone is sometimes called Spongy Bones because of its porous appearance.
Endosteum on the inside
An incomplete cellular layer:
Lines the medullary (marrow) cavity
Covers trabeculae of spongy bone
Lines central canals
Contains osteoblasts, osteoprogenitor cells, and osteoclasts
Active in bone growth and repair