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26 Cards in this Set

  • Front
  • Back
Skeletal System

Storage of minerals and lipids ( yellow marrow stores lipids; Calcium and phosphate is stored in the bones)
Blood cell production - in the red marrow
Composition of bone
Composition of Bone

Calcium phosphate (Ca3(PO4)2)makes up 2/3 of the weight of bone
Calciumphosphate interacts with calcium hydroxide to form crystals of hydroxyapatite
Collagen fibers is 1/3 the weight of bone
Cells account for 2% of mass of bone
Collagen fibers provid a framework on which hydroxyapatite crystals can form
Collagen also provides some flexibility so bone is not so brittle
Composition of matrix is the same in compact and spongy bone
Compact bone vs. Spongy bone
Compact bone basic functional unit is the osteon or Haversion system; lamellae are arranged in osteons; endosteum lines the central canal
Spongy bone - lamellae are not arranged inosteons; the matrix forms struts and plates called trabeculae; spongy bone contains red marrow or yellow marrow;
Osteocytes are arranged in concentric layers around a central canal (Haversian canal)
Haversian canal runs parallel to the bone surface and caries blood vessels to and from the osteon
Perforating canals ((Volkmann's canals) run perpendicular to the surface and cary blood to deeper osteons and tissues in the medullary cavity
Outside of bone
2 layers - fibrous outer layer and cellular inner layer
Collagen fibers of the periosteum are continuous with the bone, and attached ligaments and tendons
Fibers incorporated into the bone from tendons, ligaments and periosteum are called Sharpey's fibers
Incomplete cellular layer
Contains epithelial cells, osteoblasts, osteoprogenitor cells, and osteoclasts
Active during growth, repair, and remodelling
Covers the trabeculae of spongy bone and lines the inner surface of central canals of the osteon in compact bone
Bone Development and Growth
Formation of bony skeleton begins about the 6th-8th week of embryonic development
Ossification is the term used to describe replacing one type of tissue with bone
OOssification refers specifically to bone formation
Calcification is the depostion of calcium salts during the ossification process, but may occur in other tissues other than bone
Two type of ossification - intramembranous and endochondral

Occurs within membranous tissues that are destined to become bone, such as the flat bones of the cranium, face, and portions of clavicle
Begins when osteoblasts differentiate within mesenchymal, or fibrous connective tissue

Intramembranous Step 1
1. Mesenchymal cells cluster together and secrete the organic components of the matrix; cells arrange themselves in interconnecting rows called spicules; spicules continue to grow

Intramembranous Step 2
Blood vessels begin to grow into the area and infiltrate the region between the spicules

Intramembranous Step 3
Cells begin to produce microfibrils
Osseomucoid secretion follows and stabilizes the rows of cells together
The cells are now called osteoporgenitors and the uncalcified framework is called "osteoid" - non-mineralized bone cells

Intramembranous Step 4
Osteoblasts begin secreting alkaline phosphatase - this enzyme breaks down phosphoric esters in the interstitial fluid
Free PO4 ions unite with Ca++ and OH- to form calcium hydroxyapatie
Hydroxyapatite crystals precipitate on the osteoid and the mineralized structure is now called a trabecula
The bone continues to form and create spongy bone
Spongy bone can be removed to form marrow cavities or remodel to form compact bone

Occurs in the appendicular skeleton cartilage where cartilage dies and is replaced by bone

Endochondral Step 1
Cartilage enlarges
Chondrocytes enlarge
Matrix is reduced
Enlarged chondrocytes die and leave cavities within the cartilage

Endochondral Step 2
Blood vessels grow around the edges of the cartilage
Cells of the pericondrium convert to osteoblasts
Shaft of the cartilage becomes ensheathed in a superficial layer of bone

Endochondral Step 3
lood vessels penetrate further and invade central region
Fibroblasts differentiate into osteoblasts and produce spongy bone at a primary center of ossification
Bone formation spreads along the shaft toward both ends

Endochondral Step 4
Remodelling occurs as growth continues
Bone of the shaft becomes thicker
Cartilage near each epiphysis is replaced by shafts of bone
Further growth increases in length

Endochondral Step 5
Capillaries and osteoblasts migrate into the epiphysis and create secondary ossification centers

Endochondral Step 6
Soon the epiphyses are filled with spongy bone
An articular cartilage remains exposed to the joint cavity
At each metaphysis, an epiphyseal cartilage separates the epiphysis from the diaphysis
Bone Growth
Interstitial growth - grows by expansion of cartilage
Appositional growth - production of new cartilage at the outer surface
2 types
Endochondral - bone replaces existing cartilage
Intramembranous - bone develops directly from mesenchyme or fibrous tissue
Bone Growth

Within the metaphysis is hyaline cartilage, called the Epiphyseal Plate
Epiphyseal plate anchors the epiphysis to the diaphysis and is responsible for bone growth in length
Cartilae plate is divided into 4 zones
During rapid growth, the mitotic zzon produces cartilage at a rate that exceeds the death rate, so the bone grows
Bone growth

Bone formation at the surface of the bone produces ridges that parallel a blood vesel
The ridge enlarges and creates a pocket
The ridges meet and fuse
Bone deposition occurs inward toward the vessel and creates an osteon
Cortex thickens and diameter enlarges
Bone deposition by osteoblasts
Bone resorption by osteoclasts
Bone Remodelling
The organic and mineral components of the bone matrix are recycled and renewed
Remodeling involves a balance between osteocytes, osteoblasts, and osteoclasts
Turnover rate is high - in young adults, almost 1/5 of the skeleton is recycled and replaced
Turnover rates differ based on region - head of the femur may be replaced 2-3 times a year; compact bone in the shaft remains largely unchanged
Bone Remodelling

When bone is stressed mineral crystals generate electrical fields which attract osteoblasts and then produce bone
Bones are adapatable
Their shapes reflect forces applied to them
Bumps and ridges on the bones mark sites where tendons attach
Heavily stressed bones become thicker and stronger whereas bones not subjected to ordinary stresses become thin and brittle - problem for astronauts or bedridden individuals