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26 Cards in this Set
- Front
- Back
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Skeletal System
Functions |
Support
Storage of minerals and lipids ( yellow marrow stores lipids; Calcium and phosphate is stored in the bones) Blood cell production - in the red marrow Protection Leverage |
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Composition of bone
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Matrix
Cells |
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Composition of Bone
Matrix |
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 |
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Compact bone vs. Spongy bone
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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; |
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Osteon
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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 |
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Periosteum
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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 |
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Endosteum
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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 |
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Bone Development and Growth
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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 |
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Ossification
Intramembranous |
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 |
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Ossification
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
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Ossification
Intramembranous Step 2 |
Blood vessels begin to grow into the area and infiltrate the region between the spicules
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Ossification
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 |
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Ossification
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 |
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Ossification
Endochondral |
Occurs in the appendicular skeleton cartilage where cartilage dies and is replaced by bone
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Ossification
Endochondral Step 1 |
Cartilage enlarges
Chondrocytes enlarge Matrix is reduced Enlarged chondrocytes die and leave cavities within the cartilage |
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Ossification
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 |
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Ossification
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 |
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Ossification
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 |
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Ossification
Endochondral Step 5 |
Capillaries and osteoblasts migrate into the epiphysis and create secondary ossification centers
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Ossification
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 |
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Bone Growth
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Interstitial growth - grows by expansion of cartilage
Appositional growth - production of new cartilage at the outer surface |
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Ossification
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2 types
Endochondral - bone replaces existing cartilage Intramembranous - bone develops directly from mesenchyme or fibrous tissue |
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Bone Growth
Interstitial |
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 |
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Bone growth
Appositional |
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 |
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Bone Remodelling
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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 |
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Bone Remodelling
Exercise |
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 |
