Difference between revisions of "Bone & Cartilage Development - Anatomy & Physiology"
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| − | + | <big><center>[[Developmental Biology - Anatomy & Physiology|'''BACK TO DEVELOPMENTAL BIOLOGY]]</center></big> | |
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==Introduction== | ==Introduction== | ||
| − | + | Osteogenesis is the formation of bone. Bone forms from one of three lineages; the skull forms from neural cest; the limb skeleton forms from lateral plate mesoderm; and the axial skeleton forms from paraxial mesoderm (sclerotome). There are two methods of osteogenesis. Both involve the transformation of pre - existing mesenchymal tissue into bone. | |
| − | + | #'''Intramembranous Ossification''' - direct conversion of mesenchymal tissue into bone. Occurs in production of the skull. | |
| − | There are two methods of osteogenesis | + | #'''Endochondrial Ossification''' - mesechymal tissue first differentiates into cartilage, then into bone. This occurs in the production of limb and axial skeleton. |
| − | + | #*Limb cartilage is produced in a proximal to distal direction as a continuous structure. It becomes punctuated with joints later, and then converted to bone. | |
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| − | + | ==Endochondrial Ossification== | |
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| + | *''Bone formation via cartilage.'' | ||
| + | #Proliferating limb mesenchyme condenses. | ||
| + | #The increased cell density triggers mesenchymal cells to differentiate into chondrocytes. Proliferation continues. | ||
| + | #The bone shape is formed, with a diaphysis (shaft) and epiphysis (bulbous ends). | ||
| + | #Chondrocytes in the middle of the diaphysis stop proliferating and undergo '''hypertrophy'''. | ||
| + | #*''The shaft is surrounded by the '''perichondrium''', a restrictive membrane. This means that the bone can only grow in length, not width. The epiphysis are pushed away from each other.'' | ||
| + | #After chondrocytes have undergone hypertrophy, they die. | ||
| + | #*'''Osteoblasts''' on the inner side of the perichondrium invade the cartilage matrix. | ||
| + | #*They then secrete the extra - cellular matrix characteristic of bone. | ||
| + | #*''Ossification occurs from the outside - in. This is called primary ossification, or perichondrial ossification.'' | ||
| + | #Blood vessels invade the central region of the diaphysis to transport bone marrow stem cells and osteoclasts. | ||
| + | #*The osteoclasts break down the cartilage matrix to allow room for the bone marrow. | ||
| + | #There is no perichondrium surrounding the eiphysis. | ||
| + | #*This allows for expansion in length of the bone, but means that there are no surrounding oasteoblasts to invade. | ||
| + | #*To achieve osteogenesis, blood vessels invade from the diaphysis and carry osteoblasts with them. | ||
| + | #*''In the epiphysis, osteoblasts initiate bone growth from the inside - out. This is called secondary ossification.'' | ||
| + | #*In some mammals, secondary ossification occurs after birth. | ||
| + | #The bone becomes covered in a layer containing osteoblasts. | ||
| + | *Cartilage is ''not replaced by bone'' in two areas: | ||
| + | :In between the diaphysis and epiphysis, a region called the '''epiphyseal growth plate (EPG)'''. | ||
| + | :At the ends of the epiphysis, between the joints. Acts as a '''shock absorber'''. | ||
| − | + | ==Bone Growth== | |
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Revision as of 10:16, 31 August 2008
Introduction
Osteogenesis is the formation of bone. Bone forms from one of three lineages; the skull forms from neural cest; the limb skeleton forms from lateral plate mesoderm; and the axial skeleton forms from paraxial mesoderm (sclerotome). There are two methods of osteogenesis. Both involve the transformation of pre - existing mesenchymal tissue into bone.
- Intramembranous Ossification - direct conversion of mesenchymal tissue into bone. Occurs in production of the skull.
- Endochondrial Ossification - mesechymal tissue first differentiates into cartilage, then into bone. This occurs in the production of limb and axial skeleton.
- Limb cartilage is produced in a proximal to distal direction as a continuous structure. It becomes punctuated with joints later, and then converted to bone.
Endochondrial Ossification
- Bone formation via cartilage.
- Proliferating limb mesenchyme condenses.
- The increased cell density triggers mesenchymal cells to differentiate into chondrocytes. Proliferation continues.
- The bone shape is formed, with a diaphysis (shaft) and epiphysis (bulbous ends).
- Chondrocytes in the middle of the diaphysis stop proliferating and undergo hypertrophy.
- The shaft is surrounded by the perichondrium, a restrictive membrane. This means that the bone can only grow in length, not width. The epiphysis are pushed away from each other.
- After chondrocytes have undergone hypertrophy, they die.
- Osteoblasts on the inner side of the perichondrium invade the cartilage matrix.
- They then secrete the extra - cellular matrix characteristic of bone.
- Ossification occurs from the outside - in. This is called primary ossification, or perichondrial ossification.
- Blood vessels invade the central region of the diaphysis to transport bone marrow stem cells and osteoclasts.
- The osteoclasts break down the cartilage matrix to allow room for the bone marrow.
- There is no perichondrium surrounding the eiphysis.
- This allows for expansion in length of the bone, but means that there are no surrounding oasteoblasts to invade.
- To achieve osteogenesis, blood vessels invade from the diaphysis and carry osteoblasts with them.
- In the epiphysis, osteoblasts initiate bone growth from the inside - out. This is called secondary ossification.
- In some mammals, secondary ossification occurs after birth.
- The bone becomes covered in a layer containing osteoblasts.
- Cartilage is not replaced by bone in two areas:
- In between the diaphysis and epiphysis, a region called the epiphyseal growth plate (EPG).
- At the ends of the epiphysis, between the joints. Acts as a shock absorber.