Development of bones and cartilages
Development of bones and cartilages
begin by the condensation of mesenchymal cells into bone and cartilage models
respectively. The mesenchymal cells at first differentiate in to chondroblasts
(which in turn form the cartilage) and the osteoblasts (which form the bone).
Histogenesis of Cartilage
The cartilage is a form of connective tissue that forms part of the skeleton where more flexibility is required. It begins to develop in embryo during the fifth week of development from the mesenchyme. The mesenchymal cells differentiate into chondroblasts that secrete collagenous fibrils and the extracellular matrix. Subsequently, collagenous and/or elastic fibers are deposited in the intercellular matrix by these cells.
Based on the composition of the matrix, the cartilages are classified in to three types,
Histogenesis of Bone
The bone is a highly specialized connective tissue that makes up most of the skeleton. It consists of cells and an organic intercellular matrix that comprises of collagen fibrils embedded in an amorphous component. Bones mainly develop into two types of connective tissue, mesenchyme and cartilage. The mesenchymal cells in the body differentiate into osteoblasts (bone-forming cells).
Two main types of bone are distinguished by the relative composition of the matrix (organic matter) and by the number and size of the space they contain. They are:
The architecture and proportion of the compact and spongy bones vary according to the function. The compact bone provides strength for weight bearing and is found in greatest amount near the shaft of the long bone, while growth (lengthening) of bone occurs in the spongy bone, and is mostly found near the end of the long bone (fig 5).
Similarly, bones are classified on the basis of their shape as:
There are three types of bone cells; they are identified based on their activity:
Histogenesis of Cartilage
The cartilage is a form of connective tissue that forms part of the skeleton where more flexibility is required. It begins to develop in embryo during the fifth week of development from the mesenchyme. The mesenchymal cells differentiate into chondroblasts that secrete collagenous fibrils and the extracellular matrix. Subsequently, collagenous and/or elastic fibers are deposited in the intercellular matrix by these cells.
Based on the composition of the matrix, the cartilages are classified in to three types,
- Hyaline
cartilage, -(e.g., in joints) the most widely distributed type.
- Fibrocartilage,-(e.g., in intervertebral discs)
- Elastic cartilage,-(e.g., in auricle of ear)
Histogenesis of Bone
The bone is a highly specialized connective tissue that makes up most of the skeleton. It consists of cells and an organic intercellular matrix that comprises of collagen fibrils embedded in an amorphous component. Bones mainly develop into two types of connective tissue, mesenchyme and cartilage. The mesenchymal cells in the body differentiate into osteoblasts (bone-forming cells).
Two main types of bone are distinguished by the relative composition of the matrix (organic matter) and by the number and size of the space they contain. They are:
- Compact bone, and
- Spongy bone
The architecture and proportion of the compact and spongy bones vary according to the function. The compact bone provides strength for weight bearing and is found in greatest amount near the shaft of the long bone, while growth (lengthening) of bone occurs in the spongy bone, and is mostly found near the end of the long bone (fig 5).
Similarly, bones are classified on the basis of their shape as:
- Long bone, (e.g femur)
- Short bones, (e.g carpals and tarsal bones)
- Flat bone, (e.g flat bones of the skull )
- Irregular bones, have various shape (e.g vertebrae)
- Sesamoid, (e.g patella)
There are three types of bone cells; they are identified based on their activity:
- Osteoblasts; these produce new bone,
- Osteoclasts; these remove and resorb existing bone by secreting acid to break down mineral component of bone and enzymes to break down the collagen component of bone
- Osteocytes; these maintain equilibrium in fully formed bone, they are the matured bone cells
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(Copyright © 2011 by U. Bala)