All vertebrates have cartilage in addition to bone, or instead of bone.
Function of the Bones
1. Support. Provide a hard framework.
2. Protection of many vital organs.
3. Movement - act as levers with skeletal muscles moving them. Joints control possible movements.
4. Mineral storage.
5. Blood cell formation – hematopoiesis
Types of Bones
According to Development
Ossification is the formation of bone by the activity of osteoblasts and osteoclasts and the addition of minerals and salts. Calcium compounds must be present for ossification to take place. Osteoblasts do not make these minerals, but must take them from the blood and deposit them in the bone. By the time we are born, many of the bones have been at least partly ossified.
Formed either by direct ossification of embryonic connective tissue (intramembranous ossification) or by replacement of hyaline cartilage (intracartilaginous or endochondral ossification).
Intramembranous ossification takes place in the so-called membrane bones of the skull
Endochondral ossification is characteristic of the bones of the trunk and extremities.
a. Increased vascularity of tissue.
b. Active proliferation of mesenchymal cells. The mesenchymal cells give rise to osteogenic cells, which develop into osteoblasts.
c. Osteoblasts begin to lay down osteoid. Osteoid is the organic part of bone without the inorganic constituent.
d. Osteoblasts either retreat or become entrapped as osteocytes in the osteoid.
e. The osteoid calcifies to form spicules of spongy bone. The spicules unite to form trabeculae. The inorganic salts carried in by the blood vessels supposedly bring about calcification. The salts are deposited in an orderly fashion as fine crystals (hydroxyapatite crystals) intimately associated with the collagenous fibers. These crystals are only visible with the electron microscope.
f. Bone remodeling occurs. Periosteum and compact bone are formed.
This type of ossification involves the replacement of a cartilaginous model by bone and is best observed in long bones, such as the humerus or femur
Primary ossification center.
Secondary ossification centers
5 zones of Cartilage
Zone of reserve cartilage.
Zone of cell proliferation
Zone of cell and lacunar maturation and hypertrophy enlargement
Zone of calcification
Zone of cartilage removal and bone deposition
Types of Bone
On the basis of Structure
Compact or cortical bone, is made up many rod-like units called osteons or Haversian systems which run longitudinally within the bone. Haversian systems have a central Haversian canal which carries blood and lymphatic vessels and nerve branches.
The osteon, or Haversian system, is the fundamental functional unit of much compact bone
Each osteon consists of concentric layers, or lamellae, of compact bone tissue that surround a central canal, the Haversian canal. The Haversian canal contains the bone's nerve and blood supplies. The boundary of an osteon is the cement line
Osteons are separated from each other by interstitial lamellae between systems. Some of the osteoblasts develop into osteocytes, each living within its own small space, or lacuna. Osteocytes make contact with the cytoplasmic processes of their counterparts via a network of small canals, or canaliculi. This network facilitates the exchange of nutrients and metabolic waste.
Spongy or cancellous bone consists of a lattice of thin threads of bone called trabeculae and is less dense than compact bone. The orientation of the trabeculae is affected by the mechanical stress to which the bone is exposed .