Question

2. What is the differences in the formation of Endochondrial bone and Membrane bone?

Answer 1

The main difference between the two types of bones are listed below:

Endochondral bone	Intramembranous bone
These comprise of long bones like the femur and flat and irregular bones such as ribs and vertebrae.	These comprise of facial bones like jawbones, collar bones or clavicles.
cartilage is utilized as a frame or precursor for this bone formation.	The bone is directly formed over the mesenchymal tissue which clusters together and differentiates to ossify
The fractures in these bones are healed with the use of plaster of Paris.	The fractures treated by open reduction and internal fixation with metal plates, screws, pins, rods and nails.

FURTHER READING:

The process of bone formation is known as ossification and it starts in the 6th-7th week of embryonic development and continues till adulthood.

The skeletal system of humans, during the embryonic stage, is either formed by the embryonic connective tissue, also known as MESENCHYMAL cells or HYALINE CARTILAGE, loosely shaped like future rigid bones, These provide a frame for the ossification.

Bone formation is of mainly 2 types: Intramembranous and Endochondral

1) Intramembranous Bone: Facial bones like jawbones, scapula/shoulder blade, collar bones/clavicle

These bones ossify in the membranous- mesenchymal cells. It starts by mesenchymal cells coming together as a cluster in the and starts differentiating into capillaries and other become osteoblasts(bone-forming cells). The osteoblasts start to appear in a cluster called the ossification center.

The osteoblasts start secreting osteoid which then is calcified/mineralized after few days to harden, trapping the osteoblasts within. These entrapped osteoblasts transform into osteocytes. New osteoblasts start accumulating at the edges of the growing bone. The osteoid is accumulated around the capillaries to form a trabeculae/ spongy tissue. The osteoblasts on the surface periosteum. The spongy bone gets the supply of blood vessels, which eventually condense into the red bone marrow in the bone.

2) Endochondral Bone: Long bones like the femur and flat and irregular bones such as ribs and vertebrae.

The bone develops by using hyaline cartilage as a frame. Hyaline cartilage does not become bone but only serves as a template to be completely replaced by new bone. That's why this type of bone formation takes much longer.

Mesenchymal cells differentiate into chondrocytes that produce a cartilage model of the future bony skeletonHyaline cartilage is avascular- it has no blood vessels, flexible, semi-solid matrix produced by chondroblasts and is surrounded by a layer of the perichondrium. Supplying nutrients and removing metabolic wastes are carried by the diffusion through the matrix from vessels surrounding perichondrium.

Mesenchymal cells differentiate into chondrocytes that produce a cartilage model of the future bony skeleton which is the hyaline cartilage. This cartilage is surrounded by a layer known as perichondrium. Blood vessels surrounding the edge of the cartilage bring osteoblasts(bone-forming cells) which transforms into deposition of a bony collar. The cavities are now formes which are the continuous enlarging spaces and they eventually combine to become the medullary cavity. The capillaries penetrate this cartilage cavity and deposit bone inside the cartilage which forms the primary ossification center.

While this is taking place, the cartilage and chondrocytes continue to grow at ends of the bone and at the same time medullary cavity expands and remodels, overall lengthening of the structure. During the fetal stage, hyaline cartilage remains at epiphyseal (growth) plate and at the joint surface as articular cartilage.

After birth, this same sequence of events is repeated to grow more bones via the formation of secondary ossification centers develop. Throughout childhood and adolescence, a thin plate of hyaline cartilage is always there between the diaphysis and epiphysis known as the growth or epiphyseal plate. Later, this hyaline cartilage is removed and replaced by bone to become the epiphyseal line.