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Intramembranous ossification

 

 
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Intramembranous ossification
 
 
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Intramembranous ossification is one of the two processes during fetal development of the mammalian
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
 skeletal system
Skeleton

In biology, a skeleton is a rigid framework that provides protection and structure in many types of animal, particularly those of the phylum Chordata and of the superphylum Ecdysozoa....
 in which bone tissue is created. It is also an essential process during the healing of bone fractures
Bone healing

Bone healing, or fracture healing, is a Cell growth physiological process in which the body facilitates the repair of a bone fracture....
  and the rudimentary formation of bones
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
 of the head
Human skull

In humans, the adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures of skull, synarthrodial joints formed by bony ossification, with Sharpey's fibres permitting some flexibility....
. Unlike endochondral ossification
Endochondral ossification

Endochondral ossification is one of the two processes during fetal development of the mammal skeleton in which bone tissue is created. It is also an essential process during the rudimentary formation of long bones, the growth of the Epiphyseal plate of long bones, and the healing of bone healing....
, which is the other process, cartilage
Cartilage

Cartilage is a type of dense connective tissue. It is composed of specialized cells called chondrocyte that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers....
 is not present during intramembranous ossification.

Creation of bone tissue
Mesenchymal stem cells
Mesenchymal stem cell

Mesenchymal stem cells, or MSCs, are multipotent stem cells that can Cellular differentiation into a variety of cell types. Cell types that MSCs have been shown to differentiate into in vitro or in vivo include osteoblasts, chondrocytes, myocytes, adipocytes, and, as described lately, Beta cell....
, or MSCs, within human mesenchyme
Mesenchyme

Mesenchyme is a type of loose connective tissue, of mesodermal origin and located within the embryo mesoderm, consisting of a ground substance Matrix containing a loose aggregate of unspecialized cell which are capable of developing into connective tissue, bone, cartilage, the lymphatic system, and the circulatory system....
 or the medullary cavity
Medullary cavity

The medullary cavity is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow is stored . Located in the main shaft of a long bone , the medullary cavity has walls composed of spongy bone and is lined with a thin, vascular membrane ....
 of a bone fracture initiate the process of intramembranous ossification.






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Intramembranous ossification is one of the two processes during fetal development of the mammalian
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
 skeletal system
Skeleton

In biology, a skeleton is a rigid framework that provides protection and structure in many types of animal, particularly those of the phylum Chordata and of the superphylum Ecdysozoa....
 in which bone tissue is created. It is also an essential process during the healing of bone fractures
Bone healing

Bone healing, or fracture healing, is a Cell growth physiological process in which the body facilitates the repair of a bone fracture....
  and the rudimentary formation of bones
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
 of the head
Human skull

In humans, the adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures of skull, synarthrodial joints formed by bony ossification, with Sharpey's fibres permitting some flexibility....
. Unlike endochondral ossification
Endochondral ossification

Endochondral ossification is one of the two processes during fetal development of the mammal skeleton in which bone tissue is created. It is also an essential process during the rudimentary formation of long bones, the growth of the Epiphyseal plate of long bones, and the healing of bone healing....
, which is the other process, cartilage
Cartilage

Cartilage is a type of dense connective tissue. It is composed of specialized cells called chondrocyte that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers....
 is not present during intramembranous ossification.

Creation of bone tissue


Mesenchymal stem cells
Mesenchymal stem cell

Mesenchymal stem cells, or MSCs, are multipotent stem cells that can Cellular differentiation into a variety of cell types. Cell types that MSCs have been shown to differentiate into in vitro or in vivo include osteoblasts, chondrocytes, myocytes, adipocytes, and, as described lately, Beta cell....
, or MSCs, within human mesenchyme
Mesenchyme

Mesenchyme is a type of loose connective tissue, of mesodermal origin and located within the embryo mesoderm, consisting of a ground substance Matrix containing a loose aggregate of unspecialized cell which are capable of developing into connective tissue, bone, cartilage, the lymphatic system, and the circulatory system....
 or the medullary cavity
Medullary cavity

The medullary cavity is the central cavity of bone shafts where red bone marrow and/or yellow bone marrow is stored . Located in the main shaft of a long bone , the medullary cavity has walls composed of spongy bone and is lined with a thin, vascular membrane ....
 of a bone fracture initiate the process of intramembranous ossification. A MSC is an unspecialized cell whose morphology
Morphology (biology)

The term morphology in biology refers to form, structure and configuration of an organism. This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs....
 undergoes characteristic changes as it develops into an osteoblast
Osteoblast

An osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen....
. Before it begins to develop, the morphological characteristics of a MSC are: a small cell body with a few cell processes that are long and thin; a large, round nucleus
Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
 with a prominent nucleolus
Nucleolus

The nucleolus is a non-membrane bound structure found within the cell nucleus in which messenger RNA is Transcription , and is composed of protein and nucleic acids....
 which is surrounded by finely dispersed chromatin
Chromatin

Chromatin is the complex combination of DNA, RNA, and protein that makes up chromosomes. It is found inside the cell nucleus of Eukaryote cell , and within the nucleoid in prokaryotic cells....
 particles, giving the nucleus a clear appearance; a small amount of Golgi apparatus
Golgi apparatus

The Golgi apparatus is an organelle found in most eukaryote Cell . It was identified in 1898 by the Italian physician Camillo Golgi and was named after him....
, rough endoplasmic reticulum, mitochondria, and polyribosomes; and the cells are widely dispersed within an extracellular matrix
Extracellular matrix

In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal Cell in addition to performing various other important functions....
 which is devoid of every type of collagen
Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content....
 except for a few reticular
Reticular fiber

Reticular fibers or reticulin is a histology term used to describe a type of fiber in connective tissue composed of type III collagen. Reticular fibers crosslink to form a fine meshwork ....
 fibrils.

Then a small group of adjacent MSCs begin to replicate
Replicate

Replicate may refer to:* In biology, replication is a process by which genetic material, a cell, or an organism reproduces or makes an exact copy or copies...
 until they have formed a small, dense aggregation of cells, a nodule
Nodule (medicine)

For use of the term nodule in dermatology, see Nodule_In medicine, a nodule refers to a relatively hard, roughly spherical abnormal structure....
. Once a nodule has been formed the MSCs within it stop replicating. At this point, changes in the morphology of the MSCs occur: the cell body becomes larger and rounder; the long, thin cell processes are no longer present; and the amount of Golgi apparatus and rough endoplasmic reticulum increases. Eventually, all of the cells within the aggregate
Aggregate

An aggregate is a collection of items that are gathered together to form a total quantity. It may refer also to:* Aggregate , in materials science, a component of a composite material used to resist compressive stress....
 display the morphologic characteristics of an osteoprogenitor cell.

At this stage of development, changes in the morphology of the osteoprogenitor cells occur: their shape becomes more columnar; the amount of Golgi apparatus and rough endoplasmic reticulum increases; and the cells begin to create an extracellular matrix consisting of Type-I collagen
Type-I collagen

Type-I collagen is the most abundant collagen of the human body.It is present in scar tissue, the end product when tissue healing by repair....
 fibrils. This matrix is osteoid
Osteoid

Osteoid is the organic portion of the matrix of Osseous tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific protein....
 and the cells that created it are osteoblasts. The osteoblasts, while lining the periphery of the nodule, continue to form osteoid at its center and some of them become incorpoated within it to become osteocytes
Osteocyte

An osteocyte, a star-shaped cell , is the most abundant cell found in compact bone. Cells contain a nucleus and a thin ring of cytoplasm. When osteoblasts become trapped in the matrix they secrete, they become osteocytes....
.

At this point, the osteoid becomes mineralized resulting in a nidus consisting of mineralized osteoid which contains osteocytes and is lined by active osteoblasts. The nidus, which began as a diffuse collection of MSCs, has become rudimentary bone tissue.

Overview

The first step in the process is the formation of bone spicules which eventually fuse with each other and become trabeculae. The periosteum
Periosteum

Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
 is formed and bone growth continues at the surface of trabeculae. Much like spicules, the increasing growth of trabeculae result in interconnection and this network is called woven bone. Eventually, woven bone is replaced by lamellar bone.

Process Overview

  • Mesenchyme cell
    Mesenchyme

    Mesenchyme is a type of loose connective tissue, of mesodermal origin and located within the embryo mesoderm, consisting of a ground substance Matrix containing a loose aggregate of unspecialized cell which are capable of developing into connective tissue, bone, cartilage, the lymphatic system, and the circulatory system....
     in the membrane become osteochondral progenitor cell
  • osteochondral progenitor cell specialized to become osteoblast
  • Osteoblast
    Osteoblast

    An osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen....
     produce bone matrix and surrounded collagen fiber and become osteocyte
    Osteocyte

    An osteocyte, a star-shaped cell , is the most abundant cell found in compact bone. Cells contain a nucleus and a thin ring of cytoplasm. When osteoblasts become trapped in the matrix they secrete, they become osteocytes....
  • As the result process trabeculae will develop
  • Osteoblast will trap trabeculae to produce bone
  • Trabeculae will join together to produce spongy cell
  • Cells in the spongy cell will specialize to produce red bone marrow
  • Cells surrounding the developing bone will produce periosteum
  • Osteoblasts from the Periosteum
    Periosteum

    Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
     on the bone matrix will produce compact bone


Formation of bone spicules

Embryologic
Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
 mesenchymal cells (MSC) condense into layers of vascularized primitive connective tissue
Connective tissue

Connective tissue is a form of fibrous biological tissue.It is one of the four types of tissue in traditional classifications .Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% of the total protein content....
. Certain mesenchymal cells group together, usually near or around blood vessels, and differentiate into osteogenic cells which deposit bone matrix
Matrix (biology)

In biology, matrix is the material between animal or plant cell , the material in which more specialized structures are embedded, and a specific part of the mitochondrion that is the site of oxidation of organic molecules....
 constitutively
Secretory pathway

The secretory pathway is a series of steps a Cell uses to move proteins out of the cell; a process known as secretion. The path of a protein destined for secretion has its origins in the rough endoplasmic reticulum, a membrane bound Cellular_compartment in the cell....
. These aggregates of bony matrix
Matrix (biology)

In biology, matrix is the material between animal or plant cell , the material in which more specialized structures are embedded, and a specific part of the mitochondrion that is the site of oxidation of organic molecules....
 are called bone spicules. Separate mesenchymal cells differentiate into osteoblast
Osteoblast

An osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen....
s, which line up along the surface of the spicule and secrete more osteoid
Osteoid

Osteoid is the organic portion of the matrix of Osseous tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific protein....
, which increases the size of the spicule.

Formation of woven bone

As the spicules continue to grow, they fuse with adjacent spicules and this results in the formation of trabeculae. When osteoblast
Osteoblast

An osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen....
s become trapped in the matrix they secrete, they differentiate into osteocyte
Osteocyte

An osteocyte, a star-shaped cell , is the most abundant cell found in compact bone. Cells contain a nucleus and a thin ring of cytoplasm. When osteoblasts become trapped in the matrix they secrete, they become osteocytes....
s. Osteoblast
Osteoblast

An osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen....
s continue to line up on the surface which increases the size. As growth continues, trabeculae become interconnected and woven bone is formed. The term primary spongiosa is also used to refer to the initial trabecular network.

Primary center of ossification

The periosteum
Periosteum

Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
 is formed around the trabeculae by differentiating mesenchymal cells. The primary center of ossification is the area where bone growth occurs between the periosteum
Periosteum

Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
 and the bone. Osteogenic cells that originate from the periosteum
Periosteum

Periosteum is a membrane that lines the outer surface of all bone, except at the joints of long bones. Endosteum lines the inner surface of all bones....
 increase appositional growth and a bone collar is formed. The bone collar is eventually mineralized and lamellar bone is formed.

Formation of osteon

Osteon
Osteon

The osteon, or Clopton Havers system, is the fundamental functional unit of Cortical bone. Osteons are present in many of the bones of most mammals, birds, reptiles, and amphibians....
s are units or principal structures of compact bone. During the formation of bone spicules, cytoplasmic
Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
 processes from osteoblast
Osteoblast

An osteoblast is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen....
s interconnect. This becomes the canaliculi of osteon
Osteon

The osteon, or Clopton Havers system, is the fundamental functional unit of Cortical bone. Osteons are present in many of the bones of most mammals, birds, reptiles, and amphibians....
s. Since bone spicules tend to form around blood vessel
Blood vessel

The blood vessels are the part of the circulatory system that transport blood throughout the body. There are three major types of blood vessels: the artery, which carry the blood away from the heart, the capillary, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from...
s, the perivascular space is greatly reduced as the bone continues to grow. When replacement to compact bone occurs, this blood vessel becomes the central canal of the osteon.