It is present outer to the bone marrow cavity .Endosteum is a membrane which lies the marrow cavity.It comprises of two distinct layer,one is of fibrous connective tissue and anothe is osteoblasts.
Bone marrow is a specialized type of soft,diffuse connective tissue called,"Myeloid tissue". It takes part in production of blood cells hence known as haemopoietic tissue.It is composed of adipose tissue,areolar tissue and blood.It is of two typs:-
(i).Red bone marrow:
Red in colour due to presence of lot of blood vessels.In foetal life and at birth present in skeleton.After 5th year red bone marrowis replaced by yellow bone marrow ,at 20-25 years red bone marrow is present in ribs,sternum,clavicles, vertebrae,scapula, pelvis,epiphysis of humerus and femur.Produces RBCs,WBC,platelets,granular leucocytes like basophills eosinophils and neutrophils.
(ii)Yellow bone marrow:
Yellow in colour and has much fatty tissue(adipose tissue),present in shaft of long bone. Produces blood cells in emergency i.e.,at the time of excessive loss of blood,yellow bone marrow may be replaced by red bone marrow in anaemia.
A haversian canal,its lamellae and osteocytes form a haversian system.Haversian canals are found in bone matrix of long bone,like humerus of mammals to provide extra nutrition to living part of matrix.Haversian canals contain artery and veins,osteoblasts in areolar tissue, nerves and lymph.It is also called osteon.Haversian canals are interconnected by transverse canals known as Volkmann's canals.
Types of bone cells:
Four types of cells are found in bone:
Develops into osteoblast cell due to mitotic cell division.
Bone forming cells found in all bone surfaces.It is small cells which synthesize and secrete osteoid,an important part of ground substance.Process of osteoblast is called canaliculi.
Mature,nondividing osteoblast surrounded by matrix ,lying within lacunae.
Bone destroying cells take part in reabsorption of bones,contain large amount of acid phosphatase enzymes.
Types of bone:
On the basis of their texture:
The bones are divided into two categories spongy or cancellous or tubecular bones and compact or periosteal bones.
|Characters||Spongy bone||Compact bone|
|Arrangement of lamellae||There is no regular Haversian system so have spongy texture.||Have regular Haversian system.|
|Occurrence||In skull bones,ribs,centrum of vertebrae and epiphysis of long bones.||In the shaft(diaphysis) of long bone.|
|Types of bone marrow||Red marrow in the spaces between lamellae.||Yellow marrow in marrow cavity.|
|Function||Marrow forms RBCs and Granular WBCs ,Platelets.||Marrow stores fats.|