Definition Of Bone Cell | Bone Structure | The Microscopic Structure Of Bone | What Bone Marrow Does | Medical Representative Job Questions |
Definition Of Bone Cell: Bone is the hardest of the connective tissues. It is a specialised type of fibrous material hardened by the deposits of mineral salts, chiefly calcium phosphate, derived from the bloodstream. Fibrous-> Tissue material gives it toughness while the mineral matter gives it the rigidity which distinguishes it from other connective tissue. It forms the skeletal system.
the microscopic structure of bone
Definition Of Bone Cell
An examination of the longitudinal section of a long bone from a young person reveals the following:
(i) The periosteum
(ii) Compact tissue
(iii) Cancellous tissue
(iv) The bone marrow
Classification is made according to the density & hardness of the Cone
This is a tough membrane of fibrous tissue containing some blood vessels which covers the surface of the bones
The surface layer of bone is found immediately under the periosteum. It is a hard dense substance resembling ivory and forms the shaft of the bone.
Inner parts of the flat bones, the ends of the long bones and the body of the vertebrae, are examples of cancellous bone. It appears as a spongy porous bone containing red bone marrow.
What Bone Marrow Does
The bone marrow is a soft, pulpy tissue that is found not only in the cavities of the long bones but also in the spaces of the spongy substance of all bones.
It differs in composition in different bones and at different ages and occurs in two forms, yellow marrow and red marrow.
The marrow contains a large number of small blood vessels. The formation of red blood cells. occurs in the bone marrow.
In embryonic life, the first blood cells the primitive erythrocytes, develop in the mesenchyme of the yolk sac and chorion. Haematopoietic foci appear later in the intra-embryonic mesoderm, particularly in the liver and the spleen. After the end of the third month of embryonic life, the bone marrow becomes the chief site for the formation of red blood cells and granulocytes.
The Microscopic Structure Of Bone
Compact bone is composed of units which are called HAVERSIAN SYSTEMS. Each of these units contains a minute circular canal – the HAVERSIAN CANAL – which runs in a longitudinal direction parallel with the surface of the bone. In the bone substance surrounding the Haversian canal are a number of small spaces; called LACUNAE, arranged in concentric rings and containing the bone cells. Minute canals (canaliculi) join up. The lacunae also communicate with the central Haversian canal Small blood vessels and lymphatics run in the Haversian canals and nourish the bone substance.
Functions Of Bone
- Provides skeletal support and shape to the body.
- Affords protection from injury to the vital organs of the cranial and thoracic cavities and to the deep blood vessels and nerves.
- Reservoir of minerals, e.g. phosphorous and calcium which helps in maintaining electrolyte balance, particularly the distribution of calcium and phosphate ions.
- Serves a detoxicating function. Toxic elements such as lead, fluorine, arsenic and radium are removed from the circulation and deposited in the bones.
- Affords a haemopoietic function as it contains the bone marrow which takes care of the formation of blood cells.
- Serves as the basis of attachment of muscles.
- Chief site of reticuloendothelial cells.
- Assists information of certain important systems in the body.
Ossification Development Of Bone
Two processes of ossification
Membranous – Bones of the cranial vault and mandibles.
Cartilaginous – Bones of the limbs, trunk, and base of the skull are both cartilaginous and membranous in development.
The original matrix consists of simple embryonic tissue spread out in the form of a membrane. This becomes vascularised. Then strands of fibres appear in this medium which is known as the osteogenic fibres.
Calcium salts become deposited at one place between the fibres and this spot of first calcification (called the primary ossification to contain) Ossification begins at this centre and proceeds by the multiplication of cells within the membrane until a network of bone is formed. Eventually, a flat bone is produced.
In the developing embryo, all the long bones are first represented by rods of cartilage covered by per: chondrite (membrane covering cartilage).
A primary centre of ossification appears in the diaphunts which will eventually be the shaft of a long bone.
Calcium is laid down near the centre of the diaphysis and bone cells develop. The perichondrium becomes the periosteum and from it, bone cells are laid down so that the bone increases in circumference. The growing bone now consists of a shaft, the diaphysis and two extremities, the epiphyses.
In the process of development, a secondary centre of ossification appears at each extremity (epiphysis). Ossification begins there and extends towards the shaft and also towards the end of each epiphysis.
A layer of cartilage remains between the diaphysis and epiphysis. This layer is called epiphyseal cartilage or epiphyseal disc and persists until the bone is fully developed. The cells of this cartilage go on multiplying continuously until completely ossified. In this way, the bone grows in length.
In younger life, the rate of multiplication of the epiphyseal cartilage is proportionately more than the rate of calcification.
Consequently, the skeleton increases in length. But, as age advances, the rate of multiplication of cartilage cells slows down so that the process of calcification becomes relatively more rapid and overtakes the multiplying cartilages. Thus, the epiphyseal cartilage becomes ossified and growth in length ceases. From about the 25th year of life, all the epiphyseal cartilages are ossified.
This type of tissue is examined in section 4, The Cardiovascular System.
Muscular tissue is essentially contractile tissue and is, therefore, able to produce movement; there are three types of muscular tissue found in the body.
Medical Representative Job Questions
What is the function of bone marrow?
Bone marrow is a spongy substance found in the centre of the bones. It manufactures bone marrow stem cells and other substances, which in turn produce blood cells.
What is a bone made of?
Bone is the hardest of the connective tissues. It is a specialised type of fibrous material hardened by the deposits of mineral salts, chiefly calcium phosphate, derived from the bloodstream. Fibrous-> Tissue material gives it toughness while the mineral matter gives it the rigidity which distinguishes it from other connective tissue. It forms the skeletal system.
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