Skeleton System

 Part 2

Functions of the bones

* Support and shape

Bone provide a framework of the body.

It gives support and shape of the body.

It also gives attachment to muscles and tendons.

* Protection

The bones protect  inner soft and delicated organs , forming the boundaries of the cranial, thoracic, abdominal and pelvic cavities protecting the organs they contains by external shocks.

* Movement

It provide moment of the whole body and parts of the body by forming joints.

Bones of the body provide attachment to the muscles , these muscles provide motor power for providing movement of the body parts.

* Mineral storage

Bones serve as a reservoir for calcium and phosphate , essential minerals for various cellular activities.

* Blood cell production

The production of blood cell or hematopoiesis, occur in the  red marrow found within the cavity of the certain bone.

* Energy storage

Lipids such as fats , stored in adipose cell of the yellow bone marrow serve as energy reservoir.

General structure of long bone:--

Long bone

These have a diaphysis (shaft)and two epiphysis (extreme).

The diaphysis is composed of compact bone with the central medullary canal , containing fatty yellow bone marrow.

The epiphysis consists of an outer covering of compact bone with spongy (cancellous)bone inside containing red bone marrow.

Red bone marrow are responsible for production of blood cell or  hemopoiesis (RBC ,WBC, platelets).

The metaphysis is the part of bone between the epiphysis and the diaphysis.

It contain the connecting cartilage called epiphysial plates. It is the most actively growing area of long bone.

When  bone  oxicified the epiphysial plate (metaphysis) disappear at adulthood (18 - 20 years of age) as it convert into epiphysial line.

Long bone are covered by vascular membrane called periostium which has two layers.

The outer layer of fibrous rich in blood vessels and the inner layer contains osteoblast , which are involved in bones growth in thickness.

Maintenance and remodeling of bones and it is give attachments  to muscles and tendons and it protect bone from injury.

The periosteum covers the whole bone except for site of articulation ends.

Microscopic structure of bone

Bone are made up of cells and intracellular matrix.

The cellular component is 2% of bone mass

Matrix is made up of 40% of organic substance containing mainly of collagen fibres.

Collagen very strong and gives bone slightly flexibility.

60% of inorganic substance made up of  inorganic salts of calcium and phosphorus . This inorganic matrix gives bone great hardness.

Bones composition

Cellular Components

It consists of following cells........

1. Osteoblast

Osteoblast  is responsible for making new bone and repairing older bone.

It produce protein mixture "osteoid"  which is mineralized and becomes bone.

Osteoid is a type of protein mixture which is formed by collagens.

They are present in the dipper layers of periostium.

In the centres of ossification of immature bone.

At the site of fracture.

2. Osteocyte Cell

As bone develop osteoblast become  trapped within the newly formed bone.

They stop forming new bone and this stage are called osteocytes.

These are the mature bone cells that monitor and maintain bone tissues and are nourished by tissue fluid in the canaliculi,  it present in bone matrix.

3. Osteoclast

Osteoclast are multinucleated cell.

Osteoclast help in the reabsorption during remodelling of bones to maintain the optimum shape.

It is type of gold sale that breaks down bone tissue and releasing calcium and phosphate this process also help to regulate the level of blood calcium.

It present under periosteum and sight of old injured or unneeded bones.

                Matrix

Matrix is the extracellular component of bone which is made up of organic and inorganic components.

Organic component

This is  mostly made up of collagen fibres which are arranged in bundles . They have lamellar arrangement , which is in the form of a regular, parallel , lamilae.

Inorganic Components

The mineral components of bones gives it hardness and rigidity . It consists of calcium and phosphate they are closely packed and arranged along the collagen fibre.

Microscopic structure of compact bone

It is made up of many cube like structures called osteons . ( Habersion system)  

In between osteon a central canal is present .

The central canals contains blood vessels , nerve and lymphatic vessels are present.

 Central canal are connected neighbouring canal by perforated canals. 

If cut a series of osteon are seen  parallel series called lamellae.

 In lamellae present in small small pocket or cavities called  lacuna (containing osteocyte Cell).

Osteocyte cell maintain bone tissue.

Each lacuna are connected by canaliculus (canaliculi).

 Canaliculus are contain in interstitial fluid flow in canaliculus. This fluid provide nourishment to osteocyte cells.

Microscopic structure of spongy bone (cancellous bone)

Cancellous bone and less dense and present with large cavities in between plats of bones giving them a honeycomb appearance bone.

Cancellous bone is made up of  mashwork of bony plates or rods called "trabeculae" .

It does not contains osteons.

Each trabeculae is  made up of number of lamellae between which there are containing osteocytes.

Lacunae are interconnected by canaliculi.

The Trabeculae enclose wide spaces that are filled in by Red Bone Marrow.

They receive nutrition from blood vessels in bone marrow.

The trabecular are covered externally by vascular endosteum.

Endosteum is the lining membrane of the bone marrow cavity.