Structure And Functions Of Bone tissue

Introduction

Bone is a skeletal tissue assist in providing support, locomotion, and the protection of many vital organs within our body. The study of structure, functions of bones is known as osteology. Orthopedics is the term used to treat the medical and surgical conditions of bones. All bones join to form the skeletal system. The skeletal system is made up of a variety of bones such as long bones, short bones, small bones, irregular bones and flat bones. Bones provide a framework helping in the structural and functional integrity of other parts of the body. Our skeletal system is one of the major systems as it is linked with many other structures such as the surrounding muscles, tissues, and organs. Bones are categorized under connective tissues as they help in connecting many structures around them, tendon is the term used for the fibrous connective tissue which attaches muscle to bone. A ligament is the fibrous connective tissue help to connect bones with other bones. 

 

Formation Of Bone tissue

Osteogenesis is otherwise known as bone formation. The growth of bones starts from the pregnancy itself and it continues up to 25 years. Ossification is the process by which the bone matrix (collagen fibers and ground substance) is formed and the minerals (eg, calcium salts) are deposited on the collagen fibers. The collagen fibers give tensile strength to the bone, and the calcium provides compressional strength.

 

Structure of a long bone -Image from Brunner

 

Classification of bones

There are 206 bones in the human body. Depending upon the location and the function, bones are classified into Long bones (for example, femur), Short bones (for example, metacarpals), Flat bones (for example, sternum) and the Irregular bones (for example, vertebrae). Based on the thickness, bones can be divided into compact bones or spongy bones. Most of the long and strong bones present in the limbs are compact in nature. The smallest bone is found in the ears ( stapes) and the longest bone is the femur ( thigh-bone).

 

Gross Anatomy of a typical bone

Bones contain 2 types of tissues, cancellous (trabecular) or cortical (compact) tissues. Cancellous tissues are found along the mid-portion of most of the long bones and the rest of the bones makeup compact tissues. Bone is anatomically divided into 2 structural components along the length of the bone, they are epiphysis and diaphysis. The shaft( middle) part is known as the diaphysis primarily composed of the cortical ( compact) bone tissues. The ends of the long bones are epiphyses made up of cancellous bone tissues. The junction between the diaphysis and epiphyses is made up of special plates, growth plates or the  epiphyseal plates. The epiphyseal plates are responsible for the verticle growth of children. Until about 25 years of age, epiphyseal plates are open allowing the longitudinal expansion of the long bones. The growth of the children stops when the epiphyseal plates are closed. Epiphyseal ends have a tough articular cartilage that assists in joint movement. The innermost space in a long bone is called the medullary cavity that produces bone marrow necessary for blood production.

 

The cellular structure of bones

The outermost covering of the bone is called the periosteum. It is a membranous layer help in providing the attachment of bones to the tendons and ligaments. Just beneath the periosteum, endosteum is present. Endosteum is a thin, vascular membrane covering the marrow cavity of long bones. Bone has both cellular and non-cellular components. The non-cellular portion is made up of protein matrix and mineral deposits along the length and breadth of the bones. Cellular structure comprises  3 types of bone cells, osteoblasts, osteocytes, and osteoclasts. Bone matrix also has collagen, glycoproteins, and proteoglycans that help in providing a framework. Osteocytes are whereas the osteoblast cells are pluripotent cells found in their primordial stage. Osteoclasts are found in lacunae (bone matrix units). The major functional unit of bone is seen in a canal called the Haversian canal. Haversian canal is rich in blood supply which is again surrounded by the mineralized bone matrix known as lamellae. Canaliculi is found within the Haversian canal.

Functions of bones:

Long bones assist in weight-bearing and movement, for example, femur (thigh) bones. Short bones indirectly join the long bones to perform movement through the contraction and relaxation, for example, finger bones. Flat bones protect the vital organs. Irregular bones perform different functions based on their location.  Bones are the reservoir of many minerals such as calcium, phosphorus, magnesium, and along with the bone tissues, 98% of the total body calcium is found in our bones alone. The bone marrow found in the long bones participate in the formation of blood cells-hematopoiesis. The muscles attached to the bony skeleton contract and relax to produce movement and heat. By this way, bones assist in maintaining the body temperature

 

Conditions/Disorders of bones
Bone is vulnerable to developmental defects, injuries -fractures, and some of the infections. Following is the brief description of conditions occur in bones.

Name of the condition

Description

Fractures

It is the breakage of bones of various types as a result of a sheer mechanical force.

Osteoporosis 

The gradual loss of bone density and strength connected with ageing

Osteomyelitis 

Infection of the bone and the surrounding tissues

Osteitis 

Condition associated with the bone inflammation, for example, Paget’s disease of the bone

Acromegaly 

It is the overgrowth of bones in the face, hands and feet

Fibrous dysplasia 

An abnormal growth or swelling of bone

Rickets

A  child’s growing bones fail to develop due to the deficiency of vitamin D

Multiple myeloma

Cancer of the plasma cells in bone marrow

Bone cancer

Primary bone cancers include osteosarcomas and chondrosarcomas. However, most cancers found in bone have spread from other organs such as the breast, prostate, lung or kidney.

Scurvy

Bowed legs due to calcium deficiency

 

Names of 206  bones in our body 

Bones are distributed across an appendicular and axial skeleton. The appendicular skeleton is the skeletal bones found in the appendages such as hands and legs; Axial skeleton is made up of axis- trunk, neck, face and head). Click here for the list of bones from head to toe.

 

Further reading

1.

Epithelium                                    

2.

Connective tissues

3.

Tissues in our body

4 .  

 Cardiac muscles   

 

Questions

  1. What type of tissue is the bone?

  2. Why bone tissues are very hard? Explain.

  3. What is ossification? Explain the minerals responsible for ossification.

  4. Classify bones. Explain the structure of a long bone.

  5. Describe the functions of bones.

 

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