Introduction to Skeletal System.
Introduction:
The skeleton is the bony framework of the body.
It forms the cavities and fossae (Shallow depressions or hollow parts) that protect some important body structures, forms the joints and gives attachment to the skeletal muscles.
Divisions of Skeletal System:
Skeletal system contains 206 named bones which are divided into two main divisions as follows,
The Axial Skeleton.
The Appendicular Skeleton.
The Axial Skeleton:
Skull.
Vertebral column.
Sternum or breastbone.
Ribs.
The Appendicular Skeleton:
The upper limbs and the shoulder girdles.
The lower limbs and the innominate bones of the pelvis.
Bone and Types of Bones:
Bone is a strong and durable connective tissue.
It is made up of water, osteoid, bone cells constituting 50% part and remaining 50% of minerals like Calcium phosphate and Magnesium phosphate.
Bones are classified into 5 types as,
Long Bones.
Short Bones.
Irregular Bones.
Flat Bones.
Sesamoid Bones.
Long Bones:
These consist of a shaft and two extremities.
As the name indicates the length is much greater than the width.
Supports weight and facilitates movements.
e.g. femur, tibia and fibula.
Short Bones:
Length is almost the same as width.
Located in the wrist and ankle joints, these bones provide stability and some movement.
e.g. Carpals in the wrist, tarsals in the ankles.
Irregular Bones:
As the name indicates they vary in shape and structure.
They have a complex shape and protect the internal organs.
e.g. the vertebrae.
Flat Bones:
They are flattened bones and also called “Sutural Bones”..
Provide protection like shield and a vast area for muscle attachment.
e.g. Skull bones, Sternum, Ribs, Pelvis etc.
Sesamoid Bones:
These are bones embedded in tendons.
These small, round bones are commonly found in the tendons of the hands, knees, and feet.
Their function is to protect tendons from stress and wear.
e.g. patella (kneecap).
Bone cells:
The cells responsible for bone formation are osteoblasts (these later mature into osteocytes).
Osteoblasts:
These are the bone-forming cells that secrete collagen and other constituents of bone tissue.
They are present:
in the deeper layers of periosteum.
in the centres of ossification of immature bone.
at the ends of the cartilages of long bones
at the site of a fracture.
Osteocytes:
As bone develops, osteoblasts become trapped and remain isolated in lacunae.
They stop forming new bone at this stage and are called osteocytes.
Osteoclasts:
Their function is resorption of bone to maintain the optimum shape.
This takes place at bone surfaces:
under the periosteum, to maintain the shape of bones during growth and to remove excess callus formed during healing of fractures.
round the walls of the medullary canal during growth and to canalise callus during healing.
A fine balance of osteoblast and osteoclast activity is necessary for normal bone structure and functions.
Functions of bones:
Provide the framework of the body.
Give attachment to muscles and tendons.
Permit movement of the body as a whole and of parts of the body, by forming joints that are moved by muscles.
Form the boundaries of the cranial, thoracic and pelvic cavities, protecting the organs they contain.
Contain red bone marrow in which blood cells develop.
Provide a reservoir of minerals, especially calcium.
Commonly Asked Questions:
Write different divisions of the Skeletal System.
Write a note on different types of bones.
Write a note on different bone cells.