Skeletal System

Introduction to Human Skeletal System:

The skeletal system is the system of bones, associated cartilages, and joints of the human body. Together these structures form the human skeleton. Skeleton can be defined as the hard framework of a human body around which the entire body is built. Almost all the hard parts of the human body are components of a human skeletal system. Joints are very important because they make the hard and rigid skeleton allow different types of movements at different locations. If the skeleton were without joints, no movement would have taken place and the significance of the human body; no more than a stone.

Human Skeleton

Human Skeleton

Components of Human Skeleton: Human skeleton is composed of three main components; Bones, Associated cartilages and Joints.


Bone is a tough and rigid form of connective tissue. It is the weight bearing organ of human body and it is responsible for almost all strength of human skeleton.


Cartilage is also a form of connective tissue but is not as tough and rigid as bone. The main difference in the cartilage and bone is the mineralization factor. Bones are highly mineralized with calcium salts while cartilages are not.


Joints are important components of human skeleton because they make the human skeleton mobile. A joint occurs between “two or more bones”, “bone and cartilage” and “cartilage and cartilage”.

Divisions of Human Skeleton:

Human skeleton can be divided into two divisions.

Axial Skeleton:

Axial skeleton forms the axis of human body. It consists of Skull, vertebral column and thoracic cage.

  • Skull: Skull is that part of human skeleton that forms the bony framework of the head. It consists of 22 different bones that are divided into two groups: bones of cranium and bones of face.
  • Vertebral Column: It is a flexible column of vertebrae, connecting the trunk of human body to the skull and appendages. It is composed of 33 vertebrae which are divided into 5 regions: Cervical, Thoracic, Lumbar, Sacral, and Coccygeal.
  • Rib Cage: It is a bony cage enclosing vital human organs formed by the sternum and ribs. There are 12 pairs of ribs that are divided into three groups: True ribs, False ribs, and Floating ribs.

Axial SkeletonAppendicular Skeleton:

It is the skeleton of appendages of human body. It consists of Shoulder girdle, Skeleton of upper limb, Pelvic girdle and Skeleton of a lower limb.

  • Shoulder Girdle: It attaches the upper limb to body trunk and is formed by two bones: clavicle and scapula. The clavicle is a modified long bone and is subcutaneous throughout its position. It is also known as the beauty bone. The scapula is a pear-shaped flat bone that contains the glenoid fossa for the formation of the shoulder joint. It possesses three important processes: Spine of a scapula, Acromion process, and Coracoid process.
  • Skeleton of Upper limb: The skeleton of each upper limb consists of 30 bones. These bones are Humerus, Ulna, Radius, Carpals (8), Metacarpals (5), Phalanges (14).
  • Pelvic Girdle: There are two pelvic girdles (one for each lower limb) but unlike the pectoral girdles, they are joined with each other at symphysis pubis. Each pelvic girdle is a single bone in adults and is made up of three components: Ileum, Ischium, and Pubis.
  • Skeleton of the Lower limb: The skeleton of each lower limb consists of 30 bones. These bones are; Femur, Tibia, Patella, Tarsals (7), Metatarsals (5), Phalanges (14).

Appendicular Skeleton

Appendicular Skeleton

Human skeleton performs some important functions that are necessary for the survival of human beings.

Functions of human skeleton:

  1. STRENGTH, SUPPORT, AND SHAPE: It gives strength, support, and shape to the body. Without a hard and rigid skeletal system, the human body cannot stand upright, and it will become just a bag of soft tissues without any proper shape
  2. PROTECTION OF DELICATE ORGANS: In areas like the rib cage and skull, the skeleton protects inner soft but vital organs like heart and brain from external shocks. Any damage to these organs can prove fatal, therefore a protective function of the skeleton is very important
  3. LEVERAGE FOR MOVEMENTS: Bones of the human skeleton in all parts of the body provide attachment to the muscles. These muscles provide motor power for producing movements of body parts. In these movements, the parts of skeleton act like levers of different types thus producing movements according to the needs of the human body.
  4. PRODUCTION OF RED BLOOD CELLS: Bones like the sternum and heads of tibia have hemopoiesis activity (blood cells production). These are the sites of production of new blood cells.