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Human Skeletal System: Structure|Functions|Diseases

18-NOV-2016 15:51

    The Skeleton System provides the hard structure or framework to the human body which support and protects the body. It is composed of connective tissues like bones, cartilage, tendons and ligaments. Do you know that if the skeleton were without joints, no movement would have taken place and the significance of human body will be no more than a stone?


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    On the basis of the skeleton present in the body it is of two types:

    1. Exo Skeleton: The skeleton found on the exterior layer of the body and basically originates from embryonic ectoderm or mesoderm. It protects and preserves the inner organs and is dead. Like scales in the fishes, outer hard layer of the tortoise, feathers of the birds etc.

    2. Endo Skeleton: The skeleton found inside the human body and it originates from the mesoderm. These are found in almost vertebrate and form the main body structure. Do you know that these skeletons are covered through muscles?

    On the basis of structure Endo Skeleton is composed of two basic components:

    1. Bone: It is a solid, hard and strong connective tissue made up of fibres and matrix. Its matrix is made up of proteins and also rich in calcium and magnesium. Do you know that hardness of bones is due to the minerals present in it? The matrix of bone is in the form of concentric rings called lamella. Bone cells are called osteoblasts or osteocytes, present between the lamellae in fluid-filled spaces called lacunae.

    All around the bone there exists a double coated membrane which is made from connective tissue known as periosteum. Through this membrane muscles, ligaments and tendons are attached.

    There is a hollow cavity in the thicker and longer bones known as marrow cavity. In this cavity a fluid substance is found called bone marrow.  Amazing is that bone marrow is yellow in the middle and red at the ends of the bones and so, known as yellow bone marrow and red bone marrow respectively. Function of red bone marrow is to form RBC and that of white bone marrow is to form WBC.


    Functions of bone:

    - It provides shape to the body.

    - Protects vital organs like brain, lungs etc.

    - Provides skeletal support to the body and anchors muscles.

    - Serves storage site of calcium and phosphate.

    2. Cartilage:  It is a specialised connective tissue which is compact and less vascular. Its matrix is made up of proteins and slightly hardened by calcium salts but it is solid, cheese-like and firm but also slightly elastic i.e. why cartilage is not tough and rigid like bone.

    Its matrix has a delicate network of collagen fibres and living cells known as chondrocytes which are present in fluid-filled spaces known as lacunae. Remember blood vessels are not present in the matrix. All around the cartilage a membrane is found which is known as perichondrium.

    Cartilage is located in these body parts namely: ear pinna, nose tip, epiglottis, intervertebral discs, end of long bones, lower ends of ribs and rings of trachea i.e. wind pipe.


    Organ Systems of Human Body

    Now let us discuss about the Human Skeleton system in detail.

    In the skeleton of entire human body 206 bones exist and it is basically composed from two parts:

    1. Axial Skeleton (80 bones)

    The skeleton which constructs the main axis of the body is called the axial system. It consists of bone of skull, vertebral column, ribs and sternum.



    Components of Axial Skeleton Skull: 29 bones exist in human skull, of which 8 bones provide safety to the human mind and are connected through sutures. Rest of the bones forms the human face in which 14 bones are remarkably respondent.


    Vertebral Column: It is the main axis of the body and looks like rod which is long and thick bone exists on the back of the articular surface of the human body in the middle from the head to the waist. It is composed of 33 vertebrates and is developed cohesively and smoothly by the notochord. Centrally each vertebra is hollow.


    Sternum: The bone which connects the ribs are called sternum and it is located in the middle of the chest of the human body.

    Rib: 12 pairs of ribs are found in the human body and they are fibre like structure of the bone.

    Therefore, in Axial Skeleton:

    Skull - includes bones of the cranium, face, and ears (auditory ossicles).

    Hyoid - U-shaped bone or complex of bones located in the neck between the chin and larynx.

    Vertebral Column - includes spinal vertebrae.

    Thoracic Cage - includes ribs and sternum (breast bone).

    2. Appendicular Skeleton (126 bones)

    This system is made up of bones of the arms and legs and their supports. Under it bones of girdles, hands, legs etc. comes.



    Girdles: Two arcs type’s structures coexist to accommodate the forelimb and hindlimb on the axial skeleton known as girdles. The girdle of the forelimb is called pectoral girdle and that of hindlimb is called pelvic girdle.

    The bone of the forelimb in the pectoral girdle and hind limb in the pelvic girdle are connected through humerus and femur respectively and are accommodated in the cavities which are known as Acetabulum.

    Pectoral Girdle and Hand Bones: In the human body both parts of the pectoral girdle are separated and in each part only one flattened and triangular bone coexists called scapula and to connect the bones of the hand the pectoral girdle itself provides the joint.

    There are five parts in every forelimb and hand namely: Upper arm, Fore arm, Wrist, Palm and Fingers.

    Humerus, Radius Ulna, Carpals, Metacarpals and Phalanges are the bones of the upper arm, fore arm, wrist and fingers respectively.


    Pelvic Girdle and Legs Bones: Pelvic girdle is mainly composed of three bones; Ilium, Ischium and Pubis. In the adult these three bones are mutually connected to each other. At the joint place of these bones there exists a narrow ditch called Acetabulum in which the end of the femur bone is attached. Even the pelvic girdle provides the joints to connect the leg bones with itself. In the human beings various leg bones are present like femur, tibia, fibula, tarsals, meta tarsals etc. Among these bones tibia fibula is free and at the joint of femur and tibia fibula a round bone is found which is known as knee bone petla. The human leg turns only one time at this joint.

    Therefore, we can say that in Appendicular Skeleton:

    Pectoral Girdle - includes shoulder bones (clavicle and scapula).

    Upper Limbs - includes bones of the arms and hands.

    Pelvic Girdle - includes hip bones.

    Lower Limbs - includes bones of the legs and feet.

    Disorders of Bones

    Arthritis: At old age it is a common disease; caused by the inflammation of the joints which is characterised by pain and stiffness in the joints. There is no cure only analgesics can be used. It can be of following types:

    - Osteoarthritis: It is a degenerative joint disease characterised by the degeneration of the articular cartilage and proliferation of new bones.

    - Rheumatoid arthritis: It is diagnosed by the presence of a rheumatoid factor called immunoglobulin (IgM). And also, the primary symptom of inflammation of synovial membrane.

    - Gout arthritis: It is caused due to the excessive formation of uric acid or inability to excrete it. Basically this disease is related to the diet so patient should avoid meat.

    Osteoporosis: It is an age-dependent systemic disorder characterised by low bone mass, micro architectural deterioration of the bone, increased fragility and susceptibility to fracture.


    Joints are the place of articulation between two or more bones or between a bone or a cartilage.

    Types of Joint:

    On the basis of movement and locomotion the joint is divided into three categories: Perfect Joint, Imperfect Joint and Fixed Joint.

    1. Perfect Joint: In this joint making bones can be moved in different directions and in which movement or locomotion occurs simultaneously. On the bones of such joints, thin layer of cartilage is also found at their ends. And at the joints of the bones ligaments exist.

      Perfect Joint is further divided into five subcategories:

    - Ball and Socket Joint: In this joint ball shaped bone can turn or move in any direction like at the joint of pectoral girdle and humerus bone, at the joint of femur and pelvic girdle etc. In this femur and humerus bone can be moved or turned in any direction.

    - Hinge Joint: The bones of this type of joint can be moved or turned in only one direction. Eg. Joints of elbow and knee.

    - Pivot Joint: In such type of joint there exists a sharp pointed bulge and in another bone there exist a narrow gap in which pointed bulge is accommodated. It moves like an axle. Eg. Secondary vertebral bone and atulus.

    - Gliding Joint: In this type of joint bone can slide to each other under a definite limit but never turn or bend. Eg. The joint of ulna and carpels etc.

    - Saddle joint: In this joint the bulge of one bone is completely accommodated or adjustable in the gap of another bone but does not move or rotate easily and smoothly. Eg. The joint of Carpels and Meta Carpels of the Thimb.

    2. Imperfect Joint: Inside the bones the synovial cavity and ligaments do not exist in such type of joint. Also, some locomotional activities are found in these bones. Eg. Found in the pubis bone of the pelvic girdle and also between the joints of the verterbrae.

    3. Fixed Joint: Such types of joints are fixed and do not show any movement that is why known as fixed joint. Eg. Bones of skull and girdles.

    What do you understand by evolution?

    DISCLAIMER: JPL and its affiliates shall have no liability for any views, thoughts and comments expressed on this article.

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