Skeletal System in Human Body
Skeletal system constitutes hard internal or external living or non – living parts that form the supporting framework of body.
It is divided into 2 Parts :
Exoskeleton : It is hard, protective and supportive frame – work which is produced by ectoderm.
It is present on the outside of the body (made of either dead tissues or biochemical secretion).
Found in both invertebrates (shells of snails, corals, etc.) and vertebrates (hair, nails, claws, hooves, etc.).
Endoskeleton : It is hard, supportive framework which is produced by mesoderm.
It occurs inside the body and is made of cartilages and bones. Found in corals, echinoderms and vertebrates.
Divided into two main parts : Axial Skeleton and Appendicular Skeleton.
A. Axial Skeleton (Total 80 bones)
Skull consists of two main parts – cranium and face.
Cranium (brain box) is formed by 8 bones and provides a bony protection for the brain.
Face : There are 14 bones which form the skeleton of face.
There are also present 6 ear ossicles in the skull.
Another bone is hyoid, which is horse shoe shaped present in neck between lower jaw and sound box (or larynx).
It supports tongue.
It is a string like vertebrae which lies in the mid dorsal line of the neck and trunk.
It is made up of 33 vertebrae in which 26 bones are visible because five sacral vertebrae are fused to form one sacrum and four coccygeal vertebrae are fused to form one coccyx.
It displays four curves to enhance balancing power and firmness for upright posture of body. The curvatures are cervical, thoracic, lumbar, pelvic (or sacral).
The vertebrae are grouped into five groups – cervical (7 bones), thoracic (12 bones) lumbar (5 bones), sacral (1 bone) and coccyx (1 bone).
Ribs are 12 pairs (12 x 2) of bony bars which form the sides of chest cage.
They protect the delicate organs (heart, lungs, etc.) and provide surface for attachment of muscles concerned with respiratory mechanism.
Sternum (or Breast Bone)
It is a narrow, elongated and flattened structure, present just under the skin in the middle of front of the chest.
B. Appendicular Skeleton (Total 126 bones)
This skeleton lies laterally and is attached to axial skeleton at an angle.
It is made up of girdles (pectoral and pelvic) and limb bones (forelimb and hind – limb).
- Also known as shoulder girdle.
- Has 4 bones (two in each pectoral girdle).
Forelimbs: Consist of 60 bones
- Humerus (2): Upper arm
- Radius (2): Forearm
- Ulna (2): Forearm
- Carpals (16 = 2 x 8 ) : Wrist
- Metacarpals (10 = 2 x 5) : Palm
- Phalanges (28 = 2 x 14) : Finger
Hind – limbs : Consist of 60 bones
- Femur (2) : Thigh (longest bone in the body)
- Patella (2) : Knee
- Tibia (2) : Shank
- Fibula (2) : Shank (thinnest bone)
- Tarsals (14 = 2 x 7) : Ankle
- Metatarsals (10 = 2 x 5) : Sole
- Phalanges (28 = 2 x 14) : Toes
Pelvic Girdle : Has 2 hip bones.
Diseases of Skeletal System
- Gout : Accumulation of uric acid crystals in joints leading to painful movement. Swelling and inflammation of synovial membrane due to autoimmune reaction.
- Dislocation : In this case, the bones at the joints are dislodged from their positions e.g., the ball of one bone may slip out of the socket.
- Hard tissue deposits over articular cartilage along with higher secretion of synovial fluid causing pain and stiffness lead to rheumatoid arthritis.
- Tearing of articular cartilage and development of bony lumps at places causing pain, stiffness and permanent bending lead to osteoarthritis.
- Bursitis is inflammation of the bursae present within synovial joint as small membrane bound pockets which stores synovial fluid. It is caused by physical injury or constant pressure on a single joint for a long time.
- Osteitis is inflammation of bone.
- Osteoporosis is loss of bone density due to excessive absorption of calcium and phosphorus from the bone.
- Osteomyelitis is infection of bone.
- Osteomyelodysplasia is a condition characterized by thinning of the osseous tissue of bones and increase in size of the marrow cavities, attended with leukopenia and fever.
- Osteopetrosis is a hereditary disease marked by abnormally dense bone, and by the common occurrence of fractures of affected bone.
Articulation of Bones the Joints
A bone joint or articulation may be defined as the junction of two bones.
The study of such joints is known as arthrology.
There are 3 principal types of bone joints.
- Femur (in hind limbs) is the longest bone and stapes (in middle ear) is the smallest bone of the body.
- Sternum is absent in fish.
- Spondylitis is inflammation of vertebrae.
- Synovitis means an inflammation leading to swelling at joints.
- Osteology is study of skeleton.
- Chondrology is study of cartilages.
- Arthrology is study of joints.
- Masseters of jaw is the strongest muscle.
- Birds have spongy bones with air filled spaces, called pneumatic bones.
- Rigor mortis is the state of body stiffening after death.
- Fatigue is the inability of a muscle to contract due to depletion of its chemicals and lactic acid accumulation by repeated contraction. A completely fatigued muscle refuses to respond to nervous stimuli.
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