The hard parts of an animal body present inside or outside the body collectively form the skeletal systems or Skeleton.

Types of Skeleton

Exoskeleton

Skeleton present on the outer surface of the body is called Exoskeleton. Its generally formed of non living elements generally formed of non living elements.Eg. Calcareous shell in Molluscs

• Chitinous & Sclerotized in form in Artheopati
• Dermal scales on skin in fish
• Epidermal scales on skin in reptiles
• Claws & feathers in birds
• Hair, Nails, Claws & Hoofs in mammals

Endoskeleton

Hard parts present beneath the skin of an animal body collectively form endoskeleton. In vertebrates, its formed of bones & cartilages.

Functions of Skeleton

1.    It provides mechanical protection to internal delicate organs like brain (skull), heart, lungs (ribs) etc.

2.    Forms supporting framework of body, giving shape & form to the body.

3.    Allows various types of movements of body parts.

4.    Bone marrow inside marrow cavity of long bones acts as haemopoitic tissue and forms erythrocytes (RBCs) & granular Haemopoisis.

5.    Ribs & Sternum play role in breathing movements of chest.

6.    Bones act as reservoir of minerals like Calcium, phosphorus & Magnesium salts.

7.    Cartilages of Larynx help in sound production.

Human Skeleton

Human skeleton is formed of bones and some cartilages. It is formed of 206 bones in adult man. (No of bones in a newly born baby in 306).

It is divided into two main parts. Axial Skeleton & Appendicular Skeleton.

Types of Joints

A joint is a meeting place of 2 bones. The joints can be classified into 3 main types.

• Immovable Joints: In these joints, adjoining bones are joined by strong bundle of collagen fibres so that bones cant move upon each other such immovable joints are called Sutures. These are found between various bones of skull.
• Slightly Movable Joints: In these joints, adjoining bones permit only slightly movement. These are found in public symphysis between pubic bones of pelvic girdles.
• Freely Movable Joints: In these joints, one bone forms a knob like swelling while other bone forms a depression. Between the bones, there is synovial cavity filled with gelatinous synovial fluid. Synovial fluid is similar to lymph and lubricates the joints so these joints are freely movable. These joints are found between limb bones.

Skeletal Disorders

Arthritis (Aching Joints) :Arthritis refers to inflammation of joints and is a common disease of old age. It is characterized by pain & stiffness in the joints. There is no cure & only analgesics (pain killers) can be used.

On the basis of causative agents, there are 3 types:

(a)   Osteoarthritis (Degenerative Arthritis): It is characterized by degenerative changes in cartilages present at the joints, stopping the secretion of synovial fluid and the cartilages at the ned of the bones are replaced by bony spur. Finally, the bones fuse and the joints become totally immobile called ANKYLORIS. It is also called Wear & Tear Disease.

(b)   Rheumatoid Arthritis : It involves painful inflammation of the synovial membranes of the joints. Movements become extremely painful & may lead to deformities of joints.

(c)   Gout: It is characterized by accumulation of uric acid crystals in the synovial joints.

Osteoporosis: It is most common of all bone disease in adults, exp. in old age. It is characters by decrease in density of bones due to loss of calcium & phosphorus from the bones due to decreased osteoblastic activity in bone leading to depressed rate of bone esteoid deposition in the bone. (except in Hyperthyroidism where the cause of decrease of osteoid matrix of bone is increase in the activity of osteoclasts).

Synovitis: An inflammation leading to sevelling at the joint.

Osteitis: Inflammation of bones.

Spondylitis: Inflammation of one/more vertebral.

Slipped Disc/Prolapsed Disc: Displacement of vertebral and Inter Vertebral cartilage pads from their normal position.

Rickets: Curved bones causing bowlegs in children due to deficiency of Vit. D in died & Calcium in bones.

Endocrine System

There are many glands in the body system which release secretions through ducts associated with the glands, These are exorine glands (or duct glands), eg. Salivary and sweat glands; other glands in the body release substances (hormones directly into the blood circulation, these are endocrine glands or (ductless glands).

Chemically there are three kinds of hormones. These are:

(1)   Protein hormones: Are those produced by the hypothalamus, pituitary, thyroid, parathyroid, pancreas and one of the hormones of ovary (relaxin and one of the placenta (human chrionic gonadotropin).

(2)   Steroid hormones: Are produced by the adrenal, cortex ovaries and testes.

(3)   Biogenic amines: Are produced by the pineal gland and the adrenal medulla.

Hormonal diseases