Lucia De Stefano IV A

• A skeleton is needed by animals to move and to give their bodies structure and protection.

• There are three main types of skeleton: the hydrostatic skeleton (or hydro-skeleton), the exoskeleton, and the endoskeleton.

• The hydrostatic skeleton (or hydroskeleton) is made up of a liquid kept under pressure in a closed area of the body.

• It contributes to protect the body.

• Moreover, it gives shape to the body and gives a point of insertion for the muscles, to allow the motion. Most of the animals which have a hydrostatic skeleton have a flaccid and flexible body e. g. earthworm.

• A lot of aquatic and terrestrial animals have a rigid external skeleton, the exoskeleton.

• This is a distinctive characteristic of the arthropods phylum.

• The exoskeleton of arthropods is made up of protein layers and chitin, a polysaccharide.

• The exoskeleton does not grow together with the animal, so it has to be removed and replaced with a bigger one to allow the growth of the animal.

• The endoskeleton is made up of hard or leathery support elements situated in the interior of the animal body.

• Most of echinoderms have an endoskeleton made up of hard subcutaneous plates. The endoskeleton of echinoderms is calcareous and is called derma-skeleton.

• The endoskeleton of vertebrates is made up of cartilage or a combination of cartilage and bone.

• All vertebrates have an axial skeleton which supports the trunk of the body. It is formed by the skull, the spinal column and, in most of the vertebrates, by a rib cage.

• The spinal column is the anatomic characteristic that defines vertebrates and is formed by a series of single bones, the vertebrae, alternated with buffers of fibrous cartilage known as intervertebral disks.

• The vertebrae have the same basic structure: a cylindrical body of bone, which supports the body weight, a dorsal arch, which forms a protected passage for the spinal marrow, and several bone thorns and protuberances, which form useful areas for the insertion of muscles.

• The appendicular skeleton, which is attached to the axial skeleton, is formed by the pectoral girdle, the pelvic girdle and the bones of the upper and lower limbs.

• Their functions are:

- to make locomotion possible;

- to protect the major organs of digestion, excretion and reproduction.

• Support

• Movement

• Protection

• Blood cells production

• Storage

• Endocrine regulation

• Bone contains several types of living tissues. Most of the external area is covered by a layer of connective fibrous tissue, the periosteum.

• Other living cells, the osteoblasts, are present inside the osseous tissue where they secrete the bone matrix. The bone matrix is formed by flexible protein-based collagen fibres.

• Even the cells in the osseous tissue have a metabolism.

• The cylindrical and elongated part of long bones, e. g. the humerus, is called diaphysis and is made up of dense bone. Dense bone surrounds a central cavity containing yellow bone marrow, mainly made up of fat transported by blood and stored in the bone. • The two extremities of the bone, the epiphysis, have an external layer of dense bone and an inner layer of spongy bone. The small cavities of the spongy bone contain the red bone marrow, which produces blood cells. • The two extremities are covered by a thin layer of cartilage.

• In movable joints, bones are kept in the right position by ligaments, solid fibrous connective tissue bands.

• Between the humerus and the scapula, and between the femur and the pelvic bones, there is a particular joint called ball and socket joint (or spheroidal joint), formed by a sphere in a hollow.

• In the elbows and in the knees there are the hinge joints which allow the movement on only one level.

• The joint which allows us to rotate our forearm is a pivot articulation.

• To produce movements, the animal muscles interact with bones which act like levers.

• Muscles are connected to bones by tendons, formed by fibrous connective tissue. A muscle can only actively contract; relaxation is a passive process.

• The capacity of lifting up or lowering our arms depends on the existence of couples of antagonist muscles attached to the bones.

There are many classified skeletal disorders.

• One of the most common is osteoporosis.

• Also common is scoliosis. This

condition is most apparent during adolescence, and is most common with females.

• Arthritis is a disorder of the joints. It involves inflammation of one or more joints.

• When affected by arthritis, the joint or

joints affected may be painful to move, may move in unusual directions or may be immobile completely.

• The symptoms of arthritis will vary

differently between types of arthritis. • The most common form of

arthritis, osteoarthritis, can affect both the larger and smaller joints of the human skeleton.

• A human is able to survive with just his axial portion of the skeleton.

• Human inter-sex dental dimorphism centres on the canines, but it is not nearly as pronounced as in the other great apes.

• Long bones are generally larger in males than in females within a given population.