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Skeletal System
Types of Skeletons


Types of Skeletons
Skeletal Functions
Types of Bones
Structure of Long Bones
Microscopic Structure
Skeletal Development
Axial Skeleton
Appendicular Skeleton
Interactive Skeleton
Diseases, Disorders and Fractures

Hydrostatic Skeletons:
- consists of fluid held under pressure in a closed body compartment
- main type of skeleton in most Cnidarians, Flatworms, Nematodes and Annelids
- can control their form and movement by changing the shape of the fluid filled
      compartments with muscles in the body wall
- offer no protection of support for large land animals

Example of Hydrostatic Skeleton
The Sea Anemone has a hydrostatic skeleton & can change its shape by contracting a set of muscles.

- a hard encasement deposited on the surfave of an animal
- as the animal grows, the exoskeleton changes size by the enlargement of the
       diameter of the shell when new layers are added to the outer edge
- Cuticle (a polysaccharide similar to cellulose) makes up almost half of the cuticle. 
       Fibrils of the chitin are embedded in  a matrix made of protein and form composit
       material which increases the flexibility and strength of the exoskeleton.
- hardened via the addition of organic compounds and non-organic salts
- as the organism grows the exoskeleton must be molted and relaced by a larger
- Typically seen in arthropods and mullusks

Example of Exoskeleton
Arthropods, such as this mite, have exoskeletons creating hard shells on the outside of their body.

- consists of hard supporting elemnts buried within the soft tissues of an animal
-Characteristic of Sponges, echinoderms and chordates
        -Sponges have hard spicules of inorganic material or softer protein fibers to
           reinforce them.
       -Echinoderms have hard plates beneath their skin called ossicles which are
           either tightly bound together by protein fibers (ex: sea urchins) or loosely
           bound for changing shape (ex: sea stars).
       -Chordates have endoskeletons of bone and/or cartilage.  The mammalian
           skeleton consists of over 200 bones and is divided into the Axial and
           Appendicular skeletons.

Example of Endoskeleton
Humans contain endoskeletons, as seen in this picture of a human fetus.