The skeletal system . It has locomotion , support and protection functions. The vertebrates have an internal or endoskeleton skeleton, consisting of bones , which are joined together by joints. The science that deals with studying bones is called osteology.


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  • 1 Human skeleton
  • 2 Bird skeleton
  • 3 Constitution of the bones
  • 4 Types and classification
    • 1 External skeleton
    • 2 Internal skeleton
    • 3 Fluid or hydrostatic skeleton
  • 5 See also
  • 6 Sources

Human skeleton

In man , the skeleton is made up of cartilage , spongy tissue, medulla , compact and periosteal tissue. The joints are divided into mobile (allow wide movements), semi-mobile (with little movement) or immobile. The bones can be long, flat, and short. The cellular tissue that occupies its internal cavity is called the bone marrow. The red marrow is the one that presents the growing bone; yellow, the normal type, is mainly made up of fat cells. The endostium is the tissue that lines the medullary cavity of a bone. The periosteum is the connective tissue that surrounds all the bones .

Bird skeleton

The skeleton of the birds is very light and highly resistant, due to everything, because the bones are hollow and porous, characteristics that facilitate the task of flying; In return, this light structure is exposed to frequent fractures. For this reason, inside some bones, especially the longer ones, there are a series of trabeculae or tissue projections that increase resistance. In the skeleton of the birds one can observe one of evolutionary changes with respect to other vertebrates.

Constitution of the bones

The bones are formed by a cells called osteocytes , which are formed from the differentiation of osteoblasts. Among the mineral salts that make up the bones, calcium , carbonate and phosphate salts stand out . Deficiency of these minerals in the bones can lead to them being less resistant.

Types and classification

Skeletal systems are commonly classified into three types:

  • External
  • Internal
  • Fluid or hydrostatic skeleton.


In addition, there are other types that are not capable of supporting important structures:

  • Skeleton of salts and minerals
  • Chitinous Skeleton, Axilial Skeleton

External skeleton

The systems external support proportionally less weight than endoskeletons of the same size; For this reason , larger animals , such as vertebrates, have internal skeletal systems.

The main examples of exoskeleton are found among arthropods , some invertebrates , in which the exoskeleton forms a shell or external structure that protects the internal organs.

Internal skeleton

An internal skeleton consists of rigid or semi-rigid structures within the body , which move thanks to the muscular system . If such structures are mineralized or ossified, as in humans and other mammals , they are called bones . Another component of the skeletal system is cartilage , which complements its structure. In humans, for example, the nose and ears are supported by cartilage. Some organisms have an internal skeleton made entirely of cartilage, without calcified bones, as in the case of sharks. The bones and other rigid structures are connected byligaments and attached to the muscular system through tendons.

Fluid or hydrostatic skeleton

The hydroskeleton consists of a fluid-filled, celomatic or pseudocellomatic cavity, surrounded by muscles . The pressure of the fluid and the action of the muscles that surround it, serve to change the shape of the body and produce a movement such as digging or swimming. The successive contraction of various metamers, which are provided with bundles of circular and longitudinal muscle fibers, stretching and thickening parts of the body, allow it to move horizontally. Hydrostatic skeletons have a role in the locomotion of echinoderms (starfish, sea urchins), annelids, nematodes, and other invertebrates . The hydroskeleton has similarities to the hydrostatic muscles.


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