Navigation Links

In biology, the skeleton or skeletal system is the biological system providing support in living organisms. (By extension, non-biological outline structures such as gantries or buildings may also acquire skeletons.)

Skeletal systems are commonly divided into three types - external (an exoskeleton), internal (an endoskeleton), and fluid based (a hydrostatic skeleton), though hydrostatic skeletal systems may be classified separately from the other two since they lack hardened support structures.

Large external skeletal systems support proportionally less weight than endoskeletons of the same size, and thus many larger animals, such as the vertebrates, have internal skeletal systems. Examples of exoskeletons are found in arthropods and shellfish: the skeleton forms a hard shell-like covering protecting the internal organs.

The phyla arthropoda and mollusca both have exoskeletons. Since exoskeletons necessarily limit growth, phyla with exoskeletons have come up with various solutions. Most molluscs have calcareous shells and as they grow, the diameter of the shell is enlarged without altering its shape. On the other hand, arthropods shed their exoskeletons to grow, a process known as molting (or ecdysis). During molting the arthrpod breaks down their old exoskeleton and then regenerates a new one which they then harden through various processes (such as calcification or sclerotization).

An internal skeletal system consists of rigid structures within the body, moved by the muscular system. If the structures are mineralized or ossified, as they are in humans and other mammals, they are referred to as bones. Cartilage is another common component of skeletal systems, supporting and supplementing the skeleton. The human ear and nose are shaped by cartilage. Some organisms have a skeleton consisting entirely of cartilage and without any calcified bones at all, for example sharks. The bones or other rigid structures are connected by ligaments and connected to the muscular system via tendons.

Hydrostatic skeletons are similar to a water-filled balloon. Located internally in cnidarians and annelids, among others, these animals can move by contracting the muscles surrounding the fluid-filled pouch, creating pressure within the pouch that causes movement. Animals such as earthworms use their hydrostatic skeletons to change their body shape as they move forward from long and skinny to short and stumpy.

See also

Human skeleton


(Date:10/16/2014)... Northridge, Calif. (October 16, 2014) – Post-menopausal women ... effect on hormone levels or genital bleeding, after ... of an investigational fermented soy germ-based nutritional supplement ... according to a new peer-reviewed pilot study reported ... Society (NAMS) annual scientific meeting. , "These ...
(Date:10/15/2014)... our ability to assess the pandemic risk from strains ... we must not allow ourselves to become complacent that ... international consortium of scientists. , Influenza pandemics arise when ... yet to develop widespread immunity – spreads in the ... the past 100 years, the worst of which – ...
(Date:10/15/2014)... and to an unexpected extent. The outbreak does not ... virus shows a new disease dynamic in regions, where ... the German National Academy of Sciences Leopoldina, acatech – ... Union of the German Academies of Sciences and Humanities ... , In the statement the academies call for the ...
Breaking Biology News(10 mins):S-equol supplements associated with improved measures of reproductive health in postmenopausal women 2Scientists 'must not become complacent' when assessing pandemic threat from flu viruses 2Academies call for consequences from the Ebola virus epidemic 2Academies call for consequences from the Ebola virus epidemic 3Academies call for consequences from the Ebola virus epidemic 4Academies call for consequences from the Ebola virus epidemic 5
... from Philadelphia and Norway has determined the structure of an ... and is made at elevated levels in numerous forms of ... , led by researchers at The Wistar Institute, depicts the ... called NatA. Their findings, they believe, will allow them ...
... 2, 2013) In a new observational study published ... looked at the association of grape consumption, in the ... and 100% grape juice with the diet quality ... and adults. Their findings suggest that, among adults and ...
... Within sight of the Trans-Canada Highway, a team of ... set out on foot for a nearby site where they,d ... In the short distance they walked, with Canada,s ... in the Bow River bottomland, the team spotted five grizzly ...
Cached Biology News:Wistar scientists decipher structure of NatA, an enzyme complex that modifies most human proteins 2Grape consumption associated with healthier eating patterns in US children and adults 2Montana State University researchers highlight bears' use of Banff highway crossings 2Montana State University researchers highlight bears' use of Banff highway crossings 3Montana State University researchers highlight bears' use of Banff highway crossings 4
Other biology definitionOther Tags