Coelom can be called as the body cavity running throughout the length of the trunk in some organisms. Coelom originates by the splitting of the mesoderm (the second layer found in three-layered organisms or the triploblasts) during early embryonic stages and then later exists inner to it. Filled with coelomic fluids, it causes separation of the gut from the body wall and mainly helps in absorbing shock, improving circulation and providing rigidity. The organisms that have a coelom have a complex structure and higher in taxonomic order, and are known as Coelomates. Those organisms which lack a coelom are usually primitive in origin and are called as Acoelomates. In certain species, coelom existed in the ancestor but got lost during a certain stage in the course of evolution or still exists as false or pseudo-coelom. Human beings are Eucoelomates and that means they have a true coelom.  Lying inner to the mesodermal wall, coelom surrounds the body track of humans and is divided into three parts. Where it surrounds the heart, it is called as pericardial cavity. Similarly, coelom surrounding the lungs is pleural cavity and the one surrounding digestive organs is called as peritoneal cavity.