Extraembryonal membrane is a membrane-like structure that looked envelops the embryo and plays an important role in embryonic development. Extra embryonic membranes formed from embryos but were not part of an organism's body after the birth of the organism. Extra embryonic membranes in vertebrates include saccus vitelinus or yolk sac, amnion, allantois, and chorion / serous. • Yolk Sac
yolk sac is formed of cloaking vitellus by some cells derived from the primitive gut. vitellus yolk sac store, which is a source of food / nutrition major from non-placental embryos. Yolk sac also has blood vessels to facilitate the transport of nutrients into the body of the embryo.
• Allantois
Allantois is ekstraembryonic membrane that serves to store waste materials embryo. In placental mammals there are allantois but its function can be replaced since the storage of waste products embryos collected by the mother's body through the placenta. Chorion allantois together combine to form a membrane chorioallantois. Chorioallantois membrane facilitates gas exchange in the embryo.
• The amnion and Chorion
Amniotic sac that encloses the embryo inside filled with fluid, which protects the embryo from drought, and together with serous provide cushioning for the embryo to be protected from any mechanical shocks. While alantois continues to expand, alantois pressing vitelin serous membrane, the layer of the shell of the egg. Alantois and serous form of respiration organ that serves the embryo. The blood vessels are formed in ephitelium alantois carries oxygen to the chick embryo (Campbell, 2004).
• Placenta
The placenta is owned by placental mammals. The placenta is formed from layers of chorion embryo and the endometrium parent. Its main function is as a channel that connects the fetus and the mother's body, so that the transport of nutrients from the mother to the fetus may occur. The main substance that is transported from the mother to the fetus is water, oxygen, nutrients, and antibodies.
Pisces and amphibians have only extra embryonic membranes form the yolk sac. Mammals have but little yolk, the yolk sac in humans will cease development because its function is rudimentary, and then play a role in the formation of the midgut. In reptiles and aves there are a lot of yolk wrapped yolk sac. Amnion contained in eggs all terrestrial animal that serves to keep moisture from embryos (reptiles and aves), in mammals serve as a protective barrier against the surrounding pressure and keep the fetus is not attached to the home network.
Pisces eggs and amphibians are not equipped amnion because the environment around the eggs are moist (water). Allantois in reptiles, aves and mammals have the same functionality as shelter remnants of metabolism such as urea (mammals and reptiles) and uric acid (aves). Fish and amphibians do not have allantois for both animal eggs is equipped with a thin layer so that it can directly perform diffusion to excretion and respiration. Chorion in reptiles and aves has the same function as a gas exchange, in mammals, chorion derived from the trophoblast is formed simultaneously with the zona pellucida, and together with the allantois role in the formation of the placenta with endometrial stem. The placenta in mammals serves as the exchange of oxygen, carbon dioxide, and nutrients from or to the parent. The placenta is formed from the junction between the chorion and mucosa (Orphans, 1984).
Fish release their eggs into the water. there is no risk of drought. This is the cause why the fish do not have the amnion which serves as a protective embryo from dehydration. Fish eggs surrounded by a thin membrane in which the diffusion of gases and metabolic waste can take place so that the function as a gas exchange chorion and allantois as container waste from the embryo can be represented. fish embryos had a yolk sac to transport nutrients to the body of the embryo, thus the role of the placenta has been represented by the yolk sac.
Allantois is an adaptation for terrestrial animals because the embryos of animals such as reptiles and terrestrial ovipar aves, residual waste products of metabolism can not be simply thrown into the aquatic environment around him like embryo fish and amphibians. Allantois store waste materials until the embryo hatches.
Extra embryonic membranes in fish formed at the end of gastrulation phase. Yolk sac built by splanknopleura with endoderm and mesoderm adjacent to the splanchnic welcome. In the splanchnic mesoderm there will be blood vessels vitelin. The formation of the yolk sac, in line with the folding roof lining endoderm becomes archenteron, to form the digestive tract (Orphans, 1984).
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