Alantois is a fetal membrane that helps to form the umbilical cord. Alantois function in the gas exchange process and also collect the waste materials in the embryo. It is a membranous sac-like structure that originates from the yolk sac of different species like mammals, reptiles, and birds. Alantois are generally present in all embryos and located between the amnion and chorion as an extra-embryonic tissue. Alantois in humans ultimately regresses into a small structure within the umbilical cord. This structure is not found among vertebrates, amphibians, and non-tetrapods. In this article, we are going to discuss the alantois in detail.
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Allantois
Allantois is a tube-like structure of the yolk sac that helps to remove the nitrogenous waste materials from the embryo. It is also related to the development of the urinary bladder of an organism. It connects the bladder with the yolk sac during the time of fetal development.
Also Read: Urinary System
Here is some information about the Allantois as mentioned below.
- Allantois is the mid-layer of the placenta and the blood vessels that originate from the umbilicus traverse.
- It expands eventually with the embryo and works as a temporary respiratory organ for the fetus.
- The cavity of the allantois stores all types of excretions of the fetus.
- Allantois is filled with a clean liquid and holds different blood vessels. It helps to exchange the essential gases to the embrayo.
- The allantois's blood vessels gradually become the arteries and veins of the umbilical cord.
- The development of allantois starts around stage 15 and gradually becomes a balloon-like structure outside the body in around four days.
Read More: Labeled Diagram of Uterus and Structure
Functions of Allantois
Allantois is a multifunctional structure that plays a major role during the embryonic development of different species like mammals, birds, and reptiles. Here are some functions of the allantois as mentioned below.
- Waste Management: The primary function of the allantois is waste management. It serves as the temporary storage organ that stores the waste materials produced by the embryo. These waste products may include uric acid and urea which vary in different species. These waste products stay there until they are eliminated from the embrayo.
- Exchange of the Respiratory Materials: Allantois also works as a respiratory exchange medium. It presents between the embryo and the surrounding environment which helps to exchange the carbon dioxide by taking oxygen.
- Vascularization: Allantois also contains so many blood vessels that join the developing circulatory system to the embryo directly. These blood vessels help to transport the different nutrients, oxygen, and waste materials between the embryo and placenta.
- Fluid Exchange: Allantois also helps in the process of fluid exchange between the embryo and its surroundings. It helps to maintain the fluid balance within the embryo. Allantois contributes to the overall development of the embryo also.
Read More: Diagram of Female Reproductive System and its Anatomy
Different Parts of Allantois
The Allantois is divided into several parts or regions as mentioned below.
The Proximal Region
It is a region of allantois that originates from the embryonic hindgut of the embryo. This region is generally connected to the cloaca of the embrayo. This is a common chamber at the posterior end of the urogenital and digestive systems of an organism.
Distal Region
It is a part of allantois that extends away from the embryo. This part of allantois spread towards the extraembryonic structure. In birds and reptiles, the distal region fuses with the chorion to develop the chorioallantoic membrane. It involves the gas exchange and transfer of nutrients.
Blood Vessels
In allantois, there are so many blood vessels and networks present that connect the embryonic circulatory system. These blood vessels play a major role in transporting nutrients, gases, and waste products in between the embryo and surrounding tissues.
Connective Tissues
Allantois is generally supported by the different connective tissues. These tissues provide the structure and support to the allantois. The tissue helps the allantois with the embryo by creating connections between them.
Urachus
In mammals, a part of allantois persists after birth. This part is known as urachus. The urachus is a remnant structure that extends from the fetal bladder to the umbilicus. In adults it generally becomes the median umbilical ligament.
Allantois and Chorion
Allantois and Chorion both are crucial components of the extraembryonic membranes in vertebrate embryos. As we know allantois is a sac-like structure that develops as an outpouching of the embryonic gut and plays a major role in the process of embryonic development. The chorion is a part of the extraembryonic membrane that surrounds the embryo. It evolves from the outermost layer of the cells of the embryo. It forms the outermost membrane that covers the amniotic cavity.
The Allantois and Chorion are distinct in nature but perform so many functions during embryonic development. They are interconnected with each other and work together to ensure the growth, survival, and well-being of the embryo development.
Allantois in Human
Allantosis plays a major role in Humans, particularly in the embryonic development process. Allantosis creates the urinary bladder and also contributes to the development of the umbilical cord. During the time of early embryogenesis, the allantois become an outgrowth and form the hindgut. It extends as the connecting stalk which becomes later the umbilical cord. The development process undergoes a series of transformations as mentioned below.
- Urinary Bladder Formation: The endodermal lining of the allantosis gives rise to the urinary bladder. As the urinary system develops, the allantosis incorporates with bladder and completes the structure.
- Umbilical Cord Development: The vascular core of the allantosis is known as the stalk that becomes surrounded by so many tissues and blood vessels. They connect the developing fetus to the placenta. It allows the process of exchange of different essential gases and nutrients in the fetus.
Fate of Allantois
In human embryonic development, the allantois goes through a process of regression. Initially, the allantois forms the urinary bladder and takes a tube-like structure. The lower part of the allantois merged with the bladder and the upper part of the allantois becomes the urachus. The vascular portion of allantois known as the allantoic stalk develops as the surrounding tissues and the blood vessels. The embryonic allantosis becomes the fetal urachus that connects the fetal bladder to the yolk sac. After birth, the urachus becomes obliterated as the median umbilical ligament.
Conclusion - Allantois
Allantois is a tube-like structure of the yolk sac that helps to remove the nitrogenous waste materials from the embryo. It is the mid-layer of the placenta and the blood vessels that originate from the umbilicus traverse. Allantois is a multifunctional structure that plays a major role during the embryonic development of different species like mammals, birds, and reptiles. The primary function of the allantois is waste management. It serves as the temporary storage organ that stores the waste materials produced by the embryo. Allantois also works as a respiratory exchange medium. It helps to maintain the fluid balance within the embryo. Allantois contributes to the overall development of the embryo also.
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