Essay on the Gastrointestinal Tract (GIT)

Introduction

The gastrointestinal tract (GIT) is an organ that is found in human beings and other animals, and it is used to intake food and digest it so as to absorb energy and nutrients. Afterward, it usually expels out the remaining wastage from the body through fecal matter. The main functions of the gastrointestinal tract are usually to digest food and excrete the remaining wastage. The gastrointestinal tract and system are made up of various individual components such as the oral cavity, gut tube, mesenteries, foregut (it includes different parts such as the stomach, duodenum, the liver, and the pancreas), the midgut, and the hindgut. This paper will discuss how the various components of the gastrointestinal tract are formed and their different uses during the digestive process.

Main body

The gastrointestinal tract (GIT) or simply the digestive system is formed during the gastrulation process from the endoderm of the trilaminar embryo. This process occurs during the third week, and it usually extends to the cloacal membrane from the buccopharyngeal membrane where it is first formed. Other organs found in the GIT, including the tract, are formed later from the germ cell layers. Three different regions are distinct in the GIT, and they begin their formation during the fourth week. These regions are foregut, midgut, and hindgut (Davis et al., 2017). After the formation of the mouth (oral cavity), the next part of developing is usually the foregut. This part is comprised of the pharynx, the esophagus, and the trachea, which is usually situated behind the heart. The respiratory tract is usually formed by the ventral bud, which is usually found during this stage of development.

The mesenteries are usually a double layer that is used to enclose organs and connect them to the body wall. They are made of the peritoneum, and these organs which are enclosed are usually known as the intraperitonealorgans, whereas the organs which lie on the posterior body wall are known as the retroperitonealorgan (Davis et al., 2017). The gut tube, which is usually in contact with the posterior abdominal wall, is usually suspended by the dorsal mesentery. Further down in the stomach, the dorsal mesentery usually forms the dorsal mesogastrium in the ileum; it forms the mesenteryproper, and lastly, in the colon, it is the dorsalmesocolon. There is a margin that is free from the falciform ligament, and it is used to serve as a medium for the umbilical vein. It then becomes cut after the birth of the child, and it then makes the ligaments of the liver, which are round. The hepatoduodenal ligament then forms the portal triad, which is used to serve the bile duct, and the hepatic artery.

The foregut is also very important in the GIT as it forms different parts of the tract such as the pharynx, the lower respiratory system, the liver, part of the duodenum, the esophagus, and the pancreas. Most of the parts of the foregut apart from the pharynx and the lower respiratory system are usually served by the celiac artery (trunk). The esophagus is formed during the third week of gestation. It is usually short and small at first, but due to the growth and relocation of the heart and the lungs, it is usually elongated (“2010 Lecture 10 – Embryology”, 2011). The stomach starts appearing during the fourth week of the gestation period, and it is usually a fusiform-shaped dilation of the distal foregut. The stomach rotates in the longitudinal axis and the anteroposterior axis, and this alters the positioning of the mesenteries.

On the other hand, the duodenum does not completely form from the foregut, but it is also formed from the cranial part of the midgut. The duodenum is affected if the stomach turns, and this makes it also to rotate and become pressed against the posterior abdominal wall. Due to its duality of origin, the duodenum is usually supplied by branches that usually originate from the celiac trunk and the superior mesenteric artery.

The liver and the biliary apparatus also begin to develop during the fourth week of the gestation period. It usually starts with the appearance of the hepatic diverticulum, which grows from the ventral wall of the distal foregut (“2009 Lecture 9 – Embryology”, 2010). The bile duct is formed from the stalk which connects the diverticulum and the foregut. However, the gallbladder, together with cystic duct, is formed as a ventral outgrowth from the bile duct. As the liver grows, it usually occupies a big portion of the upper abdominal cavity, and its development is usually determined by the oxygenated blood, which flows from the umbilical cord. The liver goes through cellular proliferation, and it is faster on one side, thus making it have a large right and a significantly smaller left lobe. The development of a liver that is functional depends on the foregut and the septum transversum since hematopoietic cells, and connective tissue cells are derived from it. The pancreas is formed when the dorsal pancreatic bud and the ventral pancreatic bud join.

The midgut gives rise to various parts such as the ileum, cecum, and part of the duodenum. These parts are supplied by the superior mesenteric artery. The midgut undergoes a rapid elongation during the fifth week of the gestation period, and it leads to the formation of the primary intestinal loop. The cranial limb develops into the inferior half of the duodenum and proximal half of the ileum. By the sixth week of gestation, the jejunum and ileum continue to lengthen. The growth continues, and by the eleventh week, the intestines have completely retracted into the abdomen. The hindgut is usually comprised of the transverse, descending, and sigmoid colon. The derivatives of this gut are usually supplied by the inferior mesenteric artery. During the seventh week of the gestation period, the urorectal septum develops between the hindgut and the allantois (“2009 Lecture 9 – Embryology”, 2010). The urogenital sinus is usually the part that develops into the bladder, some parts of the urethra, and the phallus. On the other hand, the anorectal canal usually develops into the anal canal and the rectum.

Summary

The gastrointestinal tract is usually vital in the body as it is the main interface between the ingestion of food and converting it into usable energy. It usually ensures that there is transportation, digestion, and the absorption of food within the body. These roles are critical in ensuring that one has good health due to the availability of calories. The gastrointestinal tract is usually comprised of different parts that play different roles. These parts develop during the gestation period, and they determine whether the baby will be healthy or not.

References

2009 Lecture 9 – Embryology. Embryology.med.unsw.edu.au. (2010). Retrieved 7 April 2020, from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_9.

2010 Lecture 10 – Embryology. Embryology.med.unsw.edu.au. (2011). Retrieved 7 April 2020, from https://embryology.med.unsw.edu.au/embryology/index.php/2010_Lecture_10.

Davis A, Amin NM, Johnson C, Bagley K, Ghashghaei HT & Nascone-Yoder N. (2017). Stomach curvature is generated by left-right asymmetric gut morphogenesis. Development, 144, 1477-1483. PMID: 28242610; DOI.