In anatomy, the mesentery (plural: mesenteries ) is a fold of the coelom wall ( mesoderm ) in which the intestine is suspended in most animals ( coelomata ) . Mesenteries, also called sarco septa , are the partitions inside polyps that divide the gastric space . There are four mesenteries in each of the polyps of the Scyphozoa . Among the flower animals (Anthozoa) there are eight mesenteries in the Octocorallia and six or a multiple of six in the Hexacorallia .
Mesentery in humans and mammals
In humans and other mammals, the mesentery, also called mesentery , in the broader sense denotes all peritoneal duplicates (folds of the peritoneum ) on the small and large intestines. In this case, the coelom wall is the peritoneum. In the narrower sense, the term mesentery only refers to the mesentery of the jejunum and ileum . Three major mesenteries can be distinguished in the human small and large intestine:
- Mesentery in the narrower sense, also called the meso ,
- Mesocolon transversum ,
- Mesocolon sigmoideum , also called the mesosigmoideum .
Smaller mesenteries can be found on the appendix of the appendix ( mesoappendix ) and on the cranial (upper) section of the rectum ( mesorectum ).
In the quadruped mammals, however, far more sections of the intestinal canal are intraperitoneally. In the Nomina Anatomica Veterinaria , the veterinary anatomical nomenclature, a distinction is made between:
- Mesentery with radix mesenterii ( mesenteric root), mesojejunum and mesoileum
- Mesocolon with mesocolon ascendens , mesocolon transversum , mesocolon descendens and mesocolon sigmoideum
Mesenteries in Embryology
In the area of the caudal foregut
Basically, all organs of the abdomen and pelvis have a dorsal mesentery. However, the stomach and pars superior of the duodenum (section of the small intestine) have an additional, ventral mesentery, the mesogastricum ventral and the mesoduodenum ventral . Oxygen-rich blood passes through this mesentery via the umbilical vein to the liver and the inferior vena cava of the embryo. In addition, because of this mesentery, the abdominal cavity is divided into two in the area of the stomach and duodenum.
From the epithelium of the duodenum, some organs eventually develop into the mesenteries of the duodenum and stomach:
- the liver and the biliary tract in the mesoduodenum ventral to the mesogastricum ventral
- the ventral pancreatic anlage in the mesoduodenum ventral
- the dorsal pancreas anlage in the mesoduodenum dorsale
The spleen, on the other hand, develops in the 5th week of development from the mesenchyme of the retroperitoneal space and migrates into the dorsal mesogastrium . Due to the rapid growth of the liver and spleen in the embryonic organism Mesogastricum ventral and dorsal then additionally at the level of the liver in a Mesohepaticum ventral and Mesohepaticum dorsal and at the level of the spleen in a ventral Mesosplenicum and Mesosplenicum dorsal divided.
In the midgut area
In this area of the intestinal tube, the rotation of the umbilical loop is of primary importance. The intestinal tube grows strongly and finally reaches the umbilical coelom, so that it forms a loop, the umbilical loop. This loop - initially sagittal , i.e. vertical - is now rotated by 90 ° so that the upper part on the right and the lower part on the left come to rest. The loop is now set horizontally. This rotation of the umbilical loop takes place in the yolk sac; this is also known as the physiological umbilical hernia .
Since the cranial part of the intestinal tube grows significantly faster than the caudal one, the umbilical loop initially forms a few loops in the umbilical coelom and then expands further into the yolk sac because there is no longer any space within the amniotic cavity.
She now continues to rotate the umbilical loop on its own axis. The former lower part of the intestinal tube is now further cranial than the former upper part. The intestinal loops are now shifted back into the embryo, where they are then located in the left half of the abdominal cavity - framed by the transverse and descending colon. If the relocation of the relocated intestinal loops does not take place or only partially, one speaks of an omphalocele . Finally, the caecum grows downwards and an ascending colon is formed, so that the total rotation of the umbilical loop from the original position is 270 °.
It is of crucial importance for the mesenteries that the ascending and descending colon are pushed backwards due to the strong growth of the ileum and jejunum, that their mesenteries grow together with the parietal peritoneum and that they become retroperitonealized. The transverse colon, on the other hand, lies in front of the loops of the small intestine and retains its mesentery, the transverse mesocolon . The ileum and jejunum also retain their mesenteries, which are also called mesos for short .
- Mesenteric filaments in cnidarians
- Michael Schünke , Erik Schulte , Udo Schumacher : Prometheus - learning atlas of anatomy. Internal organs . 4th edition. Thieme, Stuttgart, New York 2015, ISBN 978-3-13-139534-4 , pp. 42, 43, 366, 367 .
- Calvin Coffy, Peter O'Leary: The mesentery: structure, function, and role in disease , The Lancet: Gastroenterology & Hepatology, Volume 1, 2016, pp. 238-247.
- Nomina Anatomica Veterinaria , 4th Edition, 1994, p. 57.