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MidgutEdit

Midgut refers to the middle portion of the digestive tract, bridging the foregut and hindgut in embryology and forming most of the small intestine along with a significant portion of the large intestine. In humans, it extends from the distal half of the second part of the duodenum to the proximal two-thirds of the transverse colon, and it includes the jejunum, ileum, cecum, appendix, ascending colon, and the first part of the transverse colon. The midgut’s long development, mobility within the abdomen, and close association with the mesentery and its blood supply make it central to digestion, nutrient absorption, and immune surveillance, as well as to several congenital and acute surgical conditions.

Anatomy

  • Regions derived from the midgut
    • Distal part of the duodenum through the proximal two-thirds of the transverse colon, via the small intestine segments of the jejunum and ileum, and the large intestine segments up to the proximal transverse colon.
    • The cecum, appendix, and ascending colon are midgut derivatives, as are the proximal portions of the transverse colon. See duodenum, jejunum, ileum, cecum, appendix, ascending colon, and transverse colon for related anatomy.
  • Blood supply and innervation
    • The midgut is vascularized by the superior mesenteric artery, with venous drainage into the portal vein via the corresponding mesenteric veins. Nerve supply comes from the autonomic nervous system, with parasympathetic input mainly from the vagus nerve and sympathetic input through the thoracic splanchnic nerves to the mesenteric ganglia. The enteric nervous system coordinates peristalsis and local reflexes within the midgut.
  • Lymphatics and immune components
    • Lymphatic drainage routes accompany the venous system toward the mesenteric lymph nodes, and the midgut contains substantial gut-associated lymphoid tissue, including Peyer's patches in the ileum, which participate in immune surveillance of luminal antigens.

Embryology

  • Formation and rotation
    • During early development, the midgut elongates and temporarily herniates into the umbilical cord (physiologic herniation) due to rapid growth. The midgut then undergoes a characteristic rotation around the axis of the superior mesenteric artery, with a total of about 270 degrees of counterclockwise rotation as it returns to the abdominal cavity. The return and fixation of the intestinal loops occur as the abdomen enlarges and the mesenteries fuse to the posterior abdominal wall.

  • Final arrangement

    • After completion of rotation and fixation, the duodenojejunal junction lies to the left of the midline, with the cecum positioned in the right lower quadrant and the transverse colon extending across the abdomen. See discussions of foregut and hindgut boundaries for context on how the midgut ends and the neighboring regions begin.

  • Common anomalies and controversies

    • Malrotation refers to abnormal intestinal rotation or fixation, which can predispose to volvulus (twisting) and obstruction and often requires surgical intervention such as a Ladd's procedure. See malrotation and volvulus for more.
    • Nonrotation and related variants describe alternative outcomes of the rotational process and carry different risks of obstruction or internal herniation.
    • Meckel's diverticulum is a remnant of the vitelline (omphalomesenteric) duct, typically located in the ileum; it is a midgut-derived anomaly that can be asymptomatic or cause bleeding or inflammation. See Meckel's diverticulum for details.

Clinical significance

  • Congenital and developmental issues
    • The long embryologic journey of the midgut makes it susceptible to anomalies in rotation, fixation, and recanalization. Malrotation and Meckel's diverticulum are among the most discussed midgut-related conditions in pediatrics and surgery, while other atresias or stenoses may arise from interrupted development of the intestinal lumen.
  • Acute and chronic conditions
    • Midgut volvulus, arising from malrotation or unusual mobility of midgut loops, is a surgical emergency due to risk of ischemia. Prompt imaging and operative management are critical. See volvulus.
    • Meckel's diverticulum can present with painless lower gastrointestinal bleeding, intestinal obstruction, or inflammation that mimics appendicitis; diagnosis and treatment often involve surgical resection. See Meckel's diverticulum and appendicitis for related discussions.
    • Appendectomy, due to the appendix’s midgut origin, remains a common abdominal operation, and imaging or clinical assessment may consider the appendix as part of a differential diagnosis in right lower quadrant pain. See appendix and appendicitis.
    • Other midgut-related conditions include intestinal atresias or stenoses in newborns, which reflect disrupted midgut development and may require early surgical correction.
  • Adult physiology and health
    • In adults, the midgut continues to function in digestion and absorption, particularly in the jejunum and ileum, where most nutrient absorption and bile acid recycling occur. The ileum’s immune features (Peyer’s patches) contribute to mucosal defense and tolerance to luminal antigens.

See also