Hindgut

Hindgut is the posterior portion of the digestive tract in many animals. In vertebrates, it refers to the portion of the gut tube that follows the midgut during embryological development and gives rise to parts of the large intestine and the upper anal canal. In insects and other invertebrates, the hindgut is the corresponding posterior section of the alimentary canal and often participates in water reabsorption and waste concentration, sometimes receiving Malpighian tubules.

In humans, the hindgut derivatives include the distal one-third of the transverse colon, the descending colon, the sigmoid colon, the rectum, and the upper portion of the anal canal up to the pectinate line. The area below the pectinate line is ectoderm-derived and not hindgut-derived. The hindgut is supplied by the inferior mesenteric artery; venous drainage is via the inferior mesenteric vein; lymphatics drain to the inferior mesenteric nodes. Parasympathetic innervation is via the pelvic splanchnic nerves (S2–S4); sympathetic innervation comes from periarterial and pelvic plexuses.

Functionally, the hindgut is involved in water and electrolyte reabsorption and the formation of solid waste in many species; in herbivores it can participate in fermentation processes in the colon. In humans, most microbial fermentation occurs in the large intestine, with the hindgut contributing to stool formation and content processing.

Developmentally, the hindgut arises from the caudal end of the endodermal gut tube and ends at the pectinate line in the anal canal, where the ectoderm-derived proctodeum begins. The cloaca is partitioned to form the anorectal structures.