Cecum in the context of Peritoneum

Gut microbiota, gut microbiome, or gut flora are the microorganisms, including bacteria, archaea, fungi, and viruses, that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut microbiota. The gut is the main location of the human microbiome. The gut microbiota has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the gut–brain axis.

The microbial composition of the gut microbiota varies across regions of the digestive tract. The colon contains the highest microbial density of any human-associated microbial community studied so far, representing between 300 and 1000 different species. Bacteria are the largest and to date, best studied component and 99% of gut bacteria come from about 30 or 40 species. About 55% of the dry mass of feces is bacteria. Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities. It is estimated that the human gut microbiota has around a hundred times as many genes as there are in the human genome.

The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation. The colon (progressing from the ascending colon to the transverse, the descending and finally the sigmoid colon) is the longest portion of the large intestine, and the terms "large intestine" and "colon" are often used interchangeably, but most sources define the large intestine as the combination of the cecum, colon, rectum, and anal canal. Some other sources exclude the anal canal.

In humans, the large intestine begins in the right iliac region of the pelvis, just at or below the waist, where it is joined to the end of the small intestine at the cecum, via the ileocecal valve. It then continues as the colon ascending the abdomen, across the width of the abdominal cavity as the transverse colon, and then descending to the rectum and its endpoint at the anal canal. Overall, in humans, the large intestine is about 1.5 metres (5 ft) long, which is about one-fifth of the whole length of the human gastrointestinal tract.

Eulipotyphla (/ˌjuːlɪpoʊˈtɪflə/, from eu- + Lipotyphla, meaning truly lacking blind gut; sometimes called true insectivores) is an order of mammals comprising the families Erinaceidae (hedgehogs and gymnures), Solenodontidae (solenodons), Talpidae (moles, shrew-like moles and desmans), and Soricidae (true shrews).

Cecotropes (also caecotropes, cecotrophs, caecotrophs, cecal pellets, soft feces, or night feces) are a nutrient-filled package created in the gastrointestinal (GI) tract that is expelled and eaten by many animals (such as rabbits, guinea pigs, mice, hamsters, and chinchillas) to obtain more nutrients out of their food. When food passes through the GI tract the first time, the stomach and the small intestine digest the food material, which then moves into the colon, where the food particles are sorted by size. The smaller particles of fiber are moved into the cecum where they are fermented by microbes. This creates useable nutrients which are stored and expelled in cecotropes. The nutrients from the cecotropes are absorbed in the small intestine. The nutrients gained from cecotrophy include short-chain fatty acids, vitamin B, sodium, potassium, amino acids, and protein.

Lagomorphs (a grouping including rabbits, hares, and pikas) are perhaps the most well-known for producing and eating cecotropes, but other monogastric fermenters, such as rodents, also produce cecotropes. Rodents including beavers, guinea pigs, mice, hamsters, and chinchillas are known cecotrophs. Other animals also eat cecotropes, such as the common ringtail possum and the coppery ringtail possum.

The ileum (/ˈɪliəm/) is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum. Its main function is to absorb vitamin B₁₂, bile salts, and whatever products of digestion that were not absorbed by the jejunum.

The ileum follows the duodenum and jejunum and is separated from the cecum by the ileocecal valve (ICV). In humans, the ileum is about 2–4 m long, and the pH is usually between 7 and 8 (neutral or slightly basic).

In the anatomy of humans and homologous primates, the ascending colon is the part of the colon located between the cecum and the transverse colon.

Megacolon is an abnormal dilation of the colon (also called the large intestine). This leads to hypertrophy of the colon. The dilation is often accompanied by a paralysis of the peristaltic movements of the bowel. In more extreme cases, the feces consolidate into hard masses inside the colon, called fecalomas (literally, fecal tumor), which can require surgery to be removed.

A human colon is considered abnormally enlarged if it has a diameter greater than 12 cm (4.7 in) in the cecum (it is usually less than 9 cm [3.5 in]), greater than 6.5 cm (2.6 in) in the rectosigmoid region and greater than 8 cm (3.1 in) for the ascending colon. The transverse colon is usually less than 6 cm (2.4 in) in diameter.

Hindgut fermentation is a digestive process seen in monogastric herbivores (animals with a simple, single-chambered stomach). Cellulose is digested with the aid of symbiotic microbes including bacteria, archaea, and eukaryotes. The microbial fermentation occurs in the digestive organs that follow the small intestine: the cecum and large intestine. Examples of hindgut fermenters include proboscideans and large odd-toed ungulates such as horses and rhinos, as well as small animals such as rodents, rabbits and koalas.

In contrast, foregut fermentation is the form of cellulose digestion seen in ruminants such as cattle which have a four-chambered stomach, as well as in sloths, macropodids, some monkeys, and one bird, the hoatzin.

Lipotyphla is an obsolete order of mammals, meaning lacking blind gut, including the members of the order Eulipotyphla (i.e. the solenodons, family Solenodontidae; hedgehogs and gymnures, family Erinaceidae; desmans, moles, and shrew-like moles, family Talpidae; and true shrews, family Soricidae) as well as three other families of the former order Insectivora, Chrysochloridae (golden moles), Tenrecidae (tenrecs), and Potamogalidae (otter shrews). However, molecular studies found the golden moles, tenrecs, and otter shrews to be unrelated to the others (these afrothere groups were then put in their own order, Afrosoricida). This made Lipotyphla an invalid polyphyletic order and gave rise to the notion of Eulipotyphla instead, an exclusively laurasiathere grouping.

The appendix (pl.: appendices or appendixes; also vermiform appendix; cecal (or caecal, cæcal) appendix; vermix; or vermiform process) is a finger-like, blind-ended tube connected to the cecum.

The cecum is a pouch-like structure of the large intestine, located at the junction of the small and the large intestines. The term "vermiform" comes from Latin and means "worm-shaped". In the early 2000s the appendix was reassessed and is no longer considered a vestigial organ. The appendix may serve as a reservoir for beneficial gut bacteria.