The GI tract differs substantially from animal to animal. Some animals have multi-chambered stomachs, time some animals' stomachs contain a single chamber. In a ordinary human adult male, the GI length is nearly 6.5 meters (20 feet) long and consists of the upper and lower GI tracts. The tract may also subsist divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment of the homily.
Embryology

The gut is an endoderm-derived structure. At approximately the 16th day of human development, the embryo begins to fold ventrally (with the undeveloped's ventral superficies congruous concave) in two directions: the sides of the embryo fold in on each other and the head and tail fold towards one another. The result is that a piece of the yolk sac, an endoderm-lined structure in contact with the ventral aspect of the embryo, begins to be pinched over to become the primitive gut. The yolk sac remains connected to the gut tube via the vitelline duct. Usually this structure regresses for the time of development; in cases where it does not, it is known as Meckel's diverticulum.

During fetal life, the primitive gut can be divided into three segments: foregut, midgut, and hindgut. Although these terms are often used in regard to segments of the primitive eviscerate, they are nevertheless used regularly to describe components of the definitive gut as well.

reaped ground segment of the primitive gut gives rise to specific embowel and gut-related structures in the of mature age. Components derived from the narrow pass proper, including the stomach and colon, open as swellings or dilatations of the primitive gut. In contrast, gut-related derivatives-that is, those structures that derive from the primitive gut but are not part of the gut proper-in general develop as outpouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development.

Specialization of organs

Four organs are subject to specialization in the kingdom Animalia.
The first organ is the talk which is only present in the phylum Chordata.
The second organ is the oesophagus. The crop is an enlargement of the oesophagus in birds, insects and other invertebrates that is used to store food temporarily.
The third organ is the put up through. In addition to a glandular stomach (proventriculus), birds have a brawny 'stomach' called the ventriculus or 'third part stomach.' The third stomach is used to mechanically grind up food.
The fourth organ is the large interior. An outpouching of the large intestine called the cecum is present in non-ruminant herbivores such as rabbits. It aids in digestion of plant material so as cellulose

Immune function

The gastrointestinal tract is also a prominent part of the immune system. The low pH (ranging from 1 to 4) of the stomach is fatal for many microorganisms that enter it. Similarly, phlegm (containing IgA antibodies) neutralizes many of these microorganisms. Other factors in the GI tract help with immune function as well, including enzymes in the saliva and bile. Enzymes such as Cyp3A4, along with the antiporter activities, are besides helping in the intestine's role of detoxification of antigens and xenobiotics, such as drugs, involved in first pass metabolism. Health-enhancing intestinal bacteria minister to to prevent the overgrowth of potentially disadvantageous bacteria in the gut. Microorganisms are also kept at bay by the agency of an large immune system comprising the gut-associated lymphoid tissue (GALT).

Histology

The order gastrointestinal tract has a uniform inexact histology with some differences which reflect the specialization in functional anatomy

The mucosae are in a high degree. specialized in each means of the gastrointestinal tract, facing a low pH in the stomach, absorbing a multitude of different substances in the small intestine, and also absorbing specific quantities of water in the large intestine. Reflecting the varying needs of these organs, the pile of the mucosa be possible to consist of invaginations of secretory glands (e.g., gastric pits), or it can be folded in regulate to increase surface area (examples include villi and plicae circulares).