Comparative and Evolutionary Aspects of the Digestive System and Its Enteric Nervous System Control

All life forms must gain nutrients from the environment and from single cell organisms to mammals a digestive system is present. Components of the digestive system that are recognized in mammals can be seen in the sea squirt that has had its current form for around 500my. Nevertheless, in mammals, the organ system that is most varied is the digestive system, its architecture being related to the dietary niche of each species. Forms include those of foregut or hindgut fermenters, single or multicompartment stomachs and short or capacious large intestines. Dietary niches include nectarivores, folivores, carnivores, etc. The human is exceptional in that, through food preparation (>80% of human consumption is prepared food in modern societies), humans can utilize a wider range of foods than other species. They are cucinivores, food preparers. In direct descendants of simple organisms, such as sponges, there is no ENS, but as the digestive tract becomes more complex, it requires integrated control of the movement and assimilation of its content. This is achieved by the nervous system, notably the enteric nervous system (ENS) and an array of gut hormones. An ENS is first observed in the phylum cnidaria, exemplified by hydra. But hydra has no collections of neurons that could in any way be regarded as a central nervous system. All animals more complex than hydra have an ENS, but not all have a CNS. In mammals, the ENS is extensive and is necessary for control of movement, enteric secretions and local blood flow, and regulation of the gut immune system. In animals with a CNS, the ENS and CNS have reciprocal connections. From hydra to human, an ENS is essential to life.

Automated summary

All living organisms require nutrients from their environment, and the digestive system plays a crucial role in obtaining these nutrients. Different species have varying digestive systems depending on their dietary niche, such as foregut or hindgut fermenters, and their digestive architecture is tailored to their specific needs. Humans, through food preparation, have a unique ability to utilize a wide range of foods, making them adaptable "cucinivores." As the complexity of the digestive system increases, an integrated control system, including the enteric nervous system (ENS) and gut hormones, becomes crucial for movement and assimilation of content. The ENS is present in animals with more complex digestive systems, but not all animals have a central nervous system (CNS). In mammals, the extensive ENS plays a vital role in controlling movement, secretions, blood flow, and the immune system of the gut. The ENS and CNS in animals with both systems have reciprocal connections. From simple organisms like hydra to humans, the ENS is essential for survival.