Incomplete Digestive System of Animals

The digestive system can take two forms: a complete digestive system or a complete digestive system. incomplete Digestive System, just as the digestion process itself can be differentiated into being intracellular or extracellular, these types of systems and digestion will be explained in depth in this entry.

digestive system of animals

Unlike humans in the animal kingdom there are two types of digestive systems that can be observed when studying various species, however, like people, they need both energy and food to develop, stay alive and reproduce. By eating these foods, they help their bodies to form new tissue or repair tissue that has been damaged by a fight with a predator or another member of their species.

At the same time, these foods give them the energy to move, run, travel long distances when they are looking for a shelter, they are one of the animals that migrate or they are simply looking for food, knowing that most of the daily activity of animals is focused on obtaining food through exploration, hunting, stalking prey, capturing it and then eating it.

Their digestive system is responsible for processing these foods to give them the nutrients, vitamins and energy they need, as well as to discard raw materials that are not good for them or that they cannot digest properly. They can do this through the digestive tube, but not all species have a proper digestive tube in their internal structure, that is how their digestive system can be differentiated in two ways that will be explained later.

Now, each of the animals (except sponges) have cells that associate with each other and form tissues, while the latter form the organs so that their system can be structured in a harmonic way just as human beings have a system within of the body. The digestive system of animals It is made up of many tissues of various types and various organs associated with it so that the animal can stay alive.

This digestive system will be different depending on how that species eats, that is, the type of food it consumes and how it lives its day to day life, how it carries out its activities and with what intensity.

Thus, it can be seen how a specimen that does not perform very complex or active activities that require too much energy has a simple or incomplete digestive system, while another animal that does have a lot of movement, is large and needs more energy and nutrients, will have a digestive system. full.

Types of systems and digestion

Depending on how its digestion is done and how an animal has developed its digestive system, its system can be differentiated into: complete or incomplete digestive system with intracellular or extracellular digestion.

• intracellular digestion

In this type of digestion, the food that the animal ingests is broken down into enzymes while it is kept in a digestive vacuole, then it is processed, that is, it is combined with the digestive enzymes, separated into smaller parts and thus processed inside. of the cells for the animal to absorb. However, not all the parts are digestible, so they remain in the vacuole and are then expelled to the outside so that they do not cause internal damage to the animal.

Sponges and amoebas are an example of animals that perform this type of digestion, as well as animals that have an incomplete digestive system, such as porifera. However, intracellular digestion is not only seen in these types of animals, species with more complex digestive systems (such as cnidarians or bivalves) can combine intracellular digestion with extracellular digestion, which will be explained below.

• extracellular digestion

Extracellular digestion can be seen in animals with a complete digestive system and in those with an incomplete digestive system, here, unlike the previous digestion, the processing of food is done outside the cells, specifically in a digestive cavity that is there for that purpose. . This allows the nutrients contained in that food to be absorbed much more easily by the animal, and they can also eat larger pieces.

This type of digestion requires that the system has other components that are responsible for distributing these nutrients throughout the animal's body, which is why it can be seen in animals with a tubular digestive system where nutrients are absorbed in the intestine, then enter the blood and At the same time, the parts that are not digestible or that are simply not used by the body come out through the anus.

We speak of a tubular digestive system because it is the digestive tube that has an entrance hole where the mouth is located, part that is responsible for grinding food and salivating so that everything passes more easily, then there is the pharynx, the esophagus and then the stomach and intestine, responsible for mixing and processing. It also has another hole that is where the anus is, responsible for expelling waste that is not used by the body.

• complete digestive system 

Now, the complete digestive system as indicated above is characteristic of those species that have more dynamic activities, with greater intensity, with a greater demand for nutrients and energy than that of animals that do not have as much mobility and that remain calmer. This system is characterized by having a digestive tube that has a mouth through which food enters and an anus through which non-digestible substances exit.

• incomplete digestive system

The incomplete digestive system is also called the simple digestive system, where two holes are not seen in a digestive tube but these animals have a sac with a single hole, this does not allow them to eat in large quantities or do it constantly or quickly because they only through the only opening they have is that food enters and leaves. Species that have an incomplete digestive system in their body generally carry out intracellular digestion.

dige systemcomplete status

In this section, the complete and incomplete digestive system will be discussed in depth. In this first type of system, the animal has a digestive tube where you can see its mouth and anus, food enters through the first and waste is expelled through the second.

These animals carry out extracellular digestion, where the food that enters them goes through the entire digestive tract and is processed in the mouth and then in the intestine so that the nutrients it contains can be absorbed by the body. The animals of the vertebrate subphylum have this type of system and together with other substances (such as liver secretions) carry out their digestion correctly.

This system is characterized by having specialized parts for each task of the animal's digestion, this allows them to eat in greater quantity and more quickly. Another example of animals with this type of system are the annelids, which are invertebrates such as worms, earthworms, leeches, polychaete marine animals, among others.

The description of their complete digestive system is that they have a mouth through which the food enters, a pharynx where they suck it, the crop where the food is stored, a gizzard where it is ground, the intestine and then the anus. Unlike them, arthropods have a different mouth depending on their type of food, some have trunks, others have jaws, appendages or beaks, which are one of the bird characteristics.

Not all systems are really the same, they just have similar characteristics that allow them to be classified in one way or another. Birds do not have an esophagus and a stomach but instead have a crop and gizzard like annelids, mammals that have their stomachs divided into cavities (like ruminants that have four).

Mollusks, for example, have a mouth with a radula where they scrape food and gnaw it, then there are the organs in charge of the rest of the food processing: their esophagus, their stomach, their intestine and finally their anus where they expel the waste. Within the classification of "molluscs" are the bivalves, they have a different digestive system.

Animals with a complete digestive system

Among the species that have a complete digestive system are:

• The molluscs: Most molluscs have an incomplete digestive system, except for bibalves. They are characterized by the radula found in their mouths with which they scrape the food they eat.

Their digestive system is complete because they have a digestive tube that starts with their oral cavity (with the radula), then they have an esophagus, a stomach, they have digestive glands that allow food to move into the large intestine, then the rectum, and finally year.

• the annelids: As mentioned above, they have a complete digestive system that is characterized by a mouth, a crop to store food, a gizzard to grind it and the anus through which particles that are not useful to their body are expelled.
• The vertebrates: A large majority of vertebrates with this type of system have a digestive tube that is surrounded by smooth muscle in the form of a layer, which, when contracted, allows food to be pushed towards the anus so that it can be expelled at the end of its journey. All of them have an esophagus, liver, intestine, stomach, gallbladder and this allows them to be grouped in the same scheme.
• The human being: The human digestive system, like the animal, is in charge of converting the food that is ingested by the person into nutrients and energy to maintain the organism, it is more similar to the complete digestive system because it has two openings (mouth and anus) and different organs in charge of each task of digestion: mouth, pharynx, stomach, esophagus, intestine (one large and one small), and an anus.

Where food is moved, secretion takes place, nutrients are absorbed, and then indigestible parts are defecated. In this superior species, the food is also broken down, secreted into digestive or gastric juices, converted into chyme and stored during the processing time to later be expelled.

incomplete digestive system

Now, the incomplete digestive system differs from the complete one because it does not have a digestive tube that has two holes, one through which food enters and another through which matter that cannot be digested is expelled. The incomplete digestive system has instead a sac or a bag that only has a hole or an opening that works as a mouth and as an anus at the same time, that is, food enters through the same place and is expelled after digestion.

Because it is a process where the food needs to be processed and then expelled, the species with this type of system cannot eat constantly or to the same extent as those with a complete digestive system, as they have only one entrance and exit hole. outlet they perform a different digestion.

This type of system, in addition to being called the simple digestive system, is also called the coelenteric digestive system, because one of the animal species that have this system is the coelenterate, the rest of the species will be mentioned below.

Animals with incomplete digestive system

Some of the animals with this type of system are:

• The cnidarians or coelenterates: In this type of animal the food is filtered from the water or captured with the animal's tentacles, they are called cnidocytes and allow the prey to be paralyzed and introduced into an internal gastric cavity where they are decomposed, it is there where digestive enzymes are expelled (even in inside the cavity) that work to break down the food and absorb the nutrients it contains.

An example of coelenterates are the hydras, which have extensive tentacles that allow them to capture prey with paralyzing toxins, by keeping them completely still they ingest them in their gastrovascular cavity, nutrients are acquired and substances that are not absorbed by the animal are expelled through the same hole through which the prey entered the digestive cavity.

Another example of the cnidarians are the jellyfish, they have a bell-shaped body and a mouth inside it, they have tentacles with which, in addition to eating food, they drink water and when they expel it from the same place they are propelled to move around the sea. This type of feeding is carried out by all types of jellyfish, an example is the Lion's mane jellyfish.

Its gastrovascular cavity is characterized because it has a central stomach that contains gastric bags, in addition to channels that are connected to others within the tentacles, this is how when ingesting food the nutrients can be distributed from its cavity to the tentacles, although its body It is mostly made up of water (95%), which is why it is mostly gelatinous.

• The flatworms: In the animals that belong to this phylum, food enters through a mouth that is generally connected to the whole body through channels, they secrete enzymes that work to break down the food and thus acquire its nutrients by absorbing them in your cells. Flatworm parasites are an exception to this type of digestion.

However, tapeworms are an example of animals with an incomplete digestive system where the vast majority are parasites and others are worms. Planarians are also a genus of flatworms that feed in this way. Many animals of this phylum do not have a circulatory or respiratory system, in addition to that they are hemaphrodite.

• The bibalds: Bibalves are animals with an incomplete digestive system within the great phylum of molluscs, they are generally invertebrates, they have a white or naked body and a shell. Although they do not have tentacles, they do have a mouth through which food enters, which is mostly filtered when the tide is high, they are invertebrates and have shells of various sizes, as well as their weight.

An example of activities with less intensity and mobility is what these mollusks do every day, they really do not migrate or travel very long distances because their organs allow them to filter food without having to move, their shells have valves that allow them to filter water so if they move it is usually to bury themselves in the sand when they are in some kind of danger.

Otherwise, they do not carry out activities that require a high amount of nutrients or energy, not even the variations in water temperature or its salinity influence their behavior and force them to move, what does force them is the food and the movement of water, however they usually live in waters with moderate movement where there are no turbulence. So your incomplete digestive system is in accordance with your body and your way of life.

• The porifera: the porifera or the porifera phylum encompasses the sea sponges, which are largely marine and do not have tissues like the other animals of the kingdom. They filter water and food through pores or channels that are connected in their body, they use intracellular digestion explained above but they filter their food in an internal chamber of their body.

So how is your incomplete digestive system? Phagocytosis consists of some cells of the animal surrounding the food particles and introducing them into the cell interior, pseudopods are produced inside that surround the particles, the phagosome is created and together with the lysosomes the food is degraded, that is, in the Inside, hydrolytic enzymes are released that break down the particles that entered.

Then they expel the microorganisms that are not necessary that remained in a vesicle after all the previous process, but they do this by directing these microorganisms out of the cell where they were processed and then they expel them to the outside. Pinocytosis is a process a bit similar to the previous one and both would be a kind of incomplete digestive system.

Sponges are really animals that differ greatly from all of the animal kingdom, in fact their digestion process is carried out before ingesting food, something that is completely contrary to the rest of the species that digest after ingestion.

Sponges do this when they capture their prey, but before eating it they take out a part of what would be their stomach and expel digestive enzymes to pre-digest the food particles, this allows it to be absorbed much easier. In addition to not having tissues, sponges do not have a mouth or digestive system, they actually feed through phagocytosis and pinocytosis.

animal digestion

In general, animals carry out their digestion process by transforming the food they eat into nutrients and energy by breaking them down and absorbing them in this way, these nutrients can come from plants or animals of other species that are captured by the different forms of hunting that they do. each of the species of the animal kingdom.

This type of nutrition or mode of feeding is typical of heterotrophic organisms, that is, they are living beings that cannot produce their own food and instead acquire it from other sources that are generally animal or vegetable matter, they are totally consumers, at three levels: primary, secondary and tertiary.

All animals can be classified as heterotrophs, humans, also fungi, some protists and plants, actually the five kingdoms of living beings have species within them that have heterotrophic nutrition.

The rest can be classified as autotrophs (the other nutritional mechanism of living beings), because they are producers of substances with which they can feed and stay alive, in addition to that sunlight is vital for them to convert carbon dioxide in these compounds.

Heterotrophs can consume autotrophs and even other heterotrophs of the same species, they can also be divided according to the source they use for energy. For example, a heterotroph can use chemical energy and is thus considered a chemoheterotroph (humans fall into this classification, as do fungi). Heterotrophs that do not use chemical energy but rather light are considered photoheterotrophs (some bacteria fall into this classification).

Their digestive structure (incomplete or complete digestive system) is a reflection of the type of food they eat or the diet they have, this is how they can be divided into carnivores that eat meat and have a complete digestive system, herbivores that eat whole plants or only parts of them (or the leaves or the stem of them), the omnivores, which feed on both types of food, plants or animals.

Likewise, differences can be seen in how they ingest their food to their incomplete or complete digestive system, some can do it by filtering food and others do it in another way, such as suspensivores. An example of the former are the bibald molluscs and of the latter are the whales. In either case, the type of digestion can be intracellular, extracellular, or a combination of the two.

Just as their digestive structure conditions their diet, the type of food they need to eat conditions their physical structure. Animals adapt not only to the environment but also to the type of food they consume, in this way it can be seen how some have claws, others have fangs, other beaks, others have organs with which they suck (like insects), others mouths surrounded by tentacles with which they catch their prey, etc.

Something they share is that food is always converted into substances that are digestible through intracellular or extracellular digestion, most of which are absorbed and thus the rest of the animal's body can remain active and develop over time. Those parts of what is ingested that cannot be digested are expelled through the mouth (characteristic of the incomplete digestive system) or through the anus.

The two types of systems that were explained respond to the two models of digestive systems of animals, the first encompasses those beings that have a gastric cavity that is generally located in the center of their body and that communicates with the body through channels. rest of the organs, while through a single cavity it communicates with the outside and this is how it has a mouth and anus function.

The second model encompasses animals that have a digestive tube that communicates with the outside through two holes, openings or holes (the mouth and the anus), this model is characterized by being functionally specialized since it has a set of organs that meet specific tasks of the digestion process, some are in charge of crushing or shredding the food, others of storing it, others of absorbing the nutrients, etc.