The importance of digestion and metabolism for living organisms is difficult to overestimate. After all, existence without it is simply impossible. In this article, we will consider in detail the essence of these processes, the features of the structure and the types of digestive systems in various groups of animals.
What is the metabolism?
Nutrition is one of the main signs of all living things along with breathing, movement, reproduction and adaptability. Functions of the digestive system, in the first place, consist of metabolism. They enter the body, are transformed, and then are derived from it. This function is performed not only by the digestive system. For example, due to the activity of the respiratory organs, oxygen enters the body cells and carbon dioxide is released.
Functions of the digestive system
In the digestive system, proteins, carbohydrates, lipids, mineral salts, water and vitamins that make up various products are exposed to mechanical and chemical effects. This is because the body is not able to assimilate them in an unchanged form. Therefore, all substances in the digestive tract are split into smaller ones, absorbed into the blood and digested. As a result, the body receives the energy necessary to carry out all life processes.
Is life possible without digestive system?
At first glance, such a question may seem rather strange. But there are animals that do not need to break down nutrients. They get them ready. This is primarily parasitic worms. They live in the intestinal ducts of animals and humans. For example, a representative of the class Tape worms - bovine tapeworm, absorbs nutrients through integuments. In doing so, it causes significant harm to the host's organism, poisoning it with the products of excretion.
Types of the structure of the digestive system
The structure of the digestive system can be of several types. It depends on the way you eat. Most animals have an end-to-end digestive system. It is represented by a tube of different lengths opening at both ends. Thus, in mammals it is represented by the oral cavity, pharynx, esophagus, stomach, intestine and anal opening, through which undigested food remains. Blindly closed digestive system has all representatives of the type of the intestinal. How is it arranged?
The closed digestive system
The scheme of the digestive system of a closed type is simpler. It is a mouth opening and an intestinal cavity. Undigested remains of food at the same time go out through the mouth. The blindly closed digestive system has hydra, jellyfish and polyps. They lead a different lifestyle. But the structure of this system of organs is associated with the method of nutrition. All of them are predators. Hunt them help the tentacles, on which there are special stinging cells. They consist of a capsule and a sharp twisted thread, which ends with a sharp needle. A sensitive hair is located on the surface of such cells. When he touches the body of the victim, the stinging thread reflexively with force, and digs into the prey's body, paralyzing it. If you ever felt the jellyfish burns, then it's easy for you to imagine the action of these formations. Getting food, stinging strings immediately perish and can no longer perform their functions. And new ones are formed with the help of another type of cells - educational ones.
Type of the Gehlidococcal
All members of this systematic unit of animals have an intestinal cavity. With this feature of the structure, their name is associated. Blindly closed digestive system is primarily freshwater hydra. They lead an attached way of life. Their sole is statically located on the substrate, and on the opposite side of the body is a mouth opening. It is surrounded by tentacles, which serve to catch prey. These are small crustaceans, insect larvae, small fish. Having appeared with the help of tentacles inside the intestinal cavity, the food is exposed to the action of enzymes, which are produced by specialized glandular cells. Under the influence of these biological catalysts, it breaks up into small pieces. Further, the process continues in the digestive cells of the inner wall of the body of the hydra, which have pseudopods. Digestion is completed in special vacuoles. And the remains of substances are released outward through the mouth opening. In a similar way, this happens in jellyfish and in polyps that have a closed digestive system.
A blindly closed digestive system is also found in all representatives of the type of Flatworms. It is represented by the anterior and middle intestines, which ends blindly. Both for absorption, and for allocation of food the oral aperture serves. Despite the fact that flat worms deserve the glory of the most dangerous parasites of humans and animals, free-living species are also found among them. These include marine and freshwater planaria. In the aquatic environment, they hunt hydra, small crustaceans, mollusks and insect larvae. And they capture prey in an unusual way. Planariae crawl on the body of the victim, protrude the proboscis through the mouth opening and with its help suck all the contents from the victim. This is possible due to another unusual feature of the structure. The point is that the mouth opening of free-living flatworms is located on their abdominal cavity.
So, the structure of the digestive system primarily depends on the way animals are fed. Both coelenterates and flatworms that live in salt and fresh water are predators. Their digestive system is blindly closed and is a cavity or tube with a single specialized hole through which food enters and is released after conversion.