TYPES OF ANIMAL DIGESTIVE SYSTEMS
Read the text to find out about a) the types of the digestive system and their characteristic features. Complete the table below.
Digestion is the process of breaking down feed into simple substances that can be absorbed by the body. Absorption is the process of taking the digested parts of the feed into the bloodstream.
The digestive system consists of the parts of the body involved in chewing and digesting feed. This system also moves the digested feed through the animal’s body and absorbs the products of digestion. Different species of animals are better able to digest certain types of feeds than others. This difference occurs because of the various types of digestive systems found in animals. There are four basic types of digestive systems: monogastric, avian, ruminant, and pseudo-ruminant.
A monogastric digestive system has one simple stomach. The stomach secretes acid, resulting in a low pH1. The low pH destroys most bacteria and begins to break down the feed materials. Animals with this type of digestive system are better adapted to eat rations high in concentrates. Concentrates are highly digestible feedstuffs that are high in energy and low in fiber. Examples of monogastric animals are hogs, cats, dogs, and humans.
The avian digestive system is found in poultry. This system differs greatly from any other type. Since poultry do not have teeth, there is no chewing. Poultry break their feed into pieces small enough to swallow by pecking with their beaks or scratching with their feet. Feed enters the mouth, travels to the esophagus, and empties directly into the crop. The crop is where the food is stored and soaked. Food then moves from the crop to the proventriculus. The proventriculus is the stomach in a bird, where gastric enzymes and hydrochloric acid are secreted. From the proventriculus, the food makes its way to the gizzard. The gizzard is a very muscular organ, which normally contains grit or stones that function like teeth to grind the food. The food then moves from the gizzard to the small intestine and then to the large intestine. The nondigestible food components then travel into the cloaca. Uriс acid is also emptied into the cloaca. The material is then passed out of the body through the vent. Digestion in the avian system is very rapid.
Fig.1
The ruminant digestive system is found in cattle, sheep, goats, and deer. Ruminant animals eat feed rations that are high in roughages and low in concentrates. Ruminants are different from monogastric animals in that they swallow their food in large quantities with little chewing. Later they will ruminate, or belch up the feed, chew, and swallow it again. The ruminant digestive system has a large stomach divided into four compartments - the rumen, the reticulum, the omasum, and the abomasum.
Rumen. The first and largest section of the stomach is the rumen. In the rumen, solid feed is mixed and partially broken down. The rumen contains millions of bacteria and other microbes that promote fermentation, which breaks down roughages. The rumen also contains microorganisms that synthesize amino acids and B-complex vitamins. Amino acids are the building blocks of proteins and are essential for the growth and maintenance of cells.
Reticulum. The reticulum is the second segment of the stomach. The reticulum is a small pouch on the side of the rumen that traps foreign materials, such as wire, nails, and so forth. Since ruminants do not chew their food before swallowing, they can occasionally swallow foreign objects.
 |
Omasum. The omasum is the third compartment of the stomach. The omasum produces a grinding action on the feed and removes some of the water from the feed. Hydrochloric acid and digestive enzymes are mixed with feed in the omasum.
Abomasum. The abomasum is the fourth compartment of the stomach. The abomasum is also referred to as the true stomach because it is similar to the stomach in monogastric animals.
Fig.2
A pseudo-ruminant is an animal that eats large amounts of roughage but does not have a stomach with several compartments. The digestive system does some of the same functions as those of ruminants. For example, in the horse, the cecum ferments forages. An animal with a pseudo-ruminant digestive system can utilize large amounts of roughages because of the greatly enlarged cecum and large intestine, which provide areas for microbial digestion of fiber. Pseudo-ruminants often eat forages as well as grains and other concentrated feeds. Besides horses, examples of pseudo-ruminants are rabbits, guinea pigs, and hamsters.
Notes
1. Low pH- низкий уровень кислотности 