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Biology Laboratory Manual, 6/e
Darrell S. Vodopich, Baylor University
Randy Moore, University of Minnesota--Minneapolis

Digestive Systems

The digestive system is the body system which breaks down large food particles into smaller units, which can be used by the body to promote growth, maintenance, and reproduction. The digestive systems of various vertebrate groups, such as mammals, birds, and reptiles, are all quite different. But, even within a single group, such as mammals, we can see a great variation in digestive systems, which are dictated by the type of food the organism eats.

Humans and most predators have a relatively simple digestive system. In the case of predators, this stems from their diet of primarily meat, which is rather easy to digest. In the case of humans, this is due to our lack of a specialize diet. Herbivores, however, usually have specialized structures because the cellulose in plant material is very difficult to digest.

Rats, for instance, are granivores, which means they eat seeds and grains. Two key features to their digestive system are a lack of gall bladders and the presence of a large cecum. The gall bladder is used to store bile, which is used to help break down animal fats. Because rats are strictly herbivores, they do not get much animal fat and the gall bladder is not necessary. The cecum is used as a ‘fermentation chamber’. In the cecum are bacteria that are able to digest the cellulose in the seeds. The food sits in the cecum and essentially rots. The rat is then able to absorb the byproducts of the bacteria’s work.

Cows and other livestock are ruminants, which means they have a multi-chambered stomach. Each of the chambers aids in digestion in some. The first stomach is simply a storage area from which the cow can regurgitate and remasticate. Simply, the cow ‘burps’ up a little bit of the food they have already swallowed and continue chewing it into smaller pieces. Breaking it down even further helps the other chambers do their job in digestion. Another stomach acts as a filter and yet another stomach functions in a way similar to a rat’s cecum.

The digestive system is just an example of how different the body systems of vertebrates can be. The urinary, reproductive, circulatory, and respiratory systems of different groups of vertebrates are all specially adapted for those organism’s mode of living.