A digestive system has 3 main processes that occur:
· Secretion: Delivery of enzymes, mucus, ions and the like into the lumen, and hormones into blood.
· Absorption: Transport of water, ions and nutrients from the lumen, across the epithelium and into blood.
· Motility: Contractions of smooth muscle in the wall of the tube that crush mix and propel its contents.
3 different digestive systems of animals have different diets, for example herbivores, carnivores and nectar feeders.
Herbivores – animals that eat vegetation. They are able to digest and use as food the cellulose that forms the cell walls of all plants
Carnivores – animals that eat herbivores. The carnivore’s digestion is unable break down vegetable cell walls
Nectar feeders – animals that eat nectar.
Characteristics commonly associated with carnivores include organs for capturing and disarticulating prey e.g. teeth and claws. They are also commonly referred to as predators, though some carnivores are scavengers. Carnivores have comparatively short digestive systems, as they are not required to break down tough cellulose found in plants.
Digestive System of a Bird, which is the prime example of a Nectar Eater. A bird’s bill consists of a bony framework covered by a tough layer of keratin. The keratin layer is continuously replaced throughout the life of a bird & is just as continuously worn down by eating and manipulating hard objects. The cutting edges of the beak are the Tomia. The bill plays a critical role in food acquisition &, of course as with any form of evolution, it varies with each species. Each species of bird has eating habits, which have evolved over millions of years, and although its diet at any one time may reflect the availability of food, in general there are an amazing variety of diets, ranging the full gamut from herbivorous, through omnivorous, to carnivorous.
The main difference between the digestive systems of herbivores and Carnivores is that carnivores have one stomach, where as many herbivores like sheep, goats and cows have 3 or 4 stomaches where the food has to be regurgitated and chewed again, then re-swallowed where it enters into another stomach to be digested. Although many animals share a similar anatomy and physiology, there are differences to be found. These differences become particularly apparent when you compare a carnivore like a dog with an herbivore like a goat or a horse. Goats and horses evolved from ancestors that subsisted on plants and adapted parts of their digestive tracts into massive fermentation vats, which enabled them to efficiently utilize cellulose, the major carbohydrate of plants.
In contrast, dogs evolved from animals that lived on the carcasses of other animals, and have digestive systems that reflect this history – extremely small fermentation vats and essentially no ability to utilize cellulose. Bridging the gap between carnivores and herbivores are omnivores like humans and pigs, whose digestive tracts attest to a historical diet that included both plants and animals.