Digestion and Digestive systems
The digestive system is the part of the body responsible for acquiring nutrients and expelling wastes. This semester we dissected seven different animals, observing a different digestive system in each animal. As the dissected animals progressed from more primitive to more complex, the digestive systems also increased in complexity. The first animal dissected was the earthworm, which has a fairly basic digestive system. Food is ingested by the earthworm through the mouth, and then it passes through the small buccal cavity and the pharynx. From there, the food moved to the esophagus and then to the crop, where the food is moistened and stored for a short time. After leaving the crop, the food travels to the gizzard, which grinds the food before it enters the intestine. Nutrient absorption takes place in the intestine, and finally wastes are expelled at the anus. The digestive system of the mussel is slightly more complicated than that of the earthworm, due to the addition of the stomach and digestive glands. Food enters the mussel through the mouth, and then travels along a tube to the stomach. In the stomach, enzymes produced by the digestive gland are released to break down digestible material. In addition, the stomac
It is during the dissection of the mussel that we observe the first change in the digestive system. The pig has teeth to break down the food before it enters the esophagus, in addition to saliva that softens the food and begins breaking it down, and a tongue that pushes the food toward the esophagus. The stomach allows for the break down of digestible material. The esophagus then carries the food from the mouth to the stomach, where a valve called the cardiac sphincter separates the esophagus and stomach, keeping digestive enzymes from traveling up the esophagus. The pig's digestive tract is the most complex of all the dissected animals. In the perch, the liver produces bile, which is necessary for the proper digestion of fats, while the pancreas secretes digestive enzymes into the intestine. That is truly the key to improving the efficiency of the organism's digestive system. Wastes are expelled into the large intestine where any water is reabsorbed, and they finally exit the body through the anus. It is also clear to see that each of these changes along the way greatly aid in the efficiency of the digestive system. In the perch, we begin to see organs that aid in this process. The major new development in the perch is the addition of the liver and pancreas. In the crawfish, you see an even more complex digestive system. The starfish also has digestive glands called pyloric caecae that lead to the pyloric stomach and secrete digestive enzymes. The villi of the frog greatly increases nutrient absorption, and the convoluted intestinal tract of the pig allows greater nutrient extraction.
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