Fox digestive system
Photo and Text: Nick Zolkowski and Elizabeth Farrell
The digestive tract breaks down ingested food and absorbs nutrients. The food travels from the mouth, where preliminary digestion begins, through the esophagus, and into the stomach. Here, enzymes digest a majority of the matter. The food then passes through the small and large intestines, where nutrients are absorbed through the intestinal walls. The small intestine is commonly divided into the duodenum, at the stomach end, the jejunum next, and the ileum at the most distal portion. The large intestine consists of the ascending, transverse, descending, and sigmoid colon. At the ileocolic junction is the cecum, which varies greatly in size across mammals and may be used for fermentation and the breakdown of leaves and grasses. Aiding digestion are the liver and the gall bladder. The liver stores emulsifying agents to promote fat absorption, which can be secreted into the duodenum via the common bile duct. The gallbladder is developmentally an outgrowth of the bile duct, and stores liver secretions until they are needed.
Generally, foxes eat high-quality foods, with meat comprising the majority of the diet. As a result, the fox's digestive system differs greatly from that of herbivorous mammals. Relative to other mammals of comparable size, the fox has a large liver. This may aid in the digestion of the large amounts of fat taken in through its faunivorous diet. Although the fox did possess a cecum, the small size relative to the cecums seen in other mammals indicated that it did not play a large role in digestion. In mammals such as rabbits that take in larger quantities of plant materials, the cecum plays a more important role and is typically much larger. We also found the fox to have a much longer small intestine than large intestine, and a relatively short digestive tract overall. Because meat is relatively easily digested, an extensive intestinal tract is not necessary. In comparison, a goat, which eats lower quality foods such as grass, spends a great deal of time digesting plant material, and therefore has a significantly longer intestinal tract.
Initially, we split and removed the diaphragm. After we peeled back the diaphragm and traced the esophagus, we located the liver in the upper right quadrant, and the caudal portion of the stomach more medially. Next, we gently removed the digestive tract and connective tissue from the body wall by cutting the esophagus cranial to its entry into the stomach, and the large intestine cranial to the rectum. To unravel the intestines we had to cut the mesenteries, which contained a lot of fat.
Resting anterior and to the right of the stomach is the liver, with six lobes: right medial, right lateral, left medial, left lateral, quadrate, and caudate. Situated in between the quadrate and right medial lobes of the liver is the gall bladder, which is very small and not easily visible. The surface of the liver is very smooth, and the left lateral lobe is significantly larger than the others. The liver was lifted up in order to get an unobstructed view of the stomach. The stomach was filled with liquid and had a muscular wall, which we slit with scissors. By palpating the interior of the stomach we could feel the pyloric sphincter leading to the small intestine. We then split the wall of the small intestine in the same manner, and found it contained a more concentrated liquid. Attached to the small intestine inferior to the stomach is the pancreas. The pancreas lies cranial to the duodenum and jejunum, with the majority of it lying on the right side of the body. This specimen's pancreas was diffuse, and consisted more of membranous material than glands. It was very easy to tear. Because of its diffuse nature, we were not able to locate the position of the pancreatic ducts. The fox did possess a cecum, which felt like a balloon and marked the transition between the small and large intestines. The small intestines were much longer (about 7 times) than the large intestines. The spleen looked similar to the liver, and was roughly the size of one lobe. It lies in the left cranial quadrant of the abdomen, cranial and lateral to the kidney and inferior to the diaphragm.