Ferret digestive system
Photos and Text by Catherine Lenox and Victoria Clayton
We began this dissection by making a single cut into the abdominal wall along the linea alba from the caudal end of the sternum to the pubis. Next, we made horizontal cuts through the muscle wall at the edge of the rib cage and at the pubis. We also cut the falciform ligament to reflect the abdominal muscles and expose the abdominal viscera. This ligament attaches to the abdominal muscles at the linea alba and inserts into the liver to divide it into its left and right sides [1].
After reflecting the abdominal muscles, we noticed the greater omentum, a fatty sheet of mesentery attached to the greater curvature of the stomach [1]. The greater omentum loosely drapes over the intestinal tract and separates the intestinal mass from the abdominal wall. We tucked it under the spleen to have better access to the internal organs. The entire abdominal cavity contained a large amount of congealed blood, so we rinsed the cavity under running water to clean it out. After removing the blood from the cavity, we identified each organ. Next we removed the diaphragm, cut the esophagus, cut the large intestine just cranial to the rectum, and removed the entire gastrointestinal tract from the abdominal cavity. We also cut the caudal vena cava to lift out the liver.
We removed the greater omentum by cutting it at its attachment to the stomach. The lobes of the liver were then immediately visible. The cranial surface of the liver is very smooth and follows the contours of the diaphragm. The caudal portion is very irregular and is bordered by the duodenum, stomach, and right kidney. The right section of the liver is slightly larger than the left section. The liver has six lobes. The lobes are called, from left to right, the left lateral lobe, the left medial lobe, the quadrate lobe, the right medial lobe, and just deep to the right medial lobe is the right lateral lobe. The final lobe is the caudate lobe, which is very irregular in shape and is caudal to the right lobes.
In this specimen, the lobes were dark grey with white spots. These spots were small white plaques or blister-like growths that were not present on any of the other mammals in lab, suggesting that the ferret may have had some sort of unidentifiable liver pathology. We could scrape these plaques off the liver with a scalpel blade but the tissue lying directly deep to the growths remained discolored. We identified the gallbladder, which is underneath the right medial lobe and quadrate lobe of the liver and just superficial to the right lateral lobe. This small pear-shaped sac holds bile produced by the liver. We did not remove the gallbladder because doing so would have damaged the stiff liver tissue, but we were able to see the cystic duct running between the lobes. The cystic duct combines with the hepatic duct to form the common bile duct, which secretes bile into the duodenum [2]. We were unable to find the point of intersection of these two ducts.
The stomach is just caudal to the liver. It is J-shaped and bordered ventrally by the spleen and the intestine. The longer edge of the stomach is called the greater curvature, which is the embryonic dorsal surface [2]. Opposite of the greater curvature is the lesser curvature, which is the embryonic ventral surface [2]. We traced the esophagus from the throat, underneath the liver and diaphragm, to the stomach where it attaches at the cardia. At this point is the cardiac sphincter, which regulates food entry into the stomach. The lesser omentum, a small bundle of fatty mesentery, is ventral to the stomach. Although digestion begins in the oral cavity, major chemical breakdown of food begins in the stomach, where it is mixed with gastric juices and digestive enzymes to form a mixture called chyme. We cut the stomach wall in the fundic region and in the pyloric region to compare their thickness and texture. Our specimen's stomach was completely empty. The stomach wall is of the same thickness in the two regions and is relatively thin compared to other mammals. In the pyloric region, several gastric ducts are visible in the wall, but these ducts are not visible in the fundic region.
The spleen is on the left side of the body, lateral and caudal to the stomach. It is crescent-shaped and comprised of thick, dense tissue. It is approximately the same length as the stomach, and is firmly attached to the stomach by a portion of the greater omentum.
The stomach leads to the small intestine at the pyloric sphincter. This sphincter regulates the movement of chyme from the stomach to the small intestine. The pancreatic tissue is attached to the first portion of the small intestine. The pancreas of the ferret is not a localized organ, but is a mass of glandular tissue lying within the mesentery. We cut into the small intestine to find the pancreatic ducts, but we were unable locate them. The mesentery is attached to the entire length of the small intestine. After finding the pancreatic tissue attached to the duodenum, we separated the mesentery from the small intestine so we could unwind and stretch out the intestinal tract. The mesentery is circular in shape and contains fatty and lymphatic masses as well as several blood vessels that drain into the portal vein.
The first portion of the small intestine is called the duodenum. Digestion is completed in the duodenum, with the aid of enzymes secreted by the pancreas and the intestinal cells. The other two portions are the jejunum and the ileum. These two sections absorb nutrients that are then taken to the liver by the portal vein. Externally, the three sections of the small intestine are indistinguishable. We were able to distinguish between the sections once we cut into the intestinal wall. The duodenum wall is smooth in texture, while the jejunum and the ileum walls are covered in microvilli, small hair-like structures that increase surface area to improve absorption. We could not distinguish the jejunum and the ileum by gross observations.
The large intestine is a short descending tube that is slightly darker in color than the small intestine. This section of the gastrointestinal tract is the site of water and mineral absorption. The junction between the small and large intestine is called the ileocolic junction. In many mammals, a caecum is present prior to this junction. The caecum often holds bacteria that assist in fermentative processes of digestion. Hindgut fermentors such as the rabbit have an especially long caecum, which allows them to digest and obtain nutrients from tough foods like grass. The caecum is not as enlarged in carnivores. The ferret has no caecum at all, but other carnivores such as the cat and the fox have a small caecum. Because no caecum is present, the ileocolic junction is difficult to find, especially since the small and large intestine have the same diameter in the ferret. Many mammals have a marked difference in diameter between the small and large intestine, with the large intestine being much wider than the small intestine. We found the ileocolic junction based on the color differences between ileum and the large intestine. We found further differences by cutting into the intestinal wall at the ileocolic junction. The interior of the ileum is covered in microvilli while the interior of the large intestine is covered in longitudinal ridges. The large intestine leads to the rectum.
The ferret has a proportionally long intestinal tract compared to the fox and the cat. The entire tract is about four times as long as the body length. The small intestine makes up three quarters of the total length, while the large intestine comprises only a quarter of this length.
1. Klingener, D. 1979. Laboratory Anatomy of the Mink (2nd Ed.). William C. Brown, Dubuque, Iowa.
2. Fox, J.G. 1998. Biology and Diseases of the Ferret (2nd Ed.). Williams & Wilkins, Baltimore.