Digestive System

Fish anyone? The digestive system of marine mammals consists of the mouth, esophagus, stomach, small and large intestine, colon, and rectum. Accessory organs are also critical for digestive function including the liver and pancreas.

Most marine mammals (except sea otters) don’t chew their food. Rather they pluck it out of the water and swallow it whole. The fish travel down the esophagus to the stomach. In pinnipeds, there is only one compartment to the stomach and just like in humans, it can expand greatly to accommodate a big meal. In cetaceans, the stomach has multiple compartments, separated by sphincter muscles, including the main stomach (also sometimes called the cardiac stomach or fundus) and the pyloric stomach. After moving through the pyloric sphincter, food next travels to the duodenum which is the most anterior part of the small intestine. In the duodenum, the food (now called chyme) gets mixed with the products of the pancreas including bicarbonate to increase the pH. Most of the digestion occurs in this region. The chyme then makes its way to the rest of the small intestine which consists of the jejunum and ileum. The large intestine follows the small intestine and then finally reaches the colon and rectum and waste is excreted from the anus.

During necropsy, it is important to examine each part of the digestive system. Often clues as to the cause of death can be found by looking at whether there is food in the stomach or in the small or large intestine. For example, an apparently healthy animal with a large stomach full of partially digested food might indicate a toxin, such as domoic acid, could be responsible for the animal’s death. You should also examine the digestive system for parasites and note whether there are extensive worms in the stomach for example. High parasite loads can sometimes indicate the animal was sick for weeks or months prior to death.

Detailed annotated images of the digestive system in a California Sea Lion are shown below.  CLICK on an image to see an enlarged view.