The digestive systems of whales consists of an esophagus, a compartmentalized stomach (similar to that of ruminants like cows or hippos) and an intestine. Prey, whether ingested one at a time as in toothed whales or by the thousands as in baleen whales, are not chewed but rather swallowed whole. They then pass into the esophagus, where they are pushed toward the expandable stomach. The esophagus of the blue whale, even if it takes in 2-3 tonnes of krill a day, measures just 15 to 25 cm long when fully extended. The food then reaches the first stomach compartment, the rumen. Pre-digested food is stored there. This compartment breaks down the food by mechanical muscular movements called peristalsis. Everything is then directed toward the main stomach (or cardiac stomach), where glands produce acid and enzymes used to digest the food (hydrochloric acid, pepsin). The journey continues through a narrow channel before finally reaching the last stomach compartment, the pylorus. The latter is characterized by the presence of numerous mucus glands that facilitate intestinal transit. It is the combined actions of these different compartments that notably allow whales to digest the chitin in the exoskeletons of krill and prey swallowed whole.

The digested food continues its journey into the small intestine where nutrient absorption begins. The size of the intestine varies according to the species: it can be 5 to 6 times the length of the animal, which is equivalent to 150 m in the blue whale. As cetaceans have no gall bladder, it is the liver that provides the bile needed for digestion. Cetaceans have the largest livers of all mammals. The sperm whale produces a substance called ambergris which facilitates digestion of squid beaks that can otherwise irritate the bowel. Transit time, from the stomach to the anus, is from 15 to 18 hours.

To learn more:

How whales feed

Do whales have gas?

Whale Q&A - 15/7/2015

Camille Bégin Marchand

Camille Bégin Marchand has been employed for GREMM from 2013 to 2018. Although she began as a naturalist at the Marine Mammal Interpretation Centre, Camille’s interest in scientific writing would later land her a position on the Whales Online editorial team. With a passion for biology and a deep affection for the region, she is also pursuing a Master’s degree in forest sciences in collaboration with the Tadoussac Bird Observatory (OOT).

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