The blue whale is the largest of all creatures known to have ever lived on earth and even today, the sperm whale holds the record of being the most giant toothed predator on the planet. The exciting thing about these giants is that they do not feed the way most people imagine; they eat plankton and krill while some toothed whales consume squid or fish.
But whatever the whale consumes, there is an interesting aspect to how digestion occurs in whales. The digestive system of whales, like the humpback whales, is well-suited for the digestion of krill (tiny crustaceans), small fish like mackerel and plankton. This article will explain in detail how this is done.
In biology, it is known that digestion commences from the mouth and the same thing applies to whales. In the mouths of whales is a sieve-like structure known as baleen. Situated in the upper jaw, baleen is used as a filter for plankton from the water.
The whale can open its mandible wide to allow water to rush in, and then it is expelled again via the baleen plates, leaving krill and plankton behind. Humpback whales do not possess teeth, so the food is swallowed as a lump and moves down to the esophagus then into the forestomach (also called the preliminary stomach) and ground there. Interestingly, the esophagus that connects the mouth with the forestomach measures just about 20 cm even when it is in full extension mode following ingestion.
Stomachs as Compartments
Whales have a stomach that has several chambers, and each section has its function. The first of these compartments is the fore-stomach, and scientists are still debating over its precise role. However, what is certain is that the fore-stomach in whales is very flexible and acts as a reservoir for the ingested meal. That is crucial for opportunistic feeders.
It is also believed that the forestomach has muscles that churn and grind the food, especially as whales do not have teeth. Because there is a degree of acid reflux in the main stomach, a part of the digestion activity occurs in the fore-stomach. The compartmentalized stomachs in whales are just like the types seen in herbivores or ruminants like hippos, rams, or cows.
Main and Pyloric Stomachs
Also called the fundic stomach, this is the compartment that secretes fluids like mucus, enzymes that digest proteins, and the hydrochloric acid that helps significantly in the digestion of the food and the destruction of microorganisms. The lining of the stomach has many convolutions, which increase the surface area available for digestion. The fundic stomach is also called the cardiac stomach, and it is full of glands.
Then there is the pyloric stomach, which is the compartment responsible for the secretion of enzymes responsible for the digestion of fat. It also secretes alkaline substances that help neutralize the powerful effects of the acids released from the main stomach.
After the compartmentalized stomachs, the next structure involved in digestion in whales is the duodenum. The duodenum’s initial part (which itself is a part of the small intestine) is the duodenal ampulla and has a dilated shape where some degree of digestion still happens.
The duodenum’s function is to prepare the chyme (food matter that has been digested) for absorption, which occurs in the intestines of the whales.
The food is absorbed, and the waste is expelled out.