The killer whale’s digestive system is a bit like a small mechanical factory. The animal feeds on various preys, sometimes very large and very different like fish, birds, sea lion, … But everything has been taken care of when it comes to the appetite of thus dangerous predator! Feathers, bones and flesh have no chance. Crushed, chopped, dissolved and evacuated. No mercy! So let’s have a tour on board this terrifying machine!

 

 

Une mâchoire puissante, des dents coniques pour happer ses proies

The killer whale, being under the odontoceti sub-order has identical teeth, cone shaped and of simple type.

There are an average of 22 teeth by jaw (inferior and superior), but this number can vary from 20 to 28.

The complete jaws are made of 40 to 56 teeth. Each tooth is 7.5 cm high for a 2.5 cm diameter at the gum base. However, it has been seen teeth of 13 cm high in some adults …

 

When this dangerous mouth is closing down, the teeth are going into fall in places, next to each other. Cutting an orca’s tooth in length reveals numerous lines (that go from the base of the tooth up to its axis). These allow scientists to estimate the age of an animal when it dies. No molars, incisors or canine teeth, the main function of these is not to cut the prey, but to catch and crush them (under water, fish would slip under ‘classical’ teeth). Cone shaped teeth are therefore highly efficient for the killer whale during the hunt.

There are no salivary glands. Hence there is no food preparation action. The food is sent directly to the pharynx. The pharynx is large and is in elongated shape, which means that the killer whale is capable of swallowing a large fish or a small sea lion in one go, after the jaws have pounded the animal… This pharynx is crossed directly by the larynx (see breathing system). These 2 organs are independent and distinct. The food will go, during deglutition, on each side of the larynx (schematically). It is then straight into the very large oesophagus and then the stomach.

 

The stomach has several pockets. They are called gastric bags and there are 3. The stomach is the main digestive organ as the killer whale does not chew its prey and does not have salivary glands (which is the first chemical decomposition element of the food). Because the oesophagus is very large, what is swallowed arrives as is in the stomach, or to be more precise, in the first pocket.

 

 

The first pocket, or mechanical stomach is actually a kind of crusher, which will pound and chop the prey, making them more easily digestible. This pocket has no salivary glands though. It’s a kind of post oesophagus. However, the works from Flower & Lyddeker (1891) showed that, occasionally, a small quantity of digestive juices from the second pocket passes on to the first pocket, starting the digestion process. It’s worth noting that pebbles and shells are sometimes found in this mechanical stomach, aiding in the crushing of the food.

Food is then transferred to the second pocket, the central one which is called the chemical stomach, or main stomach. Hence the walls are thicker and of course with digestive glands. The hydrochloric acid together with the digestive juices will deteriorate the large molecules so they can be absorbed by the mucous membranes of the digestive tube.

Then comes the last pocket, or pyloric stomach (because it is situated in the pylorus zone, before the intestine). It is a kind of waiting room.

 

 

The liver is small and there is no gall bladder. The pancreas is elongated and its canals reach the choledoc canal (and not the duodenum). The spleen is small and close to the duodenum.

The intestine is long and regular. It is the main absorption organ. There are no major differences between the large intestine, the small intestine and the colon. It’s purpose is to decompose (complex) food into nutriments and substances assimilable and usable by the organism (proteins, glucoses, lipids, vitamins and minerals, …).

 

The anus has no projecting area. It is narrow and ends directly outside (no pocket). It is situated in the anal slit (the most at the rear).

 

The kidneys’ purpose is to eliminate the different toxins via urine. Every kidney is actually made of a multitude of small kidneys with an independent vascular system. These kidneys are large in size because they also have another vital role. Desalinisation. Orcas do not have a chloride cell (chlorine elimination), or sudoriparous glands (elimination by the pores). It is therefore the kidneys that will deal with this vital function.

The ureters join the pear shaped bladder where urine is stocked. Its walls are particularly thick, flexible and membrane covered. Urine is then expulsed via the urethral canal.