Functional anatomy of the gastrointestinal system of Northeastern Atlantic minke whales (Balaenoptera acutorostrata)

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Abstract
The anatomy of the gastrointestinal system of Northeastern Atlantic minke whales (Balaenoptera acutorostrata) was investigated. The stomach consisted of four compartments. The first chamber, or forestomach, was non‐glandular and was lined with a keratinized stratified squamous epithelium. The tissue wet weight of the forestomach represented 10.4 ± 2.2% (n = 3) of the total gastrointestinal tract (GI‐tract). When maximally expanded with water, the forestomach contained from 68–321 litres (n = 3), while forestomach contents in situ ranged from 5–80 litres (n = 12), with a pH of 6.43 ± 0.28 (n = 12). An orifice, with a relaxed diameter of 27.8 ± 100cm (n = 8), separated the forestomach from the fundic chamber. The mucosa of the fundic chamber possessed gastric glands comprising parietal and chief cells. The contents of this chamber had a pH of 5.26 ± 1.02 (n = 12). The tissue wet weight represented 13.5 ± 1.9% (n = 3) of the total GI‐tract, and when maximally expanded with water, the fundic chamber contained 63–100 litres (n = 3). In situ contents of this chamber ranged from 2–25 litres (n = 12). A connecting channel, with a relaxed orifice diameter of 7.3 ± 3.7 cm (n = 8), joined the fundic chamber and the pyloric chamber. The mucosa of the pyloric chamber contained mucous glands only and no primary glands of digestion. The contents of the pyloric chamber had a pH of 3.60 ± 0.97 (n = 12). The tissue wet weight represented 2.8 ± 0.1% (n = 3) of the total GI‐tract, while the maximally expanded pyloric chamber contained 18–39 litres (n = 3). The pyloric sphincter, with a relaxed diameter of 3.6 ± 0.5cm (n = 8), terminated the stomach. The small intestine began with a duodenal ampulla, lined with mucous glands similar to those in the pyloric chamber. The contents of the duodenal ampulla had a pH of 3.24 ± 0.79 (n = 12). The tissue wet weight represented 1.4 ± 0.2% (n = 3) of the total GI‐tract, and its maximally expanded volume was 8–30 litres (n = 3). The tissue wet weight of the small intestine, caecum and colon represented 61.9 ± 1.3 (n = 3), 0.82 ± 0.48 (n = 3) and 8.7 ± 2.1% (n = 3) of the total GI‐tract, respectively. The lengths of the small intestine, caecum and colon were maximally 36, 0.4 and 4 m, respectively. The forestomach somewhat resembles that of ruminants, but the overall size of the stomach is small, and the length of the intestine short compared to ruminants.