Gastrointestinal tract
The small intestine begins at the duodenum and is a tubular structure, usually between 6 and 7 m long. Its mucosal area in an adult human is about 30 m. Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:
Pinniped
Pinnipeds have a simple stomach that is similar in structure to terrestrial carnivores. Most species have neither a cecum nor a clear demarcation between the small and large intestines; the large intestine is comparatively short and only slightly wider than the latter. Small intestine lengths range from 8 times (California sea lion) to 25 times (elephant seal) the body length. The length of the intestine may be an adaptation to frequent deep diving, as the increased volume of the digestive tract serves as an extended storage compartment for partially digested food during submersion. Pinnipeds do not have an appendix. As in most marine mammals, the kidneys are divided into small lobes and can effectively absorb water and filter out excess salt.