The gastrointestinal system serves the functions of input and process of nutrients necessary for life. The basic functions are ingestion, digestion, and absorption. Nutritional functions are performed by the mouth, esophagus, stomach, small intestine (duodenum, jejunum, ileum--almost all absorption of nutrients takes place in the small intestine), large intestine (colon), pancreas and liver.

In general, the gastrointestinal functions of the dog do not degenerate appreciably with age, other than the potential for dental problems and diabetes. Dental problems for the most part in dogs are not a function of aging, but of preventable disease. There is some reduction in small intestine absorption of calcium associated with very old age.

Older dogs tend to be less able to tolerate high protein levels because of age-related loss of kidney and liver efficiency. Some dogs, like some humans are lactose-intolerant, that is, they lack the enzyme lactase which allows them to digest lactose. In such animals, aging usually does not change the lactose intolerance. Many of the old age-related gastrointestinal/nutrition problems may be satisfactorily treated with special diets.

Excretory Functions