The term alvus has a couple of different meanings in biology. In an anatomical sense, it includes the stomach as well as the intestinal tube, including both the small and large intestine, and the anus. The word is also used to define the excrement that comes out of the intestines and feces in general. Medical terminology includes the term in the definitions for fecal matter in a laxative state, or diarrhea, known as alvus liquida. It is followed by the word adstricta when a person is in a state of constipation.
In the stomach, digestive juices are added to the food eaten and most of the food is broken down into a liquid state. Aspirin and alcohol get absorbed but almost everything else passes through to the duodenum, the first section of the small intestine. Bile from the liver and digestive juices from the pancreas drain into this area to further break down food into protein, fat, and enzymes. The tube of the small intestine is lined with villi, structures that absorb nutrients from within the tube and into the blood. Microvilli are located on these areas and secrete even more digestive enzymes.
The large intestine is the next part of the alvus. Water is absorbed and large quantities of bacteria actually help digest things people couldn’t ordinarily break down, like certain carbohydrates. The bacteria also help break down vitamins, and are the reason feces is comprised largely of bacterial matter. Food and digestive fluids enter through the cecum, to which the appendix is linked, and pass through the ascending, transverse, and the descending colon before the waste passes through the rectum and anus.
Alvus also refers to the state of fecal matter, which varies depending on its fluid content when it passes. The characteristic smell is caused by gases released by bacteria, most commonly coliform bacteria. While the color depends to some extent on bacteria, it is also influenced by the interaction of bilirubin, a prevalent bodily substance, and iron. Testing feces for blood, mucus, and even parasites and fat can help diagnose diseases and conditions.
Analyzing the alvus state of human excrement can determine if food is being digested properly. If undigested foods go through the digestive system faster than they should, there could be a problem in the colon. The state of fecal matter and the stomach and intestines in general is critical to determining overall health.