Digestive System

The start of the process - the mouth: The digestive process begins in the mouth. Food is partly broken down by the process of chewing and by the chemical action of salivary enzymes (these enzymes are produced by the salivary glands and break down starches into smaller molecules).

On the way to the stomach: the esophagus - After being chewed and swallowed, the food enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the throat into the stomach. This muscle movement gives us the ability to eat or drink even when we're upside-down.

In the stomach - The stomach is a large, sack-like organ that churns the food and bathes it in a very strong acid (gastric acid). Food in the stomach that is partly digested and mixed with stomach acids is called chyme.

In the small intestine - After being in the stomach, food enters the duodenum, the first part of the small intestine. It then enters the jejunum and then the ileum (the final part of the small intestine). In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food.

In the large intestine - After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process. The first part of the large intestine is called the cecum (the appendix is connected to the cecum). Food then travels upward in the ascending colon. The food travels across the abdomen in the transverse colon, goes back down the other side of the body in the descending colon, and then through the sigmoid colon.

The end of the process - Solid waste is then stored in the rectum until it is excreted via the anus.

It takes about six or seven seconds, total, to chew and swallow.

After putting the yummy stuff into your mouth, it (the bolus) then has to travel through the entire gastrointestinal tract before coming out the other end. The gastrointestinal tract for the purposes of this exercise includes the oral cavity, the oesophagus, stomach, small intestine, and colon.

Food travels down the oesophagus at a rate of approximately 3 to 4 centimetres per second (1 to 2 inches), and the entire process takes about 5 to 6 seconds. In the stomach, food tends to hang around for a little longer and this depends on a variety of factors including the amount of food you have consumed, how much fat it contains, and also the acidity of the stomach. However, all food should have left the stomach within 2 to 4 hours.

In the small intestine, digestion continues and absorption occurs. From here on, the time to defecation will vary depending on the time it takes to adequately digest and absorb in the small intestine. This will usually take 5 to 6 hours. The "food then enters the colon for further digestion and water reabsorption before defecation. The time from it's entering the colon to defecation is about 12 to 24 hours.

Thus, the time for food to travel from one end to the other probably ranges from about 20 to 30 hours. Although I haven't had the time to look further into the rest of your question, I hazard a guess that it is unlikely that meat will hang around for a week given that the gastrointestinal tract is very effective in breaking it down with various enzymes and acidity of the stomach. Foods high in protein and fats probably would probably take a little longer to pass through than if it were carbohydrate.

Ulcers in the digestive system can be the result of several different factors:

Peptic ulcers are holes or breaks in the protective lining of the duodenum (the upper part of the small intestine) or the stomach -- areas that come into contact with stomach acids and enzymes. Duodenal ulcers are more common than stomach ulcers.

Comparatively rare are esophageal ulcers, which form in the esophagus (swallowing tube) -- and are often a result of exposure to medications, like certain antibiotics or anti-inflammatories, or alcohol abuse.

While excessive stomach acid secretion certainly plays a role in the development of ulcers, a relatively recent theory holds that bacterial infection is the primary cause of peptic ulcers. Indeed, research conducted since the mid-1980s has shown that the bacterium Helicobacter pylori (H. pylori) is present in more than 90% of duodenal ulcers and about 80% of stomach ulcers. However, more recent figures indicate those percentages are declining.

Other factors also seem to contribute to ulcer formation. Overuse of over-the-counter painkillers (such as aspirin, ibuprofen, and naproxen), heavy alcohol use, psychological stress, and smoking exacerbate and may promote the development of ulcers, especially in someone with H. pylori.

Other studies show that stomach ulcers are more likely to develop in older people. This may be because arthritis is prevalent in the elderly, and alleviating arthritis pain can mean taking daily doses of aspirin or ibuprofen. Another contributing factor may be that with advancing age the pylorus (the valve between the stomach and duodoneum) relaxes and allows excess bile (a compound produced in the liver to aid in digestion) to seep up into the stomach and erode the stomach lining. Obesity can also put extra pressure on on the pylorus valve and lead to bile squeezing past the valve.

Duodenal ulcers tend to appear in people with type O blood, possibly because they do not produce the substance on the surface of blood cells that may protect the lining of the duodenum.