How gastric bypass works!
|
How It Works
All bariatric operations work by altering the digestive functions of the intestinal tract and, thereby, changing energy balance. To understand this we need to have some basic understanding of what is normal.
Normally, food passes from the mouth to the stomach by way of the esophagus. Aside from food transport, the esophagus does not have an important role in digestion.
In the stomach, however, true digestion begins. Starches and proteins are broken down by enzymes and acid produced in the stomach. The mechanical churning action of the stomach reduces food to smaller particle sizes before it is released into the small intestine. The normal adult stomach has a capacity of 1 to 1.5 liters (1,500 cc). Most bariatric procedures reduce the size of the stomach pouch, thereby limiting the amount of food that can be eaten. For example, in the Roux-en-Y gastric bypass the pouch size is as little as 20 or 30 cc, restricting daily caloric intake to well below 1,000 calories.
The first part of the small intestine is called the duodenum. Soon after entering the duodenum, food mixes with bile, which is produced in the liver, and with digestive enzymes, which are produced by the pancreas. Bile enables fat to be absorbed across the lining of the intestine and pancreatic enzymes are needed to break apart protein into smaller molecules (peptides), which can then also be absorbed and transported in the blood stream. These products are further broken down to be used as energy sources or building blocks for the cells of our bodies.
The duodenum also plays an important role in the absorption of certain vitamins and minerals. This is a favored site of iron and calcium absorption. This part of the intestinal tract is bypassed with the Roux-en-Y gastric bypass procedure. Because of this, lifelong daily mineral and vitamin supplementation is needed.
The duodenum is typically 6 to 10 inches in length. The remainder of the intestine has a length averaging 15 to 22 feet and is the major site of nutrient, mineral and vitamin absorption. The Roux-en-Y gastric bypass, as well as other bariatric procedures, a portion of the small intestine (usually 3 to 6 feet, 90 to 180 cm or 20 to 25% of the length) is placed between a gastric pouch, and a site downstream where the intestine is hooked back together to the bypassed stomach and duodenum. This hookup (anastomosis) allows bile, pancreatic secretions and stomach acid to mix with the food entering from above. The "bypassed" limb of intestine is called the alimentary or "Roux" limb. Food entering this Roux limb from the gastric pouch has not been effectively broken down by the usual exposure to acid, bile and pancreatic juices. Thus, the efficiency of nutrient absorption is decreased in this "bypassed" section of the small bowel. Some operations take this principle to extreme and bypass longer segments of the small intestine. This results in relatively higher rates of malabsorption. This generally equates with greater and more rapid weight loss, but has a trade off of higher rates of protein malabsorption and has a greater potential for dangerous consequences related to mineral and vitamin deficiencies.
Once food has been processed by the small intestine, it enters the colon or large bowel. This has a larger diameter than the small intestine but is much shorter, averaging 5 feet in length. Like the esophagus that delivered food into this system, the colon does not play a major role in digestion. It simply transports waste products of digestion out of the body. As waste is transported from the beginning of the colon to the end, water is removed, converting liquid waste to solids. The anatomy of function of the colon is not directly affected by any of the bariatric operations. However, operations that restrict food volume are associated with decreased stool volume and frequency, where as the opposite affect occurs with procedures that primarily rely on intestinal malabsorption.
In summary, bariatric procedures alter the efficiency of the digestive process by two basic mechanisms: (1) Restriction of nutrient intake, which is related to the size of the gastric pouch/outlet, and (2) By reducing efficiency in nutrient absorption by shortening the effective length of the intestine which is exposed to pre-digested nutrients; those which have been exposed to gastric, pancreatic, and biliary secretions.
We also believe that other less well-defined mechanisms exist that make these procedures effective. These mechanisms are thought to be related to gut hormones that are produced by the cells of the intestinal tract and travel in the blood stream to "talk to" the other organs of the body, as well as the brain. This is an important and exciting area of medical research from which much will be learned in the future.
OH Support Group Leader
RNY 07/27/06
sw358/ cw 175/ qw 175 to 160
I have been blessed with God's Help!
For those in GEORGIA come and join us at PEDMONT HENRY MEDICAL CENTER in the EDUCATIONAL BUILDING in Foundation Board room the 4th TUESDAY of each month at 6:30pm.
http://www.obesityhelp.com/group/jeannie4759_group/tab,0/page,1/#my_groups_main:1