Gastric bypass procedures (GBP) are any of a group of similar operations used to treat morbid obesity—the severe accumulation of excess weight as fatty tissue—and the health problems (comorbidities) it causes.
''Bariatric surgery'' is the term encompassing ''all'' of the surgical treatments for morbid obesity, not just gastric bypasses, which make up only one class of such operations.
A gastric bypass first divides the stomach into a small upper pouch and a much larger, lower "remnant" pouch and then re-arranges the small intestine to allow both pouches to stay connected to it.
Surgeons have developed several different ways to reconnect the intestine, thus leading to several different GBP names. Any GBP leads to a marked reduction in the functional volume of the stomach, accompanied by an altered physiological and psychological response to food.
The resulting weight loss, typically dramatic, markedly reduces comorbidities. The long-term mortality rate of gastric bypass patients has been shown to be reduced by up to 40%; however, complications are common and surgery-related death occurs within one month in 2% of patients.
The gastric bypass reduces the size of the stomach by well
over 90%. A normal stomach can stretch, sometimes to over 1000 ml, while
the pouch of the gastric bypass may be 15 ml in size.
Bypass pouch is usually formed from the part of the stomach which is
least susceptible to stretching. That, and its small original size,
prevents any significant long-term change in pouch volume. What does
change, over time, is the size of the connection between stomach and
bowel, and the ability of the small bowel to hold a greater volume of
Over time, the functional capacity of the pouch increases; by that
time, weight loss has occurred, and the increased capacity serves to
allow maintenance of a lower body weight.
When the patient ingests just a small amount of food, the
first response is a stretching of the wall of the stomach pouch,
stimulating nerves which tell the brain that the stomach is full. The
patient feels a sensation of fullness, as if they had just eaten a large
meal — but with just a thumbful of food.
Most people do not stop eating
simply in response to a feeling of fullness, but the patient rapidly
learns that subsequent bites must be eaten very slowly and carefully, to
avoid increasing discomfort, or even vomiting.
Food is first churned in the stomach before passing into the
small bowel. When the lumen of the small bowel comes into contact with
nutrients a number of hormones are released including cholecystikin
(CCK) from the duodenum and PYY and GLP-1 from the ileum.
inhibit further food intake and have thus been dubbed satiety factors.
''Ghrelin'', is a hormone that is released in the stomach that
stimulates hunger and food intake.
Changes in circulating hormone levels
after gastric bypass have been hypothesized to produce reductions in
food intake and body weight in obese patients. However, these findings
remain controversial, and the exact mechanisms by which gastric bypass
surgery reduces food intake and body weight have yet to be elucidated.
To gain the maximum benefit from this physiology, it is
important that the patient eat only at mealtimes, 2 to 3 small meals
daily, and avoid snacks and grazing between meals, which can effectively
"bypass the bypass". This requires a change in eating behavior, and
alteration of long-acquired habits for finding food.
In almost every
case where weight gain occurs late after surgery, capacity for a meal
has not greatly increased. The cause of regaining weight is eating
between meals, usually high-caloric snack foods.
There is no known
operation which can completely counteract the adverse effects of
destructive eating behavior.
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"Gastric bypass surgery"
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