NORMAL - If you think your stomach has a mind of its own on Thanksgiving, you're not too far off the mark. The organ that helps us to digest our food is far more than a gastric chopping block on our digestive assembly line. | Tips for a healthy tummy | Slidehow: How to cook a perfect turkey | Slideshow: Bird Carving 101 | Cook pumpkin pie like a pro

It's a flexible, generally good-humored part of our body that can change shape and size to deal with almost every type and amount of food that we send down.

"The stomach is an accommodating organ," said Dr. Kenneth Schoenig, a gastroenterologist with Digestive Disease Consultants in Normal.

But we all know what happens next: We enjoy the meal, then feel stuffed and tired.

Don't blame the stomach. It tried to warn you.

The human stomach is a thick-walled muscular sac located between the esophagus and the intestines. It changes shape and size depending on the amount of food inside.

The adult stomach is about 12 inches long and about 6 inches wide at its widest point, said Kim McClintic, a registered dietitian with the Center for Healthy Lifestyles at OSF St. Joseph Medical Center, Bloomington. It is about the size of two fists.

The average adult stomach's capacity is about one liter, or slightly less than a quart. That means the average adult can eat and drink about a liter's worth of food and drink before feeling full.

We feel full because stretch receptors within the stomach wall sense when the stomach is full and send that signal to the brain, Schoenig said.

But many of us continue to eat during Thanksgiving and other holiday feasts because we enjoy the food and because it takes about 20 minutes for the "I'm full" message to get from the stomach to the brain, McClintic and Schoenig said.

We are able to keep eating because the stomach is elastic. It can stretch to hold two to four liters of food and drink.

"You can keep pushing food down into the stomach and it'll continue to expand like a balloon," said Dr. Stephen Matter, a gastroenterologist with the Gastrointestinal Institute in Normal Matter.

At that point, even many of the biggest eaters stop because of the discomfort caused by the stomach pushing against other body organs.

"It's that uncomfortable feeling," McClintic said. "We ate too much, too fast."

While the doctors and McClintic have never seen a patient whose stomach lining has torn from overeating, overeating can lead to vomiting, and, on rare occasions, excessive vomiting can rupture the esophagus.

Eating a large, fatty meal also may cause bowel irregularities, including loose stools, McClintic said.

"Your body is trying to expel all that food - especially if your body isn't used to it (digesting a large quantity of fatty foods)," she said.

How long its takes food to pass from the stomach to the intestines depends on how much we eat. Generally, it's about three to four hours, but it takes longer for bigger meals.

Fatty foods take longer to digest, Schoenig said.

The sleepiness we experience after eating a big Thanksgiving feast has been blamed on tryptophan, an amino acid in turkey that stimulates serotonin production in the brain.

Actually, the sleepiness is because of the heavy meal.

"When we eat a big meal, all the energy and attention of our body is on its way to the gut," McClintic said. "The body is saying 'Bring in the troops, we've got work to do to digest this food.'"

Schoenig agreed. "The blood circulation has been diverted to the digestive tract."

That's why exercising right after a meal isn't a good idea. Your body needs that energy to digest the meal first.

"You can't have both," McClintic said. "Your body is saying 'You can't have it out there. We need it in here.'"

Going for a leisurely walk after a big meal is a good way to help digest the food and burn calories. But playing football or doing intensive exercise isn't a good idea until about two hours after a big meal, McClintic and Schoenig said.

Lying down isn't a good idea either. The food has trouble digesting and can re-enter the esophagus and cause vomiting.

Wait at least two hours after a meal before going to bed, otherwise you'll have trouble digesting your food and sleeping, Schoenig said.

After digestion, the stomach goes back to about its original size. But people who chronically overindulge can have a more accommodating stomach, meaning it expands more readily to hold more volume than the stomach of someone who doesn't overeat, Schoenig said.

"Eating big, big, big meals all the time will mess up our body's feeling of satiety (fullness)," McClintic said.

On the other hand, a person who eats little may not be able to overeat as easily.