Here is where it gets really juicy and interesting
Jeez, this has been a trip. We just popped through a valve called the pylorus that separates the stomach from the duodenum, which is a part of the small intestine. The trip through the stomach was like riding a small boat during a hurricane we had to hold on to keep from being thrown out. And all that stomach acid! Gimmie some air. Stinky, burns your eyes. The pylorus was a tight squeeze and sliding into the smooth eight inches of the duodenum was a relief.
The duodenum is the first and shortest section of the small intestine. It’s connected to the stomach, allowing food particles to leave the stomach to course through the intestines.
The function of the duodenum is to mix food with enzymes and bile to digest it and it is important in GI (gastrointestinal system) that helps break down nutrients from food to make them available for absorption into the bloodstream.
Anatomy
The duodenum is a 6 to 10-inch “pipe” that is a C-shaped segment of the small intestine and is located below the stomach and cozily wrapped around the pancreas which provides it with pancreatic enzymes for digestion. It also connects to the liver where it receives bile to mix with chyme, an important part of the chemical digestive process.
Four parts or segments
I am not going to spend lots of time talking in detail about the location and function of these segments except that each segment has a different structure and shape and each performs a different function. The top or superior one is immediately next to the pylorus and is where the bile enters from the liver. The next is the descending segment that is connected to the pancreas that feeds enzymes to break down the food. The third part is the part laying horizontally from right to left. This is just a short piece connecting the descending segment to the ascending (going up) section leading to the jejunum.
Layers inside the Duodenum
There are four layers each of which provides different functions. . The innermost layer is made of mucus glands and microvilli, the fingerlike projections that work to absorb nutrients. The second is the submucosa which is a rich network of blood vessels and nerves traveling its horizontal length, and it secretes mucus to help food move through and bicarbonate that neutralizes the acid in the chyme coming out of the stomach so that future digestion is possible. Then the third layer is a smooth muscle that contracts, churning the chyme and mixing it with digestive enzymes causing the foot to move forward into the jejunum. This is peristalsis, the rolling muscle movement that pushes food ahead. And the fourth is called the serosal layer, the outermost layer, providing a barrier to other organs. Whew, I feel tired just describing the process we just watched as we passed through that short length of bowel!
The Jejunum
Now we are picking up speed and entering the Jejunum. The duodenum, jejunum and ileum constitute the small intestine, connecting the stomach to the north and the large intestine to the south. This next ride is going to be the longest in our voyage. The small intestine basically performs the vital function of breaking down and absorbing nutrients. We just sailed into the jejunum which consists of about 2/3rds of the small intestine.
Riding the Peristalsis
Peristalsis, the involuntary contraction of smooth muscles that moves nutrients through the digestive system, is vigorous and quick in the jejunum. Nutrients absorbed by the jejunum enter the bloodstream, where they can then be distributed to the organs of the body. And boy we are moving fast. The peristalsis is like a huge donut of a muscle surrounding us, and we are riding on a segment of food pushed by this big muscle. It doesn’t mess around and knows its business. It is like a Sumo Wrestler; it doesn’t take any backtalk from the ball of food which is growing differently in the constituency as the nutrients are bled off into the walls of the jejunum into the bloodstream. The lining of the wall of the jejunum contains additional features to help optimize the absorption of nutrients. We sometimes slow or stop while our big Sumo continues south as the walls take a moment to absorb some nutrients, and then comes another wave and whoosh we are off again on the shoulders of another big Sumo.
Villi and Micro Villi
How does the food get absorbed in the jejunum and pass through to the bloodstream? This is the job of the Villi and Micro Villi.
Villi
Villi are located within the circular folds and measure 1 millimeter in length. They look like tiny hairs and help to increase the surface area available for nutrient absorption. Villi contain tiny blood vessels called capillaries that allow nutrients, such as sugars and amino acids, to be absorbed directly into the bloodstream.
Microvilli
As their name implies, microvilli are even smaller than villi. They’re tiny hairlike projections on the surface of the cells found on the mucosal surface of the small intestine. And there’s a lot of them — roughly 200 million per square millimeter in the small intestine. Enzymes on the surface of the microvilli can help to further digest sugars and amino acids. Wow, mother nature constantly amazes me at the clever way she accomplishes things. (Mother nature is a meticulous engineer to think of and make this complex machine so delicate yet so damn tough.)
I gotta say it is like being tickled by a warm cozy, living blanket of the tiniest of soft hairs (like tiny wriggling worms sucking at the juices that surround me and have been my companions throughout the journey.)
We are at the Ileum
The ileum is the last few inches of the small intestine before converting to the large intestine. There is no distinguishing demarcation of the end of the small intestine, but it is fatter and contains more villi and microvilli to absorb the final bits of nutrients. The main function of the ileum is to absorb vitamin B12, bile salts, and whatever products of digestion were not absorbed by the jejunum. The epithelial (any animal tissue that covers the surface or lines a cavity) cells that line these villi possess even larger numbers of microvilli. Therefore, the ileum has an extremely large surface area both for the adsorption (attachment) of enzyme molecules and for the absorption of products of digestion.
How long did it take to get here?
Digestion time varies among individuals and between men and women. After you eat, it takes about six to eight hours for food to pass through your stomach and small intestine, with the small intestine at its end measuring around 22 feet in length top to bottom. The large intestine takes much longer. Stay with me we are going down to the end of the line.
Wow, that has been a ride! Approaching the large intestine.
Throughout the past hour or so that lapsed as we passed down, around, and up and down the twists and turns of the jejunum, as our delicious pork chop, sweet potatoes, green beans, and banana pudding changed to a slurry that looks nothing like what I had for dinner.
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