As we continue on our adventurous journey through the digestive tract, we remember the first four (4) sections: preparing for the journey, entering the mouth to get on the subway, being swallowed on our descent into the amusement park ride of the Stomach. Once we are in the small intestine we notice that this is quite a different environment than what you have encountered so far on your journey. Up to this point, very little – except some simple carbohydrates and possibly a little bit of alcohol, has been absorbed. The first two stages of your physical journey were all about mixing and the starting of the breakdown phases. Well that is all changing rapidly, as you move through the Small Intestine – it is all about absorption here. Yes, the small intestine will continue to break down the chyme: both chemically with enzymes, and with the aid of microorganisms, but its major goal is to get down to the business of absorbing nutrients into the body. Remember, as long as it is in the tube (hole in the donut), it is not really in the body yet.
Here are a few of the jobs that the small intestine is about to do:
- Break down food into small enough molecules so you can absorb them.
- Segregate molecules that you can absorb from indigestible food particles and bad organisms, and shunt each into its correct place.
- House as much as 70% of your immune system.
- Protect the friendly flora that acts as your symbiotic helpers.
- Absorb nutrients, fats, and proteins so you can build a strong and healthy body.
Now to do this, the small intestine has a few prominent helpers.
The Pancreas, Gallbladder, and Liver – Digestive Collaborators
This group plays a significant dual role in the process of digestion, and can be distressed with illness if digestion doesn’t go well.
The pancreas plays and important role in digestion, because it produces 40 – 50 oz. (1200 – 1500 ml) of digestive juices and enzymes a day. This includes a concert of players, acting as chemical scissors to snip apart proteins, sugars and even some fibers:
- Pancreatic amylase (polysaccharides into di/trisaccharides),
- Trypsinogen (which is converted into trypsin by enterokinase for proteins),
- Chymotypsinogen (catalyzed into chymotrypsin by trypsin, breaking down proteins),
- Procarboxypeptidase into carboxypeptidase by trypsin, pancreatic lipase (triglycerides that have been emulsified), ribonuclease (breaks down RNA),
- Deoxyribonuclease (breaks down DNA),
- Trypsin inhibitor (deactivates trypsin if accidentally released)
The gallbladder is a small bladder tucked in between the liver and the small intestine. Its basic job is to store bile produced by the liver, ready to be secreted when the occasion is called for. This is mostly due to fatty or oily foods, but just as important to help the absorption of fat soluble vitamins like vitamin D, A and E. Bile is a yellowish-brown to greenish-brown liquid of which the liver produces 27 oz. to about a quart (800-1000 mL) daily. It has an alkaline pH of about 7.6-8.6, and consists of water, bile acids, bile salts, cholesterol, lecithin, bile pigments, and several ions, which are comprised mostly of sodium and potassium salts. This will help to neutralize the strong acid juices coming out of the stomach.
If you have had reason to remove your gallbladder, you can still digest some fats and oils, but in much smaller amounts, and separated over a longer period of time. Since the gallbladder doesn’t really produce the bile (the liver does), bile will still ‘trickle out’. When the gallbladder is functioning optimally, it can produce surges of bile necessary to emulsify oily meals like bacon, French fries, or those eggs benedict you like on special occasions. Good reason to keep it, hey? Eating lots of greens and roughage on a regular basis and detoxification will help to clear it out. Smaller proportion of fatty and oily food will be OK if you have lost your gallbladder. Some people take fat digesting enzymes with fatty food, to assist in this process.
The liver is a significant player at this point of the production as it is what actually produces the bile but it plays an even more important role after absorption of food.
Now not only do your surroundings in the small intestine look different, once you left the stomach, the atmosphere and environment were quite different as well. The stomach is very acidic, but the small intestine produces it own alkaline digestive fluids – and with the help from bile and the pancreatic juices, its environment is quite alkaline.
As an observant and seasoned adventurer, you start to perceive a trend. The environment started out alkaline (in the mouth), became acid in the stomach, and back to alkaline in the small intestine. The yin (alkaline) and yang (acid) pushing and pulling on the food is an interesting sequence – a sequence that will be continued in the large intestine, whose internal environment is acidic.
Now that the bile has emulsified the fatty material, breaking the surface tension – much as soapsuds do to the grease in a frying pan, and the enzymes have broken down the chyme into smaller components, we are ready move on to absorption.
The small intestine is somewhat poorly named, as it isn’t small at all when it comes to length. It is about 22 ft. (6.7 m) long. This makes it nearly four times taller than you are. Its length has nothing on the surface area though, which is the size of a doubles tennis court. Those little projections that looked like stalactites with smaller stalactites growing out of them, and the folds that you observed around you can really make up a large surface area. The reason that this intestine is called small, even though it is much longer than the colon, is because it is small in diameter.
The small shag carpet-like projections are called villi and, as eluded to earlier, they have microvilli on them. The villi and microvilli are where the real action happens. This is where most of the absorption takes place. The villi surface is kind of like a specialized skin that is extremely thin. It is only one cell thick, and has about 150 times the surface area of your external skin. It has a pretty sophisticated job: it has to keep pathogens out while letting in as many nutrients, phytochemicals and other food components as possible. It does this by employing the ‘gut-immune system,’ which can be considered similar to a secret service organization – just on a very personal and small scale.
We will look at this Secret Service in more detail in our next blog. . .