If we’re going to talk about food, it would probably be a good idea to get a basic sense of what goes on, from a physiological perspective, when we eat. This is the point of this post. Think of it as a reference point when I get around to talking about nutrition and the like. This is not an in depth post, so some allowance for broad terminology is asked for. Also, this gets a tad graphic, so if your bothered by such things, it might be best to come back on Wednesday when I offer up something a little more palatable.
The digestive system works like this – When you put food in your mouth, your teeth mash said food, and your salivary starts to secrete saliva into the mashed food. This mashed food is termed bolus.
Swallowing uses your tongue to push the bolus down your esophagus, which is a long tube lined with muscles that ripple. This helps push the bolus through the cardiac valve valve and into your stomach.
The stomach is a muscle, or a bag of muscles really, that can hold up close to 3 pints of food. Inside the stomach, it releases protein-digesting enzymes such as pepsin and hydrochloric acid. These mix with the bolus to break down the the complex molecules of the protein, carbohydrates, and fat, making them easier to absorb. This mixture is called chyme, and will remain in your stomach from anywhere between 30 minutes to a few hours.
At the other end of the stomach is the pylorus, which regulates the chyme into the small intestine.
The small intestine is anywhere between 15 feet to 20 feet long. This is where the lion’s share of nutrition absorption takes place. It is divided into the parts: the duodenum, the jejunum, and the ileum. In the duodenum, the chyme is mixed with bile from the pancreas. Bile is used to dissolve fats/lipids so as to be absorbed. Also, iron and calcium are typically absorbed in the duodenum.
In the jejunum is where a great majority of the broken down nutrients are absorbed, most of which are passed straight on to the liver, where the nutrients are further filtered and detoxified. The last segment of the small intestine is the ileum, where fat soluble vitamins such as vitamins A, D, E, K, and a few others are absorbed into the system.
From the small intestine, the remaining mixture is passed into the large intestine. It is here that a fair amount of water is absorbed, and billions of bacteria breakdown whatever indigestible carbohydrates remain. Typically this is your soluble fiber.
Anything that cannot be digested after this point combines with some dead blood cells that were in the bile, where it is passed to the rectum. When the rectum is full, we are alerted to the need to go to the bathroom. From there, feces are then forced out through the anus.