Digestion 101

You may not have been expecting it, but you're going to get a bit of an anatomy lesson! Understanding how the digestive system works is important in understanding the care and treatment of this vital part of your immune system.

Six Stages of Digestion

Stage One

You walk into your mom's house and smell the distinctive aroma of fresh baked apple pie. What immediately happens? 

Memories...emotions...salivation...stomach gurgling? Imagine biting in to a tart lime and more than likely you will notice saliva building in your mouth. You may also notice tummy activity increasing. What has this to do with your digestive system? Well, digestion starts in the brain!

We all know how powerful scent is to stimulating memory, and any good chef will tell you that the aroma of food is vital to the dining experience. When you first witness a plate of food, your mind registers the look and smell of the dish. When you take the first bite, your brain registers the taste, from there your brain initiates the digestive process.

Stage Two

Once you begin to chew that delicious bit of food an enzyme called amylase is secreted. Amylase initiates the break down of starches and carbohydrates. As well as causing the stimulation of enzymes, chewing also adds moisture to the food to make it easier to swallow.

Swallowing involves the tongue pushing food to the back of the mouth closing the airway and causing the relaxation of the upper esophageal sphincter. Here, the immune system gets its first bat at protection with tonsils, adenoids and lymph glands.

Stage Three

Now the food has entered the esophagus. Through a process called peristalsis, muscles of the esophagus contract and propel food towards the stomach. Just before it gets to the stomach the bolus, or ball of food needs to pass through the lower esophageal sphincter. This valve allows food to enter the stomach but prevents acid from backing up into the esophagus. Just in case acid does get in to the esophagus the esophagus is lined with glands that secret mucus. The mucus protects the lining from damage from strong stomach acids.

Stage Four

Now the food enters the stomach where it is bathed in acid. This acid is strong stuff and undiluted could burn a hole through your skin. Fortunately, the lining of your stomach is protected by more mucus secreting glands. The acid plays a vital role in killing bacteria and protecting the body from infection. It also aids in absorption of vital nutrients.

The stomach, by now, has signaled the intestine to begin the secretion of enzymes and chemicals needed to continue the digestive process. In the meantime, food is stored in the stomach where muscles process it from a semi-solid to a more liquid consistency. Absorption of nutrients does not happen in the stomach, that's been saved for farther down the digestive system. Only water, alcohol and aspirin are absorbed directly through the stomach.

Stage Five

The gallbladder, liver and pancreas all play a vital role in digestion by secreting specific compounds to aid in the digestive process. Digestive juices cause the release of hormones called cholecystokinin, which in turn cause the gallbladder to contract and secrete bile. Bile is stored in the liver and its job is to digest and emulsify fats. Lipase, amylase and peptidases are secreted from the pancreas and aid in the break down of fats, carbohydrates and proteins into a size that are more absorbable. Both the liver and the pancreas secrete compounds that help lower the intensity of the stomach acids.

Stage Six

The small intestine includes the duodenum, jejunum, and ileum and is about 25 - 30 feet long. Here is where the nutrients are absorbed from food and liquid. Peyer's patches are immune tissue and are part of the gut-associated lymph tissue. This tissue is vital for proper immune function in the gut.

By the time food particles reach the small intestine they've been broken down into their constituent parts: carbohydrates into starch and simple sugars, proteins into peptides and amino acids, and fats into particles like triglycerides and cholesterol. All of these substances cross through membranes in the small intestine to be absorbed into the bloodstream.

The liver now comes into play by processing these particles further. Not only does it break the particles down into smaller parts, it also filters them for any impurities or toxic components.

The ileum now moves the remnants of food to the cecum or colon. The first part of the cecum is the appendix which is full of more immune cells.

Stage Seven

The U-shaped colon becomes the ascending, transverse, descending, and sigmoid colon and leads to the rectum and anus. Colon does more than process waste products from digestion, it also extracts water, vitamins, minerals and other nutrients. What remains is compacted and converted into stool. The colon houses billions of healthy bacteria that protect the body and aid in the final processing of waste.

Once the stool has been compacted and moved to the sigmoid colon and rectum, nerves send signals to your brain prompting the need for defecation.

The journey your food takes sounds complex, but when the body is in good health, it is a smooth and relatively painless process. You can also see from this journey through the digestive process that there are several stages at which negative events can impact digestion and the break down off food into healing and maintaining nutrients.

Return to Home Page from Digestion 101

View our Archive