Have you ever wondered what your food goes through as it passes though your body? Everything you ingest goes through a pretty complex process in order for the nutrients to be absorbed into your bloodstream. Today, we'll look at the path of a meal consisting of steak, potatoes, and sour cream as it passes from ingestion to your bloodstream. Starting with the oral cavity we'll see what happens as it pass through the pharynx and esophagus into the stomach, and finally into the small and large intestine.
The digestive process starts in your mouth. Your saliva, consisting mainly of water with a few other things, lubricates the food making it easier to swallow. It also contains enzymes that begin breaking down the complex carbohydrates in the potatoes. You use your teeth to break up the tough tissues of the steak and to mix all your food with the lubricants and enzymes. Your tongue is important to manipulate the food into position for chewing and swallowing.
Swallowing forces the food down the pharynx and the esophagus. Involuntary muscle contractions, called a peristaltic wave, move the food from your pharynx to your stomach in about nine seconds.
The stomach continues the digestive process through mechanical and chemical actions. Many chemicals are secreted into the stomach during digestion. Hydrochloric acid breaks down the cell walls and connective tissue of the food while also killing many microorganisms that may have been ingested. Intrinsic factor is added to the mixture to promote vitamin B12 absorption. Pepsinogen is secreted which turns into pepsin by the hydrochloric acid. Pepsin is an enzyme necessary to break down the proteins that make up the steak. And the enzymes from your saliva are still present, breaking down the complex carbohydrates. All of these form the intestinal juices, which when mixed with the food through the mechanical churning and mixing, form what is called chyme. This process can last up to several hours, and when it is done, the chyme works it's way down to the bottom of the stomach where it will enter the small intestine.
The chyme enters the first part of the small intestine, called the duodenum, where it mixes with excretions from the pancreas and liver. The pancreas produces enzymes that further digest the food. Lipases acts on the fats contained in the sour cream and steak. Carbohydrases continue to digest the sugars and starches from the potatoes. And proteases break the proteins from the steak down even further. Buffers are also secreted at this point to reduce the acidity of the chyme. Bile is also introduced here. Bile consists of water, pigment, cholesterol, and bile salts. Bile salts are essential for the digestion of the fats contained in the sour cream and steak you just ate. The bile salts basically increases the surface area of fats by creating tiny droplets, to increase the efficiency of the fat digesting enzymes.
The carbohydrates in the potatoes are ultimately broken down into simple sugars so they can be absorbed into the bloodstream through the small intestine. The fats from the sour cream are broken down into micelles and as they pass though the intestinal wall, are used to form triglycerides and coated with proteins before they are introduced to the bloodstream. The protein from the steak is finally broken down into amino acids for diffusion into the bloodstream.
Finally, what is left enters the large intestine. The large intestine is mainly used to prepare the waste for removal from the body, but two other important actions take place here. First, water is reabsorbed into the body. Second, some vitamins are absorbed here.