The purpose of eating food is to nourish our body with nutrients to maintain life. Nutrients consist of molecules, however, these molecules are too big for our body to process. The body naturally breaks down these molecules to allow for proper digestion in the body. Many organs in our body act together in this process to form the digestive system. These include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
Despite popular belief, the digestion process does not begin in the stomach but begins in the brain. As soon as we see or smell a food, Our brains tell our body to start salivating. The salivatory glands in our mouth begin to secrete saliva to help digest our food, along with our teeth. Salivary amylase, an enzyme in saliva begins to break down starches in the mouth. Glands in the tongue secrete an enzyme (lingual lipase) which then begins the digestion process of dietary fats. These enzymes will stay with the chewed food as it passes through the digestive tract for about an hour breaking down food. Once chewed the lump of chewed food (aka bolus) then travels through the esophagus to the stomach.
A meal can be eaten much quicker than it can be digested so the stomach acts as a holding chamber for the food before it enters into the small intestines. The average stomach can hold up to 6 quarts of food at 1 time. Every 15-25 seconds the stomach contracts to mix the bolus with gastric juices (hydrochloric acid produced by parietal cells) to eventually become a soupy liquid form called chyme. An enzyme called pepsin is released from the stomach (by chief cells) to start digestions of protein as well. A deficiency in either of these two substances can result in digestive dysfunction.
After about 2-4 hours of time in the stomach, the chyme travels to the small intestines, first passing through the pyloric sphincter to the duodenum (beginning of the small intestines). When the highly acidic chyme enters the duodenum, the acidity triggers a few reactions. First, to neutralize the chyme before entering into the small intestines Cholecystokinin (a hormone) is released from the duodenum signaling the pancreas to releases pancreatic juice that consists of water, some salts, sodium bicarbonate, and enzymes. Meanwhile, Cholecystokinin also signals the gallbladder to release bile juice into the small intestines to aid in digestions and the absorption of fats.
Note that if the chyme entering into the duodenum is not acidic enough (a high ph level, meaning not enough stomach acid), the pancreas and liver will not be triggered to release enzymes and bicarbonate. We are left with a highly acidic clump of chyme. About 90% of all absorption of nutrients takes place in the small intestines. The small intestines even choose what to absorb what nutrients they feel you need while rejecting what it doesn’t.
Next, the remainder of the chyme that wasn’t absorbed travels to the large intestines where more mucus is secreted, first passing through the ileocecal valve. Bacteria ferments any remaining carbohydrates and releases hydrogen and methane gases. It also breaks down remaining proteins to amino acids. The large intestines will absorb much of the remaining water as well. Many vitamins are also absorbed through the colon, bile is also reabsorbed so be used again by the liver. At this point, the digestive process has taken about 3-10 hours. The chyme has now become a semisolid piece (feces) and exits the body through the rectum and anus.
Many problems can arise in the digestive process is the body doesn’t produce the correct or sufficient enzymes or if the body is not provided with proper nutrients or cannot absorb the nutrients it is given of digestions.
COMING SOON – BREAKING DOWN DIGESTION PHASE 2: YOU ARE WHAT YOU ABSORB