Did you know that digestion begins in the mouth well before food reaches the stomach? When we see, smell, taste, or even imagine a tasty meal, our salivary glands in front of the ear, under the tongue, and near the lower jaw begin making saliva in preparation for the digestive process to begin. Our digestive system is designed to turn our food into nutrients for the body to use for energy, growth and cell repair.
The mouth is the beginning of the digestive tract. In fact, digestion starts here as soon as you take the first bite of a meal. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can readily absorb and use.
Also called the pharynx, the throat is the next path for the food you’ve just chewed as it passes through the esophagus or swallowing tube.
The esophagus is a muscular tube extending from the pharynx to the stomach. By a series of contractions, called peristalsis, the esophagus delivers food to the stomach. However, just before the connection to the stomach there is a “high-pressure zone,” called the lower esophageal sphincter; this is a “valve” meant to keep food from passing back into the esophagus.
The stomach is a sac-like organ with strong muscular walls. In addition to holding food, it also acts as a mixer and grinder. This organ secretes acid and powerful enzymes that continue the process of breaking down the food. When it leaves the stomach, food should be the consistency of a liquid or paste. Next, it makes its way into the small intestine.
Made up of three segments, called the duodenum, jejunum, and ileum, the small intestine is a long tube loosely coiled in the abdomen (laid out, it would be more than 20 feet long). The small intestine continues the process of breaking down food by using enzymes released by the pancreas and bile from the liver. Bile is a substance that aids in the digestion of fat and eliminates waste products from the blood. Peristalsis or contraction like movements contractions is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream. Three organs play a pivotal role in helping the stomach and small intestine digest food:
Among other functions, this oblong organ called the pancreas secretes enzymes into the small intestine to help break down protein, fat, and carbohydrates from the foods we eat.
Like the pancreas, the liver has many functions too but two of its main functions within the digestive system are to produce and secrete bile and to cleanse and purify the blood coming from the small intestine containing the absorbed nutrients.
Another vital organ is the gallbladder, a pear-shaped reservoir that sits just under the liver and stores bile. Bile is made in the liver and travels to the gallbladder through a channel called the cystic duct. During a meal, the gallbladder contracts, to send bile to the small intestine. Once the nutrients have been absorbed and the leftover liquid has passed through the small intestine, anything leftover food is handed over to the large intestine, or the colon.
Colon (Large Intestine)
The colon is a 5 to a 6-foot-long muscular tube that connects the cecum (the first part of the large intestine to the rectum (the last part of the large intestine). It is made up of the cecum, the ascending (right) colon, the transverse (across) colon, the descending (left) colon, and the sigmoid colon which connects to the rectum. Stool, or waste left over from the digestive process, is passed through the colon by means of peristalsis (contractions), first in a liquid state and ultimately in solid form as the water is removed from the stool. A stool can be stored in the sigmoid colon until a “large movement” empties it into the rectum hopefully once or twice a day. It normally takes about 36 hours for stool to get through the colon. The stool itself is mostly food debris and bacteria. These bacteria perform several functions such as synthesizing various vitamins, processing waste products, and food particles and protecting against harmful bacteria. Once the descending colon becomes full of stool, or feces, it empties into the rectum to eliminated.
The rectum is an 8-inch passage that connects the colon to the anus. It is the rectum’s job to receive stool from the colon and to signal the body that there is a stool to be evacuated and/or hold the stool until evacuation happens. When gas or stool comes into the rectum, sensors send a message to the brain. The brain responds if the rectal contents can be released or not. If all is well, the sphincters (muscles) relax and the rectum contracts, expelling its contents. If the contents cannot be expelled, the sphincter contract and the rectum compensates so the sensation goes away temporarily.
The digestive system is designed to help us get the most efficient nutrition from the foods and drinks we consume. The next time you reach for something to eat or drink remember the journey that food will take through your system from beginning to end.