The digestive process starts the moment the nose catches an aroma of food wafting through the air. This sense initiates a buildup of saliva in the mouth. Once a morsel of food enters the mouth, it begins the hours-long process of food digestion. It may seem like a straightforward process, but digestion involves a variety of organs, enzymes, hormones, and interactions in the body. Also known as the gastrointestinal tract, the digestive system is 30 feet long, and it takes an average healthy person about 40 hours to fully process food, from eating to elimination.
Hunger is the result of the brain and the digestive system interacting with each other. Once the stomach has burned up the food and completed its part of digestion, blood sugar and essential hormone levels begin to drop. Ghrelin, also known as a “hunger hormone,” is produced by the stomach and signals the hypothalamus in the brain that the body needs food. The vagus nerve serves as the line of communication between the brain and the stomach. The hypothalamus then releases a very abundant peptide called neuropeptide Y that stimulates appetite.
The first bite of food signals the salivary glands, and they begin to produce saliva. The average person produces about two pints of saliva each day. Chewing breaks the food down into digestible pieces. The tongue pushes the food around the mouth during chewing. Saliva mixes with the chewed food, transforming it into an absorbable form. Most of the salivary glands are in the lining of the mouth, but there are three additional pairs - the parotid, the sublingual, and the submandibular glands. A small fold of tissue called the epiglottis folds over the windpipe to prevent food from entering this opening.
Once chewing reduces the food to a soft mass or bolus, the muscles in the mouth and throat propel it into the esophagus. The esophagus connects the throat and the stomach. The muscles in the esophagus begin a series of contractions called peristalsis, where the muscles behind the bolus push it forward, and the muscles in front of the bolus relax. The bolus continues its trek until it reaches a muscular valve at the lower end of the esophagus called the lower esophageal sphincter. The valve relaxes, allowing the bolus to pass into the stomach.
Some people think all digestion takes place in the stomach, but this isn’t true. Most of it happens in the small intestine. However, the stomach does take care of some important aspects of the digestion process. Aided by the digestive glands in the lining, the stomach produces acids and enzymes that break down the food further. The acids in the stomach mix with the food, creating a paste called chyme. Powerful muscles in the stomach contract in a wave-like pattern, and help propel the chyme into the first part of the intestine, the duodenum.
Once the food reaches the duodenum, other organs get involved. The 22-foot small intestine is made up of three parts: the duodenum, the jejunum, and the ileum. The duodenum continues breaking down the food. The pancreas adds digestive enzymes to break down fats, carbohydrates, and proteins. The liver helps process the nutrients but also detoxifies harmful chemicals. The gallbladder produces bile, which absorbs and digests fats. Nutrients and water from the food move to the jejunum for absorption, and the ileum completes the process. Any leftover liquid food residue passes through the small intestine.
Connecting the small intestine to the rectum is the 6-foot long colon or large intestine. The digestive process creates waste products, and it is the colon’s job to absorb any water and remove any leftover food particles or old cells remaining in the GI tract. The large intestine changes the liquid into a solid, forming stool. The muscles perform peristalsis again, pushing the stool through to the end of the large intestine, the rectum. During a bowel movement, the body eliminates the stool.
A whole ecosystem of bacteria lives in the human gut, consisting of trillions of microbes. These gut bacteria not only help digestion, but they also alter how the body stores fat. Gut bacteria assist in balancing glucose levels in the blood and control how humans respond to those hunger hormones -- ghrelin. In recent years, researchers have connected incorrect gut microbe mixes to obesity and diabetes. The clean and sterile intestinal tract in newborns at birth doesn’t stay that way for long. Environmental factors and bad gut bacteria start affecting the body soon after birth.
A "second brain" located in the walls of the digestive system is called the enteric nervous system, or ENS. These two thin layers of more than 100 million nerve cells, found in the lining of the gastrointestinal tract, control much of the digestion process. A high number of people who experience irritable bowel syndrome (IBS) also experience depression and anxiety. Researchers believe irritation in the gastrointestinal system could be sending signals to the central nervous system via the ENS causing mood changes. For years, experts believed the opposite was true -- that depression and anxiety cause digestive issues.
Numerous issues may affect the digestive system and cause pain and discomfort. Celiac disease is a serious sensitivity to gluten that triggers the immune system to react. It interferes with the small intestine’s ability to absorb nutrients. Inflammatory bowel diseases such as Crohn’s disease, which affects the small bowel, and ulcerative colitis, which affects the colon, have been diagnosed in an estimated 2 million adults and children. Diverticulitis causes weak spots in the lining of the digestive system, especially in the colon.
To ensure the digestive system can deliver nutrients to the body as it requires, medical professionals suggest sticking to a healthy diet, rich in fresh vegetables, fruits, and whole grains. Processed foods should be avoided whenever possible. Overeating puts stress on the digestive system. Take the time to eat slowly and chew food. A relaxed meal results in better digestion. Avoid skipping meals, which causes fluctuations in blood sugar levels and may cause overeating at the next meal. Regular exercise is crucial to maintain weight and strengthen abdominal muscles. Managing stress levels might be one of the most important factors in healthy digestion.
This site offers information designed for educational purposes only. You should not rely on any information on this site as a substitute for professional medical advice, diagnosis, treatment, or as a substitute for, professional counseling care, advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other healthcare professional.