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Digestive System Function - Anatomy & Physiology 

Digestive System Function - Anatomy & Physiology 


The digestive system is the interface between our inner and outer worlds, and amazingly the inside of the digestive tract is not “inside” of our bodies at all. We begin development as a donut-like tube with the same cells covering our outer body as line our GI tract. Without digestion and absorption nothing that enters our mouths and passes through the digestive tract gets inside of our bodies.  

The function of the digestive system is to break down food into its component parts (sugars, amino acids, and fatty acids) that can be absorbed by the bloodstream to fuel our bodies.  

This is a complex process that begins before food even enters the mouth. Just seeing and smelling food sends signals to the body to begin producing digestive juices.  

The digestive tract is a tube consisting of the mouth, esophagus, stomach, small intestine, colon, rectum, and anus. The digestive organs: the liver, gallbladder, and pancreas are connected to the digestive tract and aid in chemical breakdown of food.  

How Do the Parts of the Digestive Tract Function? 

Mouth and Esophagus  

The process of digestion begins in the mouth where food is broken down mechanically by chewing. The food mixes with saliva that contains enzymes that begin the chemical breakdown of carbohydrates into sugars. Once swallowed, the mass of partially broken-down food is called a bolus and is moved through the esophagus via muscular contractions that take it through the lower esophageal sphincter into the stomach.  


In the stomach, food is mixed with gastric acid and digestive enzymes, forming a semi-liquid mixture called chyme. The stomach's muscular contractions help further break down food and facilitate the release of nutrients before passing through the pyloric sphincter into the small intestine.  

Small Intestine  

The small intestine is where most of the digestion and absorption of nutrients occurs and is the longest portion of the digestive tract (about 22 feet long). The walls of the small intestine are made up of many folds covered in small projections called villi. This complex structure gives the small intestine a huge surface area for secretion and absorption. The walls also contain both glands that secrete mucus and enzymes and others that absorb the nutrients from your food. The small intestine is broken into three parts: the duodenum, jejunum, and the ilium.  

Ducts from the organs of digestion (Liver, gallbladder, pancreas) feed into the duodenum. In the duodenum chyme is mixed with bile from the liver and gallbladder and various digestive enzymes from the pancreas to break down fats, proteins, and carbohydrates into smaller molecules. Absorption of these molecules takes place in the jejunum and ilium.  

Food is moved by both segmentation and peristalsis in the jejunum and changes to slower movement from peristalsis alone in the ilium. These portions of the small intestine produce mucus to keep things moving while absorbing different nutrients in each part. The mixture of mostly broken-down food and liquids now passes through the ileocecal valve into the large intestine.  

Large Intestine & Appendix  

The main function of the large intestine is to absorb water and electrolytes, produce and absorb vitamins, and form digested food into feces. The three parts of the large intestine are the colon, the rectum, and the anus.  


There is no true division in the parts of the colon, but it is divided into segments based on directional placement. These segments are the cecum, ascending colon, transverse colon, descending colon, and finally the sigmoid colon. The colon is full of bacteria known as our gut biome. These bacteria protect our GI system from invading bacteria and produce vitamin K and B vitamins. The appendix is attached to the first part of the large intestine (cecum). Although not fully understood, it is packed with immune tissue that helps fight bad bacteria in the gut and houses populations of gut bacteria to repopulate the gut biome after gastrointestinal problems that cause mass die-off. Food waste enters the large intestine as a liquid and loses about 80% of that liquid before leaving as feces.  


The rectum serves as a temporary storage site for feces before elimination. The feces now contain only indigestible material, dead cells from your mucosal lining, water, and mucus. When the rectum is full, pressure signals that you need to use the bathroom.  


The anus is the final part of the digestive tract where waste material, in the form of feces, is expelled from the body through muscular contractions called defecation. It is made up of two sphincters. The inner sphincter opens automatically which puts pressure on the outer sphincter letting you know you need to go to the bathroom. The outer sphincter is under conscious control which allows you to wait and decide when you are ready to release the feces.  

Function of the Digestive Organs  


The liver has a multitude of functions related to all body systems. The liver plays a crucial role in digestion by producing bile, a substance that helps break down fats into smaller droplets, aiding their absorption in the small intestine. It also processes harmful substances and stores essential nutrients.  

The liver possesses remarkable mechanisms to handle waste solubility. It uses specialized cells called hepatocytes, which are equipped with many enzymes and transporters. These hepatocytes convert waste products into more soluble forms that can be easily eliminated from the body. The digestive system is both an eliminatory pathway and filter all thanks to the liver. All the blood leaving the stomach and intestines must pass through the liver where toxins such as drugs, alcohol, and metabolic byproducts are removed through a process known as biotransformation. The liver then uses this waste filtrate (bile) to further break down our food in the small intestine.  

Once its role in digestion is fulfilled, bile continues its path through the intestines. Most bile is reabsorbed in the lower part of the small intestine and recycled back to the liver through a specialized circulation system. This recycling process allows the liver to reuse and optimize bile production, ensuring efficient fat digestion and absorption. The rest of the bile remains in the feces giving it its characteristic brown color. 

The liver is also a storage organ for important vitamins (A, D, E, K, and B12) and minerals (copper and iron) as well as sugar in the form of glycogen for later use.  


The gallbladder is a small organ located beneath the liver, on the right side of the abdomen. The gallbladder stores and concentrates bile produced by the liver. When we consume fatty foods, the gallbladder contracts, releasing bile into the small intestine where it breaks down and emulsifies fat-soluble vitamins and fatty acids for better absorption. 

Although we can function and digest without a gallbladder our ability to digest fats is highly reduced, requiring specialized low-fat diets.  


The pancreas is both an organ of the digestive system and of the endocrine system. Digestive enzymes, such as amylase, lipase, and proteases are all produced by the pancreas. These enzymes help break down carbohydrates, fats, and proteins for the digestive system. Sodium bicarbonate is also produced by the pancreas to neutralize gastric acid, so it does not damage tissues after its role in the stomach is complete. The hormones insulin and glucagon are produced by a small glandular portion of the pancreas called the islets of Langerhans’. Insulin and glucagon both help regulate blood sugar levels.  

Take Aways  

Due to the immense complexity of the digestive system with inputs from many different organs and its impact on all our body systems it is incredibly important to care for our digestive health. Look for our article on Digestive System Protocols coming soon with information on common imbalances of this system and ways to support and heal.  


  *FDA warning: This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. 

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