Anatomy of the Gastrointestinal System

How the digestive system works

Gastroenterology is the study of the digestive system, the system that’s responsible for turning the food you eat into the energy you need to live. But what exactly happens when you swallow your lunchtime sandwich? Read on to learn about the mysteries behind the digestive system.

Even before you swallow that first bite of sandwich, your digestive system is already hard at work. Just the smell of your sandwich (and food in general) triggers the salivary glands in your mouth to secrete saliva. When that first bite of sandwich enters your mouth, your saliva begins to break down the food as you chew it.

The act of swallowing your sandwich triggers the tongue to push your food into the pharynx (the technical term for throat) and into the esophagus. A series of muscle contractions moves the food down through the esophagus and towards the stomach. Just before your sandwich hits your stomach, it passes through a ring-shaped muscle called the lower esophageal sphincter (LES). LES opens to let food enter your stomach and closes to keep food in there. If your LES doesn’t properly close, you may experience the sensation of food coming back up, also known as heartburn or GERD.

Your stomach works like a blender, secreting acids and enzymes to break down your sandwich and turn it into a well-mixed paste. The digestion process continues in the small intestine, where enzymes from the pancreas and bile from the liver further break down the remains of your sandwich. As food passes through the end of the small intestine, nutrients are absorbed into the blood stream. The leftovers then pass into the large intestine, also known as the colon.

The large intestine processes the remaining waste so that defecation will be easy. Any remaining liquid is absorbed to form a solid stool. This process of waste moving through the colon to create a stool typically takes about 36 hours. The stool is stored is the sigmoid colon until a bowel movement pushes it into the rectum for defecation.

The anus is considered the final part of the digestive system. It’s from here that the remains of your lunchtime sandwich will eventually be expelled from your body. Muscles in your anus keep the stool inside your body until your brain sends a signal that it is okay to defecate.