What Is the Digestive System?

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the digestive system is made up of the gastrointestinal tract – also called the GI tract or digestive tract – and the liver, pancreas, and gallbladder.

The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus.  The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus.  The liver, pancreas, and gallbladder are the solid organs of the digestive system.

The small intestine has three parts.  The first part is called the duodenum.  The jejunum is in the middle and the ileum is at the end.  The large intestine includes the appendix, cecum, colon, and rectum.  The appendix is a finger-shaped pouch attached to the cecum.  The cecum is the first part of the large intestine.  The colon is next.  The rectum is the end of the large intestine.

Why Is Digestion Important?

Digestion is important because your body needs nutrients from food and drink to work properly and stay healthy.  Proteins, fats, carbohydrates, vitamins, minerals, and water are nutrients.  Your digestive system breaks nutrients into parts small enough for your body to absorb and use for energy, growth, and cell repair.

• Proteins break into amino acids
• Fats break into fatty acids and glycerol
• Carbohydrates break into simple sugars

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How Does My Digestive System Work?

Each part of your digestive system helps to move food and liquid through your GI tract, break food and liquid into smaller parts, or both.  Once foods are broken into small enough parts, your body can absorb and move the nutrients to where they are needed.  Your large intestine absorbs water, and the waste products of digestion become stool.  Nerves and hormones help control the digestive process.

The Digestive Process

How Does Food Move Through My GI Tract?

Food moves through your GI tract by a process called peristalsis.  The large, hollow organs of your GI tract contain a layer of muscle that enables their walls to move.  The movement pushes food and liquid through your GI tract and mixes the contents within each organ.  The muscle behind the food contracts and squeezes the food forward, while the muscle in front of the food relaxes to allow the food to move.

How Does My Digestive System Break Food into Small Parts My Body Can Use?

As food moves through your GI tract, your digestive organs break the food into smaller parts using:

• motion, such as chewing, squeezing, and mixing
• digestive juices, such as stomach acid, bile, and enzymes

Mouth. The digestive process starts in your mouth when you chew.  Your salivary glands make saliva, a digestive juice, which moistens food so it moves more easily through your esophagus into your stomach.  Saliva also has an enzyme that begins to break down starches in your food.

Esophagus. After you swallow, peristalsis pushes the food down your esophagus into your stomach.

Stomach. Glands in yur stomach lining make stomach acid and enzymes that break down food.  Muscles of your stomach mix the food with these digestive juices.

Pancreas. Your pancreas makes a digestive juice that has enzymes that bread down carbohydrates, fats, and proteins.  The pancreas delivers the digestive juice to the small intestine through small tubes called ducts.

Liver. Your liver makes a digestive juice called bile that helps digest fats and some vitamins. Bile ducts carry bile from your liver to your gallbladder for storage, or to the small intestine for use.

Gallbladder. Your gallbladder stores bile between meals.  When you eat, your gallbladder squeezes bile through the file ducts into your small intestine.

Small intestine. Your small intestine makes digestive juice, which mixes with bile and pancreatic juice to complete the breakdown of proteins, carbohydrates, and fats.  Bacteria in your small intestine make some of the enzymes you need to digest carbohydrates.  Your small intestine moves water from your bloodstream into your GI tract to help break down food.  Your small intestine also absorbs water with other nutrients.

Large intestine. In your large intestine, more water moves from your GI tract into your bloodstream.  Bacteria in your large intestine help bread down remaining nutrients and make vitamin K.  Waste products of digestion, including parts of food that are still too large, become stool.

What Happens to the Digested Food?

The small intestine absorbs most of the nutrients in your food, and your circulatory system passes them on to other parts of your body to store or use.  Special cells help absorbed nutrients cross the intestinal lining into your bloodstream.  Your blood carries simple sugars, amino acids, glycerol, and some vitamins and salts to the liver.  Your liver stores, processes, and delivers nutrients to the rest of your body when needed.

The lymph system, a network of vessels that carry white blood cells and a fluid called lymph throughout your body to fight infection, absorbs fatty acids and vitamins.

Your body uses sugars, amino acids, fatty acids, and glycerol to build substances you need for energy, growth, and cell repair.

How Does My Body Control the Digestive Process?

Your hormones and nerves work together to help control the digestive process.  Signals flow within your GI tract and back and forth from your GI tract to your brain.

Hormones

Cells lining your stomach and small intestine make and release hormones that control how your digestive system works.  These hormones tell your body when to make digestive juices and send signals to your brain that you are hungry or full.  Your pancreas also makes hormones that are important to digestion.

Nerves

You have nerves that connect your central nervous system – your brain and spinal cord – to your digestive system and control some digestive functions.  For example, when you see or smell food, your brain sends a signal that causes your salivary glands to “make your mouth water” to prepare you to eat.

You also have an enteric nervous system (ENS) – nerves within the walls of your GI tract.  When food stretches the walls of your GI tract the nerves of your ENS release many different substances that speed up or delay the movement of food and the production of digestive juices.  The nerves send signals to control the actions of your gut muscles to contract and relax to push food through your intestines.

Clinical Trials

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions.

What Are Clinical Trails, and Are They Right for You?

Clinical trials are part of clinical research and at the heart of all medical advances.  Clinical trials look at new ways to prevent, detect, or treat disease.  Researchers also use clinical trials to look at other aspects of care, such as improving the quality of life for people with chronic illnesses.

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What Clinical Trials Are Open?

Clinical trials that are currently open and are recruiting can be viewed at www.ClinicalTrials.gov.