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Bleeding. Bleeding can occur anywhere in the digestive tract, from the mouth to the anus, The Merck Manuals remind us. Blood in vomit reveals bleeding in the upper part of the digestive system, and blood in the stools from the lower part. Blood in the stools can be either bright red, or can turn the stools tarry and black. The higher up in the tract the bleeding occurs, the darker the stools.
Bloating. This is a condition in which the stomach appears swollen and feels full, because of a build-up of gas, fluid or ingested food in the small intestine. This could occur in isolation, or in conjunction with other intestinal disorders, according to the Merck Manuals. Read more on bloating and Irritable Bowel Syndrome.
Diarrhoea. This describes the frequent passing of watery stools. Many people experience this from time to time, and often it is not a symptom of a serious disease, especially if it clears within a day or two. But chronic diarrhoea could point to a more bloatingcondition and definitely warrants medical attention sooner rather than later. Read more on diarrhoea.
Heartburn. When acid reflux spills into the oesophagus, the burning sensation it causes is called heartburn. Symptoms can include a burning feeling in the throat, and possible chest pain. Most people get heartburn occasionally, especially after a heavy, spicy or fatty meal, but if it happens several times a week, you could have gastro-oesophageal reflux disorder (GORD).
Incontinence. This term is used to describe leakage of faeces from the bowel due to poor bowel control, says the Continence Foundation of Australia. Some medications such as certain antibiotics could cause this on a temporary basis. Or it could be a symptom of bowel diseases, such as coeliac disease or certain nerve disorders.
Nausea and vomiting. Vomiting describes the process when the contents of the stomach are forced up out of the oesophagus and out of the mouth, says the National Institutes of Health. Nausea is the feeling of abdominal discomfort that precedes the act of vomiting. It can be a symptom of a wide range of conditions from an allergy, to kidney stones to cancer or a tumour. If the nausea and vomiting persist, medical attention must be sought.
Abdominal pain. This refers to a pain anywhere between your chest and your groin. It can be localised, general, cramp-like or come in waves according the National Institutes of Health. The intensity of the pain is not always proportionally related to the seriousness of the condition by which it is caused. Abdominal pain is a symptom of the majority of digestive diseases, and it is advisable to go to a doctor if the pain does not resolve itself in a day or two.
Swallowing problems. This is also known as dysphagia. This refers to the feeling of difficulty in passing food or liquid from the mouth to the stomach, according to the American Academy of Otolaryngology. This is mostly not a symptom of serious disorders, but can cause a fair amount of discomfort. All cases should be examined by a medical doctor to exclude sinister causes.
Weight loss or gain. Weight gain for no apparent reason could be the result of poor digestion, or because of a metabolic disorder, or because of taking certain medications, or because of the shortage or malabsorption of certain nutrients. Unexplained weight loss can be the result of something such as flu or an oral ulcer, but could also be a more serious warning sign of conditions such as diabetes or cancer.
The main aim of the digestive system is to process the food we eat and drink in order to provide the body with its energy and nutrient needs, and then to deal with its waste products. The energy is needed to ensure our survival and to repair our body tissues.
Digestive tract
The digestive tract starts at the mouth and ends at the anus.
Read more here about how the whole digestive system works from start to finish.
A lack of food can lead to starvation and a lack of nutrition can lead to malnutrition. An inability or reduced ability to absorb nutrients from the diet can lead to both starvation and/or malnutrition.
Digestive disorders are the cause of ill health for millions of people the world over and the causes and symptoms of these are numerous. They range from minor, such as slight heartburn or nausea after eating a big meal, to serious, such as colon cancer.
Symptoms of digestive diseases
Symptoms of digestive diseases can include diarrhoea, nausea, heartburn, vomiting, constipation, abdominal swelling, abdominal pain, flatulence, bleeding from the digestive tract, and loss of appetite, according to the Merck Manuals. The Merck Manuals also remind us that some disorders can affect several parts of the digestive system and not just one.
Here’s more about some of the main types of diseases that can affect the digestive system:
Infections • Appendicitis is a bacterial inflammation of the appendix. • Food poisoning can be caused by many different types of bacteria. • Viral gastroenteritis is a inflammation of the stomach and intestines caused by a virus. • Hepatitis A, hepatitis B and hepatitis C all indicate an inflammation of the liver. • Peptic ulcers are open sores that can develop on the lining of the oesophagus, stomach and small intestine.
Inflammatory and auto-immune conditions • Gastritis is a group of conditions caused by an inflammation of the stomach lining. • Haemorrhoids are swollen and inflamed veins in the anus and lower rectum. • Crohn’s disease and ulcerative colitis are both types of inflammatory disorders of the digestive tract. • Irritable Bowel Syndrome is a common disorder affecting the large intestine. • Pancreatitis is an inflammation of the pancreas.
Functional or structural problems • Anal fissure refers to a tear in the mucosa (thin tissue layer) that lines the anus • Anal fistula is a small channel between the end of the bowel and the skin close to the anus. • Cirrhosis of the liver is a late stage of liver scarring. • Coeliac disease is a chronic disorder caused by an intolerance to gluten. • Constipation is infrequent bowel movements or stools that are hard to pass. • Diarrhoea is the passing of loose and frequent stools. • Diverticular disease describes a condition where small bulging "pockets" develop in the colon. These can get inflamed. • Flatulence is the passing of wind or gas through the anus. • Faecal incontinence is leakage from the bowel owing to poor bowel control. • Gallstones are hard deposits in your gallbladder. • Gastritis is a term used to describe inflammation of the lining of the stomach. • Hiatal and abdominal hernias describe what happens when an organ pushes through the tissue that holds it in place. • Indigestion, heartburn and Gastro-oesophageal reflux disease (GORD) and Irritable Bowel Syndrome • Intestinal obstruction is a blockage of the large or small intestine.
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.
image: niddk.nih.govThe digestive system
Bacteria in your GI tract, also called gut flora or microbiome, help with digestion. Parts of your nervous and circulatory systems also help. Working together, nerves, hormones, bacteria, blood, and the organs of your digestive system digest the foods and liquids you eat or drink each day.
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.
image:niddk.nih.govYour digestive system breaks nutrients into parts that are small enough for your body to absorb.
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.
Upper muscle in stomach relaxes to let food enter, and lower muscle mixes food with digestive juice
Small intestine
Peristalsis
Pancreas
None
Liver
None
Large intestine
Peristalsis
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.
niddk.nih.govThe digestive process starts when you put food in your mouth.
Mouth. Food starts to move through your GI tract when you eat. When you swallow, your tongue pushes the food into your throat. A small flap of tissue, called the epiglottis, folds over your windpipe to prevent choking and the food passes into your esophagus.
Esophagus. Once you begin swallowing, the process becomes automatic. Your brain signals the muscles of the esophagus and peristalsis begins.
Lower esophageal sphincter. When food reaches the end of your esophagus, a ringlike muscle—called the lower esophageal sphincter —relaxes and lets food pass into your stomach. This sphincter usually stays closed to keep what’s in your stomach from flowing back into your esophagus.
Stomach. After food enters your stomach, the stomach muscles mix the food and liquid with digestive juices. The stomach slowly empties its contents, called chyme, into your small intestine.
Small intestine. The muscles of the small intestine mix food with digestive juices from the pancreas, liver, and intestine, and push the mixture forward for further digestion. The walls of the small intestine absorb water and the digested nutrients into your bloodstream. As peristalsis continues, the waste products of the digestive process move into the large intestine.
Large intestine. Waste products from the digestive process include undigested parts of food, fluid, and older cells from the lining of your GI tract. The large intestine absorbs water and changes the waste from liquid into stool. Peristalsis helps move the stool into your rectum.
Rectum. The lower end of your large intestine, the rectum, stores stool until it pushes stool out of your anus during a bowel movement.
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 your 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 break 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 bile 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 break 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 trials, 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. Find out if clinical trials are right for you .
What clinical trials are open?
December 2017
This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.
The digestive system is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract). The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines. In addition to the alimentary canal, there are several important accessory organs that help your body to digest food,
CONTINUED FROM ABOVE... but do not have food pass through them. Accessory organs of the digestive system include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. To achieve the goal of providing energy and nutrients to the body, six major functions take place in the digestive system:
Ingestion
Secretion
Mixing and movement
Digestion
Absorption
Excretion
Digestive System Anatomy
Mouth
Food begins its journey through the digestive system in the mouth, also known as the oral cavity. Inside the mouth are many accessory organs that aid in the digestion of food—the tongue, teeth, and salivary glands. Teeth chop food into small pieces, which are moistened by saliva before the tongue and other muscles push the food into the pharynx.
Teeth. The teeth are 32 small, hard organs found along the anterior and lateral edges of the mouth. Each tooth is made of a bone-like substance called dentin and covered in a layer of enamel—the hardest substance in the body. Teeth are living organs and contain blood vessels and nerves under the dentin in a soft region known as the pulp. The teeth are designed for cutting and grinding food into smaller pieces.
Tongue. The tongue is located on the inferior portion of the mouth just posterior and medial to the teeth. It is a small organ made up of several pairs of muscles covered in a thin, bumpy, skin-like layer. The outside of the tongue contains many rough papillae for gripping food as it is moved by the tongue’s muscles. The taste buds on the surface of the tongue detect taste molecules in food and connect to nerves in the tongue to send taste information to the brain. The tongue also helps to push food toward the posterior part of the mouth for swallowing.
Salivary Glands. Surrounding the mouth are 3 sets of salivary glands. The salivary glands are accessory organs that produce a watery secretion known as saliva. Saliva helps to moisten food and begins the digestion of carbohydrates. The body also uses saliva to lubricate food as it passes through the mouth, pharynx, and esophagus.
Pharynx
The pharynx, or throat, is a funnel-shaped tube connected to the posterior end of the mouth. The pharynx is responsible for the passing of masses of chewed food from the mouth to the esophagus. The pharynx also plays an important role in the respiratory system, as air from the nasal cavity passes through the pharynx on its way to the larynx and eventually the lungs. Because the pharynx serves two different functions, it contains a flap of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx.
Esophagus
The esophagus is a muscular tube connecting the pharynx to the stomach that is part of the upper gastrointestinal tract. It carries swallowed masses of chewed food along its length. At the inferior end of the esophagus is a muscular ring called the lower esophageal sphincter or cardiac sphincter. The function of this sphincter is to close of the end of the esophagus and trap food in the stomach.
innerbody.com
Stomach
The stomach is a muscular sac that is located on the left side of the abdominal cavity, just inferior to the diaphragm. In an average person, the stomach is about the size of their two fists placed next to each other. This major organ acts as a storage tank for food so that the body has time to digest large meals properly. The stomach also contains hydrochloric acid and digestive enzymes that continue the digestion of food that began in the mouth.
Small Intestine
The small intestine is a long, thin tube about 1 inch in diameter and about 10 feet long that is part of the lower gastrointestinal tract. It is located just inferior to the stomach and takes up most of the space in the abdominal cavity. The entire small intestine is coiled like a hose and the inside surface is full of many ridges and folds. These folds are used to maximize the digestion of food and absorption of nutrients. By the time food leaves the small intestine, around 90% of all nutrients have been extracted from the food that entered it.
Liver and Gallbladder
innerbody.com
The liver is a roughly triangular accessory organ of the digestive system located to the right of the stomach, just inferior to the diaphragm and superior to the small intestine. The liver weighs about 3 pounds and is the second largest organ in the body.
The liver has many different functions in the body, but the main function of the liver in digestion is the production of bile and its secretion into the small intestine. The gallbladder is a small, pear-shaped organ located just posterior to the liver. The gallbladder is used to store and recycle excess bile from the small intestine so that it can be reused for the digestion of subsequent meals.
Pancreas
The pancreas is a large gland located just inferior and posterior to the stomach. It is about 6 inches long and shaped like short, lumpy snake with its “head” connected to the duodenum and its “tail” pointing to the left wall of the abdominal cavity. The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods.
Large Intestine
The large intestine is a long, thick tube about 2.5 inches in diameter and about 5 feet long. It is located just inferior to the stomach and wraps around the superior and lateral border of the small intestine. The large intestine absorbs water and contains many symbiotic bacteria that aid in the breaking down of wastes to extract some small amounts of nutrients. Feces in the large intestine exit the body through the anal canal.
Digestive System Physiology
The digestive system is responsible for taking whole foods and turning them into energy and nutrients to allow the body to function, grow, and repair itself. The six primary processes of the digestive system include:
Ingestion of food
Secretion of fluids and digestive enzymes
Mixing and movement of food and wastes through the body
Digestion of food into smaller pieces
Absorption of nutrients
Excretion of wastes
1
Ingestion
The first function of the digestive system is ingestion, or the intake of food. The mouth is responsible for this function, as it is the orifice through which all food enters the body. The mouth and stomach are also responsible for the storage of food as it is waiting to be digested. This storage capacity allows the body to eat only a few times each day and to ingest more food than it can process at one time.
2
Secretion
In the course of a day, the digestive system secretes around 7 liters of fluids. These fluids include saliva, mucus, hydrochloric acid, enzymes, and bile. Saliva moistens dry food and contains salivary amylase, a digestive enzyme that begins the digestion of carbohydrates. Mucus serves as a protective barrier and lubricant inside of the GI tract. Hydrochloric acid helps to digest food chemically and protects the body by killing bacteria present in our food. Enzymes are like tiny biochemical machines that disassemble large macromolecules like proteins, carbohydrates, and lipids into their smaller components. Finally, bile is used to emulsify large masses of lipids into tiny globules for easy digestion.
3
Mixing and Movement
The digestive system uses 3 main processes to move and mix food:
Swallowing. Swallowing is the process of using smooth and skeletal muscles in the mouth, tongue, and pharynx to push food out of the mouth, through the pharynx, and into the esophagus.
Peristalsis. Peristalsis is a muscular wave that travels the length of the GI tract, moving partially digested food a short distance down the tract. It takes many waves of peristalsis for food to travel from the esophagus, through the stomach and intestines, and reach the end of the GI tract.
Segmentation. Segmentation occurs only in the small intestine as short segments of intestine contract like hands squeezing a toothpaste tube. Segmentation helps to increase the absorption of nutrients by mixing food and increasing its contact with the walls of the intestine.
4
Digestion
Digestion is the process of turning large pieces of food into its component chemicals. Mechanical digestion is the physical breakdown of large pieces of food into smaller pieces. This mode of digestion begins with the chewing of food by the teeth and is continued through the muscular mixing of food by the stomach and intestines. Bile produced by the liver is also used to mechanically break fats into smaller globules. While food is being mechanically digested it is also being chemically digested as larger and more complex molecules are being broken down into smaller molecules that are easier to absorb. Chemical digestion begins in the mouth with salivary amylase in saliva splitting complex carbohydrates into simple carbohydrates. The enzymes and acid in the stomach continue chemical digestion, but the bulk of chemical digestion takes place in the small intestine thanks to the action of the pancreas. The pancreas secretes an incredibly strong digestive cocktail known as pancreatic juice, which is capable of digesting lipids, carbohydrates, proteins and nucleic acids. By the time food has left the duodenum, it has been reduced to its chemical building blocks—fatty acids, amino acids, monosaccharides, and nucleotides.
5
Absorption
Once food has been reduced to its building blocks, it is ready for the body to absorb. Absorption begins in the stomach with simple molecules like water and alcohol being absorbed directly into the bloodstream. Most absorption takes place in the walls of the small intestine, which are densely folded to maximize the surface area in contact with digested food. Small blood and lymphatic vessels in the intestinal wall pick up the molecules and carry them to the rest of the body. The large intestine is also involved in the absorption of water and vitamins B and K before feces leave the body.
6
Excretion
The final function of the digestive system is the excretion of waste in a process known as defecation. Defecation removes indigestible substances from the body so that they do not accumulate inside the gut. The timing of defecation is controlled voluntarily by the conscious part of the brain, but must be accomplished on a regular basis to prevent a backup of indigestible materials.
Digestive Disorders
Many diseases and health conditions - such as ulcers, GERD, IBD and celiac disease, just to name a few - lead to dysfunction in our digestive system. Learn about them by visiting our section on digestive diseases and conditions. (Also, now you can test for your genetic risk of acquiring celiac disease - learn more about DNA health testing.)
Prepared by Tim Taylor, Anatomy and Physiology Instructor
