The human body is an amazing thing. For each one of us, it’s the most intimate object we know. Yet most of us don’t know enough about it. While you may only think of your stomach when you’re eating or it catches your attention with a gurgle or burble, it’s much more than a repository for the food you eat. Your stomach kills microbes, secretes hormones and mucus, and absorbs nutrients. Your stomach has 3 main functions: The temporary storage for food, which passes from the esophagus to the stomach where it is held for 2 hours or longer. Mixing and breakdown of food by contraction and relaxation of the muscle layers in the stomach and The digestion of food.
While food is only in the stomach for two to five or six hours before it’s sufficiently broken down to pass along the line to the intestines. The abdomen contains all the digestive organs, including the stomach, small and large intestines, pancreas, liver, and gallbladder. These organs are held together loosely by connecting tissues that allow them to expand and to slide against each other. Below you will find everything you need to know about your vital digestive organs.
1. What exactly is the Gut?
The gut (gastrointestinal tract) is the long tube that starts at the mouth and ends at the back passage (anus). The mouth is the first part of the gut (gastrointestinal tract). When we eat, food passes down the gullet (esophagus), into the stomach, and then into the small intestine. The small intestine has three sections – the duodenum, jejunum, and ileum. The duodenum is the first part of the small intestine and follows on from the stomach. The duodenum curls around the pancreas creating a c-shaped tube. The jejunum and ileum make up the rest of the small intestine and are found coiled in the center of the tummy (abdomen). The small intestine is the place where food is digested and absorbed into the bloodstream.
Following on from the ileum is the first part of the large intestine, called the caecum. Attached to the caecum is the appendix. The large intestine continues upwards from here and is known as the ascending colon. The next part of the gut is called the transverse colon because it crosses the body. It then becomes the descending colon as it heads downwards. The sigmoid colon is the s-shaped final part of the colon which leads on to the rectum. Stools (feces) are stored in the rectum and pushed out through the back passage (anus) when you go to the toilet. The anus is a muscular opening that is usually closed unless you are passing stool. The large intestine absorbs water and contains food that has not been digested, such as fiber.
The gut (gastrointestinal tract) processes food – from the time it is first eaten until it is either absorbed by the body or passed out as stools (feces). The process of digestion begins in the mouth. Here your teeth and chemicals made by the body (enzymes) begin to break down food. Muscular contractions help to move food into the gullet (esophagus) and on to the stomach. Chemicals produced by cells in the stomach begin the major work of digestion.
While some foods and liquids are absorbed through the lining of the stomach, the majority are absorbed in the small intestine. Muscles in the wall of the gut mix your food with the enzymes produced by the body. They also move food along towards the end of the gut. Food that can’t be digested, waste substances, germs (bacteria) and undigested food are all passed out as feces.
The mouth contains salivary glands which release saliva. When food enters your mouth the number of saliva increases. Saliva helps to lubricate food and contains chemicals (enzymes) that start chemically digesting your meal. Teeth break down large chunks into smaller bites. This gives a greater surface area for the body’s enzymes to work on. Saliva also contains special chemicals that help to stop germs (bacteria) from causing infections. The amount of saliva released is controlled by your nervous system.
A certain amount of saliva is normally continuously released. The sight, smell or thought of food can also stimulate your salivary glands. To pass food from your mouth to the gullet (esophagus) you must be able to swallow. Your tongue helps to push food to the back of the mouth. Then the passages to your lungs close and you stop breathing for a short time. The food passes into your esophagus. The esophagus releases mucus to lubricate food. Muscles push your meal downwards towards the stomach.
The esophagus is a muscular tube that connects the pharynx (throat) to the stomach. The esophagus contracts as it moves food into the stomach. A “valve” called the lower esophageal sphincter (LES) is located just before the opening to the stomach.
This valve opens to let food pass into the stomach from the esophagus and it prevents food from moving back up into the esophagus from the stomach. Medical conditions related to the esophagus include: Barrett’s Esophagus, Dysphagia (difficulty swallowing), Eosinophilic esophagitis (EoE), and GERD.
The stomach is a J-shaped organ that lies between the esophagus and the small intestine. It has three main functions: Stores ingested food and releases it into the small intestine at a rate that is optimal for digestion and absorption. The stomach has four major regions: the cardia, fundus, body, and pylorus. The cardia (or cardiac region) is the point where the esophagus connects to the stomach and through which food passes into the stomach. Located inferior to the diaphragm, above and to the left of the cardia, is the dome-shaped fundus.
Below the fundus is the body, the main part of the stomach. The funnel-shaped pylorus connects the stomach to the duodenum. The wider end of the funnel, the pyloric antrum, connects to the body of the stomach. The narrower end is called the pyloric canal which connects to the duodenum. The smooth muscle pyloric sphincter is located at this latter point of connection and controls stomach emptying. In the absence of food, the stomach deflates inward, and its mucosa and submucosa fall into a large fold called a ruga.
The stomach receives food from the esophagus. As food reaches the end of the esophagus, it enters the stomach through a muscular valve called the lower esophageal sphincter. Your stomach is a sac-like organ with strong muscular walls located on the left side of the upper abdomen. In addition to holding food, it serves as the mixer and grinder of food. Its main function is to help digest the food you eat. The other main function of the stomach is to store food until the gastrointestinal tract (gut) is ready to receive it. You can eat a meal faster than your intestines can digest it. Your stomach makes acid and powerful enzymes that break the food down and change it to a liquid or paste. From there, food moves to your small intestine.
Digestion involves breaking food down into its most basic parts. It can then be absorbed through the wall of the gut into the bloodstream and transported around the body. The wall of the stomach has several layers. The inner layers contain special glands. These glands release enzymes, hormones, acid, and other substances. These secretions form gastric juice, the liquid found in the stomach. The stomach secretes acid and enzymes that digest food. The stomach muscles contract periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.
A few minutes after food enters the stomach the muscles within the stomach wall start to tighten (contract). This creates gentle waves in the stomach contents. This helps to mix the food with gastric juice. Using its muscles, the stomach then pushes small amounts of food (now known as chyme) into the duodenum. The stomach has two sphincters, one at the bottom and one at the top. Sphincters are bands of muscles that form a ring. When they contract the opening, the control closes. This stops chyme going into the duodenum before it is ready. Digestion of food is controlled by your brain, nervous system, and various hormones released in the gut.
Even before you begin eating, signals from your brain travel via nerves to your stomach. This causes gastric juice to be released in preparation for food arriving. Once food reaches the stomach, special cells that detect changes in the body (receptors) send their own signals. These signals cause the release of more gastric juice and more muscular contractions. When food starts to enter the duodenum this sets off different receptors. These receptors send signals that slow down the muscular movements and reduce the amount of gastric juice made by the stomach. This helps to stop the duodenum from being overloaded with chyme.
The stomach is surprisingly small when it’s empty, “about the size of a person’s palm”, says Dr Paul Ng, a Hong Kong-based specialist in gastroenterology and hepatology. Yet as everyone with a good appetite knows, the stomach is elastic and can expand too many times that size. “There are two openings in the stomach” Ng explains. “Sometimes when there is a blockage at the lower opening (pylorus), gastric outlet obstruction (GOO) can occur, in which the stomach becomes extremely distended. Even when that happens, people would vomit instead of having their stomach torn apart by the accumulation, so the stomach doesn’t explode”.
It has some serious storage capacity. While your stomach is resting, it holds about 7 ounces of stomach acid and bile. However, it has the capacity to hold nearly a half-pound of food at a time if necessary. (The average capacity is about 32 ounces or a quarter-gallon.) It normally takes from four to six hours to digest one meal, so this capacity can be important. Depending on the position of your body and the amount of food inside it, your stomach is capable of alterations in size and shape. Your empty stomach is about 12 inches long. At its widest point, it’s about 6 inches across.
Thanks to the high production of hydrochloric acid, which is highly potent, the stomach regenerates its lining frequently. The stomach cavity has a powerful protective process in place that normally keeps the pH of the stomach balanced. Potassium ions help to modulate the hydrochloric acid, and the stomach lining itself produces high numbers of goblet mucous cells to protect the lining.
The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide. A pH of 7 is considered neutral. Below 7 pH is acidic and above 7 pH is basic. The farther away from a neutral ph of 7, the stronger the acid or base.
Normally, vitamin B12 is readily absorbed in the last part of the small intestine (ileum), which leads to the large intestine. However, to be absorbed, the vitamin must combine with intrinsic factor, a protein produced in the stomach. Your stomach is responsible for helping to release the crucial vitamin B12 [PDF] from the proteins you eat.
Hydrochloric acid and an enzyme called pepsin to break the locked B12 out of its protein so it can be absorbed into your bloodstream. “The metabolism of vitamin B starts in the stomach in the parietal cells,” Lisa Ganjhu, associate professor of gastroenterology and hepatology at NYU Langone Medical Center. Vitamin B “is one of the main vitamins in our body to help with metabolism and energy production,” she says.
Eating and digesting your food is most likely something you never have to think about. Yet your GI tract is home to a veritable orchestra of hormones stimulated by epithelial cells that line the stomach and small intestine. These hormones engage in a wide range of functions, including stimulating appetite, encouraging the secretion of enzymes and gastric acid, and reminding the gall bladder to contract and empty. These hormones directly enter the blood and eventually affect the function of other parts of the digestive system, including the liver and pancreas, and even your brain. Gastrin is a hormone that is produced by ‘G’ cells in the lining of the stomach and upper small intestine.
During a meal, gastrin stimulates the stomach to release gastric acid. This allows the stomach to break down proteins swallowed as food and absorb certain vitamins. Ghrelin is produced in the stomach, and its function is to tell the brain that the body has to be fed. It increases appetite. It stimulates the release of gastric juice rich in pepsin and hydrochloric acid. Secretin is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver. It is a peptide hormone produced in the S cells of the duodenum, which are located in the intestinal glands. For more info on hormones, see this article.
Besides just digesting your food, the stomach helps protect your entire body. The acidity in our stomach helps to sterilize whatever you’re eating. It kills off bacteria and potential food toxins. Your gastrointestinal tract also has patches of lymphoid defense cells it sends out when something makes it through the stomach, such as a virus or bacterial infection. In fact, about 70 percent of the immune system is housed in the gut, so making sure our digestive system is in tip-top shape can be key to addressing many of our bodily woes.
“All Disease Begins in The Gut.” – Hippocrates. It’s common to overlook the health of our gastrointestinal system, even though it contains 10 times more health-determining bacteria than the rest of our body. Protecting us from infection, supporting our metabolism, and promoting healthy digestion and elimination. Getting your gut bacteria healthy is one of the most important things you can do to get and stay healthy. If your bacteria are sick, so are you! Your gut wall houses 70 percent of the cells that make up your immune system. For optimal immunity, detoxification and nourishment, your gut must function seamlessly.
Your stomach may very well be a key player in keeping your mood balanced. New research suggests links between the gut microbiome (the microorganisms that live in any environment) and your mental health. A recent study in the Journal of Psychiatric Research found that transferring the gut microbiota of depressed human patients into rats induced depressive symptoms in rodents, opening up a whole new realm of possible bacteria-based treatments. The gut and brain talk to each other through nerve signals, the release of gut or stress hormones, and other pathways.
We have long known that emotions can directly alter gut function. Lately, research at Harvard Medical School has discovered that it works the other way too: our gut actually has an effect on our brain. It goes both ways. The gastrointestinal tract is sensitive to emotion as well. Anger, anxiety, sadness, elation – all of these feelings (and others) can trigger symptoms in the gut. Therefore, a person’s stomach or intestinal distress can be the cause or the product of anxiety, stress, or depression.
If you’ve ever had the misfortune to find yourself stranded by the toilet for 24 to 48 hours purging the contents of your stomach, you may have described the cause as stomach flu. However, actual influenza is primarily a respiratory infection. What keeps you in the bathroom is likely some form of norovirus or rotavirus, which causes gastroenteritis of the stomach and intestines, and usually resolves in one to two days.
The flu shot protects against influenza, which isn’t the same thing as the stomach flu (gastroenteritis). Gastroenteritis is an infection caused by a variety of viruses, including rotaviruses and noroviruses. Although it is often called the stomach flu, gastroenteritis is not caused by influenza viruses. “No,” said Oklahoma Medical Research Foundation immunologist Hal Scofield, M.D. “Although some may call it the “stomach flu”, it actually has nothing to do with the influenza virus.” More accurately called gastroenteritis, contagious stomach illness is most often caused by two viruses, rotavirus or norovirus.
The causes of ulcers have perplexed medical researchers for years. However, recent studies have found a link between the bacteria H. pylori and inflammation of the stomach lining, gastritis, and ulcers. In fact, new research suggests that the bacteria may also be linked to stomach cancer. Helicobacter pylori bacteria commonly live in the mucous layer that covers and protects tissues that line the stomach and small intestine. Often, the H. pylori bacterium causes no problems, but it can cause inflammation of the stomach’s inner layer, producing an ulcer.
Stress ulcers come on suddenly, usually as a result of physiological stress. Some acidic foods can make ulcers worse, as can physical stress, such as the stress of a serious injury or infection. This may be because stress increases stomach acid. You will most likely feel burning pain or discomfort between your belly button and breastbone. You might especially notice it on an empty stomach, such as between meals or at night. The pain may stop for a little while if you eat or take an antacid but then return. The pain can last for a few minutes or a few hours and may come and go for many days or weeks.
Gastroesophageal reflux: Stomach contents, including acid, can travel backward up the esophagus. There may be no symptoms or reflux may cause heartburn or coughing.
Dyspepsia: Another name for stomach upset or indigestion. Dyspepsia may be caused by almost any benign or serious condition that affects the stomach.
Gastric ulcer (stomach ulcer): an erosion in the lining of the stomach, often causing pain and/or bleeding.
Peptic ulcer disease: Doctors consider ulcers in either the stomach or the duodenum (the first part of the small intestine) peptic ulcer disease.
Gastritis: Inflammation of the stomach, often causing nausea and/or pain. Gastritis can be caused by alcohol, certain medications, H. pylori infection, or other factors.
Gastric varices: In people with severe liver disease, veins in the stomach may swell and bulge under increased pressure. Called varices, these veins are at high risk for bleeding, although less so than esophageal varices are.
Stomach bleeding: Gastritis, ulcers, or gastric cancers may bleed. Seeing blood or black material in vomit or stool is usually a medical emergency.
Gastroparesis (delayed gastric emptying): Nerve damage from diabetes or other conditions may impair the stomach’s muscle contractions. Nausea and vomiting are the usual symptoms.
The small intestine also has special features that help to increase the number of nutrients absorbed by the body. The inner layer of the small intestine has millions of what are known as villi. These are tiny finger-like structures with small blood vessels inside. They are covered by a thin layer of cells. Because this layer is thin, it allows the nutrients released by digestion to enter the blood. Most of the important nutrients needed by the body are absorbed in different points of the small intestine. Following on from the ileum is the large intestine. The inside of the large intestine is wider than the small intestine. It does not contain villi, and mainly absorbs water.
Bacteria in the large intestine also help with the final stages of digestion. Once chyme has been in the large intestine for 3-10 hours it becomes semi-solid. This is because most of the water has been removed. These remnants are now known as stools. Movements of the muscles found in the large intestine help to digest the chyme and move feces towards the rectum. When feces are present in the rectum, the walls of the rectum stretch. This stretch activates special receptors. These receptors send signals via nerves to the spinal cord. The spinal cord signals back to the muscles in the rectum, increasing pressure on the first sphincter of the back passage.
The liver is a large, meaty organ that sits on the right side of the belly. The liver also detoxifies chemicals and metabolizes drugs. As it does so, the liver secretes bile that ends up back in the intestines. The liver also makes proteins important for blood clotting amongst other things. The liver is an organ with many functions. Your liver’s two main responsibilities in the process of digestion are:
To make and secrete bile. And to process and purify the blood containing newly absorbed nutrients that are coming from the small intestine. Bile has two main purposes: to help absorb fats and to carry waste from the liver that cannot go through the kidneys. Bile is made in the liver travels to the small intestine through the bile ducts. If the bile isn’t needed immediately, it is stored in the gallbladder.
Your gallbladder is a four-inch, pear-shaped organ. It’s positioned under your liver in the upper-right section of your abdomen. The gallbladder stores bile, a combination of fluids, fat, and cholesterol. The gallbladder sends this stored bile into the small intestine to aid in the digestion of food. It then delivers bile into the small intestine. Your gallbladder serves as a storage pouch. It concentrates the bile into the form that’s best used for digestion. When you eat, the bile is squeezed out of the gallbladder and goes into the first part of the small intestine, the duodenum, through the common bile duct.
While the liver is hard at work making the dark green bile that helps with digestion, the gallbladder holds the bile until you actually need it, says Erin Gilbert, MD, an assistant professor of surgery at Oregon Health and Science University in Portland. “It concentrates the bile into the form that’s best used for digestion,” Dr. Gilbert says. “When you eat, the bile is squeezed out of the gallbladder and goes into the first part of the small intestine, the duodenum, through the common bile duct.” The liver produces anywhere from 500 to 1,000 milliliters (ml) of bile per day, but the gallbladder can concentrate that bile up to tenfold and store 30 to 50 ml of the denser bile.
Your pancreas is located behind your stomach and is attached to both your gallbladder and your small intestines. Among other functions, the pancreas aids in digestion by producing digestive enzymes and secreting them into the duodenum (the first segment of the small intestine). These enzymes break down protein, fats, and carbohydrates.
The pancreas is an organ located in the abdomen. It plays an essential role in converting the food we eat into fuel for the body’s cells. The pancreas has two main functions: an exocrine function that helps in digestion and an endocrine function that regulates blood sugar. Now, it is possible for people to live without a pancreas. Surgery to remove the pancreas is called pancreatectomy. Removing the pancreas can also reduce the body’s ability to absorb nutrients from food. Without artificial insulin injections and digestive enzymes, a person without a pancreas cannot survive.
The large intestine, also called the colon, is part of the final stages of digestion. It is a large tube that escorts waste from the body. The body has two types of intestines. The small intestine is connected to the stomach and handles the middle part of the digestion process. A 5- to 7-foot-long muscular tube that connects the small intestine to the rectum and is responsible for processing waste so that defecation is easy and convenient. It is made up of the ascending (right) colon, the transverse (across) colon, the descending (left) colon, and the sigmoid colon, which connects to the rectum.
The 4 major functions of the large intestine are the recovery of water and electrolytes, formation and storage of feces, and fermentation of some of the indigestible food matter by bacteria. The ileocaecal valve controls the entry of material from the last part of the small intestine called the ileum. The colon is much wider than the small intestine but is also much shorter. According to the Cleveland Clinic, the small intestine is 22 feet (6.7 meters) long. The colon is only 6 feet (1.8 m) long. This 6 feet of dense muscle is divided into four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon.
An 8-inch chamber that connects the colon to the anus. The rectum receives stool from the colon, sends signals to the brain if there is stool to be evacuated, and holds stool until evacuation can happen. The last part of the digestive tract is the anus, which consists of pelvic floor muscles and two anal sphincters (internal and external). Together their jobs are to detect rectal contents.
Whether they are liquid, gas, or solid, and then control when stool should and shouldn’t be excreted from your body. The external sphincter of the anus is under voluntary control. This means you can decide whether you will open your bowels or not. Young children have to learn to control this during toilet training.
23. Medical Conditions Involving Multiple Digestive Organs
There are many medical conditions that involve more than one digestive organ. These include: Gallstones, hard deposits that form in your gallbladder. Celiac Disease, a serious sensitivity to gluten that damages your villi, in your small intestines that help you to absorb nutrients from the foods you eat. Crohn’s Disease, an inflammatory bowel disease that can affect any part of the digestive tract.
Ulcerative Colitis, similar to Crohn’s, but the part of the digestive tract affected is solely the large intestine. Irritable Bowel Syndrome, stomach pain or discomfort at least three times a month for several months. Hemorrhoids, inflammation of the blood vessels at the end of your digestive tract. Diverticulitis, Small pouches can form anywhere there are weak spots in the lining of your digestive system. Anal Fissure, tiny oval-shaped tears in the lining of the very end of your digestive tract.
Candidiasis is a fungal infection due to any type of Candida (a type of yeast). When it affects the mouth, it is commonly called thrush. Signs and symptoms include white patches on the tongue or other areas of the mouth and throat. Other symptoms may include soreness and problems swallowing. The 7 main symptoms of Candida overgrowth are: Oral Thrush. Candidiasis that develops in the mouth or throat is called “thrush.” Tiredness and Fatigue.
Recurring Genital or Urinary Tract Infections. Digestive Issues. Sinus Infections. Skin and Nail Fungal Infections, and Joint Pain. One of the symptoms of systemic Candida is weight gain, or difficulty losing weight. It can cause the kind of stubborn fat deposits that are hard to shake off, no matter how little you eat or how much exercise you do. Candida can lead to excess fat deposits in a few different ways.
Small intestinal bacterial overgrowth (SIBO) is a serious condition affecting the small intestine. It occurs when bacteria that normally grow in other parts of the gut start growing in the small intestine. That causes pain and diarrhea. It can have mild symptoms or full-blown malabsorption. Small intestine fungal overgrowth (SIFO) occurs when excessive amounts of fungus populate the small bowel. If SIBO is left untreated it can lead to other conditions such as IBS, leaky gut, obesity, acne, anemia, fatigue and an increase of symptoms in gut-brain disorders such as anxiety, depression, and autism.
It can also cause weight gain. SIBO can slow down metabolism and affect your insulin and leptin resistance, both of which help regulate hunger and satiety. The most common symptoms of SIBO include: Abdominal pain/discomfort. Bloating and abdominal distention. Diarrhea. Constipation (generally associated with methanogens). Gas and belching. In more severe cases, there may be weight loss and symptoms related to vitamin deficiencies.
The stomach is the widest part of the digestive system. Your stomach not only digests food, but it also stores it. It can hold a bit more than a quart (1 liter) of food at once. The design of the stomach allows a person to eat a large meal that can be digested slowly over time. The stomach secretes acid and enzymes that digest food. Ridges of muscle tissue called rugae line the stomach. The stomach muscles contract periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.
The stomach has 3 main functions: temporary storage for food, which passes from the esophagus to the stomach where it is held for 2 hours or longer. Mixing and breakdown of food by contraction and relaxation of the muscle layers in the stomach. The digestion of food. It is part of your gut (gastrointestinal tract). A healthy gut contains healthy bacteria and immune cells that ward off infectious agents like bacteria, viruses, and fungi. A healthy gut also communicates with the brain through nerves and hormones, which helps maintain general health and well-being.