The esophagus is involved in the processes of swallowing and peristalsis to move substances from the mouth to the stomach. The swallowing food begins in the mouth and continues with the contraction of skeletal muscles in the pharynx and esophagus. The upper esophageal sphincter dilates to permit the swallowed substance to enter the esophagus. From this point, waves of muscle contraction called peristalsis move food toward the stomach. In peristalsis, regions of the esophagus closer to the stomach open to permit food to pass through while the region just above the food contracts to push the food onward. Peristalsis works so well that food can be swallowed even while the body is lying down, upside down, or even in zero-gravity. A final function of the esophagus is its participation in the vomiting reflex to void the contents of the stomach. Peristalsis is reversed in the esophagus during vomiting to forcefully remove toxic or pathogen-laden food from the body. The esophagus is made of four distinct tissue layers, The mucosa layer, the submucosa layer, the muscularis layer and the adventitia layer. The mucosa layer forms the inner lining of the esophagus and is the only tissue layer that has direct contact with substances passing through the esophagus. Non-keratinized stratified squamous epithelial tissue makes up the majority of the mucosa layer and provides protection to the esophagus from rough food particles and acid from the nearby stomach. Mucous glands in the mucosa produce mucus to lubricate the esophagus and help shield the mucosa from stomach acid. Deep to the mucosa is the submucosa layer that contains connective tissue and provides blood and nerve supply to the mucosa and other tissues of the esophagus.
Surrounding the submucosa is the muscularis layer that allows the esophagus to contract and expand to move substances. Skeletal muscle is mostly found in the superior region of the esophagus to aid in the swallowing reflex while smooth muscle in the inferior esophagus pushes substances toward the stomach via peristalsis. Finally, the adventitia layer forms an outer covering of loose connective tissue around the esophagus and attaches it loosely to the surrounding organs. The esophagus is a long, thin, and muscular tube that connects the pharynx (throat) to the stomach. It forms an important piece of the gastrointestinal tract and functions as the conduit for food and liquids that have been swallowed into the pharynx to reach the stomach. The esophagus is about 9-10 inches (25 centimeters) long and less than an inch (2 centimeters) in diameter when relaxed. It is located just posterior to the trachea in the neck and thoracic regions of the body and passes through the esophageal hiatus of the diaphragm on its way to the stomach. At the superior end of the esophagus is the upper esophageal sphincter that keeps the esophagus closed where it meets the pharynx. The upper esophageal sphincter opens only during the process of swallowing to permit food to pass into the esophagus. At the inferior end of the esophagus, the lower esophageal sphincter opens for the purpose of permitting food to pass from the esophagus into the stomach. Stomach acid and chyme (partially digested food) is normally prevented from entering the esophagus, thanks to the lower esophageal sphincter. If this sphincter weakens, however, acidic chyme may return to the esophagus in a condition known as acid reflux. Acid reflux can cause damage to the esophageal lining and result in a burning sensation known as heartburn. If these symptoms occur with enough frequency, they are known as GERD (gastroesophageal reflux disease). Source
The gallbladder is a pear-shaped, hollow structure located under the liver and on the right side of the abdomen. Its primary function is to store and concentrate bile, a yellow-brown digestive enzyme produced by the liver. The gallbladder is part of the biliary tract. The gallbladder serves as a reservoir for bile while it’s not being used for digestion. The gallbladder’s absorbent lining concentrates the stored bile. When food enters the small intestine, a hormone called cholecystokinin is released, signaling the gallbladder to contract and secrete bile into the small intestine through the common bile duct. The bile helps the digestive process by breaking up fats. It also drains waste products from the liver into the duodenum, a part of the small intestine. Source
The liver is an essential organ that has many functions in the body, including making proteins and blood clotting factors, manufacturing triglycerides and cholesterol, glycogen synthesis, and bile production.
The liver is a large organ that sits on the right hand side of the belly.The liver is the body’s largest internal organ. Many different disease processes can occur in the liver, including infections such as hepatitis, cirrhosis (scarring), cancers, and damage by medications or toxins. Alcohol can be toxic to the liver (hepatotoxic), especially in high doses, and long-term alcohol abuse is a common cause of liver disease. The liver is involved in metabolizing many toxins, including drugs and medications, chemicals, and natural substances. The liver plays an important role in detoxifying the body by converting ammonia, a byproduct of metabolism in the body, into urea that is excreted in the urine by the kidneys. The liver also breaks down medications and drugs, including alcohol, and is responsible for breaking down insulin and other hormones in the body. The liver is also stores vitamins and chemicals that the body requires as building blocks. These includes vitamin B12, folic acid, iron required to make red blood cells, vitamin A for vision, vitamin D for calcium absorption, and vitamin K to help blood to clot properly. Source
The duodenum is the first and shortest segment of the small intestine. It receives partially digested food (known as chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine. Many chemical secretions from the pancreas, liver and gallbladder mix with the chyme in the duodenum to facilitate chemical digestion. Located inferior to the stomach, the duodenum is a 10-12 inch (25-30 cm) long C-shaped, hollow tube. The duodenum is a part of the gastrointestinal (GI) tract, attached to the pyloric sphincter of the stomach on its superior end and to the jejunum of the small intestine on its inferior end. The pancreas, liver and gallbladder all deliver their digestive secretions into the duodenum through an orifice known as the ampulla of Vater, which is located roughly in the middle of the duodenum on the left side. The walls of the duodenum are made of four layers of tissue that are consistent with the structure of the rest of the gastrointestinal tract: The innermost layer, the mucosa, the submucosa, the muscularis layer and lastly the outermost layer. The innermost layer, the mucosa, lines the inner surface of the duodenum and is in contact with chyme passing through the intestinal lumen. It is made of simple columnar epithelial tissue with microvilli on its surface to increase its surface area and improve the absorption of nutrients. Plentiful mucous glands secrete mucus into the lumen to lubricate the intestinal wall and protect it from friction and acidic chyme. Surrounding the mucosa layer is the submucosa, a layer of connective tissue that supports the other tissue layers. Many blood vessels and nerves pass through the submucosa, while protein fibers give strength and elasticity to the duodenum. Surrounding the submucosa is the muscularis layer that contains the smooth muscle tissue of the duodenum. Contractions of the muscularis mix chyme and propel it through the duodenum toward the rest of the small intestine. Lastly, the serosa is the outermost layer of the duodenum that acts as the outer skin of the intestine. Serous membrane made of simple squamous epithelium provides a smooth, slick surface to prevent friction between the duodenum and the surrounding organs. The serosa also secretes serous fluid to further reduce friction and keep the duodenum’s surface moist. Source
The transverse colon is the lengthy, upper part of the large intestine. Ingested food exits the small intestine and enters the cecum. As digestion continues, the ingested matter moves up the ascending colon and into the transverse colon. During this phase, bacteria further breaks down the food matter in a process called fermentation, water and nutrients are removed, and feces form. From there, feces moves through the descending colon and into the rectum, ultimately exiting the body through the anus as stool. Because of its importance, the transverse colon requires a constant supply of oxygenated blood. This comes by way of two arteries. The medial colic artery branches off the superior mesenteric artery, and it serves most of this part of the large intestine. One third also receives oxygenated blood from the inferior mesenteric artery. Like other parts of the large intestine, the transverse colon is susceptible to tumors and the onset of colon cancer. These cancers may also be preceded by polyps or other growths, which should be surgically removed when detected. Source
The transverse colon is the lengthy, upper part of the large intestine. Ingested food exits the small intestine and enters the cecum. As digestion continues, the ingested matter moves up the ascending colon and into the transverse colon. During this phase, bacteria further breaks down the food matter in a process called fermentation, water and nutrients are removed, and feces form. From there, feces moves through the descending colon and into the rectum, ultimately exiting the body through the anus as stool. Because of its importance, the transverse colon requires a constant supply of oxygenated blood. This comes by way of two arteries. The medial colic artery branches off the superior mesenteric artery, and it serves most of this part of the large intestine. One third also receives oxygenated blood from the inferior mesenteric artery. Source
The ascending colon is one of the four major regions of the colon, which is itself one of the parts of our large intestine. The ascending colon carries feces from the cecum superiorly along the right side of our abdominal cavity to the transverse colon. In the ascending colon, bacteria digest the transitory fecal matter in order to release vitamins. The intestinal wall absorbs water, nutrients, and vitamins from the feces and deposits these materials into our bloodstream. Source
Cecum, also spelled caecum, pouch or large tube-like structure in the lower abdominal cavity that receives undigested food material from the small intestine and is considered the first region of the large intestine. It is separated from the ileum (the final portion of the small intestine) by the ileocecal valve (also called Bauhin valve), which limits the rate of food passage into the cecum and may help prevent material from returning to the small intestine. The main functions of the cecum are to absorb fluids and salts that remain after completion of intestinal digestion and absorption and to mix its contents with a lubricating substance, mucus. The internal wall of the cecum is composed of a thick mucous membrane, through which water and salts are absorbed. Beneath that lining is a deep layer of muscle tissue that produces churning and kneading motions.
The appendix sits at the junction of the small intestine and large intestine. It’s a thin tube about four inches long. Normally, the appendix sits in the lower right abdomen. The function of the appendix is unknown. One theory is that the appendix acts as a storehouse for good bacteria, “rebooting” the digestive system after diarrheal illnesses. Other experts believe the appendix is just a useless remnant from our evolutionary past. Surgical removal of the appendix causes no observable health problems. There is condition named appendicitis and for unclear reasons when a person has appendicitis the appendix often becomes inflamed, infected, and can rupture. This causes severe pain in the right lower part of the belly, along with nausea and vomiting. Source
The spleen is an organ in the upper far left part of the abdomen, to the left of the stomach. The spleen varies in size and shape between people, but it’s commonly fist-shaped, purple, and about 4 inches long. Because the spleen is protected by the rib cage, you can’t easily feel it unless it’s abnormally enlarged. The spleen plays multiple supporting roles in the body. It acts as a filter for blood as part of the immune system. Old red blood cells are recycled in the spleen, and platelets and white blood cells are stored there. The spleen also helps fight certain kinds of bacteria that cause pneumonia and meningitis. A ruptured spleen can cause serious life-threatening internal bleeding and is a life-threatening emergency. An injured spleen may rupture immediately after an injury, or in some cases, days or weeks after an injury. In this inherited form of anemia, Sickle cell disease is when abnormal red blood cells block the flow of blood through vessels and can lead to organ damage, including damage to the spleen. People with sickle cell disease need immunizations to prevent illnesses their spleen helped fight. Source
The upper part of the stomach next to the cardia (the upper opening of the stomach, where the esophagus enters). Chief cells of the gastric fundus produce the pro-enzyme pepsinogen, which is converted to its active form by acid produced by parietal cells. Source
The cardia is the first portion of the stomach and is where food content passes from the esophagus into the stomach. The acids and enzymes referred to as the gastric juices are manufactured in the cardia. The fundus stores undigested food and also the gases released from the chemical digestion of food. The body of the stomach or the corpus is the largest of the four parts that make up the stomach. And this is where the bulk of the partial digestion occurs. The pylorus is connected to the duodenum or the beginning of the small intestine. The contents of the stomach move into the small intestine via the pyloric canal. Source
The stomach is the main food storage tank of the body. If it were not for the stomach’s storage capacity, we would have to eat constantly instead of just a few times each day. The stomach is a muscular organ located on the left side of the upper abdomen. 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. The stomach secretes a mixture of acid, mucus, and digestive enzymes that helps to digest and sanitize our food while it is being stored. 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. Source
Pylorus, cone-shaped constriction in the gastrointestinal tract that demarcates the end of the stomach and the beginning of the small intestine. The main functions of the pylorus are to prevent intestinal contents from reentering the stomach when the small intestine contracts and to limit the passage of large food particles or undigested material into the intestine. The internal surface of the pylorus is covered with a mucous-membrane lining that secretes gastric juices. Beneath the lining, circular muscle tissue allows the pyloric sphincter to open or close, permitting food to pass or be retained. The sphincter remains in an open or relaxed state two-thirds of the time, permitting small quantities of food to pass into the duodenum, the upper portion of the small intestine. When the duodenum begins to fill, pressure increases and causes the pyloric sphincter to contract and close. Muscular contractions (peristaltic waves) in the duodenum then push food deeper into the intestine. Because the pyloric sphincter is relatively narrow, only small amounts of well-emulsified food can pass through it even while it is open. Source
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. The pancreas is located behind the stomach in the upper left abdomen. It is surrounded by other organs including the small intestine, liver, and spleen. The head of the pancreas is where the stomach empties partially digested food into the intestine, and the pancreas releases digestive enzymes into these contents. A healthy pancreas produces the correct chemicals in the proper quantities, at the right times, to digest the foods we eat. Source
The common bile duct is a small, tube-like structure formed where the common hepatic duct and the cystic duct join. Its physiological role is to carry bile from the gallbladder and empty it into the upper part of the small intestine (the duodenum). The common bile duct is part of the biliary system. Descending Colon: Bile is a greenish-brown fluid that helps digest fats from our food intake. It is produced by the liver and stored and concentrated in the gallbladder until it is needed to help digest foods. When food enters the small intestine, bile travels through the common bile duct to reach the duodenum. Source
This is the final section of the small intestine. The function of the ileum is mainly to absorb vitamin B12 and bile salts and whatever products of digestion were not absorbed by the jejunum. The wall itself is made up of folds, each of which has many tiny finger-like projections known as villi on its surface. In turn, the epithelial cells that line these villi possess even larger numbers of microvilli. Therefore, the ileum has an extremely large surface area both for the adsorption (attachment) of enzyme molecules and for the absorption of products of digestion. The DNES (diffuse neuroendocrine system) cells of the ileum secrete various hormones (gastrin, secretin, cholecystokinin) into the blood. Cells in the lining of the ileum secrete the protease and carbohydrase enzymes responsible for the final stages of protein and carbohydrate digestion into the lumen of the intestine. These enzymes are present in the cytoplasm of the epithelial cells. The villi contain large numbers of capillaries that take the amino acids and glucose produced by digestion to the hepatic portal vein and the liver. Lacteals are small lymph vessels, and are present in villi. They absorb fatty acid and glycerol, the products of fat digestion. Layers of circular and longitudinal smooth muscle enable the chyme (partly digested food and water) to be pushed along the ileum by waves of muscle contractions called peristalsis. The remaining chyme is passed to the colon. The digestive system in the body plays a significant role in the metabolism of food. This vital system of the body consists of the stomach, liver, pancreas, and small and large intestine. The food is digested in the stomach, with the help of the enzymes secreted by the liver and the pancreas. The digested food is then passed through the small intestine where the nutrients are absorbed and assimilated in the bloodstream. The undigested food is then passed on to the large intestine, from where it is eliminated from the body through the anus. Whatever is left unabsorbed by the duodenum and jejunum is absorbed in the ileum. The ileum is one of the parts of the small intestine, the others being duodenum and jejunum. Source
The jejunum is a continuation of the small intestine following the duodenum. It begins at the duodenojejunal flexure, where the small intestine turns sharply toward the anterior direction. From the duodenojejunal flexure, the jejunum follows a convoluted path through the abdomen before continuing as the ileum. While the jejunum does not have an anatomical landmark to separate it from the ileum, it slowly changes its anatomical structure along its length as it transitions into the ileum. Partially digested food, known as chyme, enters the jejunum from the duodenum. As chyme enters the jejunum, it is mixed by segmentations, or localized smooth muscle contractions in the walls of the jejunum. These segmentations help to circulate chyme and increase its contact with the walls of the jejunum. The walls of the jejunum are folded many times over to increase its surface area and allow it to absorb nutrients. Each epithelial cell on the surface of the jejunum contains microscopic folds of cell membrane called microvilli that create tiny pockets and increase the contact between the cells and chyme. The entire wall of the jejunum is also folded into microscopic finger-like ridges known as villi that form larger pockets and further increase the surface area of the jejunum. At the macroscopic level, the inner surface of the jejunum contains many wrinkles of tissue known as circular folds, which create even more pockets for chyme and further increase the surface area available for absorption. Thus, the entire structure of the jejunum is optimized for the absorption of nutrients from chyme. By the time chyme has passed through the jejunum and enters the ileum, around 90% of all available nutrients have been absorbed into the body. Source
The sigmoid colon is a curved, S-shaped region of the large intestine and is the final segment of the colon. It transports fecal matter from the descending colon to the rectum and anus. Feces are stored in the sigmoid colon until they are ready to be eliminated from the body through the anal canal. The intestinal wall of the sigmoid colon also plays a small role in the absorption of water, nutrients and vitamins from feces. Four major tissue layers surround the hollow lumen of the sigmoid colon and provide its structure and function. the mucosa, the submucosa, The muscularis and the serosa layer. The innermost layer, the mucosa, is made of a mucous membrane consisting of simple stratified columnar epithelium and an underlying areolar connective tissue. The mucosa is the only tissue layer in contact with the contents of the sigmoid colon, acting as the interface between the colon and feces. Nutrients, vitamins and water present in feces are absorbed through the epithelium of the mucosa, while goblet cells produce thin, slick mucus to help feces move through the colon. The next layer outside the mucosa is the submucosa, a layer of connective tissues and nerves that support the mucosa. Blood vessels in the submucosa transport nutrients to and from the sigmoid colon, while nervous tissue monitors the contents of the sigmoid colon to manage the defecation reflex. The muscularis layer surrounds the submucosa and contains several layers of smooth muscle tissue. Contraction of smooth muscle tissue both forms the haustra of the sigmoid colon and propels feces out of the sigmoid colon and into the rectum during defecation. The outermost layer of the sigmoid colon is covered by the serosa layer, which extends as a thin membrane known as the mesentery. Although it is made of thin simple squamous epithelial tissue, the serosa protects the sigmoid colon from external friction by giving it a smooth surface and secreting lubricating serous fluid into the abdominal body cavity. The mesentery secures the colon along the posterior body wall and provides blood vessels and nerves to the colon, while the serosa protects the colon from friction caused by the body’s movement. Source
The rectum is a hollow muscular tube about 8 inches (20 cm) in length and 2.5 inches in diameter at its widest point. It extends from the inferior end of the sigmoid colon along the anterior surface of the sacrum and coccyx in the posterior of the pelvic cavity. At its inferior end, the rectum tapers slightly before ending at the anus. The mucosa forms the innermost layer of the rectum that is in contact with fecal matter. The mucosa is made of epithelial tissue that secretes mucus from specialized cells known as goblet cells. Mucus helps to protect the walls of the rectum and lubricate the feces as they pass through the rectum. Deep to the mucosa is the submucosa layer that supports the other layers of the rectum. Many blood vessels and nerves pass through the submucosa to provide nutrients, oxygen, and nerve signals to the mucosa and muscle tissue. Next is the muscularis layer, which contains layers of visceral (smooth) muscle. Contractions of the muscularis allow the rectum to expel feces during defecation. Finally, the serosa forms the outermost layer of the rectum and protects it from external damage. The serosa is made of a thin layer of simple squamous epithelium that secretes serous fluid to lubricate the exterior of the rectum and prevent damage caused by friction between the moving organs of the pelvic cavity. Source
The anus is the last part of the digestive tract. It is a 2-inch long canal consisting of the pelvic floor muscles and the two anal sphincters (internal and external). The lining of the upper anus is specialized to detect rectal contents. It lets you know whether the contents are liquid, gas, or solid. The anus is surrounded by sphincter muscles that are important in allowing control of stool. The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The internal sphincter is always tight, except when stool enters the rectum. It keeps us continent when we are asleep or otherwise unaware of the presence of stool. When we get an urge to go to the bathroom, we rely on our external sphincter to hold the stool until reaching a toilet, where it then relaxes to release the contents. Source