hello students welcome to e patiala let us have a general idea on the structure and functions of gastrointestinal tract in this module human beings build their body and obtain energy from other living organisms such as plants and animals by ingesting them the ingested food materials are passed through the digestive system which forms a tubular cavity in the body it is opened at both the ends and referred to as the elementary canal or gastrointestinal tract the digestive and accessory organs of gastrointestinal system helps in the process of digestion by secreting the enzymes and digestive juices for hydrolysis the digested food materials are absorbed and transported to different parts of the body by the respective organs the food materials transported gets metabolized and used for various cellular activities with this background it is essential to understand the anatomy and digestive system before knowing its mechanism objectives of this module this module enables a learner to understand the structure of an elementary canal and its associated organs and to describe the functions of different parts of alimentary canal in digestion process coming to the organization of the digestive system the human digestive system consists of the gastrointestinal tract and the accessory organs of digestion of complex food materials into simpler components which can be absorbed and assimilated into the body mouth the gastrointestinal tract starts at the mouth which is also known as oral or buccal cavity and comprises several structures which aid in digestion the mouth consists of vestibule and oral cavity proper the area between teeth lips and cheeks constitutes a vestibule whereas salivary gland and tongue forms the oral cavity proper the oral cavity is lined with oral mucosa and mucous membrane that secretes lubricating mucus which is made up of glycoprotein mucin the roof of the mouth is known as palate which separates oral cavity from the nasal cavity the heart palate covers the roof of mouth and is formed by maxilla and palatine bones it helps to facilitate the movement of food backwards towards the larynx the soft palate a muscular flap occupies the back of the roof of mouth it can be raised so as to shut off the nasal passage and prevent the airflow through nose at the base of the soft palate is uvula which prevents the food that is swallowed from passing into the nasal cavity the lips are soft fleshy folds of tissues that border the mouth and it is covered interiorly with mucous membrane and exteriorly by skin it also encompasses the upper and outer lip lateral two lips are the fleshy structures the cheeks that forms the sides of the mouth tongue is a muscular organ that forms the floor of mouth and has many taste buds which produce the sense of taste by detecting chemicals present in food the tongue has small ridges called papillae that helps it to grip and move around the mouth the tongue also helps to produce speech by altering the airflow through mouth and produce sound of different consonants teeth is made up of dentine and covered by the hardest tissue enamel tea chops and grind the food material into smaller pieces with the help of saliva and thereby increases the surface area for the action of digestive enzymes during mastication incisors are used for cutting the food pieces canines for tearing premolars and molars for chewing and grinding mastication of the food with saliva secreted by salivary gland in mouth moistens and lubricates the food particles to form a soft bolus before swallowing the digestion is aided by the oral digestive saliva which is secreted by salivary glands namely parotid sub maxillary or submandibular and sublingual glands present in the mouth these glands moisten and lubricate the food particles before swallowing a watery or serous type of saliva containing enzymes but not mucus is secreted by parotid glands both mucus producing elements and enzymes are secreted by submandibular gland which is present below the jaw the sublingual gland located underneath the tongue produces only the mucus type of saliva thus the main function of mouth is ingestion of food materials chewing and mixing of food with saliva and transfer of food to esophagus by swallowing followed by mouth is the pharynx which is also known as throat is a muscular tube-like organ which extends to the esophagus the swallowed food that is the bolus enters the stomach from mouth through oropharyns by passing through constricted opening called fossils fahren serves as a common path for both respiration and digestive tract since air and food must pass through it before entering the digestive tube esophagus is a long masculine collapsible mucous lined tube which extends from parents to stomach it serves as a dynamic passageway for food and pushes the food towards stomach by peristaltic waves the esophagus is guarded by muscular spinster at each end the upper esophageal spinster prevents air entering during respiration the lower esophageal spinster or cardiac spinster is located near an opening in the diaphragm known as esophageal hiatus the esophageal hierarchies permits the passage of esophagus into the abdomen the junction between esophagus and stomach is controlled by lower esophageal spinster which stays constricted during swallowing and vomiting to prevent backflow of food materials from stomach to esophagus diaphragm the thoracic cavity is separated from abdominal cavity by the muscular diaphragm the deodonym is attached to the diaphragm by suspensory muscles which pave way for the easier passage of digestive materials through deodinogenal flexure stomach the stomach is an elongated pouch or sac like organ located between the esophagus and small intestine the curve formed by the upper right and lower left surface of the stomach is known as lesser or greater curvature respectively the stomach has three regions namely fundus body and pylorus the fundus is the largest region of the stomach and is elevated above the level of esophageal opening the body is a central part and pylorus is a lower portion of this tumor the pylorus has two regions namely the proximal antrum and distal pyrolic canal which ends in pyloric spinster and opens into the diodinum the junction between the body and the antrum is called insisura angularis the war of the stomach has four layers of tissue a mucous lining submucous layer mucol layer and a fibro serous layer the innermost layer of gastrointestinal wall is a mucosa which is made up of a linear mucous epithelium a large loose connective tissue lamina propria and a thin layer of smooth muscles muscularis mucosa the submucosal layer is composed of connective tissues blood vessels lymph vessels alveolar tissues and master snowplexes it is thicker than mucosal layer and the muscular layer is thick that wraps submucosa and contains mitric plexus which lies between the inner circular and outer longitudinal smooth muscles lining the muscularis it regulates the movement of digestive tract and secretion the outermost layer serosa is made up of connective tissues and peritoneum it covers the stomach where momenta are attached the epithelial lining of the stomach is thrown into folds called ruggage which are marked by depressions known as gastric pits below the level of gastric bits particularly in the fungus and the body of stomach numerous coiled tubular glands called gastric glands are present these glands secrete gastric juice which contains hydrochloric acid and digestive enzymes the hydrochloric acid dissolves a particulate matter in food and particularly gets digested in the stomach by pepsin hydrochloric acid also kills the bacteria that enters along with the food and fuel survey to colonize and multiply in gastrointestinal tract mainly the large intestine the entire surface of the stomach gastric beds and gastric glands are covered by secretory cells namely chief cells which secretes enzymes of digastric juice parietal cells which secrete hydrochloric acid and intrinsic factors which binds to vitamin b12 to protect them from digestive juices and gets absorbed when they reach small intestine and endocrine cells which secretes geralin a hormone that stimulates the hypothalamus to increase apatite and gastrin which influences the digestive function the gastric glands in antrim contains anteroendocrine cells which secrete gastrin and intrachromaphin like cells which release histamine and d cells secrete somatostatin the stomach functions to store dissolve and partially digest the macromolecules into food and regulate the rate of which the contents of the stomach empty into the small intestine the small intestine is a long coiled loop found in the abdominal cavity it consists of short deodorant which is about 20 to 25 centimeter long surrounds the head of the pancreas and the uppermost region followed by diodinam is the jejunum which is 2.5 meter long and the longest segment ilium which is 3 meter long the mucosal layer of small intestine has many folds and tiny projections called bili which have velvety appearance each village consists of an arteriole venule and lacteal or lymph cells and resembles a fine brush this brush border is formed of microvilli which increases the surface area of the small intestine and helps in digestion and absorption in villi and crypts mucous secreting global cells are found where the intestinal crypts serve as a site of rapid mitotic cell division at the base of each crypt secretary cells produce enzymes that inhibit bacterial growth in small intestine the small intestine which is named as workhouse of digestion since nutrient absorption is higher in this region the crime mixes with the digestive secretions received from the pancreas and liver by peristaltic movement the continuous breakdown of food material occurs in the diodinum whereas the jejunum and ilium are mainly responsible for the absorption of nutrients into the bloodstream a worm-like structure known as vermiform appendix is present at the posterior end of small intestine which has no functional activity the cecum is a pouch which marks division between small intestine and the large intestine the cecum receives chyme from the ilium of small intestine and connects to the ascending colon of the large intestine at this junction there is a spinster or valve the ilioceical valve which slows the passage of time from the ilium allowing further digestion it is also the site of appendix attachment the large intestine bars the lowest part of the elementary cannot unnoticeably larger than that of small intestine it is a five to seven foot long muscular tube that connects a small intestine to the rectum the large intestine comprises the colon rectum and anus which bears a lower part of the elementary canal and noticeably larger than the small intestine iliocolic spinster is present at the junction between ilium and c-com and no villi is present numerous molecular secreting global cells are present and it is divided into cecum colon and rectum the colon is divided into ascending transverse descending and sigmoid portions the presence of intestinal mucous gland in the large intestine produces the lubricating mucus that coats the feces as they are formed uneven distribution of fibers in the muscle layer or longitudinal muscles are grouped into tape like strips called the tinia choli the circular muscles are formed into rings which produce pouch like hostra between them thus in the large intestine undigested materials gets concentrated the water and salts are absorbed and stored the descending colon is followed by the rectum and eight inch chamber that connects the coherent to the anus the rectum also serves as a reservoir for feces the contraction of rectum relaxes the associated spinster muscles to expel the fecus by defecation the rectum opens into anus through anal canal anus is lined with pelvic floor muscles and the internal and external anal spinster the pelvic floor muscle creates an angle between the rectum and the anus which stops the stool from coming out when it is not supposed to the anal spinster provide fine control of stool and the internal spinster is always tight except when the stool enters the rectum it keeps the continent when we are asleep or otherwise unaware of the presence of stool when we get an urge to defecate the external spinster keeps this tool unreleased the liver which is the largest gland and master gland and an accessory digestive gland in the body is located in the upper right portion of the abdomen and just beneath the diaphragm the liver is made of soft pinkish brown tissue encapsulated by connective tissue the capsule the capsule is covered and reinforced by the peritoneum of abdominal cavity which protects the liver and holds it in the place within the abdomen the peritoneum connects the liver by coronary ligament right and left triangular ligament and the false form ligament these connections are the condensed regions of peritoneal membrane that support the liver the coronary right and left triangular ligaments connect the liver to the diaphragm whereas the falsiform ligament connects the liver to umbilicus the liver consists of four lobes namely the left right chordate and quadrate lobes the left and right lobes are the largest lobes which are separated by falsiform ligament the right lobe is five to six times larger than the left lobe the cardiac lobe extend from the posterior side of the right lobe and surrounds the inferior vena cava the quadrate lobe also extends from the posterior side of the right lobe and wraps around the gallbladder each lobe is divided into numerous lobules by fibrous trans and small blood vessels which form a supporting framework for them the lobules appear like a honeycomb and are made up of liver cells called hepatocytes each lobule has three vessels namely hepatic artery portal vein and hepatic or bile duct the branches of hypertech artery and portal vein open into sinusoids a capillary-like tube this in turn opens into central vein which empties into hepatic vein sinusoids is a in the lobule or lined with reticular endothelial cells in between these cells macrophages called kapha cells are present which kills the bacteria onenote rbcs and other particles from the bloodstream bile secreted by the hepatic cells is collected by inuit by canaliculi which then enters a bile duct these bile ducts join together to form left and right hepatic depth which carry by from the left and right lobe of the liver the common hepatic duct finally joins with the cystic duct from the gallbladder to form the common bile duct carrying bile to the deodorant of the small intestine the blood supply of liver is unique among all organs of the body because of hepatic portal vein system blood traveling through the spleen stomach pancreas gallbladder and intestine passes through the capillaries of these organs and collected into hepatic portal vein it then delivers the blood to the tissues of liver where the contents of the bloods are divided into smaller vessels and processed before being passed on to the other parts of the body the exhaust of blood from the hepatocytic tissues are collected into the hepatic vein which leads to vena cava and returned back to the heart the liver also has its own arteries and arterioles which provides oxygenated blood to its tissues the liver being the most vital organ of the body perform many functions such as detoxification of various substances metabolizes proteins carbohydrates and fats store iron vitamin a b12 and d and also produces important plasma proteins and also serves as a site of hematopoiesis during fetal development the gallbladder which is a pure shaped organ lies beneath the liver the wall of the gallbladder is composed of serus muscular and mucus layer it consists of three sections namely fundus body and neck a duck causes stick duck arrives from the gallbladder and opens into hepatic duct these two ducts join together to form a common duct called common bile duct which opens into the duodenum along with pancreatic duct at this junction is a mucosal fold called hartman's pouch where gal stones get stuck the gallbladder functions as a storehouse of bile produced by the liver before being released into the small intestine the hydrogen ion secreted from the inner lining of gall bladder keep the bile in acidic condition and prevent hardening water and electrolytes from the digestive system are added to the dilute the bile in order to keep the bile and crystalline form salts attach themselves to cholesterol molecules present in the bile when bile is released into the intestine it helps with the digestion of fats by breaking down these larger particles into smaller ones after the absorption of fat the bile also gets absorbed and transported back to liver for reuse pancreas the pancreas is an elongated and a necessary digestive gland located behind the stomach which exhibits both endocrine and exocrine functions the exocrine part of pancreas is made up of axines or alveolar cells which possess the digestive enzymes a small duct arise from the lumen of each alveolus and they unite to form intra lobular duct which in turn joins to form the main duct of pancreas the viscence drug the wisson's dog joins with common bile duct to form ample air of batter which opens into the diodinum the pancreas plays an important role in digestion by secreting digestive enzyme found in the pancreatic juice the beta cells of pancreas secrete insulin which control carbohydrate metabolism and alpha cell secrete glucagon thus to ensure proper digestion and absorption of ingested food materials the integration and coordination of the digestive organs and activities are vital and necessary the physical and chemical changes in the ingested food materials were brought in the oral cavity and the digestive food materials were transported to different parts of the alimentary canal the stomach which aids in digestion passes the digested food material to the small intestine where it gets absorbed and further metabolized the process gets completed in large intestine where the undigested remnants are concentrated as pieces and expelled out hence the structure and gastrointestinal tract and its relationship are coupled with the functioning of other organisms organs the digestive efficiency of the organs in the digestion and absorption are very well related with the anatomy of the digestive system