Small role in neutralising the acidity of

Small intestines:Digestion,absorption and motility,different food groups.Small intestines are located within the gastrointestinal tract and they assist in the digestion and absorption of ingested food.They extend from the stomach(pylorus) to ghe large intestines where they meet at the ileocecal junction.Small intestines are anatomically divided into 3 parts ;Duodenum,Jejunum,Ileum.DuodenumThis is the most proximal portion of the small intestines.It recieves partially digested food(chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption.Pancreatic secretions are emptied into the duodenum where they mix with the chyme , as well as bile from the liver and gallbladder.These play an important role in neutralising the acidity of the chyme and completing chemical digestion.Brunner’s gland in the mucosa of the duodenum secrete alkaline mucus containing a high concentration of bicarbonate ions to neutralise the HCL present in the chyme..The alkaline mucus also protects the walls of the duodenum.Bile acts as an emulsifier breaking down lipids into smaller globules to increase surface area.Pancreatic juice contains many enzymes to break carbohydrates ,lipids,proteins and nucleic acids into their monomer subunits.These secretions are thoroughly mixed with the chyme until all of the digestible material is chemically digested.Slow waves of smooth muscle contraction known as peristalsis flow down the length of the gastrointestinal tract to push chyme through the duodenum.Each wave begins at the stomach and pushes chyme a short distance toward the jejunum.Small regional contaractions of the intestinal wall known as segmentations help mix chyme and increase the rate of digestion.They also increase the contact of chyme with the mucosal cells to increase the absorption of nutrients through the intestinal wall.JejunumIt begins at the duodenojejunal flexure and is located between the duodenum and ileum. Most of the nutrients present in food are absorbed by the jejunum before being passed on to the ileum for further absorption. Partially digested food known as chyme enter the jejunum from the duodenum.The chyme is then mixed by smooth muscle contractions in the walls that help circulate chyme and increase its contact with the walls of the jejunum.Walls of the jejunum and folded many times over to increase its surface area and allow to absorb nutrients.The entire wall of the jejunum is also folded into the villi that further increase the surface area of the jejunum.The entire structure of the jejunum is optimised for further absorption of chyme by the time chyme has passed through the jejunum 90% of available nutrients have been absorbed into the body.IleumIleum is the last part of the small intestine and ends of the ileocecal junction.It is where the remaining nutrients are absorbed before moving into the large intestine.Smooth muscle spinster controls the flow of chyme into the large intestines.CarbohydratesThese are broken down by pancreatic amylase into simple sugars (monosaccharides).LipidsBroken down by pancreatic lipase with the help of bile into fatty acids and glycerol.Proteins and peptidesBroken down by trypsin and chymotrypsin into amino acids.(5)Accessory organs of the GIT: liver , pancreas and gallbladder.PancreasThis is a flattened oblong shaped organ that lies behind the peritoneal cavity in the upper abdomen behind the stomach.Pancreas is divided into 4 parts;the head,which is connected to the duodenum through the pancreatic duct uncinate process neck body TailPancreas has two functions exocrine and endocrine.Where the exocrine function is involved in digestion while the endocrine function helps maintain blood sugar levels.The pancreas containing cells that produce the digestive enzymes and secretions, called pancreatic acini.They produce pancreatic juice which contains digestive enzymes and bicarbonate ions and empties them into the duodenum.Pancreatic juice is released into ducts which join with the common bile duct before entering the duodenum via the hepatopancreatic ampulla which has a smooth muscle spincter that controls the release of pancreatic juice and bile into the duodenum.Pancreatic juice contains mostly water,some salts, digestive enzymes and sodium bicarbonate.Sodium bicarbonate is responsible for the slight alkalinity of pancreatic juice which neutralizes acidic gastric juice in chyme.Pancreas produces protein digesting enzymes in their inactive forms to prevent them from digesting the pancreas.They are activated in the duodenum.Enteropeptidase stimulates the activation of trypsin from trypsinogen which in turn changes the pancreatic enzymes procarboxypeptidase and chymotrypsinogen into the active forms carboxypeptidase and chymotrypsin enzymes that digest starch(amylase), fat(lipase) and nucleic acids (nuclease) are secreted in their active forms.LiverThis is a peritoneal organ and is the largest visceral structure in the abdominal cavity.It is located in the right hypochondrium and epigastric areas.It is divided into two lobes;the right lobe and the left lobe by the attachment of the falciform ligament.There are two further lobes that arise from the right lobe the caudate lobe and the quadrate lobe.The liver has three main components:hepatocytes,bile canaliculi and hepatic sinusoids.Hepatocytes produce bile which flows into bile ducts which unite to form the right and left hepatic duct which in turn merge and exit the liver as a common hepatic duct.Bile is produced by the liver for the emulsification of lipids in the small intestines.Bile contains important components which are bile salts and phospholipids.Phospholipids aid in breaking down of the lipids thus increase surface area available for lipid digestive enzyme activity.Bile salts acts as emulsifying agents so they are also important for the absorption of digested lipids.Once bile salts reach the ileum they are absorbed and returned to the liver in the hepatic portal bloo, thus recycled.Bilirubin present in bile is a product of the liver’s digestion of worn out red blood cells,it gives bile its distinctive greenish colour.Gall bladderThis is a peritoneal structure found in the right hypochondriac region.It is pear shaped and is divided into 3 parts;FundusBodyNeckIt is a small storage organ that stores,concentrates and when stimulated propels the bile into the duodenum via the common bile duct.The tapered end of the gallbladder narrows into the cystic duct which connects to the common hepatic duct that carries bile from the liver.The ducts merge to form the common bile duct that extends to the wall of the duodenum. From the cystic duct bile is pushed into the gallbladder by peristalsis( muscle contractions that occur in orderly waves)Bile is then slowly concentrated by absorption of water through the walls of the gallbladder.The gallbladder stores this concentrated bile until it is needed to digest the next meal.The walls of the duodenum contain sensory receptors that monitor chemical makeup of chyme, when these cells detect fats they respond by producing the cholecystokinin which enters the bloodstream and travels to the gall bladder where it stimulates the smooth muscle tissue of the walls of the gallbladder.These forces bile out of the gallbladder and into the cystic duct.From the cystic duct bile enters the common bile duct and flows into the ampulla of vater,where the bile ducts merge with the pancreatic duct.From where it flows into the duodenum.Bile in the gallbladder may crystallize and form gallstones which can be a potentially life-threatening condition.References of medical physiology Unit XII Gastrointestinal physiology


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