GASTROINTESTINAL

GASTROINTESTINALEmbryoGI developmentForegut pharynx to duodenumMidgut duodenum to proximal 2/3rd of transverse colonHindgut distal 1/3rd of transverse colon to anal canal above pectinate lineDuodenal atresia failure to recanalize (trisomy 21)Jejunal, ileal, colonic atresia due to vascular accident (apple peel atresia)Midgut development:6th week midgut herniates through umbilical ring10th week returns to abdominal cavity + rotates around SMADis-developmentGastrochisis extrusion of abdominal contents through abdominal folds; not covered by peritoneumOmphalocele persistence of herniation of abdominal contents into umbilical cord; covered by peritoneumAnomaliesEsophageal atresia drooling, choking, and vomiting with first feeding.Allows air to enter stomach (visible on CXR).Cyanosis secondary to laryngospasmCongenital pyloric stenosis Hypertrophy of the pylorus causes obstructionPalpable olive mass in epigastric regionNonbilous-projectile vomiting

Pancreas and spleen embryoPancreas derived from the foregutAnnular pancreas ventral pancreatic bud abnormally encircles 2nd part of duodenum, forming a ring of pancreatic tissue that may cause duodenal narrowingPancreas divisum ventral and dorsal parts fail to fuse at 8 weeksSpleen arises in mesentery of stomach, but supplied by celiac artery in the foregut

AnatomyRetroperitoneal stricturesSAD PUCKERSuprarenal (adrenal) glandsAorta and IVCDuodenumPancreas UretersColonKidneysEsophagusRectum PhysiologyCHOLECYSTOKININ

Action

RegulationI cells (Duodenum, Jejunum)

pancreatic secretions gallbladder contraction gastric emptying relaxtion in sphincter of Oddi

fatty acids, amino acidsGASTRIN

Action

RegulationG cells (antrum of stomach)

gastric H+ secretion growth of mucosa gastric motility through stomach distention, vagal stimulation

by stomach pH falling below 1.5GLUCOSE-DEPENDENT INSULINOTROPIC PEPTIDE (GIP)

Action

RegulationK cells (duodenum, jejunum)

insulin release gastric secretions

fatty acids, amino acids, oral glucoseMOTILIN

Action

RegulationSmall intestine

Produces migrating motor complexes (they produce electric waves that trigger persistalsis) Motilin agonists (erythromycin) used in stimulating intestinal peristalsis

in fasting stateSECRETIN

Action

RegulationS cells (duodenum)

pancreatic Bicarbonate secretion gastric acid secretion bile secretion

by fatty acids, and acid in stomachSOMATOSTATIN

Action

RegulationD cells (pancratic islets, GI mucosa)

gastric acid secretion and pepsinogen secretion gallbladder contraction insulin and glucagon release

by acid by vagal stimulation

INTRINSIC FACTOR

Action

Parietal cells (stomach)

Vitamin B12-binding protein (require for B12 uptake in ileum)Autoimmune destruction of parietal cells is called Pernicious anemia

GASTRIC ACID (HCl)

Action

RegulationParietal cells (stomach)

stomach pH

By histamine, Ach, gastrin By somatostatin, GIP, Pges, secretinPEPSIN

Action

RegulationChief cells (stomach)

Protein digestion

vagal stimulation, local acidHCO3 (BICARBONATE)

Action

RegulationMucosal cells (stomach, duodenum, salivary glands, pancreas), Brunner glands (duodenum)HCO3 is trapped in mucosa that covers gastric epithelium

Neutralizes acid

by pancreatic and biliary secretion with secretin

Pancreatic secretionsAmylase Starch digestionLipase, phospholipase, colipase Fat digestionProteases (trypsin, chymotrupsin, elastase, carboxypeptidases) Protein digestionTrypsinogen converted to active enzyme by trypsin (look above) by enterokinase

CARB ABSORPTIONGlucose, galactose, fructose absorption by enterocytes. Transported to blood by GLUT-2Glucose and galactose by SGLTI Fructose taken up by facilitated diffusion by GLUT-5

Vitamin/mineral absorptionIron absorbed by Fe2+ in duodenumFolate absorbed in the jejunum and ileumB12 absorbed in terminal ileum along with bile acids (intrinsic factor required)Peyer patchesIn ileumNOT encapsulated by lymphoid tissueFound in lamina propria and submucosa of ileumContain specialized M cells that sample and present antigens to immune cellsB cells stimulated in germinal centers of Peyer patches differentiate into IgA secreting plasma cellsIgA receives protective secretory componentBileComposed of bile salts (conjugated to glycine or taurine), phospholipids, cholesterol, bilirubin, water, and ionsChplesterol 7-hydroxylase cataluzes rate limiting step of bile synthesisFunctions:Digestion and absorption of lipids and fat-soluble vitaminsCholesterol excretion (bodys only means of eliminating cholesterol)Antimicrobial activity (membrane disruption)

Bilirubin Product of heme metabolismBilirubin is removed from blood by liver, conjugated with glucuronate, and excreted in bileDirect bilirubin conjugated with glucuronic acid (water soluble)Indirect bilirubin unconjugated, water insolublePathology