DIGESTIVE TUBES AND ASSOCIATED GLANDS

DIGESTIVE SYSTEMBy Dr SaminaAnjumFORMATION OF PRIMITIVE GUTCephalocaudal foldingLateral foldingFORMATION OF PRIMITIVE GUTIncorporation of endoderm lined cavity in embryoYolk sac and allantois remain outside the body of embryo

DIVISIONS OF PRIMITIVE GUT

Foregut & hind gut are the blind ending tubesEndoderm forms:The epithelial lining of gutParenchyma of glandsVisceral mesoderm forms:Stroma of glandsMusculature of organsPeritoneum

MESENTERIES

FOREGUT

The derivates of foregut are:The primordial pharynx and its derivates namely, oral cavity, pharynx, tongue, tonsils, salivary glands and upper respiratory system.The lower respiratory system.The esophagus and stomach.The duodenum, proximal to the opening of the bile duct.The liver, biliary apparatus (hepatic ducts, gall bladder, bile duct and pancreas)All these foregut derivatives, except the pharynx respiratory tract and most of the esophagus are supplied by celiac trunk. DEVELOPMENT OF ESOPHAGUS

Initially short, but with the descent of the heart and lungs, it lengthens rapidly. The muscular coat & Innervation

Abnormalities Of EsophagusTracheoesophageal fistula and atresia

Polyhydramnios.

Esophageal stenosis in the lower third.

Congenital hiatal hernia occurs when the esophagus fails to lengthen sufficiently and the stomach is pulled up into the esophageal hiatus through the diaphragm.

Development of Stomach

Fusiform dilation of the foregut in the fourth weekDorsal & Ventral mesenteriesThe stomach rotates around a longitudinal and an anteroposterior axis.

The stomach rotates 90 degrees clockwise around its longitudinal axis, causing its left side to face anteriorly and its right side to face posteriorly.

Vagus nervesDuring this rotation, the original posterior wall of the stomach grows faster than the anterior portion, this differential growth forms the greater and lesser curvatures.

The cephalic and caudal ends of the stomach originally lie in the mid line, but during further growth, the stomach rotates around an anteroposterior axis so that the pyloric part moves to the right and upward and cardiac portion moves to the left and slightly downwards.

Rotation about the longitudinal axis pulls the dorsal mesogastrium to the left and creates a space behind the stomach called the lesser sac. This rotation pulls the ventral mesogastrium to the right.

The spleen primordium appears as a mesodermal proliferation between the two leaves of the dorsal mesogastrium during 5th week. The posterior leaf of the dorsal mesogastrium and the peritoneum along this line of fusion degenerate. Lienorenal and gastrolienal ligaments.

Initially pancreas grow in the dorsal mesoduodenum, but eventually its tail extends into the dorsal mesogastrium and is covered by peritoneum on its anterior surface only and therefore lies in a retroperitoneal position. Secondarily retroperitoneal organs: pancreas

Forms by the dorsal mesogastrium as it bulges down and forms a double layered sac extending over transverse colon and small intestinal loops. Later it layers fuse and forms a single sheet hanging from the greater curvature of stomach. The posterior layer of greater omentum fuses with the mesentery of transverse colon. GREATER OMENTUM Forms from the ventral mesogastrium. Its derivatives are:Falciform ligament- free margin contains left umbilical vein; obliterates after birth to form ligamentum Teres hepatis Lesser omentum- Right free margin(hepatoduodenal ligament) contains portal triad and forms the roof of the epiploic foramen

FALCIFORM LIGAMENT & LESSER OMENTUM Abnormalities Of StomachPyloric stenosis is one of the most common abnormalities of the stomach in infants which is believed to develop during fetal life. Occurs when circular muscle hypertrophies.Extreme narrowing of the pyloric lumen and the passage of food is obstructed, resulting in severe projectile vomiting. DEVELOPMENT OF DUODENUMThe terminal part of the foregut and the cephalic part of the midgut form the duodenum.The junction of the two parts is directly distal to the origin of the liver bud.

Due to the rotation of the stomach, the duodenum takes on the form of a C-shaped loop and rotates to the right. Ultimately, the duodenum swings from its initial midline position to the right side of the abdominal cavity

Once developed, the hepatic and cystic ducts connect to the duodenum by the common bile duct . The entrance of the bile duct into the small intestine gradually shifts from an initial anterior position to a posterior one and passes behind the duodenum.

The duodenum and head of the pancreas press against the dorsal body wall and the right surface of the dorsal mesoduodenum fuses with the adjacent peritoneum and subsequently disappear.

The dorsal mesoduodenum disappears entirely except in the region of the pylorus of the stomach where a small portion of the duodenum (duodenal cap) retains its mesentery and remains intraperitonealCont During the 2nd month, the lumen of the duodenum is obliterated. However, the lumen is recanalized shortly thereafter.

Celiac ArterySuperior mesenteric Artery

///LIVER & GALL BLADDERHepatic diverticulum appears - middle of 3rd week as an outgrowth of the endodermal epithelium at the distal end of foregutLiver bud consists of rapidly proliferating liver cells that penetrate the Septum Transversum

ContWith further proliferation connection between liver bud & foregut narrows to form bile ductA small ventral outgrowth is formed by bile duct , this outgrowth give rise to gallbladder and the cystic duct.

Hepatic sinusoidsFormed by vitelline & umbilical veinsEpithelial Liver cordsDifferentiate into parenchyma & form lining of biliary ducts Mesoderm of septum transversumHematopoietic cellsKupffer cellsConnective Tissue cellsMesoderm of septum transversum becomes membranous forming lesser omentum & falciform ligament Mesoderm on the surface of the liver differentiates into visceral peritoneum except on its cranial surface.Here, the liver remains in contact with the rest of the original septum transversum which form the central tendon of the diaphragm - Bare area of liver6th weekHematopoiesis10th weekWeight of the liver - 10% of total body weight12th week Bile formed by hepatic cellsBile duct formed & bile can enter the GIT Last two months Hematopoietic function reducedWeight of the liver only 5% of total body weight

Development of Pancreas

In dorsal mesenteryWhen duodenum rotates to right and becomes C- shaped, the ventral pancreatic bud moves dorsally and comes to lie immediately below and behind the dorsal bud. Later, the parenchyma and the duct systems of the dorsal and ventral pancreatic buds fuse.

DERIVATIVES OF PANCREATIC BUDS & DUCTSThe ventral bud the uncinate process inferior part of the head of the pancreas. The dorsal bud The remaining part of the gland. The main pancreatic duct of Wirsung, together with the bile duct enters the duodenum at the site of the major papilla. The distal part of the dorsal pancreatic duct The entire ventral pancreatic duct. Accessory pancreatic duct of SantoriniThe proximal part of the dorsal pancreatic duct. The entrance of the accessory duct is at the site of the minor papilla.

Third month pancreatic islets (of Langerhans) develop from parenchymal cells.Fifth monthInsulin secretion Glucagon and somatostatin-secreting cells also develop from parenchymal cells. Splanchnic mesoderm surrounding the pancreatic buds forms the pancreatic connective tissue. Annular pancreas

MIDGUTBegins distal to the entrance of bile duct into duodenum and terminates at the junction of right two-thirds of the transverse colon with the distal third.Superior mesenteric artery

In the 5th week midgut Is suspended from the dorsal abdominal wall by a short mesentery.Communicates with the yolk sac through vitelline duct until the tenth week

Development of midgut: Is characterized by rapid elongation of gut and its mesentery to form the primitive intestinal loop.Midgut loop hasCephalic limb--- Distil part of duodenum, jejunum and part of ileumCaudal limb--- Lower portion of ileum, cecum , appendix, ascending colon and proximal 2/3rd of transverse colon

Physiological umblical HerniationCause: Due to rapid growth and expansion of liver, abdominal cavity becomes smaller Movement of intestinal loops into EEC in the umbilical cord during 6th week.

The midgut loop during herniation in the umbilical cord, rotates 90 counterclockwise (when viewed from the anterior aspect) around the axis of the superior mesenteric artery. The cranial limb swings down and right while the caudal limb swings up and leftDuring rotation, the cranial limb of the midgut elongates and formsjejunal-ileal loopswhile the expanding cecum sprouts asvermiform appendix.

ROTOATION OF MID GUT

ContAdditional rotation at 180 counterclockwise when intestinal loops return into abdomen during 10th week.Total rotation of midgut= 270 counterclockwise

RETRACTION OF HERNIATED LOOPSCauses: Regresssion of mesonephric kidneyReduced growth of liverExpansion of abdominal cavityDuring 10th week herniated intestinal loops return to the abdominal cavity. Proximal portion of jejunum is the first part to reenter the abdominal cavity. Later remaining loops settle more and more to right. Thecaecal diverticulumis the last part of the gut to reenter the abdominal cavity, temporarily lying in the right upper quadrant directly below the right lobe of the liver.The caecal bud descends to the right iliac fossa, placing the ascending colonand thehepaticflexureon the right side of the abdominal cavity. As the appendix forms during the caecum's descent, it frequently lies posterior to the caecum (retrocaecal) or posterior to the colon (retrocolic).

The derivatives of the midgutThe small intestine, including most of the duodenum The cecum, appendix, ascending colon and the right two-thirds of the transverse colon

FATE OF MESENTERIESThe mesentery of the primary intestinal loop becomes very twisted with the movements of the bowel. Dorsal mesentery of small intestine twist around the origin of superior mesenteric artery when caudal limb of loop moves to right side of abdomenMesenteries of ascending and descending colon press against the peritoneum of the posterior abdominal wall, fuse & degenerate so that these organs become secondarily retroperitoneal.

ContThe mesentery of transverse mesocolon fuses with the posterior wall of the greater omentum.

The appendix, lower end of the cecum and sigmoid colon retain their free mesenteries.ContAfter the mesentery of the ascending colon disappears, the fan-shaped mesentery of the small intestine (mesentery proper) acquires a new line of attachment running from the duodenojejunal junction in an inferolateral direction to the ileocaecal junction

ABNORMALITIES OF THE MESENTERIESPersistence of a portion of the mesocolon gives rise to a mobile cecum. If the mesentery of the ascending colon fails to fuse with the posterior body wall abnormal movements of the gut occurs or volvulus of the cecum and colon occurs. OMPHALOCELEfFailure of bowel to return during physiological herniation

GASTROSCHISIS

Abnormal closure of body wall around the connecting stalk, cocaine use increases the tendency in young women

GUT ROTATION DEFECTS

A: Abnormal rotation of the primary intestinal loop. Only 90 degree rotation occurs , resulting in left sided colon. B: The primary intestinal loop is rotated 90 degree clockwise (reversed rotation). The transverse colon passes behind the duodenum & SMA. REVERSED ROTATION

SUBHEPATIC CECUM & APPENDIX

In 2-4% cases vitelline duct persists forming Meckels diverticulum, 40-60cm from ileocecal valve on the antimesenteric border of ileumINTESTINAL RECANALIZATION & DUPLICATION

GUT ATRESIAS & STENOSIS

A: Region of bowel is lost--- 50%B: A fibrous cord remains --- 25%C: Narrowing , with a thin diaphragm separating the larger & smaller pieces of bowel--- 25%D: Stenosis---5%DEVELOPMENT OF HIND GUTThe derivatives of the hind gut are:The left 1/3rd of the transverse colon, the descending colon and sigmoid colon, the rectum and the upper part of the anal canal.The endoderm of hind gut also forms the internal lining of the urinary bladder and most of the urethra.DEVELOPMENT OF HINDGUT

DEVELOPMENT OF ANAL CANAL

B.S

HINDGUT ABNORMALITIEES

A: Urorectal fistulaB: Rectovaginal fistulaD: Imperforate anusCONGENITAL MEGACOLONAlso called HIRSCHSPRUNG DISEASE or AGANGLIONIC MEGACOLON.Absence of parasympathetic ganglia in the bowel wall distal to the dilated segment. Failure of neural crest cells to migrate in the wall of colon.Rectum & sigmoid colonMale to female ratio is 4:1

RADIOGRAPH OF COLON AFTER BARIUM ENEMA71sTHANK YOU