Gastro-Intestinal Tract Anatomy PDF

Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Layers of Anterior abdominal wall 1. Skin...

Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Layers of Anterior abdominal wall 1. Skin 2. Fascia 3. Muscles 4. Fascia transversalis  Thin skin Superficial Lateral  Thin  Contain umbilicus fascia: formed abdominal apponeurosis (which is remnant of two layers; muscles: present between of umbilical cord 1. External 1. External transversus stump at level of L3- layer of oblique abdominis L4), umbilicus is adipose 2. Internal muscle and 5. Extra-peritoneal fat innervated by T10. tissue oblique extraperitoneal 6. Peritoneum  Contain linea alba (Camper 3. Transversus fat in its midline fascia) abdominis  Contain the (which is a vascular 2. Internal Anterior deep inguinal structure formed layer of abdominal ring by thickening of dense muscles: fascia) connective 1. Rectus  Hair distribution tissue abdominis along it has (Scarpa 2. Pyramidalis different patterns fascia) muscle among males and Note: there is females) no deep fascia in the abdomen PAGE |1  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Muscles of Anterior abdominal wall Muscle Origin Insertion Action Nerve supply External oblique outer surface of 5th –12th linea alba, pubic ribs tubercle, and iliac (Fibers directed crest  Intercostal nerves (T7–T11), downward, forward & medially)  Subcostal nerve (T12),  Iliohypogastric nerve  Compresses and supports the internal viscera Internal oblique anterior iliac crest, inferior borders of thoracolumbar fascia, 10th –12th ribs and and lateral 3rd of the linea alba  Flexes and rotates the trunk inguinal ligament  Assists with expiration (Fibers directed upward, forward & medially) Transversus inner surface of 7th -12th linea alba abdominis costal cartilages, iliac crest, thoracolumbar fascia, and lateral 3rd of the inguinal ligament (Fibers run horizontally) Rectus abdominis pubic symphysis and xiphoid process and Intercostal crest 5th-7th costal cartilages nerves (pair of muscles runs (T7–T11), vertically from Subcostal downward upward. nerve Each muscle is separated (T12) by 3 tendinous intersections into 4 parts) Pyramidalis pubic symphysis and linea alba tenses linea subcostal pubic crest alba nerve (may be absent in 20% (T12) of population) Note: oblique muscles split near the midline into anterior and posterior layers before joining the linea alba forming aponeurotic sheath around rectus abdominis muscle known as rectus sheath. PAGE |2 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ PAGE |3  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Inguinal canal Definition Passage in the lower part of anterior abdominal wall just above the inguinal ligament. Boundaries Anterior wall Posterior wall Roof Floor external internal oblique Internal oblique inguinal ligament oblique muscle, transversus muscle, and the lower border muscle abdominis muscle& Transversus of external oblique fascia transversalis abdominis muscles muscle Openings Deep inguinal ring Superficial inguinal ring  Formed by an opening in the  Formed by an opening in external transversalis fascia. oblique.  Located at mid-point of inguinal  Located 1 cm superiorly and medially ligament (halfway between the to the pubic tubercle pubic tubercle and the anterior superior iliac spine) Contents Ilioinguinal nerve (L1) & Ilioinguinal nerve (L1) & Spermatic cord in men Round ligament of the uterus in women PAGE |4  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Abdominal planes The abdomen can be divided into The abdomen can also be divided into 9regions 4quadrants with transverse and sagittal using the following planes: planes. Midclavicular planes: Transverse (transumbilical) plane: vertical planes extending from the Passes through the abdomen at the level of midclavicular lines to the midinguinal points the umbilicus Upper horizontal (subcostal) plane: Sagittal (vertical) plane: inferior to the costal margin at the level of L3 Passes through the body at the level of the Lower horizontal (transtubercular) plane: umbilicus between the 2 tubercles of the iliac crest at the The intersection of these 2 planes defines 4 level of L5 quadrants: The planes define 9 regions:  Right Upper Quadrant (RUQ)  Rt,lt Hypochondrium  Left Upper Quadrant (LUQ)  Rt,lt iliac/ inguinal  Right Lower Quadrant (RLQ)  Rt,lt lateral abdominal/ flank  Left Lower Quadrant (LLQ)  Epigastric  Umbilical  hypogastric PAGE |5  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Blood supply of Anterior abdominal wall Artery Origin Area supplied Musculo-phrenic internal thoracic artery superior anterolateral abdominal wall Superficial epigastric femoral artery inferior anterolateral abdominal wall Superficial circumflex iliac femoral artery inferior anterolateral abdominal wall Superior epigastric internal thoracic artery superior part of the abdominal wall Inferior epigastric artery external iliac artery inferior part of the abdominal wall (anastomoses with the superior epigastric artery) 10th and 11th intercostal lateral abdominal wall arteries and the subcostal artery Note: Veins follows the arteries of the same name. The superficial veins around the umbilicus anastomose with the deep veins through the paraumbilical veins. PAGE |6  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Peritoneum Definition serous membrane lining the abdominal and pelvic cavity and covering its organs Functions 1. suspends the organs in its position. 2. Allows organs to move smoothly. 3. Allows entry and protection of neurovascular bundle supplying organs. Layers 1. Visceral layer: covers the abdominal visceral organs 2. Parietal layer: lines the inside of the abdomino-pelvic wall Note: There are no organs (only a serous fluid) between the parietal peritoneum and the visceral peritoneum. Sub- Greater sac: Lesser sac: divisions Lies in the anterior portion of the cavity lies in the upper posterior portion of the abdomen Greater sac communicates with the lesser sac through the epiploic foramen (foramen of Winslow) Boundaries of the epiploic foramen:  Anterior: Hepatoduodenal ligament  Posterior: Inferior vena cava  Superior: Caudate lobe of the liver  Inferior:1st part of the duodenum Parts Peritoneal ligaments Omentum Mesentry (peritoneal (mesocolon) folds)  Double layer of peritoneum that connect 2  Multi-layered  Double layer organs to each other or attach an organ to the sheet of of peritoneum body wall peritoneum that holds the  Examples are: 1. Splenorenal: spleen & left kidney  Prevent visceral 2. Phrenicocolic: diaphragm & transverse colon adhesions organs to the 3. Gastrophrenic: stomach & diaphragm between viscera posterior 4. Gastrocolic: stomach & transverse colon and abdominal abdominal 5. Gastrosplenic: stomach & spleen wall wall 6. Hepatogastric: liver & stomach  Examples:  Contains: 7. Falciform ligament: liver & anterior abdominal wall Greater neurovascular 8. Hepatoduodenal: liver & duodenum omentum, lesser bundle and (Contains the portal triad: hepatic artery, portal omentum lymphatics vein, and common bile duct) PAGE |7 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Peritoneal divisions PAGE |8  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Layers & folds of peritoneum PAGE |9  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Oral cavity Subdivided into Vestibule Mouth cavity proper  The space between the lips, cheeks and  The rest of mouth that bounded by: the gums, teeth.  Roof: palate  Floor: tongue & floor of mouth  Receives the opening of parotid duct  Lateral wall: cheeks opposite the upper second molar tooth.  Posterior: oro-pharynx Tongue Muscular organ that is covered by mucus membrane. It is connected to the floor of Definition mouth by the frenulum. Parts Anterior 2/3 (palatine/buccal): Posterior 1/3 (pharyngeal): Rough surface, due to presence of Smooth due to absence of taste buds. numerous taste buds. Note: The tongue is divided by V-shaped sulcus, sulcus terminal, which represent separation of the two embryological sources of tongue. Innervation Sensory: Motor:  Ant.2/3: All muscles of tongue  Taste sensation by chorda tympani of facial supplied by hypoglossal  General sensation by trigeminal nerve. nerve except palate-  Post.1/3: both taste and general sensation by glossus muscle which is glosso-pharyngeal nerve. innervated by vagus nerve. Muscles Intrinsic muscles: Extrinsic muscles:  Have both origin and insertion  Connect tongue to adjacent bones. from the tongue itself.  They move the tongue in different  They alter the shape of tongue directions.  Include:  Include: 1. Longitudinal muscle 1. Stylo-glossus 2. Horizontal muscle 2. Palate-glossus 3. Vertical muscles 3. Hyo-glossus 4. Genio-glossus P A G E | 10  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Salivary glands Parotid Submandibular Sublingual Number One Pair of glands on both sides of One pair of glands One pair of face. glands Site It is situated in front of the ear, It is situated at the It is situated bounded by: submandibular fossa, under the tongue  Zygomatic arch, superiorly bounded by:  Angle of mandible, Inferiorly  inferior border of  Masseter muscle, anteriorly mandible,  ear and sternocleidomastoid, superiorly posteriorly  digastric muscle, anterior and posterior by its two bellies Duct Stensen duct, Wharton’s duct, There are 8-20 excretory It arises from the anterior Opens into sublingual ducts per gland, each part of the gland, traversing papilla at the base of opening out onto the the masseter muscle then the frenulum. sublingual folds. pierces the buccinator Note: a major sublingual muscle. It opens out into the duct (of Bartholin) can be vestibule near the second present in some people. upper molar. Relations Structure passing through the gland: submandibular gland 1. Facial nerve: gives five terminal and duct have close branches within the gland anatomical 2. External carotid artery: gives relationship with three posterior auricular artery within principal nerves; the the parotid gland then divides into lingual nerve, its two terminal branches & hypoglossal nerve and maxillary artery and superficial facial nerve; temporal artery. so the surgeon must 3. Retromandibular vein: formed by take care of this union of superficial temporal and regional anatomy. maxillary veins. Blood Arterial: External carotid artery Sublingual and Sublingual and supply through posterior auricular and submental arteries and submental superficial temporal arteries. veins arteries and veins Venous: retromandibular vein P A G E | 11 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ P A G E | 12  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Esophagus Definition Muscular tube that connects the pharynx to the stomach Site from C6 to T11 vertebra (average length is 25 cm) Constrictions 1. Pharyngo-esophageal constriction: Caused by the cricoid cartilage Narrowest portion of the esophagus 2. Aorto-bronchial constriction: where the aortic arch and the left main bronchus indents the esophageus (approximately T4) 3. Diaphragmatic constriction: where the esophagus passing through the diaphragm Parts Cervical part Thoracic part Abdominal part (pars cervicalis) (pars thoracis) (pars abdominalis)  Starts at C6 (lower  Starts at thoracic  Starts at the esophageal border of cricoid inlet (at T1) opening of the diaphragm cartilage)  Relations: (at T10)  Relations: Lies in the superior  Relations:  Anterior: and posterior  Anterior: liver trachea mediastinum  Posterior: descending  Lateral: carotid  Arterial supply: aorta sheath Esophageal and  Arterial supply:  Posterior: bronchial branches cervical Esophageal branch of the from aorta left gastric artery and Left vertebrae  venous drainage:  Arterial supply: phrenic artery azygos, hemiazygos  venous drainage: inferior thyroid artery left gastric vein that drains  venous drainage: into portal vein vertebral, brachiocephalic, inferior thyroid vein Nerve supply Vagus and sympathetic trunk P A G E | 13 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ P A G E | 14  Gastro-intestinal Tract Anatomy Stomach ------------------------------------------------------------------------------------------------------------ Definition J-shaped thick-walled organ that acts mainly as reservoir of food beside its functions regarding food digestion Site Left upper quadrant of abdomen (epigastric, umbilical, left hypochondriac, and left flank regions) Parts 1. cardia: the part between stomach and esophagus, it contains the cardiac orifice that is gurded by cardiac sphincter. The sphincter prevents food reflux into esophagus. 2. Fundus: the superior dilation of the stomach 3. Body: the largest part of stomach 4. Pylorus: the outflow part of stomach into duodenum, pylorus is divided into pyloric antrum and pyloric canal. Surfaces Has anterior and posterior surfaces, while has right and left borders (lesser & & borders greater curvature) Relations Posterior relations (Stomach bed): 1. Left crus of diaphragm 2. Pancreas 3. left kidney and adrenal gland 4. Spleen 5. splenic artery 6. lesser sac 7. transverse mesocolon 8. splenic flexure Blood Arterial Venous supply 1. Right gastric: branch of the proper hepatic The veins have the same names artery as arteries. 2. Left gastric: arises directly from the coeliac  The right and left gastric trunk. veins drain into the 3. Right gastro-epiploic: terminal branch of the hepatic portal vein. gastroduodenal artery, which arises from the  The short gastric vein, common hepatic artery. left and right gastro- 4. Left gastro-epiploic: branch of the splenic omental veins drain into artery, which arises from the coeliac trunk. the superior mesenteric 5. Short gastric arteries: arise from splenic artery vein Nerve Parasympathetic: from the anterior and posterior vagal trunks, derived from the supply vagus nerve. Sympathetic; from the T6-T9 spinal cord segments and passes to the coeliac plexus via the greater splanchnic nerve. P A G E | 15 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Parts of stomach Stomach bed Arteries of stomach P A G E | 16  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Small intestine Length : average 7 meteres. Parts: duodenum, jejunum, ileum. Duodenum Site C-shaped structure extends from pylorus of stomach to the duodenojejunal junction, it is about 25 cm. Parts 1st part 2nd part 3rd part 4th part (Superior) (Descending) (Inferior) (Ascending) At the At the level of L1-L3 At the At the level of L3-L2 level of L1 Note: Characterized by level of Note: suspensory muscle of the the major duodenal L3 duodenum is present at duodeno- papilla – the opening at jejunal junction, its contraction which bile and pancreatic widens the angle of the flexure, secretions to enter from and aids movement of the the ampulla of Vater intestinal contents into the (hepatopancreatic jejunum. ampulla) Blood Arterial Venous supply  gastroduodenal artery, proximal to Same names as arteries and drain into hepatic major papilla portal vein  inferior pancreaticoduodenal artery, distal to major papilla Jejunum Ileum Note: There is no clear line of demarcation between the jejunum and ileum, surgical marks are:  Located in upper left quadrant  Located in lower right quadrant  Thick wall  Thin wall  Longer vasa recta (straight  Shorter vasa recta arteries)  More arcades  Less arcades (arterial loops)  Pink in colour  Red in colour Blood  Arterial: supply superior mesenteric artery  venous: superior mesenteric vein P A G E | 17 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ P A G E | 18  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Large intestine Length : average 1,5 meteres. Parts: caecum, ascending, transverse, descending, sigmoid colon, rectum Caecum Ascending colon Transverse colon Descending Sigmoid colon colon Right iliac from the cecum to from the right From left colic from the fossa the right lobe of colic flexure to flexure to left iliac the liver where it the spleen, where the left iliac fossa to turns 90 degrees it turns 90 fossa the level horizontally degrees inferiorly of the S3 Site forming the right forming the left vertebra colic flexure colic flexure it is the least fixed part of the colon  Ascending colon and proximal 2/3 of the transverse colon: superior mesenteric artery Blood supply  Distal 1/3 of the transverse colon, descending colon and sigmoid colon: inferior mesenteric artery.  (Veins have the same names as arteries) P A G E | 19  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Rectum Site Continuation of sigmoid colon at the level of L3 Flexures 1. Sacral flexure: anteroposterior curve formed by the curve of the sacrum and coccyx 2. Anorectal flexure: anteroposterior curve formed by the tone of the puborectalis muscle, (it contributes significantly to faecal continence) 3. lateral flexures (superior, intermediate and inferior), formed by transverse folds of the internal rectum wall. Peritoneal  superior third: anterior surface and lateral sides are covered by peritoneum. coverings  middle third: only has an anterior peritoneal covering  lower third: has no peritoneal covering Note:  recto-vesical pouch: is the reflection of peritoneum from the rectum to the urinary bladder, in males.  Recto-uterine pouch (Douglas pouch): is the reflection of peritoneum from the rectum to vagina and cervix, in females. Blood 1. Superior rectal artery -terminal continuation of the inferior mesenteric artery. supply 2. Middle rectal artery – branch of the internal iliac artery. 3. Inferior rectal artery – branch of the internal pudendal artery. Veins have the same names as arteries Note: The superior rectal vein drains into portal venous system, whie the middle and inferior rectal veins drain into the systemic venous system. Anastomoses between the portal and systemic veins are located in the wall of anal canal, making this a site of porto-systemic anastomosis. Nerve  Sympathetic: supply from the lumbar splanchnic nerves and superior and inferior hypogastric plexuses.  Parasympathetic: from S2-4 via the pelvic splanchnic nerves and inferior hypogastric plexuses Lymph pararectal lymph nodes, which drain into the inferior mesenteric nodes. drainage P A G E | 20 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ P A G E | 21  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Anal canal Site Begins as a continuation of the rectum and passes infero-posteriorly to terminate at the anus. Anal 1. Internal anal sphincter: sphincters  Involuntary  surrounds the upper 2/3 of the anal canal.  formed by the circular smooth muscle in the bowel wall. 2. External anal sphincter:  voluntary  surrounds the lower 2/3 of the anal canal  skeletal muscle surrounding the inferior portion of anal canal Internal  The anal mucosa is arranged into longitudinal folds which known as anal structure columns.  Anal columns are joined at their inferior ends by anal valves.  Above the anal valves there are small pouches which are known as anal sinuses.  Anal sinuses contain glands that secrete mucus.  The anal valves collectively form an irregular circle – known as the pectinate line (or dentate line). Blood Arterial: Venous: supply  Superior rectal  Superior rectal vein, which drains into the artery, above dentate inferior mesenteric vein (portal venous line system).  Inferior rectal artery,  Inferior rectal vein, which drains into the below dentate line internal pudendal vein (systemic venous system). Nerve o Visceral innervation via the inferior hypogastric plexus. supply (sensitive to stretch) o Somatic innervation via the inferior rectal nerves (Sensitive to pain, temperature, touch and pressure) Note: Haemorrhoids are vascular cushions found within the anal canal of healthy individuals. If they become swollen and distended, they are referred to as pathological haemorrhoids. They can cause bleeding and itchiness, and can be managed conservatively or surgically. P A G E | 22 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ P A G E | 23  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Liver Site In the Right Upper Quadrant of abdomen (right hypochondrium, epigastric, and left hypochondrium areas) Surfaces 1. Diaphragmatic (anterosuperior) surface:  smooth and convex, fitting under the curvature of the diaphragm.  Its posterior part is not covered by peritoneum, and is in direct contact with the diaphragm (Bare area of liver). 2. Visceral (posteroinferior) surface:  Irregular, due to its relations with abdominal organs.  It is covered with peritoneum except area of porta hepatis and gall bladder fossa. Ligaments 1) Falciform ligament: o Attaches the liver to the anterior abdominal wall. o Its free edge contains the ligamentum teres which is a remnant of the umbilical vein. 2) Coronary ligament: o attaches the liver to the inferior surface of the diaphragm o its anterior and posterior folds unite to form the triangular ligaments 3) Triangular ligaments 4) Lesser omentum: o Attaches the liver to the lesser curvature of the stomach and first part of the duodenum Lobes 1. Right lobe 2. Left lobe 3. Caudate lobe 4. Quadrate lobe Note: Porta hepatis is a fissure separating caudate and quadrate lobes. It transmits all the vessels, nerves and ducts entering or leaving the liver with the exception of the hepatic veins. Blood Arterial Venous supply 1. Hepatic artery proper (25%) – supplies the non- hepatic veins which parenchymal structures of the liver with arterial blood. It open into inferior is derived from the coeliac trunk. vena cava. 2. Hepatic portal vein (75%) – supplies the liver with partially deoxygenated blood, carrying nutrients absorbed from the small intestine. P A G E | 24  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Gall bladder Site Undersurface of liver (at right hypochondrium) Function Act as reservoir for bile that is synthesized by the liver Capacity 30-50 ml Parts Pear-shaped sac formed of 3 parts: 1. Fundus 2. Body 3. Neck; continuous with the cystic duct Note: Hartmann’s Pouch is mucosal fold present at the neck. This is a common location for gallstones to become lodged. Relations Anteriorly and superiorly: inferior border of the liver and the anterior abdominal wall. Posteriorly: transverse colon and proximal duodenum. Inferiorly :biliary tree and distal duodenum. Blood Arterial: Venous: supply cystic artery; branch of the right cystic veins, which drain directly into the hepatic artery portal vein Nerve Sympathetic (and sensory): coeliac plexus supply Parasympathetic: vagus nerve Biliary tree 1.Right and left hepatic ducts; transmit bile that synthesized in liver 1. Common hepatic duct; formed by union of Rt &Lt hepatic ducts 2. Cystic duct; the duct of gall bladder Parts 3. Common bile duct;  formed by union of common hepatic and cystic ducts  joined by the main pancreatic duct, forming the hepatopancreatic ampulla (Ampulla of Vater), then opens into the 2nd part of duodenum via the major duodenal papilla. This papilla is regulated by a muscular valve, the sphincter of Oddi. P A G E | 25 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Lobes of liver Peritoneum of liver P A G E | 26 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Gall bladder Biliary tree P A G E | 27  Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Development of GIT The gut develops from the primitive gut tube, which is formed after the process of folding (during the 3-4 weeks of intrauterine life). The primitive gut tube is divided into 3 parts: Foregut Midgut Hindgut Gives rise to the Gives rise to the distal Gives rise to distal 1/3 of the esophagus, stomach, liver, duodenum, jejunum, ileum, transverse colon, descending gallbladder, bile ducts, cecum, appendix, ascending colon, sigmoid pancreas and proximal colon, and proximal 2/3 of colon and the upper ½ of anal duodenum transverse colon canal P A G E | 28 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Esophagus Mechanism:  Lateral grooves invade the proximal part of foregut forming trachea- esophageal septum which divide it into ventral respiratory part and dorsal intestinal part.  The dorsal part elongates as longitudinal tube forming the esophagus.  lumen of the esophagus becomes temporarily occluded due to cell proliferation around the 5th week.  Recanalization of the tube forming its lumen. Congenital anomalies: 1. Esophageal stenosis: due to failure of recanalization 2. Esophageal atresia 3. Congenital hiatal hernia: due to short esophageus 4. Tracheo-esophageal fistula: due to failure of septum development P A G E | 29 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Stomach Mechanism:  Appear as fusiform dilatation of the foregut distal to esophageal region  Rotation 90◦ around its long axis resulting in; its ventral border becomes to the left; its right surface become posterior surface  Rotation around its transverse axis resulting in its upper part becomes to left, while its lower part becomes to right Congenital anomalies: Hypertrophic pyloric stenosis: due to oveproliferation of the smooth muscle of the pyloric sphincter P A G E | 30 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Liver Mechanism: The hepatic bud develops from the foregut and extends to the septum transversum and divides into cranial part which forms liver, caudal part which forms the gall bladder, while its main stalk forms the biliary tree Congenital anomalies:  Biliary atresia P A G E | 31 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Pancreas Mechanism:  It is formed of 2 buds from the foregut distal to hepatic bud; ventral bud and dorsal bud.  the ventral pancreatic bud FORMS the uncinate process and lower part of the head of the pancreas.  the dorsal pancreatic bud FORMS the remaining portion of the head, body, and tail of the pancreas Congenital anomalies:  annular pancreas P A G E | 32 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Mid-gut Mechanism:  develops as U-shaped loop that herniates into the umbilicus with its midpoint attached to the vitello-intestinal duct  it undergoes a PRIMARY rotation of 90 degrees counterclockwise thus the lower loop (which has the appendix) is on the embryo's left side.  as the abdominal cavity expands, the gut tube is drawn back into the abdomen, during this time the gut tube further rotates another 180 degrees such that the appendix ends up in the upper right quadrant. Congenital anomalies: 1. Omphalocoele: Due to failure to pull all of the gut contents back into the abdominal cavity or to completely close off the ventral body wall at the umbilicus 2. Volvulus: due to malrotation which resulting in stenosis and ischemia. Omphalocoele P A G E | 33 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Rotation of gut P A G E | 34 Gastro-intestinal Tract Anatomy ------------------------------------------------------------------------------------------------------------ Hind-gut Anomalies: 1. Imperforate anus: due to failure of the cloacal membrane to break down anal atresia 2. Hirschsprung disease or congenital megacolon: due to absence of the ganglion cells 3. Recto-vesical fistula Recto-vesical P A G E | 35 fistula