1. الثلاثاء 4/3/2014 أ. د. عبد الجبار الحبيطي

2.  It grows faster than the vertebral column,thus it will become U-Shaped structure with an inverted apex.This U-shaped structure has a proximal(cranial) & distal (caudal)limbs with the superior mesenteric artery running in between the 2 limbs,while the apex is connected to the umbilicus by Vitelline ligament.  The cranial limb will give rise to the following parts of the G.I.Tract: 1-The caudal half of the duodenum(The cranial half comes from the fore-gut derivatives. 2-The Jejunum. 3-Most of the Ileum.

3.  While the Caudal limb will give the following derivatives: 1-The terminal part of the Ileum. 2-The Caecum & Appendix. 3-The Ascending colon and 2 / 3 of the transverse colon.  The caecum with the apex attached to its tip arises a conical diverticulum from the caudal limb close to the apex of the loop i.ei near the point of attachment of Vitellointestinal duct.

4.  The U –shaped loop projects inside the umbilical cord to form the umbilical hernia,which is a normal feature between 6 th – 12 th weeks of intra-uterine life.Such a hernia is due to the inadequacy of the abdominal cavity which is largly occupied by the following structures. 1-The rapidly growing liver. 2-The large sized mesonephros on each side of the vertebral column.  By the end of the 12 th weeks of development,the loop of the intestine starts to return back in to the abdominal cavity because of the following reasons: 1-Regression of the mesonephros. 2-No more increases in the size of the liver. 3-An increases in the expansion of the abdominal cavity with an increase in the abdominal wall.

5.  Just before the start of reduction,the loop will rotates 90 degree Unti-clock wise,thus the original proximal limb comes to the right,while the distal limb comes to the left.  Once reduction starts the loop will complete its anti-clock wise rotation to An angle of 270,so that the original cranial limb comes to the left(deeper),while the original caudal Limb comes to the right side(Superficial).  The original cranial limb (to the left & deeper)reurns first and occupies the right side of The abdominal cavity(to form the coils of small intestine).The caudal limb (left & superficial)

6.  Re-inters superficial to the cranial limb and occupies the left side of the abdominal cavity and forms the colon.The last segment to inter is caecum which comes to lie superficial to the small intestine,the caecum then descends from just below the liver to reach its adult positrion in the right iliac fossa.

7. 1-Omphalocele,where the loop is trapped out side & covers only by amnion due to incomplete reduction of the intestinal loop. 2-Congenital umbilical hernia,which is mainly due to defects in central part of the anterior abdominal wall and the skin around the region of the umbilicus,thus the loop fails to completes its reduction and stay out side and covers by peritoneum,amnion &skin. 3-The loop may rotates in clock wise direction instead of being roting in Anti-clock wise,thus the duodenum becomes in a reversed position & superficial to the transverse colon. 4-Anti-clock wise rotation for only 90 degree leads to reversed position of the abdominal contents and is usually associated with congenital heart defect ( Situs inversus). 5-Sub hepatic position of caecum & appendix as it fails to descent ro right iliac fossa.

8. 6-Anomalies related to the Vetelline ligament including the followings: A-Meckl's diverticulum is present 2 % of the population, 2 feet from the ilio- caecal valve & is about 2 inches in length. B-Vitello-intestinal fistula connects the intestine with the umbilicus & discharge some of the Intestinal contents in to the umbilicus. C-The whole duct may persist as a fibrosed band extending from the umbilicus to the ileum. D-Part of the duct may persist & forms a vitelline cyst along the course of the duct.

9.  The hind gut gives rise to the following parts of the G.I.Tract: 1-The left one third of the transverse colon. 2-The descending colon. 3-The sigmoid colon. 4-The rectum. 5-The upper half of the Anal canal.

10.  The most caudal part of the hind gut(caudal to the origin of the allantois) is known as Endodermal cloaca with the cloacal membrane lying in its ventral wall.The Endodermal cloaca is divided by mesodermal septum (Uro-rectal septum)in to two parts; A-Ventral part known as Urogenital sinus. B-Dorsal part forms the rectum & upper half of the anal canal.

11. At the mean time the cloacal membrane is divided in to two parts too : A-Urogenital membrane ventrally. B-Anal membrane dorsally.  The mesoderm surrounding the cloacal membrane thickened & elevated,so the whole membrane comes to lie at the depression of Ectodermal cloaca.The anal membrane becomes surrounded by anal tubercle (mesodermal proliferation)that will form the external anal sphincter.Thus the anal membrane becomes at the bottom of the proctodeum(anal pit) Which gives rise to the lower half of the anal canal.Rupture of the membrane leads to continuity between the 2 halves of the anal canal& the site of the anal membrane represented in adult by anal valves.

12. 1-Imperforated anus due to failure of rupture of the anal membrane. 2-Congenital Recto-vaginal(in females) or Recto-Vesical (in males) fistula due to defective Uro-rectal septum. 3-Rectal atresia i.e obliteration of the lower part of the rectum due to replacement of the caudal part of the ano-rectal canal by fibrous tissues.

13.  Starts as a ventral out growth (Diverticulum) from the ventral aspect of the caudal part of the fore gut.It grows in to the ventral mesogastrium & divides in to 2 Buds with a stem  (stalk),these buds are known as pars hepatica(develops in to R & L lobes of the liver) and pars cystica which forms the gall bladder,while the stem of the diverticulum forms the Bile Duct.The cells of the liver are arranged in strands,which are separated from each other by blood sinusoids(from mesoderm of septum transversum).The mesoderm is also responsible for the formation of stroma & capsule of the liver,while kupffer cells form from mesenchym

14.  It takes origin from 2 pancreatic Buds (from the endodermal lining of the Duodenum),these buds are one dorsal & one ventral buds.The dorsal pancreatic bud grows in to the mesoduodenum & forms the tail,body & the major part of the head of the pancrease.It also give the major part of the main pancic duct & the accessory pancreatic duct.

15.  The Ventral pancreatic bud accompanies the hepatic diverticulum & forms the remaining part of the head of the pancrease and the uncinated process,it also share in the formation Of the main pancreatic duct which drains the rest of the head &uncinated process.  The endodermal cells of the pancreatic buds forms: 1-The secretory acini which secretes the pancreatic enzymes. 2-Islets of Langerhans that secretes insulin from B –cells & Glucagon from Alpha cells.

16. 1-Pancreatic tissue may invade the pyloric part of the stomach. 2-Annular pancrease,where a ring of pancreatic tissue surrounds the whole circumference of the Duodenum due to a bnormal migration of the pancreatic buds. 3-Cystic Fibrosis of the Pancrease results in very viscous pancreatic secretions as a result of obstruction of the pancreatic duct.

17.  It develops from the mesoderm in the dorsal mesogastrium which becomes divided in to gastro-splenic and lieno-renal ligaments.It is at first lobulated,but later on the lobes become confluent together.The presence of notches in the upper border of the adult spleen is an indication of its earlier lobulation.  The main Congenital Anomalies of Spleen are: 1-Lobulated spleen due to failure of the lobes to become confluent.  2-Accessory splenules.

18.  Its cranial half develops from the fore-gut,while its caudal half develops from the mid-gut.  This explains its blood supply from both Coeliac trunk & Superior mesenteric arteries. It is at first has a dorsal mesenmtery known as Mesogastrium attacheit to the posterior wall of the abdomen.As aresult of rotation of the stomach,the Duodenum comes to lie at the right side & becomes C-shaped structure tjat loses its mesentery & becomes as retroperitoneal structure exceopts its first one inch

28.  The face develops from five processes theses are the followings  1-The Fronto-nasal Process.  2-Two Maxillary Processess.  3-Two Mandibular Processess.  The mesoderm covering the fore brain proliferates to form a single median process termed the frontonasal process.On the ventromedial part of the free end of the frontonasal process an ectodermal thickening area termed olfactory placode(this will become depressed to form the olfactory pit).The olfactory pit has media &lateral folds.

29.  Part of the frontonasal process is called the intermaxillary (Premaxilla)segment.It lies between the 2 maxillary processes & gives rise to the followings:  1-Philtrum of the upper lip.  2-Median part of the upper jaw.  3-The primitive palate.

30.  On each side of the Stomodaeum the first branchial arch gives rise to 2 processes.  A-Maxillary processes,which fuses with the lateral nasal fold.  B-Mandibular processes:The 2 meet together in the mid line.  The maxillary process extends medially to fuse with the lower end of the frontonasal process to form the lower lip & upper jaw.

31.  Each maxillary process extends medially from below the olfactory pit to fuse with the tends medial nasal fold.As a result the olfactory pit becomes converted in to the primitive nasal cavity with 2 openings,one leads to the surface called the primitive anterior naris & another one opens in to the stomodaeum ( posteriorly) called the primitive posterior naris. Then the 2 primitive cavities are separated from each other by the primitive nasal septum ( from the Frontonasal septum).

32.  The lower end of the frontonasal process grows back ward to form the primitive palate,which is limited anteriorly by the 4 incisors.It is derived from the intermaxillary segment. A horizontal palatine process extends medially from the inner aspect of the side of each maxillary process.In the mid line this palatine process meets & fuses with each other as with the lower border of the nasal septum.  Anteriorly each palatine process fuses with the primitive palate at an oblique line.Posterior to the nasal septum,the fused palatine processes are not ossified & forms soft palate&uvula

33.  1-Hare lip,is due to failure of fusion between the Maxillary process & Medial Nasal fold..It leads to a fissure between the philtrum & upper lip, it could be.  A-Lateral hare lip  BMedian hare lip.  C-Bilateral hare lip.  2-Oblique facial cleft,which is due to failure of fussion between the maxillary process & the side of the frontonasal process along the side of the nose.

34.  3-Cleft palate:  A-Unilateral,due to failure of one horizontal palatine process to extnd medially,thus failing to fuse with the primitive palate..  B-Bilateral cleft palate,,here the 2 palatine processes fail to fuse with the primitive palate.  C-Isolated cleft palate,here the defect is in the mid line of the palate behind incisive fossa.  D-Bifid soft palate ( Bifid Uvula ), here the 2 palatine processes fail to fuse together in the mid line place in their most posterior part.