1. DIGESTIVE SYSTEM By
Dr SaminaAnjum

2. FORMATION OF PRIMITIVE GUT
Cephalocaudal folding
Lateral folding

3. FORMATION OF PRIMITIVE GUT
Incorporation of endoderm lined cavity in embryo
Yolk sac and allantois remain outside the body of embryo

4. DIVISIONS OF PRIMITIVE GUT
Foregut & hind gut are the blind ending tubes

5. Visceral mesoderm forms:
Endoderm forms:
The epithelial lining of gut
Parenchyma of glands
Visceral mesoderm forms:
Stroma of glands
Musculature of organs
Peritoneum

6. MESENTERIES

7. 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.

8. DEVELOPMENT OF ESOPHAGUS

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

10. Abnormalities Of Esophagus
Tracheoesophageal 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.

12. Development of Stomach
Fusiform dilation of the foregut in the fourth week
Dorsal & Ventral mesenteries
The stomach rotates around a longitudinal and an anteroposterior axis.

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

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

15. 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.

16. 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.

17. 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.

18. 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

19. GREATER OMENTUM
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.

20. FALCIFORM LIGAMENT & LESSER 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

21. Abnormalities Of Stomach
Pyloric 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.

22. DEVELOPMENT OF DUODENUM
The 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.

23. 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

24. 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.

25. 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.

26. 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 intraperitoneal

27. Cont…
During the 2nd month, the lumen of the duodenum is obliterated. However, the lumen is recanalized shortly thereafter.
Celiac Artery
Superior mesenteric Artery

28. ///LIVER & GALL BLADDER
Hepatic diverticulum appears - middle of 3rd week as an outgrowth of the endodermal epithelium at the distal end of foregut
Liver bud consists of rapidly proliferating liver cells that penetrate the Septum Transversum

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

30. Epithelial Liver cords
Hepatic sinusoids
Formed by vitelline & umbilical veins
Epithelial Liver cords
Differentiate into parenchyma & form lining of biliary ducts
Mesoderm of septum transversum
Hematopoietic cells
Kupffer cells
Connective Tissue cells

31. Mesoderm 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 liver

32. 6th week Hematopoiesis 10th week 12th week Last two months
Weight of the liver - 10% of total body weight
12th week
Bile formed by hepatic cells
Bile duct formed & bile can enter the GIT
Last two months
Hematopoietic function reduced
Weight of the liver only 5% of total body weight

33. Development of Pancreas
In dorsal mesentery

34. When 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.

35. DERIVATIVES OF PANCREATIC BUDS & DUCTS
The 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 Santorini
The proximal part of the dorsal pancreatic duct. The entrance of the accessory duct is at the site of the minor papilla.

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

38. Annular pancreas

39. MIDGUT
Begins 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

40. 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

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

42. Physiological umblical Herniation
Cause: 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.

43. ROTOATION OF MID GUT
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 left
During rotation, the cranial limb of the midgut elongates and forms jejunal-ileal loops while the expanding cecum sprouts as vermiform appendix .

44. Cont…
Additional rotation at 180° counterclockwise when intestinal loops return into abdomen during 10th week.
Total rotation of midgut= 270° counterclockwise

45. RETRACTION OF HERNIATED LOOPS
Causes:
Regresssion of mesonephric kidney
Reduced growth of liver
Expansion of abdominal cavity
During 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.

46. The caecal diverticulum is 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 colon and the hepatic  flexure on 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).

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

49. FATE OF MESENTERIES
The 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 abdomen
Mesenteries of ascending and descending colon press against the peritoneum of the posterior abdominal wall, fuse & degenerate so that these organs become secondarily retroperitoneal.

50. Cont…
The 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.

51. Cont…
After 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

53. ABNORMALITIES OF THE MESENTERIES
Persistence 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.

54. fFailure of bowel to return during physiological herniation
OMPHALOCELE
fFailure of bowel to return during physiological herniation

55. GASTROSCHISIS

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

57. 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.

58. SUBHEPATIC CECUM & APPENDIX
REVERSED ROTATION
SUBHEPATIC CECUM & APPENDIX

59. In 2-4% cases vitelline duct persists forming Meckel’s diverticulum, 40-60cm
from ileocecal valve on the antimesenteric border of ileum

60. INTESTINAL RECANALIZATION & DUPLICATION

62. GUT ATRESIAS & STENOSIS
A: Region of bowel is lost--- 50%
B: A fibrous cord remains %
C: Narrowing , with a thin diaphragm separating the larger & smaller pieces of bowel--- 25%
D: Stenosis---5%

63. DEVELOPMENT OF HIND GUT

64. The 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.

65. DEVELOPMENT OF HINDGUT

68. DEVELOPMENT OF ANAL CANAL
B.S

70. HINDGUT ABNORMALITIEES
A: Urorectal fistula
B: Rectovaginal fistula
D: Imperforate anus

71. RADIOGRAPH OF COLON AFTER BARIUM ENEMA
CONGENITAL MEGACOLON
Also 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 colon
Male to female ratio is 4:1 s
RADIOGRAPH OF COLON AFTER BARIUM ENEMA

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