4. A. LATERAL VIEW OF A 4-WEEK EMBRYO SHOWING THE RELATIONSHIP PRIMORDIAL GUT TO YOLK SAC.
B. DRAWING OF MEDIAN SECTION OF THE EMBRYO SHOWING EARLY DIGESTIVE SYSTEM AND ITS BLOOD
SUPPLY.
THE PRIMORDIAL GUT IS A LONG TUBE EXTENDING THE LENGTH OF THE EMBRYO. ITS BLOOD VESSELS ARE
DERIVED FROM THE VESSELS THAT SUPPLIED THE YOLK SAC.
5. MIDGUTDERIVATIVES ARE
The small intestine, including most of the
duodenum ( the part caudal to the major
duodenal papilla )
The caecum; appendix; ascending colon and the
right half or two- third of the transverse colon
All these midgut derivatives are supplied by the
superior mesenteric artery
6. FORMATION OF THE MIDGUT LOOP [ SHADED ]
NOTE – HOW THE SUPERIOR MESENTERIC ARTERY AND VITELLINE
DUCT FORM AN AXIS FOR THE FUTURE ROTATION OF THE MIDGUT
LOOP
7. THE MIDGUT LOOP IS SUSPENDED FROM
THE DORSAL ABDOMINAL WALL BY AN
ELONGATED MESENTERY.
AS IT ELONGATES, THE VENTRAL U –
SHAPED LOOP OF GUT ( MIDGUT LOOP )
PROJECTS INTO THE REMAINS OF THE
EXTRAEMBRYONIC COELOM IN THE
PROXIMAL PART OF THE UMBILICAL CORD
AT THE END OF THE 5TH WEEK.
AT THIS STAGE, THE INTRAEMBRYONIC
COELOM ( PERITONEAL CAVITY )
COMMUNICATES WITH THE
EXTRAEMBRYONIC COELOM AT THE
UMBILICUS.
8. PHYSIOLOGICAL UMBILICAL HERNIATION OCCURS AT THE
BEGINNING OF 6TH WEEK.
The midgut loop communicates with the yolk sac through the narrow yolk stalk or vitelline duct ( vitello-
intestinal duct ) until the 10th week. So, the herniated intestine is derived from the midgut loop in the
proximal part of the umbilical cord.
Umbilical herniation occurs because there is not enough room in the abdomen for rapidly growing midgut.
The shortage of space is caused by the relatively massive liver and the 2 kidneys
9. THE MIDGUT LOOP HAS A CRANIAL LIMB AND A CAUDAL LIMB. THE YOLK STALK IS ATTACHED TO THE APEX OF THE MIDGUT
LOOP WHERE THE 2 LIMBS JOIN.
THE CRANIAL LIMB GROWS RAPIDLY AND FORMS SMALL INTESTINAL LOOPS. THE CAUDAL LIMB UNDERGOES VERY LITTLE
CHANGE EXCEPT FOR DEVELOPMENT OF THE CAECAL DIVERTICULUM ( THE PRIMORDIUM OF THE CECUM AND APPENDIX.
10. ROTATION OF MIDGUT
LOOP
• While it is in the umbilical cord, the midgut loop rotates
90 degrees counterclockwise around the axis of the
superior mesenteric artery and yolk stalk. This brings the
cranial limb of the midgut loop to the right and the caudal
limb to the left.
• During rotation the cranial limb elongates and forms
jejunum & ileum ( intestinal loops)
11. FIXATION OF INTESTINE
DURING THE 10TH WEEK, THE INTESTINES RETURN TO
THE ABDOMEN. IT IS NOT KNOWN WHAT IS THE
CAUSES. HOWEVER, THE DECREASE IN THE SIZE OF THE
LIVER AND KIDNEYS AND THE ENLARGEMENT OF THE
ABDOMINAL CAVITY ARE IMPORTANT FACTORS. THIS
PROCESS IS CALLED REDUCTION OF THE
PHYSIOLOGICAL MIDGUT HERNIA.
THE SMALL INTESTINE ( FORMED FROM THE CRANIAL
LIMB ) RETURNS FIRST AND PASSES POSTERIOR TO THE
SUPERIOR MESENTERIC ARTERY AND OCCUPIES THE
CENTRAL PART OF THE ABDOMEN.
AS THE LARGE INTESTINE RETURNS, IT UNDERGOES A
FURTHER 180 DEGREE COUNTERCLOCKWISE ROTATION.
13. • Later it comes to occupy the right side of the abdomen.
• The ascending colon becomes recognizable as the posterior
abdominal wall progressively elongates. The cecum is
rotating to its normal position in the lower right quadrant of
the abdomen.
• Rotation of the stomach and duodenum causes the
duodenum and pancreas to fall to the right. The enlarged
colon presses the duodenum against the posterior abdominal
wall. As a result, most of the duodenal mesentery is
absorbed and the duodenum, except for about the first 2.5
cm ( derived from the foregut ), has no mesentery and lies
retroperitoneally.
14. AT FIRST THE DORSAL MESENTERY IS IN THE MEDIAN PLANE. AS
THE INTESTINES ENLARGE, LENGTHEN AND ASSUME THEIR FINAL
POSITION, THEIR MESENTERIES ARE PRESSED AGAINST THE
POSTERIOR ABDOMINAL WALL. SO, THE MESENTERY OF THE
ASCENDING COLON FUSES WITH THE PARIETAL PERITONEUM ON
THIS WALL AND DISAPPEARS. THE DESCENDING COLON ALSO
BECOMES RETROPERITONEAL
Other derivatives of the midgut loop ( jejunum
& ileum ) retain their mesenteries. The
mesentery is at first attached to the median
plane of the posterior abdominal wall.
After the mesentery of the ascending colon
disappears, the fan- shaped mesentery of the
small intestine acquires a new line of
attachment that passes from the
duodenojejunal junction inferolaterally to the
ileocecal junction.
15. Succesive stages in the development of caecum and
appendix
at birth – appendix is relatively long and is continuous with the apex of the caecum.
adult – appendix is now relatively short and lies on medial side of the caecum. In about 64% of the
people, the appendix is located posterior to the caecum (retrocaecal) or posterior to the ascending colon
(retrocolic). The tenia colia is a thickend band of longitudinal muscle in the wall of colon which ends at
the base of appendix.
16. THE CECAL DIVERTICULUM ( PRIMORDIUM OF THE CECUM AND VERMIFORM
APPENDIX ) APPEARS IN THE 6TH WEEK AS A SWELLING ON THE
ANTIMESENTERIC BORDER OF THE CAUDAL LIMB OF THE MIDGUT LOOP.
THE APEX OF THE CECAL DIVERTICULUM DOES NOT GROW AS RAPIDLY AS
THE REST OF IT. THUS, THE APPENDIX IS INITIALLY A SMALL
DIVERTICULUM OF THE APEX OF THE CECUM.
THE APPENDIX INCREASES RAPIDLY IN LENGTH SO THAT AT BIRTH IT IS A
RELATIVELY LONG TUBE ARISING FROM THE DISTAL END OF THE CECUM.
AFTER BIRTH THE WALL OF THE CECUM GROWS UNEQUALLY, WITH THE
RESULT THAT THE APPENDIX COMES TO ENTER ITS MEDIAL SIDE. THE
APPENDIX MAY PASS POSTERIOR TO THE CAECUM ( RETROCECAL ) OR
COLON ( RETROCOLIC ). IT MAY DESCEND OVER THE BRIM OF THE PELVIS
( PELVIS APPENDIX ).
IN ABOUT 64 % OF PEOPLE THE APPENDIX IS LOCATED RETROCECALLY
17. CONGENITAL OMPHALOCELE
THIS ANOMALI IS PERSISTENCE OF THE HERNIATION OF
ABDOMINAL CONTENTS INTO THE PROXIMAL PART OF THE
UMBILICAL CORD AND FAILURE OF THE INTESTINE TO
RETURN TO THE ABDOMINAL CAVITY FROM THE
EXTRAEMBRYONIC COLEOM DURING THE 10TH WEEK.
THE COVERING OF THE HERNIAL SAC IS THE EPITHELIUM
OF UMBILICAL CORD ( A DERIVATIVE OF THE AMNION ).
HERNIATION OF THE INTESTINES INTO THE CORD
OCCURS IN ABOUT 1 OF 5000 BIRTHS AND HERNIATION OF
THE LIVER AND INTESTINES IN 1 OF ABOUT 10000 BIRTHS.
THE SIZE OF THE HERNIA DEPENDS ON ITS CONTENTS.
WHEN THERE IS SMALL ABDOMINAL CAVITY, THERE IS
OMPHALOCELE.
IMMEDIATE SURGICAL REPAIR IS REQUIRED
18.
19. THE YOLK STALK. IT TYPICALLY APPEARS
AS A FINGERLIKE POUCH ABOUT 3 TO 6
CM LONG THAT ARISES FROM THE
ANTIMESENTERIC BORDER OF THE
ILEUM 40 T0 50 CM FROM THE
ILEOCECAL JUNCTION.
IT IS COMMON. MECKEL DIVERTICULUM
OCCURS IN 2 TO 4 % OF PEOPLE AND IS
3 TO 5 TIMES MORE PREVALENT IN
MALES THAN FEMALES. WHEN IT
INFLAMES, IT CAUSES SYMPTOMS THAT
MIMIC APPENDICITIS.
THE WALL OF THE DIVERTICULUM
CONTAINS ALL LAYERS OF ILEUM AND
MAY CONTAIN SMALL PATCHES OF
GASTRIC AND PANCREATIC TISSUES.
20. AN ILEAL DIVERTICULUM MAY BE CONNECTED TO THE UMBILICUS BY A FIBROUS
CORD OR AN OMPHALOENTERIC FISTULA WHICH RESULTS FROM PERSISTENCE OF
THE ENTIRE INTRAABDOMINAL PORTION OF THE YOLK STALK ( VITELLINE DUCT ).
ON THE FIBROUS REMNANT OF THE OF THE YOLK STALK A VITELLINE CYSTS IS FORMED.
UMBILICAL SINUS RESULTS FROM THE PERSISTENCE OF THE YOLK STALK NEAR THE
UMBILICUS. IT IS USUALLY APPEAR WITH VOLVULUS OF THE DIVERTICULUM.
THE YOLK STALK HAS PERSISTED AS A FIBROUS CORD CONNECTING THE ILEUM WITH THE
UMBILICUS AND CONTAINING A PERSISTENT VITELLINE ARTERY .
21. HINDGUT
IT IS DERIVATIVES ARE :
- THE LEFT ONE THIRD TO ONE HALF OF THE TRANSVERSE COLON; THE
DESCENDING COLON ; SIGMOID COLON; RECTUM AND THE SUPERIOR PART OF THE
ANAL CANAL.
- THE EPITHELIUM OF THE URINARY BLADDER AND MOST OF THE URETHRA.
- THESE DERIVATIVES ARE SUPPLIED BY THE INFERIOR MESENTERIC ARTERY.
- THE DESCENDING COLON BECOMES RETROPERITONEAL AS ITS DORSAL
MESENTERY FUSES WITH THE PERITONEUM ON THE LEFT POSTERIOR ABDOMINAL
WALL AND THEN DISAPPEARS.
- THE MESENTERY OF THE SIGMOID COLON IS RETAINED BUT IT IS SHORTER
THAN IN THE EMBRYO.
22. CLOACA
THE CLOACA IS THE EXPANDED TERMINAL PART OF THE HINDGUT WHICH RECEIVES THE ALLANTOIS VENTRALLY ( A FINGERLIKE
DIVERTICULUM ).
IT IS AN ENDODERM- LINED CHAMBER THAT CONTACT WITH THE SURFACE ECTODERM AT THE CLOACAL
MEMBRANE. THIS MEMBRANE IS COMPOSED OF ENDODERM OF THE CLOACA AND ECTODERM OF THE
PROCTODEUM ( ANAL PIT ).
THE CLOACA IS DIVIDED INTO DORSAL AND VENTRAL PARTS BY A WEDGE OF MESENCHYME ( THE URORECTAL
SEPTUM ) WHICH DEVELOPS IN THE ANGLE BETWEEN THE ALLANTOIS AND HINDGUT.
AS THE SEPTUM GROWS TOWARD THE CLOACAL MEMBRANE, IT DEVELOPS FORKLIKE EXTENSIONS.
THE 2 PARTS ARE : A- RECTUM AND CRANIAL PART OF THE ANAL CANAL DORSALLY.
B- UROGENITAL SINUS VENTRALLY.
23. RADIOGRAPHY OF COLON AFTER A BARIUM ENEMA IN
A ONE MONTH OLD INFANT WITH CONGENITAL
MEGACOLON OR HIRSCHSPRRUNG DISEASE. THE
AGANGLIONIC DISTAL SEGMENT (RECTUM AND DISTAL
SIGMOID COLON) IS NARROW, WITH DISTENDED
NORMAL GANGLIONIC BOWEL, FULL OF FACEAL
MATERIAL, PROXIMAL TO IT.
Congenital Megacolon ( Hirschsprung
Disease )
It is a dominant inherited multigenic disorder. It is the most common
cause of neonatal obstruction of the colon and occurs for about 33% .
Males are affected more often than females ( 4- 1 ).
A part of colon is dilated because oF absence of autonomic ganglia
cells in myenteric plexus distal to the dilated segment of colon.
The enlarged colon has normal number of ganglion cells. The
dilatation results from failure of peristalsis in aganglionic segment (
transition zone ) which prevents movement of the intestinal
contents.
In most cases only the rectum and sigmoid colon are involved. Also,
ganglia may be absent from more proximal parts of the colon.
It results from failure of the neural crest cells to migrate into the wall
of the colon during the 5th to 7th weeks. This results in failure of
parasympathetic ganglion cells to develop in the Auerbach and
Meissner plexuses.
The cause of failure of some neural crest cells to complete their
