Transcript 07-digestive+urinary2008-04

Development of Midgut loop:
 Derivatives of midgut loop are:
1-Small intestine, including most of
duodenum.
2-Cecum & appendix.
3-Ascending colon.
4-Right 2/3 of transverse colon.
 All these derivatives are supplied by
superior mesenteric artey (artery of midgut)
Development of midgut loop
At the biginning of 6th week, the
midgut elongates to form a
venteral U-shaped midgut loop
projecting into extra-embryonic
coelom of proximal part of
umbilical cord …this called
physiological umbilical herniation.
At this stage the arrow indicates
communication of intraembryonic
coelom (peritoneal cavity) with
extraembryonic coelom.
At this stage ,the abdominal
cavity is temporarily too small in
comparison to relatively massive
liver & kidnes to contain the
developing rapidly growing
intestines.
Development of midgut loop
The midgut loop joined with
Yolk sac through yolk stalk or
vitelline duct until 10th week.
Midgut loop consists of 2
limbs, cranial limb & caudal
limb. (A)
Cranial limb grows rapidly
forming the small intestines.(B)
Caudal limb gives rise to
cecal diverticulum, the
primordium of cecum &
appendix. ( C )
Rotation of midgut loop
While midgut loop is in the
umbilical cord, it rotates 90
degrees counterclockwise
around axis of superior
mesenteric artery. (A),(A1)
This brings the cranial limb to
the right and caudal limb to left.
(B), (B1).
Return of midgut to abdomen
(reduction of physiological hernia) :
During 10th week the small
intestine (formed of cranial
limb) returns first to abdomen
due to enlagement of
abdominal cavity ….this is
called reduction of physiological midgut hernia.(C&D)
large intestine (formed from
caudal limb) undergoes a
further 180 degree
counterclockwise rotation to
occupy right side of abdomen.
(D),(D1)
Ascending colon becomes
recognizable as posterior
abdominal wall elongates. (E)
Fixation of various parts of intestines
At first the dorsal mesentry is in
the median plane. As the intestines
lenghthen,and obtain their final
position, some mesentries are
fused with posterior abdominal
wall.
A,Venteral view of the intestine Prior to
Fixation.
B,T.S showing areas of fusion.
C, Sagittal S. showing greater omentum overhanging the transverse colon, arrows indicate
areas of subsequent fusion.
Mesentry of ascending&
descending colon disappears, so
ascending & descending colon
becomes fixed to posterior
abdominal wall and they become
retro-peritoneal. (B)
Transverse mesocolon persists
and fuses with posterior wall of
greater omentum and maintains its
mobility. (C)
Fixation of various parts of intestines
With rotation of stomach,
duodenum & pancreas are
pressed against posterior
abdominal wall by the colon.
Intestines prior to fixation
Adjacent layers of peritoneum
fuse and disappear, so most of
duodenum & pancreas become
retroperitoneal.
E, T.S after disappearance of
mesentry of ascending &
descending colon.
Intestines after fixation
F, sagittal S.showing fusion of
layers of greater omentum and
fusion of greater omentum with
mesentery of transverse colon.
Development of Cecum & Appendix
At 6th week, cecal
diverticulum appears as a
swelling on the antimesenteric border of caudal
limb of midgut loop. (A)
Cecal diverticulum gives
rise to cecum & appendix.(B)
Appendix is intially a small
diverticulum of the cecum,
arising from distal end of
cecum.(B)
A,6 weeks .
B, 8 weeks.
C,12 weeks
D,at birth …appendix is long and is continuous
with apex of cecum. E, After birth
(adult appendix) It is short as a result that the
appendix enters medial side of cecum.
As ascending colon
elongates, appendix
elongates and may be
retrocecal or retrocolic or
pelvic appendix. In 64% of
people, it is retrocecally.
Congenital Omphalocele
It is a persistence of herniation
of abdominal contents into
proximal part of umbilical cord
due to failure of reduction of
physiological hernia to abdominal
cavity at 10th week.
Herniation of intestines occurs
in 1 of 5000 births – herniation of
liver & intestines occurs in 1 of
10,000 births.
It is accompanied by small
abdominal cavity.
The hernial sac is covered by
the epithelium of the umbilical
cord, the amnion.
Immediate surgical repair is
required.
Umbilical Hernia
 The intestines return to
abdominal cavity at 10th week,
but herniate through an
imperfectly closed umbilicus
 It is a common type of hernia.
 The herniated contents are
usually the greater omentum &
small intestine.
 The hernial sac is covered by
subcutaneous tissue & skin.
 It protrudes during
crying,straining or coughing and
can be easily reduced through
fibrous ring at umbilicus.
 Surgery is performed at age of
3-5 years.
Ileal (Meckel) Diverticulum
It is one of the most common anomalies of the
digestive tract, present in about 2% of people.
It is a small pouch from the ileum, and may
contain small patches of gastric & pancreatic
tissues.The gastric mucosa often secretes acid
producing ulceration & bleeding.
It is the remnant of proximal part nonobliterated
part) of yolk stalk (or vitelline duct).
It arises from antimesenteric border of ileum,1/2
meter from ileocecal junction.
It is more common in males.
It is sometimes becomes inflamed and causes
symptoms that mimic appendicitis.
It may be connected to the umbilucus by a
fibrous cord or Omphalo-enteric fistula
(vitello-intestinal duct remains patent and faecal
matter is carried through the duct into umbilicus).
Hindgut
 Derivatives of hindgut are :
 1-left 1/3 of transverse colon.
2-Descending colon & sigmoid colon.
 Part of hindgut dilate to form Cloaca which gives rise to:
3-Rectum.
4-Superior part of anal canal.
5-Certain urogenital structures
(epithelium of urinary bladder & most of urethra)
 Inferior mesenteric artery is the artery of hindgut.
Partitioning of
cloaca into rectum
and uro-genital sinus
by urorectal septum.
A,C,E cloaca at 4,6
and 7 weeks.
B,D,F cloacal
region.note
degeneration and
disappearance of the
postanal or tailgut (B)
as the rectum forms
from dorsal part of
cloaca.
B1,D1,F1, T.S.of
cloaca.
Development of Rectum & Anal canal
Cloaca, the expanded
terminal part of hindgut,
receives allantois ventrally.
cloacal membrane, is
composed of endoderm of
cloaca + ectoderm of
proctodeum (or anal pit).
Cloaca is divided into dorsal
& ventral parts by a
mesenchyme-urorectal
septum- between allantois and
hindgut, producing infoldings of
lateral walls of cloaca.
These folds fuse forming a
partition that divides cloaca into
1-Rectum + cranial (superior)
part of anal canal, dorsally.
2-Urogenital sinus, ventrally.
Development of Rectum & Anal Canal
At 7th week, urorectal septum
fused with cloacal membrane,
dividing it into:
1-dorsal anal membrane.
2-ventral urogenital membrane.
Area of fusion of urorectal
septum with cloacal membrane
gives rise to perineal body.
Urorectal septum also divides
cloacal sphincter into anterior &
posterior parts. The posterior part
becomes external anal sphincter/
and anterior part develops into
superficial transverse
perineal,bulbospongiosus and
ischiocavernosus muscles that
supplied by one nerve,the
pudendal nerve.
Development of Rectum & Anal Canal
Mesenchymal proliferations
produce elevations of the surface
ectoderm around anal membrane.
So the anal membrane is located at
the bottom of an ectodermal
depression-the proctodeum (or anal
pit ).
Anal membrane usually ruptures
at the end of 8th week, bringing
distal part of anal canal into
communication of amniotic cavity.
Development of Anal Canal
Superior 2/3 of anal canal derived
from hindgut, whereas inferior 1/3 of
anal canal is derived from
proctodeum.
Pectinate line -located inferiorly to
anal valves is the junction of
epithelium derived from ectoderm of
proctodeum & endoderm of hindgut.
It is the former site of anal
membrane.
White line / or anocutaneous line, 2
cm superior to anus,where the anal
epithelium changes from columnar to
stratified squamous cells.
At anus, epithelium is keratinized
and continuous with skin around
anus. Wall of anal canal is derived
from splanchnic mesenchyme.
Development of Anal Canal
Because of different embryological
origin of anal canal, superior and inferior
parts of anal canal are supplied by
different arteries ,nerves and have
different venous and lymphatic
drainage. This is important clinically in
spread of cancer cells.
Superior rectal artery (continuation of
inferior mesenteric,artery of hindgut /
inferior rectal artery – superior rectal
vein/ inferior rectal veininferior
mesenteric L.N/ superficial inguinal L.N.
Tumors in superior part of anal canal
are painless (supplied by autonomic
N.S) and arise from columnar
epithelium, / whereas those of inferior
part are painful (supplied by inferior
rectal N.) and arise from stratified
squamous epithelium.
Congenital Megacolon
(hirschsprung disease):
It is a dilated segment of the colon,
due to failure of development of
parasympathetic ganglion cells distal to
the dilated part but the dilated part has
a normal ganglion cells.
The dilatation results from failure of
neural crest cells to migrate into wall of
colon during 5-7th week, leading to
loss of peristalsis in the aganglionic
segment of colon, so no movement of
intestinal contents.
Mostly,only the rectum & sigmoid
colon are involved.
It is the most common cause of
neonatal obstruction of colon
Imperforate Anus
(membranous anal atresia):
A thin membrane separates the anal
canal from the exterior. this membrane is
thin enough to bulge on straining and
appears blue due to presence of meconium
above it.
It results from failure of anal membrane
to perforate at the end of 8th week.
The anus is at normal position.
It is more common in males.
Ileal (Meckel) diverticula