Transcript digestive system - MBBS Students Club

By
Dr SaminaAnjum
FORMATION OF PRIMITIVE GUT
 Cephalocaudal folding
 Lateral folding
FORMATION OF PRIMITIVE GUT
 Incorporation of endoderm lined cavity in embryo
 Yolk sac and allantois remain outside the body of embryo
DIVISIONS OF PRIMITIVE GUT
Foregut & hind gut are the blind ending tubes
Endoderm forms:
 The epithelial lining of gut
 Parenchyma of glands
Visceral mesoderm forms:
 Stroma of glands
 Musculature of organs
 Peritoneum
MESENTERIES
FOREGUT
 The derivates of foregut are:
 The primordial pharynx and its derivates namely, oral



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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.
DEVELOPMENT OF ESOPHAGUS
 Initially short, but with the descent of the heart and lungs, it
lengthens rapidly.
 The muscular coat & Innervation
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.
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.
 The stomach rotates 90 degrees clockwise around its
longitudinal axis, causing its left side to face anteriorly
and its right side to face posteriorly.
 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.
 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.
 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.
 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.
 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
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.
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
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.
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.
 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
 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.
 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.
 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
Cont…
 During the 2nd month, the
lumen of the duodenum is
obliterated. However, the
lumen is recanalized shortly
thereafter.
 Celiac Artery
 Superior mesenteric Artery
///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
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.
 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
 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
 6th week
Hematopoiesis
 10th week
 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
Development of Pancreas
In dorsal mesentery
 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.
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.
 Third 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.
Annular pancreas
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
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
 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
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.
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 .
Cont…
 Additional rotation at 180° counterclockwise when
intestinal loops return into abdomen during 10th week.
 Total rotation of midgut= 270° counterclockwise
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.
 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).
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
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.
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.
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
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.
OMPHALOCELE
fFailure of bowel to return during physiological herniation
GASTROSCHISIS
Abnormal closure of body wall around the connecting stalk, cocaine use
increases the tendency in young women
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.
REVERSED ROTATION
SUBHEPATIC CECUM &
APPENDIX
In 2-4% cases vitelline duct persists forming Meckel’s diverticulum, 40-60cm
from ileocecal valve on the antimesenteric border of ileum
INTESTINAL RECANALIZATION & DUPLICATION
GUT ATRESIAS & STENOSIS
A: Region of bowel is
lost--- 50%
B: A fibrous cord
remains --- 25%
C: Narrowing , with a
thin diaphragm
separating the larger
& smaller pieces of
bowel--- 25%
D: Stenosis---5%
 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.
DEVELOPMENT OF HINDGUT
DEVELOPMENT OF ANAL CANAL
B.S
HINDGUT ABNORMALITIEES
A: Urorectal fistula
B: Rectovaginal fistula
D: Imperforate anus
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
RADIOGRAPH OF COLON AFTER
BARIUM ENEMA
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