Embryology of GIT Flashcards
cavity becomes incorporated into the embryo to become the primitive gut.
Cephalocaudal and lateral folding of the embryo
foregut develops on the cephalic end, and the hindgut caudally.
Closing of caudal and cephalic ends.
Midgut now communicates with the yolk sac through the
vitelline duct.
Results from the cephalocaudal and lateral folding of the embryo.
primitive gut
Embryo, foregut caudal to
pharyngeal tube
embryo, midgut caudal to _____ and at the junction of the ____ .
- liver bud
- right two thirds and left third of the transverse colon
Part of tge primitive gut that is temporarily connected to the yolk sac
midgut
embryo of git, hindgut is from the ___ to ___
left third of the transverse colon to the cloacal membrane
is also part of the primitive gut BUT is important for the development of head and neck
The pharyngeal gut/ Pharynx is also part of the primitive gut BUT is important for the development of head and neck
Layer that gives rise to what?
Endoderm – epithelial linings of GIT, parenchyma of pancreas and liver
Mesoderm(Splanchnic) – muscles, connective tissues, and peritoneal coverings of GIT
Double layer of peritoneum that encloses an organ and connects it to the body wall
mesenteries
Iliac artery from the aorta forming branches that will supply
foregut
Functions as pathway for:
- Iliac artery from the aorta forming branches that will supply foregut
- Superior mesenteric artery – supplies midgut
- Inferior mesenteric artery – supplies hindgut
- Vitelline artery – forms the terminal portion of the superior iliac artery
Structures that suspend portions of the gut tube and its derivatives from the dorsal and ventral body wall.
mesenteries
Organs enclosed by mesenteries are classified as:
a) Intraperitoneal - Freely suspended by mesenteries.
- E.g.: stomach, liver, gall bladder
b) Retroperitoneal
- E.g.: kidneys, pancreas
c) Peritoneal ligament
- Organs that are enclosed by mesenteries and are connected to the body wall.
Intraperitoneal
- Organs that lie against the posterior body wall and are covered by peritoneum only on its anterior surface.
Retroperitoneal
Provides pathways for vessels, nerves and lymphatics to and from abdominal canal.
Peritoneal ligament
___ extends the distal portion of the esophagus up to almost all parts of the hindgut/region of cloaca
Dorsal Mesentery - 5th week
___ attaches the distal portion of the esophagus up to the upper or proximal part of the duodenum.
Ventral Mesentery - 5th week
- Mesenteries that pass from one organ to another or from an organ to the abdominal wall.
Peritoneal ligament
At 5th week caudal part of primitive gut is suspended from abdominal wall by __
dorsal mesentery.
embryology, Dorsal mesentery becomes
Greater omentum(dorsal mesogastrium) – attaches to the stomach. Mesoduodenum – attaches to the duodenum (it contains the pancreatic duct) Dorsal Mesocolon – attaches to the Large intestine Mesentery proper – extends the jejunoileal loops to the midgut
Ventral Mesentery is derived from the ___
SEPTUM TRANSVERSUM
is derivative of primitive diaphragm, extension at the thick mesodermal bridge and it is situated b/w the thoracic cavity and vitelline duct
Septum transversum
Septum transversum thinned out and became membranous when the liver expanded during the development and its distal part becomes the
Visceral Peritoneal hepatic covering
o Lesser Omentum – attaches the liver to lower esophagus, stomach, and upper duodenum
o Falciform Ligament – attaches the liver to the anterior abdominal wall
Lengthening of esophagus happens on what week?
5th week
At the 5th week, the esophagus is initially short but lengthens rapidly with the descent of the heart and lungs. Upper 2/3 = ____ and lower 1/3 = ____
vagus n
splanchnic n
____ prevents the normal passage of amniotic fluid into the intestinal tract results in _____
- Esophageal atresia / tracheoesophageal fistula
- polyhydramnios
polyhydramnios accumulation of excess fluid in the ____
amniotic sac
Esophageal atresia / tracheoesophageal fistula results either from:
- spontaneous posterior deviation of the tracheoesophageal septum
- or from some mechanical factor pushing the dorsal wall of the foregut anteriorly
Esophageal atresia / tracheoesophageal fistula most common form:
- proximal part of esophagus ends as a blind sac
- distal part is connected to the trachea by a narrow canal just above the bifurcation.
___ usually in the lower third of the esophagus
Esophageal Stenosis
Esophageal Stenosis may be caused by:
incomplete recanalization
vascular abnormalities
accidents that compromise blood flow.
Occasionally, esophagus fails to lengthen sufficiently, stomach is pulled up in the esophageal hiatus through diaphragm =
congenital hiatal hernia
4th week: stomach appears as a ____ of the foregut
fusiform dilation
During the following weeks (after 4th week), the stomach’s appearance and position change greatly as it rotates around a ___
longitudinal and an anteroposterior axis.
The right side of the unrotated stomach will become the ____ and the left side will form the___ after rotation
- posterior side of the stomach
- anterior side of the stomach
The vagus nerves will also rotate along with the stomach, that’s why the left vagus nerve innervates the stomach____, and the right vagus nerve ____
- anteriorly
- posteriorly
The stomach will rotate 90˚ to the ____
right
The faster growth of the former posterior part
(the left side of the stomach now) forms the _____
greater curvature of the stomach
The former anterior part of the stomach grows slower which results to the rotation of the stomach in an____
antero-posterior axis
The ____ part shifts upward and to the right while the ____ part shifts downward and to the left
- pyloric
- cardiac
There will also be a shift in the orientation of the _____ as the stomach rotates in the longitudinal axis.
dorsal and ventral mesogastrium
the cavity that is left behind as the dorsal mesogastrium moves to the left during rotation
Omental bursa (lesser peritoneal sac)
The ventral mesogastrium then moves to the right due to the growth of the ____
liver
As the stomach rotates longitudinally, the dorsal mesogastrium will lengthen and move to the left. A part of the mesogastrium will touch and adhere to the peritoneum lying in the posterior abdominal wall to form the so called ____
line of fusion.
The line of fusion will degenerate as the fusion between the part of the ___ becomes complete
mesogastrium and peritoneum
Organs that will be enclosed by this folding (fusion of mesogastrium and peritoneum) will become ____.
retroperitoneal
such as the kidney, pancreas, part of the duodenum
organs in the abdominal cavity that is not covered completely by peritoneum.
Retroperitoneal organs
These organs are covered by peritoneum only on its anterior surface.
Retroperitoneal organs that initially develops in an intraperitoneal manner.
Secondary Retroperitoneal Organs
E.g. Pancreas
During the 5th week of development, the spleen arises as a ___ proliferation in between the leaves of the ___.
- mesodermal
- dorsal mesogastrium
The spleen will retain its intraperitoneal position
During the 5th week of development, The spleen is suspended by two ligaments:
Lienorenal ligament – connects the spleen to the posterior abdominal wall near the left kidney.
Gastrolienal ligament – connects the spleen to the stomach.
connects the spleen to the posterior abdominal wall near the left kidney
Lienorenal ligament
connects the spleen to the stomach
Gastrolienal ligament
Formed when the stomach rotates in an antero-posterior axis. The dorsal mesogastrium that is attached to the greater curvature will grow and bulge downward.
GREATER OMENTUM
As it grows in length, it will cover the transverse colon and the small intestinal loops. It take on an apron-like form as it drapes over the intestinal segments
GREATER OMENTUM
GREATER OMENTUM Initially composed of 2 sacs of mesentery, but will eventually form a single sheath that hangs over the transverse colon and intestinal loops as it fuses with the ___
transverse mesocolon
extends from the distal portion of the esophagus to the upper part of the duodenum, and also attaches to the liver
LESSER OMENTUM
the free margin of the lesser omentum that attaches the duodenum with the liver
Hepatoduodenal ligament
Hepatoduodenal ligament contains the portal triad which is compose of :
portal vein, hepatic artery, bile duct
opening that connects the lesser peritoneal sac (sac behind the stomach) to the greater peritoneal sac
Omental foramen (or epiploic foramen of Winslow) –
Duodenum and Liver Bud are supplied by _
celiac artery and the superior mesenteric artery.
remnant of the left umbilical vein that is contained within the free margin of the falciform ligament
Ligamentum Teres Hepatis
____ is the junction between the foregut and the midgut receives blood from both the _____
- duodenum
- celiac artery and the superior mesenteric artery
Formed partly by the foregut and the midgut
duodenum
The change in the orientation of the stomach causes the duodenum to shift from its ____ position into its position in the ___.
- midline
- right side
The duodenum is a retroperitoneal segment except for the ____, the most proximal part of the duodenum that
retains its _____
- duodenal cap
- mesentery
By the 2nd month, the duodenum goes through a solid stage wherein the rapid proliferation of duodenal cells will cause the___ to obliterate. It will then recanalize to establish ____ of the duodenum
- canal or lumen
- patency
The liver primordium starts to form at around ___
3 ½ weeks.
The liver primordium arises from the ___ in which it will be penetrated by cells that will proliferate to form ___
- foregut
- hepatocytes
The ____ serves as a connection between the foregut, liver and duodenum.
- bile duct
Bile duct originally opens on the ___ aspect of the duodenum but will eventually move to a ___ position due to the rotation of the duodenum.
- anterior
- posterior
The gall bladder will start off as a bud on the___ aspect of the bile duct and will eventually connect to each other through the ____
- ventral
- cystic duct
By the 10th week, the Liver will weigh about 10% of the total body weight. It will also begin to function as a site of ____
hematopoiesis
During the 12th week, the liver will start to produce ___, which will go to the____ which causes the contents of the intestine to have a dark green color
- bile
- intestinal tract
The septum transversum will also give rise to the___ which is responsible for ____
- Kupffer cells
- immunity
___ is a cranial surface above the liver that remains uncovered by peritoneum. It is in contact with the original _____ .
- Bare area
- septum transversum
In this area where cranial surface above the liver that remains uncovered by peritoneum, there is a densely packed mesoderm from the septum transversum which will give rise to the ____.
central tendon of the diaphragm
_____ are derived from mesoderm of the septum transversum.
Hematopoietic cells, Kupffer cells, and connective tissue cells
Pancreas rises from 2 buds coming from the ___ of the gut
endodermal lining
The pancreas is a secondary retroperitoneal organ
located on the posterior aspect of the duodenum. Enclosed within the mesentery
Dorsal pancreatic duct –
lies close to the bile duct. Shifts position with the duodenum and will lie eventually in the dorsal aspect of the duodenum just below and behind the dorsal pancreatic bud.
Ventral pancreatic duct
The _____ of the two buds in the pancreas will fuse together.
After fusion, the____ will become the uncinate process of the pancreas while the rest of the pancreas will be formed by the ____.
- duct systems and parenchyma
- ventral bud
- dorsal bud
formed when the distal portion of the dorsal pancreatic duct fuses with the whole ventral pancreatic duct.
Principal Pancreatic duct of Wirsung
an accessory duct that is formed when proximal portion of the dorsal pancreatic duct fails to obliterate.
Accessory duct of Santorini
The duct systems of the duct of Wirsung and the duct of Santorini will often fuse together and drain to a common opening called the
duodenal papilla of Vater
However in 10% of cases, the duct of Santorini will have its own opening in the duodenum through the_____, leading to a double duct system.
minor duodenal papilla
On the ____ of development, Islets of Langerhans begin to appear.
3rd month
Insulin production will start by the ___
5th month
Extends from the point below the origin of the liver bud to the proximal 2/3 of the transverse colon
midgut
Characterized by the rapid elongation of the gut and mesentery
connection to the cavity of the duct to the vitelline duct or yolk stalk
Lumen of the midgut
Blood supply of midgut
Branches from superior mesenteric a.
Primary intestinal loop
- ) Cephalic limb – gives rise to the distal parts of the duodenum, jejunum, and upper part of the ileum
- ) Caudal limb – gives rise to the lower part of the ileum, cecum, appendix, ascending colon, and proximal 2/3 of the transverse colon
In the midgut,
Vertex formed by the ____
Axis follows the _____
vitelline duct
superior mesenteric a.
Midgut undergoes a total of ____ rotation around an axis
270degrees CCW
Midgut during 6th week:
- The primary intestinal loop rotates 90O CCW
- The primary intestinal loop herniates thru the umbilicus > makes 90 O CCW turn > future SI & LI
- Most of the parts of SI – right side; LI – left side
Midgut during10th week:
Herniated bowel loops return to the abdominal cavity, rotates another 180O CCW, resulting to the duodenum lying posterior to the transverse colon
___ gives rise to most of the small intestinal loops, elongates rapidly, forming coils
Cephalic limb
- The large intestine also lengthens but does not participate in the coiling phenomenon.
Physiological Umbilical Herniation, 6th week caused mainly by the ____ thereby making the space within the abdominal cavity too small to accommodate all of the loops and the LI. Thus, they have a tendency to herniate thru the umbilicus in the extraembryonic cavity
- increased growth and expansion of the liver
10th week, the loop starts to retract w/in the abdominal cavity, more space w/in the abdominal space due to the
- regression of the kidneys
- decreased liver growth
- expansion of the abdominal cavity
–(1st to reenter) the 1st part of the herniated loops to return into the abdominal cavity
Proximal portion of the jejunum
Cecal bud – last part to reenter
Proximal portion of the jejunum settles on the left side of the ___ and the ff loops will go to the right side
abdominal cavity
Conical dilation of the caudal limb which gives rise to ___ . Settles to the ____. Eventually descends w/in the _____
- cecum & appendix
- right upper quadrant
- right iliac fossa (right lower quadrant)
_____ are pulled towards the right side of the abdominal cavity. At this time, during the descent of the cecal bud, it forms a narrow diverticulum called the ____
- Ascending colon & hepatic flexure
- appendix
That’s why, in 50% of cases, the appendix is found behind the cecum (retrocecal or retrocolic appendix)
Mesenteries of Intestinal Loops Initially not fused to the post. abdominal wall. When the ascending and descending colon settles at the____, their mesenteries fuse with the peritoneum of the post. abdominal wall.
- R & L of the abdominal cavity
___ are the retroperitoneal segments of the intestine.
the ascending & descending colon
they are fixed to the post. abdominal wall.
Fate of Transverse Mesocolon: Fuses with the____, but remains mobile and suspended w/in abdominal cavity from ____ to the _____
- post. part of the greater omentum
- hepatic flexure
- splenic flexure
Fate of the Jejunoileal Loops: Initially continuous with the mesentery of the ascending colon but when the mesentery of the ascending mesocolon fuses with the___, the mesentery of ____ obtains a new line of attachment that extends from the area where the duodenum becomes intraperitoneal to the_____
- post. abdominal wall
- jejunoileal loops
- ileocecal junction
Closure of the body wall fails or is incomplete at the region of
the umbilicus that is why it occurs lateral to the umbilicus
GASTROSCHISIS
Herniates thru the abdominal wall but actually lateral to the
umbilicus, therefore it will neither be covered by peritoneum
or amnion, rather exposed to the corrosive effects of the
amniotic fluid and therefore could damage the abdominal
viscera
Abdominal viscera has herniated thru an enlarged umbilical vein into the umbilical cord and the herniated loops are covered by amnion
OMPHALOCELE
o May include liver, spleen, gallbladder o Origin of defect – when bowel loops herniate thru the umbilicus during the physiological herniation but fails to return
should only be a temporary connection between
the lumen of the ileum & the umbilicus
Vitelline Duct
Part of vitelline duct does not obliterate and forms an
outpocketing of the ileum
Ileal/Meckel’s Diverticulum
Rule of 2s – Meckel’s diverticulum occurs in 2-4% of the pop’n;
usually lies around 2 feet from the ileocecal valve; approx. 2 inches long
Asymptomatic patients
if vitelline duct, on both of its ends, becomes fibrous cords but
the middle portion is retained and becomes an enlarged cyst
Vitelline Cyst/Enterocystoma - Intestinal loops rotate & strangulate
Vitelline duct fails to obliterate all throughout
Patients – with fecal discharge at the umbilicus
Vitelline/Umbilical Fistula
GUT ROTATION DEFECTS:
- Primary intestinal loop arrests at 90 degrees only
- Reverse rotation of intestinal loop (primary intestinal loop rotates
at 90 degress CW
- left-sided colon & small intestine on the right side
- duodenum lying on top of transverse colon
Extends from the distal 1/3 of the transverse colon upto the upper
part of the anal canal
hindgut
Distal portion of this & that of hindgut open into a common chamber called the cloaca. Involved in the urinary system
ALLANTOIS
An endoderm-lined cavity that is formed by the distal portion of
the hindgut
CLOACA
Cloaca:
External part covered by ____
Posterior portion gives rise to the ___
Anterior portion gives rise to ____
- ectoderm
- primitive ano-rectal canal
- primitive urogenital sinus
ventral covering of the cloaca; formed by
layers of the endoderm and ectoderm
Cloacal Membrane
a mesodermal tissue that separates the
allantois & hindgut; eventually elongates and comes close to
the cloacal membrane
Urorectal Septum
At the end of the 7th wk:
- ____ ruptures
- ____ becomes the perineal body
- ____goes through a solid stage, proliferation of ectodermal
cells at the lower part of the anal canal and then, recanalization
- Cloacal membrane
- Urorectal septum
- Hind gut
Upper 2/3 of anal canal lined by ____; lined by _____
epithelium; supplied by_____, which is a branch of
______
- endoderm
- columnar
- superior rectal a
- inferior mesenteric a.
Lower 1/3 of anal canal lined by _____; lined by _____
epithelium; supplied by _____, coming from the
____
- ectoderm
- stratified squamous
- inferior rectal a
- internal pudendal a.
Pectinate line delineates between the parts with_____. (lower anal canal) & ____. (upper anal
canal)
- stratified squamous ep
- columnar ep
anal membrane fails to
break down; fails to recanalize
after the solid stage
IMPERFORATE ANUS
absence of parasympathetic ganglia in the bowel wall so that part
of the wall will not relax thereby forming a functional obstruction
CONGENITAL/AGANGLIONIC MEGACOLON/HIRSCHSPRUNG’S DIS.
