Embryology GI

cranial end name

oropharyngeal membrane

caudal end name

cloacal membrane

light blue- endoderm

red- mesoderm

dark blue- ectoderm

cavity dark blue- amniotic cavity

4th week what is this duct

vitelline duct

connects the yolk sac to the midgut of the developing embryo

what happens to the vitelline duct in the 6th week

it obliterates leaving only the umblilical cord

what happens if the vitelline duct doesn’t obliterate

meckel’s diverticulum.

outpouching of the small intestine occurs, vitelline duct forms a ligament between the midgut and the anterior abdominal wall

what is natural herniation

during 6th week, the small intestines will form a loop and herniate through the umbilical cord

because the developing organs within the abdominal cavity grow and push out the small intestines.

do intestines remain herniated

when the abdominal cavity becomes larger, the intestines return back into them during 10th/11th week

what happens if herniation persists past 11th/10th week

o Omphalocele

Results from the failure of the intestinal loop to return inside the abdominal cavity

how to detect omphalocele

Can be detected through fetal ultrasound or serum alpha fetoprotein levels of the mother

amniotic cavity folds down

splanchnic mesoderm surrounds endoderm, vitelline duct and yolk sac

somatic mesoderm surrounds the amniotic cavity

in the transverse plane what should the lateral folds do

lateral folds of the amniotic cavity fuse

Once the vitelline duct obliterates, the two endoderm folds can merge, forming a closed gut tube

what if the two lateral folds fail to fuse

Gastroschisis

The lateral folds fail to fuse, resulting in the herniation of abdominal contents
The herniated intestines are not covered in peritoneum, which could irritate the abdominal cavity

what forms the visceral peritoneum

splanchnic mesoderm

what forms the parietal peritoneum

somatic mesoderm

what connects the parietal to the visceral peritoneum

mesentery

what is a mesentery

is a double-layered serous membrane made up of simple squamous epithelial tissue

Underneath the serous layer is areolar connective tissue (basal layer)

Mesentery is where blood vessels, lymphatic vessels, and nerves can pass through

if an organ has a mesentery and has a visceral and parietal peritoneum, what is it

intra-peritoneal organ

if an organ doesn’t have a mesentery and a visceral and parietal peritoneum

retroperitoneal organ

primary retroperitoneal organ

Organs that develop and remain retroperitoneal—they never had a mesentery or peritoneal covering on their posterior surface.

secondary retroperitoneal organ

Organs that start life intraperitoneal (with a mesentery) but, during gut rotation and fusion in development, lose their dorsal mesentery and become fixed to the posterior abdominal wall.

what ar the primary retroperitoneal organs

-abdominal orta

-inferior vena cava

-kidney

-adrenal glands

-bladder

-ureter

-upper rectum

-esophagus

what are the secondary peritoneal organs

Duodenum (2nd–4th parts)
Pancreas (head, neck, body- not tail)
Ascending colon
Descending colon

what anchors retroperitoneal organs to the posterior abdominal wall

adventitia- a dense fibrous irregular CT

what mesentry is found on foregut

ventral mesogastrium

dorsal mesogastrium

in foregut

what does the ventral mesogastrium give rise to

will eventually develop into the lesser omentum, which is made up of the:

o Hepatogastric ligament
o Hepatoduodenal ligament

what does the dorsal mesogastrium give rise to

will eventually develop into the greater omentum, which is made up of:

-gastrophrenic ligament

-gastrocolic ligament

-gastrosplenic ligament

which organ does the ventral mesogastrium help develop

liver

The dorsal mesogastrium will give rise to the (organ)

spleen

why is liver found on right and spleen on left

Further rotation will bring the ventral mesogastrium to the right side and the dorsal mesogastrium to the left side

o This explains why the liver is located on the right side of the body, and the spleen is located on the left side

what does the middle gut tube give rise to

stomach

reference

Subdivisions of the Peritoneal Cavity

greater and lesser peritoneal sacs.

Greater Sac is divided by

divided into two compartments by the mesentery of the transverse colon (known as the transverse mesocolon)

divisions of greater sac

• Supracolic compartment – lies above the transverse mesocolon and contains the stomach, liver and spleen.

• Infracolic compartment – lies below the transverse mesocolon and contains the small intestine, ascending and descending colon. The infracolic compartment is further divided into left and right infracolic spaces by the mesentery of the small intestine.

Lesser Sac (Omental Bursa) location

posterior to the stomach and lesser omentum

The omental bursa is connected with the greater sac through

an opening in the omental bursa – the epiploic foramen (of Winslow).

The epiploic foramen is situated posterior to the free edge of the lesser omentum (the hepatoduodenal ligament).

what artery supplies the foregut

the celiac trunk

branches:

-left gastric

-common hepatic: branches into cystic artery (to gallbladder), gastroduodenal artery, superior pancreatic duodenal

-splenic

what organs are formed by foregut

stomach

spleen

liver

gallbladder

proximal duodenum

pancreas

what supplies the stomach

Left gastric a.

what supplies the spleen

Left gastric a.

what supplies the liver

Common hepatic a.

what supplies the gallbladder

Cystic a.

what supplies the Pancreas

Gastroduodenal a.

what supplies the Proximal half of duodenum

Gastroduodenal a.

spleen mesentery

gastrosplenic ligament

stomach mesentery

Greater omentum, Lesser omentum

liver and gall bladder mesentery

lesser omentum including:

o Hepatogastric
o Hepatoduodenal

o Falciform

Pancreas mesentery Head & Body

retroperitoneal; no mesentery

Pancreas mesentery tail

splenorenal ligament (greater omentum)

Proximal half of duodenum mesentery

lesser omentum- Hepatoduodenal ligament

what supplies the midgut

superior mesentric artery

branches of superior mesentric artery

o Intestinal arteries

o Ileo-colic artery
o Right colic artery

o Middle colic artery

organs formed by midgut

-Distal half of Duodenum

-jejunum

-ileum

-Distal Ileum (at the ileo- cecal junction)

-cecum

-appendix

-ascending colon

-Proximal 2/3 of the Transverse colon

intestinal arteries supply

-Distal half of Duodenum

-jejunum

-ileum

Ileo-colic artery suplies

-Distal Ileum (at the ileo- cecal junction)

-cecum

-appendix

Right colic a. supplies

ascending colon

middle colic a. supplies

-Proximal 2/3 of the Transverse colon

-Distal half of Duodenum mesentery

no mesentery

-retroperitoneal organ

Jejunum mesentery

-Small bowel mesentery

-Ligament of Treitz – suspends the fourth part of the duodenum (marks start of jejunum)

Ileum mesentery

-Small bowel mesentery/ mesentery proper

cecum mesentery

Small bowel mesentery; can be retroperitoneal in some

appendix mesentery

mesoappendix

ascending colon mesentery

Retroperitoneal; no mesentery

Proximal 2/3 of the Transverse colon mesentery

Transverse mesocolon

The main vascular supply of the hindgut

inferior mesenteric artery

branches of the inferior mesenteric artery

o Left colic artery
o Sigmoidal arteries
o Superior rectal arteries

organs formed by hindgut

-Distal 1/3 of Transverse Colon

-Descending colon

-Sigmoid colon

-Upper rectum (above the pectinate line)

Left colic a. supplies

-Distal 1/3 of Transverse Colon

-Descending colon

Sigmoidal arteries supplies

-Sigmoid colon

Superior rectal artery supplies

upper rectum (above the pectinate line)

Distal 1/3 of Transverse Colon mesentery

Transverse mesocolon

Descending colon mesentery

Retroperitoneal; no mesentery

Sigmoid colon mesentery

Sigmoid mesocolon

Upper rectum mesentery

Retroperitoneal; no mesentery

reference