GI embryology - development of the peritoneum and foregut Flashcards
In the fourth week what two types of folding occur?
Lateral and craniocaudal folding
What are the affects of lateral folding?
- Creates ventral body wall
2. Primitive tube becomes tubular
What are the affects of craniocaudal folding?
- Creates cranial and caudal pockets from yolk sac endoderm (beginning of primitive gut development).
When does the primitive gut tube begin to develop?
Week 3 when it pinches off from the yolk sac cavity.
What is the stomatodeum?
Future mouth (stomata=primitive mouth)
What is the proctodeum?
Future anus (procta=anus)
Describe the morphology of the primitive gut tube
It runs from the rostral stomatodeum to the caudal proctodeum, with an opening at the umbilicus.
Which of the three trilaminar layers is the primitive gut tube derived from?
Endoderm - interling lining -> future epithelial linings
Splanchnic mesoderm - external lining -> future musculature of gut wall and visceral peritoneum.
Which new cavity is the primitive tube suspended in by a double layer of splanchnic mesoderm?
Intraembryonic coelom
Describe the adult derivatives of the foregut
Oesophagus -> duodenum (proximal to entrance of bile duct)
Describe the adult derivatives of the midgut
Duodenum (distal to entrance of bile duct) -> proximal 2/3 of transverse colon.
Describe the adult derivatives of the hindgut
Distal 1/3 of transverse colon -> upper anal canal (to the pectinate line).
Also includes the internal lining of bladder and urethra.
What is the pectinate line?
A line 2/3 down the anal canal which corresponds to the developmental junction between the hindgut and the proctodeum.
What reflects the embryonic derivates of the foregut, midgut and hindgut?
Blood supply
Lymphatic drainage
In the fourth week, what constitutes the ends of the foregut?
At the cranial end the lung bud and at the caudal end, the liver bud.
In the fourth week, what happens to the ventral wall of the foregut at the junction with the pharyngeal gut?
A respiratory diverticulum (blind-ended tube) forms creating the respiratory primordium (ventral) with the oesophagus (dorsal).
What is the name of the tissue that divides off the respiratory primordium from the oesophagus?
Tracheoesophageal septum.
Up to 1 in 3000 live birth can have oesophageal abnormalities. Describe what abnormalities can occur.
Consequences of abnormal positioning of the tracheoesophageal septum. The following (individually or in combination):
- Proximal blind-end oesophagus
- Tracheoesophageal fistula (abnormal connection between oesophagus and trachea)
- Distal blind-end oesophagus
In the middle of the fourth week a slight dilation in the distal foregut indicates the position of what?
The stomach primordium.
What side of the stomach primordium creates the greater curvature?
The dorsal border - which has a faster growth.
Name the foregut derived glands.
Liver
Pancreas
Biliary System
Which foregut derived glands are derived from the dorsal mesentery?
Pancreas (superior head, neck, body and tail).
Which foregut derived glands are formed in the ventral mesentery?
Part of the pancreas (uncinate process and inferior head)
Liver
Billiary system
Which is the earliest GI tract associated glands which develops?
The liver
Where does the liver develop?
The hepatic bud develops in the ventral mesentery and occupies a large part of the abdomen during development.
What is the name of the area of the liver that is not covered by the shiny, moist peritoneum and is attached to the diaphragm?
Bare area
What is the falciform ligament?
The remains of the ventral mesentery which connects the liver to the anterior abdominal wall?
What are the developmental derivatives of the duodenum?
It develops from the caudal foregut and the cranial midgut.
Why does the duodenum become a C-shaped loop?
Due to rotation of the stomach
What happens to the lumen of the duodenum during the 5th and 6th week of development?
The tissue surrounding the lumen becomes so thick it is obliterated. It is then recanalised by the end of the embryonic period.
What effect does rotation of the stomach have on the position of the duodenum?
It pushes it to the right and posterior - against the posterior abdominal wall.
What is meant by secondarily retroperitoneal?
A structure which develops intraperitoneally but is pushed back against the parietal peritoneum of the posterior abdominal wall, during the rapid development of the GI tract, and the mesentery of the structure fuses with the fascia.
The parietal peritoneum then grows back over this structure.
Name two secondarily retroperitoneal structures?
The pancreas.
The duodenum, except the duodenal cap (the first part of the duodenum attached to the stomach).
What is the yolk stalk attached to?
Endometrium of mother
In which cavity is the primitive gut tube suspended and by what?
Intraembryonic coelom.
Suspended by a double layer of splanchnic mesoderm.
Each embryonic segment receives a blood supply from a distinct branch of which vessel?
Abdominal aorta.
What is the name of the aorta branch that supplies the foregut?
Coeliac trunk.
What is the name of the aorta branch that supplies the midgut?
Superior Mesenteric Artery (SMA).
What is the name of the aorta branch that supplies the hindgut?
Inferior Mesenteric Artery (IMA).
Which two structure that develop close to the junction between the foregut and midgut, have a mixed blood supply?
Duodenum and pancreas
Which two arteries coeliac trunk arteries and which SMA artery supply the duodenum?
Proximal to entry of bile duct - the coeliac arteries: gastroduodenal & superior pancreaticoduodenal.
Distal to entry of bile duct - SMA artery: inferior pancreaticoduodenal.
Which coeliac trunk artery and SMA artery supply the head of the pancreas?
superior pancreaticoduodenal (CT) Inferior pancreaticoduodenal (SMA)
What are the derivatives of the intraembryonic coelom?
The body cavities
Which two cavities is the intraembryonic coelom later divided into?
It is later subdivided into the abdominal and thoracic cavities by the future diaphragm.
What does the peritoneum do?
Lines the abdominal cavity and invests the viscera.
What does the peritoneal cavity do?
It is a potential space only and under normal conditions it should contain nothing (just a little bit of lubricating fluid).
What is mesentery?
A double layer of peritoneum suspending the gut tube from the abdominal wall.
What is the purpose of mesentery?
It is a conduit for blood and nerve supply and allows for mobility.
Which type of mesoderm surrounds the primitive gut tube?
Splanchnic mesoderm.
Which type of mesoderm lines the abdominal walls?
Somatic mesoderm.
The fusion of the somatic and splanchnic mesoderm creates what structure?
Mesentery.
Where does dorsal mesentery suspend the gut tube from the dorsal body wall?
Along the entire length of the gut.
Where does ventral mesentery suspend the gut tube from the ventral body wall?
In the foregut only.
Where is there a free edge of ventral mesentery?
Foregut and midgut junction
The dorsal and ventral mesentery of the foregut divide the cavity into what?
A left and right sac.
Which adult structure do the left and right sac contribute to?
The left sac contributes to the greater sac and the right sac becomes the lesser sac (comes to lie behind the stomach).
Caudal to the foregut how many sacs are there?
One - the cavity is not divided into two like in the foregut as it does not have ventral mesentery.
What are omenta?
Specialised regions of peritoneum/ specialised mesentery. A fold of peritoneum that connect the stomach to other abdominal organs.
What is the greater omentum formed from?
Dorsal mesentery.
What does the greater omentum look like?
A fatty apron. It is the first structure seen when the abdominal cavity is opened anteriorly.
What is the lesser omentum formed from?
The ventral mesentery.
What does the free edge of the lesser omentum conduct?
Portal triad: branches of the biliary ducts, hepatic artery and portal vein (plus Lymphatics and nerves).
Which two directions does the stomach rotate during development?
90 degrees around the longitudinal axis.
Around the anteroposterior axis.
What is the result of rotation of the primitve stomach around the longitudinal axis?
The greater and lesser curvature come to lie first on the right and left side (originally the lesser curvature is ventral and the greater curvature dorsal).
What is the result of rotation of the primitive stomach around the anteroposterior axis?
The cardia and pylorus move horizontally, pushing the greater curvature inferiorly (originally the stomach lies in an upright position with the cardia directly superior to the body and pylorus).
Where is the greater omentum suspended from?
It extends from the greater curvature of the stomach, passing anteriorly to the small intestines and reflects on itself to ascend to the transverse colon before reaching the posterior abdominal wall.
Where is the lesser omentum suspended from?
It extends from the liver to the lesser curvature of the stomach (this is called the hepatogastric ligament) and the first part of the duodenum (hepatoduodenal ligament).
Where does the liver develop?
The liver develops from a hepatic bud inside the ventral mesentery.
Where does the stomach develop?
The dorsal mesentery.
Which side of the intraembryonic coelom does the liver grow rapidly into?
The right-hand side.
What affects does the rotation of the stomach have?
- Puts the vagus nerves anterior and posterior to the stomach instead of left and right.
- Shifts cardia and pylorus from midline (stomach lies obliquely)
- Contributes to moving the lesser sac behind the stomach.
- Creates the greater omentum.
What is a peritoneal reflection?
A change in direction from:
- Parietal peritoneum to mesentery
- Mesentery to visceral peritoneum
- Visceral peritoneum to mesentery
- Mesentery to parietal peritonuem
Where is the peritoneum two cell layers thick?
At the mesentery, the rest of the peritoneum is a single membrane (one cell thick).
What is meant by retroperitoneal structures?
Structures that are not suspended within the abdominal cavity. They were never in the peritoneal cavity and never had a mesentery.
Give two retroperitoneal structures?
Kidneys and abdominal aorta.
What is meant by secondarily retroperitoneal?
Structures that began development invested by peritoneum, had a mesentery, but with successive growth and development the mesentery is lost through fusion at the posterior abdominal wall.
What is the difference between structure suspended in the peritoneal cavity and those that are retroperitoneal?
Retroperitoneal are not able to be mobilised.
What is another name for the lesser sac?
Omental bursa
What affect does rotation of the stomach hav on the left and right vagus nerves?
Rotation around the longitudinal axis puts the:
Left vagus nerve -> anterior (now anterior vagal trunk)
Right vagus nerve -> posterior (now posterior vagal trunk).
What is the lesser omentum?
A fold of peritoneum that is attached to the liver and extends over to the lesser curve of the stomach and proximal duodenum
What is the name of the fold of peritoneum that extends between the transverse colon and the greater curve of the stomach?
Gasto-colic ligament (part of the greater omentum)
What is the name of the fold of peritoneum which attaches the anterior abdominal wall and liver?
Falciform ligament (in embryological terms it is the remnant of ventral mesentery)
What is the name of the double fold of peritoneum which attaches the small bowel to the posterior abdominal wall?
Mesentery of small intestines
What is the name of the fold of peritoneum that attaches the sigmoid colon to the posterior abdominal wall?
Sigmoid mesentery (normally called sigmoid mesocolon)
What is meant by mesocolon?
The fold of peritoneum attaching the colon to the posterior abdominal wall: ascending mesocolon, transverse mesocolon, descending mesocolon and sigmoid mesocolon
The parietal peritoneum is in direct contact with which structure/s?
Abdominal wall
What surface of retro-peritoneal organs does the parietal peritoneum cover?
Anterior surface
What is the lesser sac?
Part of the peritoneal cavity that lies behind the stomach
How does the lesser sac communicate with the greater sac?
Via the Foramen of Winslow (epiploic foramen)
What is the name of the extension of the peritoneal cavity that lies between the uterus and bladder?
Uterovesicular pouch
What is the name of the extension of the peritoneal cavity that lies between the rectum and uterus?
Rectouterine pouch or Pouch of Douglas
What is the name for the part of the peritoneal cavity that lies between the liver and the right kidney?
hepatorenal pouch (Pouch of Morison)
What is the name for the part of the peritoneal cavity that lies lateral to the ascending colon and descending colon?
Paracolic gutters
