Embryology 1 Flashcards
When does embryonic folding take place
Week 4
Consequences of lateral folding
Creates ventral body wall
Primitive gut tube becomes tubular
Consequences of craniocaudal folding
Creates cranial and caudal pockets from yolk sac endoderm
Divisions of the primitive gut tube
Foregut
Midgut
Hindgut
When does the primitive gut tube begin to develop
Week 3 when it pinches off from the yolk sac cavity
Where does the primitive gut tube run from and to
From the stomatodeum to the proctodeum
What is the opening of the primitive gut tube called and where is it
Vitelline duct at the umbilicus
What are the origins of the internal and external lining of the primitive gut tube
Internal lining - endoderm
External lining - splanchnic mesoderm
What is the intraembryonic coelom/ coelomic cavity
Cavity created between the somatic and splanchnic mesoderm layers which the primitive gut tube is suspended in
Adult derivatives of foregut
Oesophagus Stomach Pancreas Liver Gall bladder Duodenum proximal to entrance of bile duct
Adult derivatives of midgut
Duodenum distal to entrance of bile duct Jejunum Ileum Caecum Ascending colon Proximal 2/3 transverse colon
Adult derivatives of hindgut
Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder and urethra
Blood supply of foregut
Celiac trunk
Blood supply and innervation of midgut
Superior mesenteric artery and vein
Parasympathetic - vagus nerve
Sympathetic - superior mesenteric ganglion and plexus
Blood supply and innervation of hindgut
Inferior mesenteric artery and vein
Parasympathetic - pelvic nerve (S2-4)
Sympathetic - inferior mesenteric ganglion and plexus
Adult derivative of somatic mesoderm surrounding the gut
Muscles and fascia of abdominal wall
Adult derivative of splanchnic mesoderm surrounding the gut
Smooth muscle of gut wall
How does the linea alba form
Progression of lateral folding leads to the 2 sides of the developing anterolateral abdominal wall to meet in the midline
What is the inguinal canal and what does it allow in males
Oblique through the layers of the abdominal wall
In males, it allows passage of developing testes into the scrotum
What is an inguinal hernia
Abdominal contents push against the inguinal canal and herniate through as it is a potential site of weakness
What is an umbilical hernia
Congenital malformation
Abdominal contents push against the umbilicus and herniate through as it is a potential site of weakness
How is the intraembryonic coelom divided and by what
Diaphragm divides the intraembryonic coelom into the:
Abdominal cavity
Thoracic cavity
What connects the primitive gut tube to the abdominal wall
Dorsal mesentery - foregut, midgut and hindgut to the roof of the abdominal cavity
Ventral mesentery - foregut to the floor of the abdominal cavity
What do the dorsal and ventral mesenteries in the foregut region divide the peritoneal cavity into
Greater peritoneal sac (left)
Lesser peritoneal sac (right)
What is an omentum
A double layered extension/fold of peritoneum that passes from the stomach and proximal duodenum to adjacent abdominal organs
What is the greater omentum
4 layered peritoneal fold that descends from the greater curve of the stomach, folds back, and attaches to the anterior transverse colon and its mesentery
(Formed from dorsal mesentery of stomach)
What is the lesser omentum
Double layered peritoneal fold that connects the lesser curvature of the stomach and proximal duodenum to the liver
It’s made up of the hepatogastric and hepatoduodenal ligaments
(Formed from ventral mesentery of stomach)
How do the omenta form
Rotation of the stomach
How is the greater curvature of the stomach created
Dorsal border of stomach grows faster than the ventral border
What axes does the primitive stomach rotate about
Longitudinal
Anteroposterior
Consequences of stomach rotation
Original left side becomes anterior (greater sac)
Original right side becomes posterior (lesser sac)
Vagus nerve lies anterior/posterior instead of left/right
Shifts cardia and pylorus from the midline
Creates the greater omentum
What is meant by a peritoneal reflection
A change in direction/reflections of peritoneum
- mesentery to visceral peritoneum (and vice versa)
- mesentery to parietal peritoneum (and vice versa)
What determines the mobility of abdominal contents
Whether it has a mesentery or not
Define retroperitoneal organs and give some examples
Were never in the peritoneal cavity and therefore don’t have a mesentery
E.g kidneys, aorta, oesophagus
Define secondary retroperitoneal organs and give some examples
Began development invested by peritoneum and had a mesentery but with progressive growth the mesentery is lost by fusion at the posterior abdominal wall
E.g ascending colon, descending colon, duodenum
Why is the duodenum secondary retroperitoneal
Rotation of the stomach pushes the duodenum against the posterior abdominal wall because the liver is so large
How is fusion fascia created
Peritoneum of the posterior abdominal wall is squished together with the duodenum and its mesentery and grows over it, creating fusion fascia
How can the duodenum be made mobile
Removal of fusion fascia (avascular so no damage)
What happens to the duodenum during weeks 5-6
Lumen is obliterated due to rapid growth of its lining
It’s recanalised by the end of the embryonic period (before week 9)
When and where is the respiratory diverticulum created
Week 4
In the ventral wall of the foregut at the junction with the pharyngeal gut
What does the respiratory diverticulum become and how
Ventrally - respiratory primordium
Dorsally - oesophagus
Divided by the tracheoesophageal septum
Incidence of abnormal positioning of the tracheoesophageal septum
Up to 1 per 3000 live births
Which foregut derived glands are formed in the ventral mesentery
Liver
Biliary system
Ucinate process and inferior head of pancreas
Which foregut derived glands are formed in the dorsal mesentery
Superior head, neck, body and tail of pancreas
What does the liver develop from
Hepatic bud
