Developemnt Flashcards
Describe the gut tube
• Endoderm lined tube • Runs the length of the body • Blind pouches at the head and tail
ends • Opening at the umbilicus • Splanchnic mesoderm covering
What er teh embryonic divisions of he gut?
• Foregut and hindgut begin as blind diverticula
• Midgut has an opening at first and is continuous with the yolk sac
• These embryonic divisions have implications for blood supply and lymphatic drainage in the adult
Caudal most part if hindgut
What are the derivatives of the foregut
Oesophagus Stomach Pancreas, liver & gall bladder Duodenum (proximal to entrance of bile duct)
What are the derivatives of the midgut
Duodenum (distal to entrance of bile duct) Jejunum Ileum Cecum Ascending colon Proximal 2/3 transverse colon
What are the derivatives of the hindgut
Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder & urethra
Also holds the cloaca which is divided to give anorectal canal and urethra etc
What are the implications of blood supply for the gut
• Arterial supply reflects embryonic development • Each embryonic segment receives blood supply from a distinct branch of the abdominal aorta
What is the foregut, midgut and nindgut blood supply
Celiac trunk, SMA, IMA respectively
What are 2 structures in the gut that have a mixed bld supply
– Duodenum • Proximal to entry of bile duct – gastroduodenal a & superior pancreaticoduodenal a (CT) AND • Distal to entry of bile duct – inferior pancreaticoduodenal a (SMA) – Pancreas • Head – superior pancreaticoduodenal a (CT) AND – inferior pancreaticoduodenal a (SMA)
What is the intraembryonic coelom?
• Formed as the embryo folds
• Begins as one large cavity
• Later subdivided by the future diaphragm into abdominal
and thoracic cavities
Describe the membrane of the intraembryonic coelom
• One membrane lining the whole intraembryonic cavity – Specialises as the cavities specialise • pericardium • pleural membrane
Describe the peritoneal cavity development
• Peritoneum & peritoneal cavity
– the peritoneal membrane lines the abdominal
cavity and invests the viscera
• during development it grows, changes shape &
specialises
– the peritoneal “cavity” is a potential space only
• under normal conditions it should contain nothing Copyright © 20
What is a mesentery
• What?
– double layer of peritoneum suspending the gut tube from the abdominal
wall
• Why?
– allow a conduit for blood and nerve supply
– allow mobility where needed - aka allow structures to move around in cavity
How does a mesentery form?
• The new primitive gut is suspended within the intraembryonic coelom
– Splanchnic mesoderm surrounds new
gut
– Mesentery formed from a condensation of this mesoderm
Where are the mesenteries located?
- Dorsal mesentery suspends the entire gut tube from the dorsal body wall
- Ventral mesentery ONLY in the region of the foregut - foregit tightly attached, but leaves a free edge
What are the greater and lesser peritoneal sacs
• Dorsal and ventral mesenteries in the region of the foregut divide the cavity into left and right sacs in this region only – the left sac contributes to the greater sac – the right sac becomes the lesser sac • comes to lie behind the stomach
What are teh greater ad lesser omenta?
• Omenta are specialised regions of peritoneum • Greater omentum – formed from the dorsal mesentery – first structure seen when the abdominal cavity is opened anteriorly • Lesser omentum – formed from the ventral mesentery – free edge conducts the portal triad
What influences the position of the greater and lesser sacs?
Rotation around longitudinal acc is causes membrane to fold , as it then tilts on the anterior/posterior axis it drops drown
What is a peritoneal reflection?
• What is a peritoneal reflection? – A change in direction • from parietal peritoneum to mesentery • from mesentery to visceral peritoneum • from visceral peritoneum Innervation depends on where its is attaches
What about structures with no mesentery/not in the perinoteal space?
• Structures that are not suspended within the abdominal cavity are retroperitoneal
– retroperitoneal
• were never in the peritoneal cavity & never had a mesentery – secondarily retroperitoneal
• began development invested by peritoneum, had a mesentery BUT, with successive growth & development, the mesentery is lost through fusion at posterior abdominal wall
What happens to he foregut in week 4
• Extends from the lung bud to the liver bud
– ? Lung bud • In the 4th week, a respiratory diverticulum
forms in the ventral wall of the foregut at the junction with the pharyngeal gut
– Respiratory primordium (ventrally)
– Oesophagus (dorsally)
How are the GI and resp tracts separated?
By the tracheoeophageal septum
Wha are consequences of abnormal postioning of the tracheoespohageal septum?
variety of oesophageal abnormalities occurring in up to 1 in 3000 live births
Give an overview of the development of he foregut-derived glands
• Liver and biliary system – Ventral mesentery • Pancreas – Components develop in both • Uncinate process and inferior head = ventral • Superior head, neck, body & tail = dorsal
Describe the peritoneal reflections of the liver
See slide
Describe the development of the duodenum
• Its shape is determined by rotation of the stomach • Rotation of the stomach pushes duodenum to right, then against posterior
abdominal wall • Therefore it becomes secondarily retroperitoneal
What does secondarily retroperitoneal mean ?
- A structure that developed intraperitoneally whose mesentery was lost to fusion with posterior abdominal wall parietal peritoneum due to massive expansion of GI tract during development
- Fusion fascia
What is fusion fascia
Fascia attaching structure to the abdominal wall, see slide, Can exploit to make structure mobile
