Lecture 2 Embryology of the GI Flashcards
How long is the time between fertilisation and implantation
1 week
When does the bilaminar germ layer arise
Week 2
What gene is responsible for establishing left sidedness
PTX2
What week does the trilaminar disc arise
Week 3
Define Gastrulation
This is when the bilaminar disc is converted into a trilaminar disc. Going from amnion sac and yolk sac to ectoderm, mesoderm and endoderm
What is the primitive streak
Dip in epiblast where cells have started to divide
What structures are the ectoderm layer responsible for
Skin, nervous system, ear, nose, adrenal medulla
What structures are the mesoderm layer responsible for
Skeleton, muscle, kidney, heart, blood, conceive tissue
What structures are the endoderm responsible for
Gut, liver, lungs, pancreas, urinary bladder
Describe Notochord formation
Some cells continue to proliferate and lose contact with ectoderm from primitive streak. The cells sunk down and form a solid tube
What is Neurulation
Notochord sends out a signal which acts on ectoderm and induces cells to form neural tube. neural plate sinks down and edges come together to form a tube once it loses contact with ectoderm
When does Organogenesis occur
Week 3 to 8
What are he 3 phases of embryo development
- Growth/proliferation
- Morphogenesis
- Differentiation
What is growth/proliferation during embryo development
Cell division and elaboration of products
What is morphogenesis during embryo development
Development of shape, size of a particular organ or body part
What is differentiation during during embryo development
Maturation of physiological processes
Exposure to teratogens during what weeks may causes congenital anomalies
Week4-8
The lateral plate of the mesoderm gives rise to what
Parietal and visceral mesoderm
When does the gut tube form from the endoderm lining of the yolk sac
3rd and 4th week
The gut tube is closed by what at its cranial end
Oropharyngeal membrane
The gut tube is closed by what at its caudal end
Cloacal membrane
What gene is secreted from the endoderm and what does it induce in the gut
SHH and HOX
What does the foregut consist of
Pharynx,Oesophagus Stomach and upper duodenum
Where does the foregut develop from
The cranial part of the primitive gut
Where does the Laryngo-tracheal diverticulum (lung bud) develop from
The ventral wall of the foregut
What divides the foregut tube into the trachea and oesophagus
Tracheo-oesophagel septum
What week does the foregut dilate an form the stomach
4th
What creates the greater curve and lesser curve
Differential growth
What side is the greater curvature
Posterior
What side is the lesser curvature
Anterior
Describe the development the stomach undergoes
undergoes 90 degree rotation around town longitudinal axis. Ventral border now left side (LC), dorsal border right side (GC)
The stomach undergoes an ____ to create final adult position
anterior-posterior
What is the Mesogastrium
It is where the stomach is attached to both the dorsal and ventral wall by a mesentery called this
What creates the mental bursa
Rotation along the longitudinal axis pulls the dorsal mesentery to the left created the lesser sac and the ventral mesogastrium is pulled to the right
How many layers does the greater sac have
4 layers which become 2 layers of peritoneum and forms the transverse mesocolon
What is the duodenum formed from
The caudal part of the foregut and the cranial part of the midgut
What is the blood supply of the duodenum
Coeliac trunk and superior mesenteric artery
What part of the duodenum retains its dorsal mesentery
Dorsal cap
When do the liver buds appear and what are they
middle of 3rd week
Outgrowths of endoderm (epithelia) in the distal end of the foregut
The connection between the liver bud and foregut narrowing forms
The bile duct
Ventral outgrowth from the bile duct forms
Gallbladder and cystic duct
Where is the hepatic vein located
In the falciform ligament
At the end f the 4th week the mesenchymal condensation develops in where
Dorsal mesogastrium
What week does the mesenchyme differentiate into the spleen
5th
What organ is a mesoderm derivative
Spleen
Up to what week does the spleen act as a haematopoietic organ
14 week
What happens to the spleen in week 15-17
Colonised by t-lymphocytes
What happens to the spleen in week 23
the B cell precursors arrive and the spleen can start its lymphoid function
How does the pancreas form
From 2 buds which grow from the endodermal lining in week 5. As the duodenum rotates ventral bud moves to lie closer to dorsal bud and in week 6 they fuse
Name an development anomaly of the foregut
oesophageal atresia (no connection) and tracheo-oesophageal fistula (abnormal connection)
What is the cause of anomalies in the foregut
if the tracheo-oesophageal septs deviates incorrectly then there is an incomplete separation of the lung bud (laryngo-tracheal tube) oesophagus and trachea
What is the most common foregut anomaly
Tracheo-oesophageal fistula (90%)
What causes annular pancreas and what are the consequences
Failure of ventral bud to migrate around duodenum to dorsal bud and may cause duodenal stenosis and pancreatic tissue may develop in other ares of the foregut (accessory pancreatic tissue)
What is the midgut
Distal part of duodenum, jejunum, ileum, caecum, appends, ascending colon, primal 2/3rds of transverse colon
Describe the early development of the midgut
Rapid elongation of the gut tube and its associated mesentery described as the primary intestinal loop.
What does the caudal part of the primary intestinal loop become
Distal ileum, caecum, appendix, ascending colon and proximal 2/3 of transverse colon
What does the cephalic part of the primary intestinal loop become
Distal duodenum, jejunum and proximal ileum
To reach adult pattern what must the primary intestinal loop undergo
Rotation and Herniation
When does rotation of the primary intestinal loop occur
6th week
Where does the rotation of the primary intestinal loop occur
Around the axis of the superior mesenteric artery 90 degrees anti-clockwise and the cranial part of the midgut is carried to the right
When does physiological herniation occur
Week 6
Describe physiological herniation
Gut tube herniated into the extra embryonic cavity in the umbilical cord
What is the purpose of herniation
Allows the growth of the gut tube as there is not enough room due to the liver and kidneys
When does the abdominal cavity become relatively spacious and also the loops to move back in
10th week
Name a developmental anomaly in the midgut
Abnormal rotation
Omphalocele
Gastochisis
Remnants of vitelline duct
What is Omphalocele
Herniation of abdominal viscera through an enlarged umbilical ring and the failure of the reaction of the ring
What is Gastrochisis
Herniation of abdominal contents directly through the body wall through a weak area in the umbilicus in the amniotic cavity not covered by peritoneum or amnion
Describe remnants of the vitelliue duct
Small vitelliue duct (remnants f yolk sac) persist in 2-4% of people and forms Meckl’s diverticulum, fistula or vitelliue cyst/ligament. Fistula will open and leak
What is the hindgut
Distal 1/3rd transverse colon, descending colon, sigmoid colon, rectum, upper part of anal canal
The endoderm of the hind gut also forms the
Lining of bladder and urethra
Where does the terminal portion of the hindgut join with
Posterior part of the cloaca (primitive anal canal)
What is the allantois
Bladder and urethrea
What is Cloaca
Endoderm lined cavity with surface ectoderm at its ventral boundary
Blood supply of foregut
Coeliac artery
Blood supply of midgut
Superior mesenteric artery
Blood supply of hindgut
Inferior mesenteric artery
Name development anomaly of hindgut
Urorectal fistula
Rectovaginal fistula
Rectoanal atresia
Imperforate anus
