Embryology of Alimentary system Flashcards
What closes the primordial gut at the cranial end?
Oropharyngeal membrane
What closes the primordial gut at the caudal end?
The cloacal membrane
What are the divisions of the primordial gut tube?
The foregut, midgut and the hindgut
What happens early in the 4th week to the embyonic coelom?
The embryonic coelom is formed by the folding of the germ layers
It becomes the embryonic body cavity.
It divides into 3 well defined pericardial, peritoneal cavity and two pericardio-peritoneal canals
What are the derivatives of the foregut?
Primordial pharynx and its derivatives
Lower Respiratory tract
Oesophagus and stomach
Duodenum –Part above the opening of bile and pancreatic duct
Liver, biliary apparatus and pancreas
What is oesophageal artresia?
A congenital medical condition (birth defect) that affects the alimentary tract. It causes the esophagus to end in a blind-ended pouch rather than connecting normally to the stomach.
What is an oesophageal fistula?
An abnormal connection in one or more places between the esophagus and the trachea
What causes Oesophageal Atresia and Tracheoesophageal fistula?
Abnormal deviation of trachea-oesophageal septum - Fistula
Failure of recanalization –Oesophageal atresia
Polyhydramnios (excess fluid in the amniotic sac)– Due to atresia
How does the stomach rotate on development?
It rotates 90 degrees clockwise
What is hypertrophic pyloric stenosis?
Muscular hypertrophy of the pyloric sphincter associated with projectile vomiting appearing two to three weeks after birth
What does the liver form from?
The hepatic diverticulum
Give an example of an anomaly of the liver
Extra hepatic ducts
What is meant by extrahepatic biliary artresia?
One or more bile ducts are abnormally narrow, blocked, or absent.
What is an annular pancreas?
Annular pancreas is a rare condition in which the second part of the duodenum is surrounded by a ring of pancreatic tissue continuous with the head of thepancreas. This portion of the pancreas can constrict the duodenum and block or impair the flow of food to the rest of the intestine (duodenal stenosis)
Happens when the ventral bud fails to migrate around the duodenum correctly.
Pancreatic tissue may form in other areas of the foregut = accessory pancreatic tissue
What does the spleen derive from?
The mesoderm and NOT the endoderm
What is derived from the midgut?
Distal part of duodenum, jejunum, ileum, caecum, appendix, ascending colon, proximal 2/3rds of the transverse colon
What are the main events of the midgut loop?
Herniation – Physiological umbilical herniation
Rotation of midgut loop – 90 degrees counterclockwise in the umbilical cord
Retraction of intestinal loops – 180 degrees more counterclockwise rotation
Fixation of intestines
What happens to the vitelline duct?
In 2-4% people a small vitelline duct persists
Forms Meckel diverticulum
May form fistula or vitelline cyst / ligament
Define omphalocele
A hernia in which abdominal organs protrude into a baby’s umbilical cord.
May include liver, stomach, intestinal loops
Viscera is covered by a layer of amnion
Why does growth of the midgut result in physiological herniation?
Abdominal cavity is too small as a result of the large liver.
Define Gastroschisis
The baby’s intestines are found outside of the baby’s body, exiting through a hole beside the belly button. The hole can be small or large and sometimes other organs, such as the stomach and liver, can also be found outside of the baby’s body.
Herniates through a weak area to the right if the umbilicus. Not covered by peritoneum and amnion.
How is the duodenum located in relation to the large intestine?
The duodenum is located posterior to the large intestine.
There can however be abnormal rotation of the primary intestinal loop or reversed rotation.
What forms from the hindgut?
The distal 1/3rd transverse colon, descending colon, sigmoid colon, rectum and upper part of the anal canal
Endoderm of hindgut also forms the lining of the bladder and urethra
What is the cloaca?
A cavity at the end of the digestive tract. Formed by the terminal part of the hindgut and the endoderm.
What is the allantois?
The ventral diverticula of the cloaca.
What is the function of the cloacal membrane?
Separates cloaca with anal pit (ectoderm)
What is the function of the urorectal membrane?
Urorectal septum divides the lower part of the hindgut into anal region and urinary region
What does the urorectal membrane lie close to, during the growth of the embryo?
The cloacal membrane
What are the stages of the opening of the anal canal?
At the end of week 7 the cloacal membrane ruptures = opening for hindgut
Ectoderm of the anal canal proliferates – closing the caudal end
Week 9 – anal canal re-opens
What are the common abnormalities for the formation of the anus.
A – Urorectal fistula
B - Rectovaginal fistula
C - Rectoanal atresia
D - Imperforate anus-
(failure of anal membrane to
break down)
