Embryology of Alimentary system

Question 1

What closes the primordial gut at the cranial end?

Answer 1

Oropharyngeal membrane

Question 2

What closes the primordial gut at the caudal end?

Answer 2

The cloacal membrane

Question 3

What are the divisions of the primordial gut tube?

Answer 3

The foregut, midgut and the hindgut

Question 4

What happens early in the 4th week to the embyonic coelom?

The embryonic coelom is formed by the folding of the germ layers

Answer 4

It becomes the embryonic body cavity.

It divides into 3 well defined pericardial, peritoneal cavity and two pericardio-peritoneal canals

Question 5

What are the derivatives of the foregut?

Answer 5

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

Question 6

What is oesophageal artresia?

Answer 6

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.

Question 7

What is an oesophageal fistula?

Answer 7

An abnormal connection in one or more places between the esophagus and the trachea

Question 8

What causes Oesophageal Atresia and Tracheoesophageal fistula?

Answer 8

Abnormal deviation of trachea-oesophageal septum - Fistula

Failure of recanalization –Oesophageal atresia

Polyhydramnios (excess fluid in the amniotic sac)– Due to atresia

Question 9

How does the stomach rotate on development?

Answer 9

It rotates 90 degrees clockwise

Question 10

What is hypertrophic pyloric stenosis?

Answer 10

Muscular hypertrophy of the pyloric sphincter associated with projectile vomiting appearing two to three weeks after birth

Question 11

What does the liver form from?

Answer 11

The hepatic diverticulum

Question 12

Give an example of an anomaly of the liver

Answer 12

Extra hepatic ducts

Question 13

What is meant by extrahepatic biliary artresia?

Answer 13

One or more bile ducts are abnormally narrow, blocked, or absent.

Question 14

What is an annular pancreas?

Answer 14

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

Question 15

What does the spleen derive from?

Answer 15

The mesoderm and NOT the endoderm

Question 16

What is derived from the midgut?

Answer 16

Distal part of duodenum, jejunum, ileum, caecum, appendix, ascending colon, proximal 2/3rds of the transverse colon

Question 17

What are the main events of the midgut loop?

Answer 17

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

Question 18

What happens to the vitelline duct?

Answer 18

In 2-4% people a small vitelline duct persists

Forms Meckel diverticulum

May form fistula or vitelline cyst / ligament

Question 19

Define omphalocele

Answer 19

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

Question 20

Why does growth of the midgut result in physiological herniation?

Answer 20

Abdominal cavity is too small as a result of the large liver.

Question 21

Define Gastroschisis

Answer 21

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.

Question 22

How is the duodenum located in relation to the large intestine?

Answer 22

The duodenum is located posterior to the large intestine.

There can however be abnormal rotation of the primary intestinal loop or reversed rotation.

Question 23

What forms from the hindgut?

Answer 23

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

Question 24

What is the cloaca?

Answer 24

A cavity at the end of the digestive tract. Formed by the terminal part of the hindgut and the endoderm.

Question 25

What is the allantois?

Answer 25

The ventral diverticula of the cloaca.

Question 26

What is the function of the cloacal membrane?

Answer 26

Separates cloaca with anal pit (ectoderm)

Question 27

What is the function of the urorectal membrane?

Answer 27

Urorectal septum divides the lower part of the hindgut into anal region and urinary region

Question 28

What does the urorectal membrane lie close to, during the growth of the embryo?

Answer 28

The cloacal membrane

Question 29

What are the stages of the opening of the anal canal?

Answer 29

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

Question 30

What are the common abnormalities for the formation of the anus.

Answer 30

A – Urorectal fistula

B - Rectovaginal fistula

C - Rectoanal atresia

D - Imperforate anus-

(failure of anal membrane to

break down)