Embryology of GI tract

Question 1

Pharyngeal arch 1

Answer 1

Tuberculum impar, lateral lingual swellings, Jaw, muscles of mastication and Maxillary artery

Question 2

Pharyngeal Arch 2

Answer 2

Copula and Hyoidal artery innervated by Facial nerve

Question 3

Pharyngeal Arch 3

Answer 3

Copula, Hyoid bone, Common carotid artery and distal internal carotid

Question 4

Pharyngeal Arch 4

Answer 4

Epiglottal swellings, Copula, Cricothyroid, levator veli palatini and pharyngeal constrictor muscles, subclavian artery and aortic arch

Question 5

Tuburculum ampar

Answer 5

Tuberculum ampar gives rise to the anterior part of the tongue. From pharyngeal arch 1

Question 6

Lateral lingual swellings

Answer 6

Lateral lingual swellings give rise to the anterior 2/3 of the tongue. From pharyngeal arch 1

Question 7

Copula

Answer 7

Copula of the tonuge gives rise to the tongue root. From pharyngeal arch 2, 3, and 4

Question 8

Epiglottal swelling

Answer 8

Epiglottal swelling gives rise to the epiglottis. From pharyngeal arch 4.

Question 9

How does the lingual frenulum form?

Answer 9

Degeneration of the tongue from the floor of the oral cavity occurs via cell division and a remnant of this attachment is the lingual frenulum

Question 10

Embryological origin of the tongue muscles

Answer 10

Both the intrinsic and extrinsic muscles are derived from the somatic mesoderm. This is arranged as somites and the somites located in the occipital region are myogenic precurosrs to the tongue muscles.

Question 11

How does the gut form?

Answer 11

Craniocaudal folding of the yolk sac forms two blind end pouches called the foregut and hindgut. Midgut is in between and connects the yolk sac to the umbilicus via the vitelline duct.

Question 12

Mesentery

Answer 12

Double folds of peritoneum formed from the reflections of the visceral and parietal peritoneum which connect organs to the abdominal wall and suspend them in the abdomen. It provides a path for blood and nerve supply.

Question 13

Portal triad development

Answer 13

Foregut is lined with ventral mesentery. The hindgut is lined with dorsal mesentery. Ventral mesogastrium does not extend beyond foregut, so there is a free edge which allows the structures of the portal vein, bile duct and hepatic vein to enter and leave.

Question 14

Greater sac and lesser sac

Answer 14

Greater sac is a cavity anterior in the abdomen. Lesser sac is a cavity posterior in the abdomen. They communicate via the Epiploic Foramen of Winslow. They form due to the absence of attachments of the ventral mesentery beyond the foregut during development

Question 15

Omenta

Answer 15

Sheets of visceral peritoneum which connect organs to organs

Question 16

Greater omentum

Answer 16

Extends from the greater curvature of the stomach to attach to the transverse colon. It is composed of 4 layers of peritoneum.

Question 17

Lesser omentum

Answer 17

Attaches the lesser curvature of the stomach to the liver. It is composed of only 2 layers of peritoneum.

Question 18

What organs are in the foregut?

Answer 18

Oesophagus to the superior duodenum , proximal to the ampulla of Vater. Supplied by the coeliac trunk

Question 19

What organs are in the midgut?

Answer 19

Descending duodenum to the 2/3 of the transverse colon. Supplied by the superior mesenteric artery

Question 20

What organs are in the hindgut?

Answer 20

Distal 1/3 of the transverse colon to end where the anal canal begins. Supplied by the inferior mesenteric artery.

Question 21

What does the cloaca give rise to?

Answer 21

Anal canal and bladder

Question 22

Intraembryonic caecum

Answer 22

A cavity in the centre of the embryo, derived from mesoderm which forms the thoracic and abdominal cavities.

Question 23

Dorsal mesentery

Answer 23

Lines the entire gut tube

Question 24

Ventral mesentery

Answer 24

Lines only the foregut, leaving a free edge for the portal triad to enter.

Question 25

Stomach in development

Answer 25

Dorsal mesentery attaches stomach to posterior wall. Ventral mesentery attaches stomach to anterior wall. It forms a right and left sac.

Question 26

Left sac

Answer 26

Left sac formed by the dorsal and ventral mesentery attachments to the stomach becomes the greater sac.

Question 27

Right sac

Answer 27

Right sac becomes the lesser sac.

Question 28

Meckel’s diverticulum

Answer 28

Meckel’s diverticulum is a ligament that contains ectopic tissue such as gastric. If this is secreted in the intestine it may lead to damage, bleeding and create an opening in the intestines for faeces to collect in the recess and lead to peritonitis.

Question 29

How does the umbilical cord form?

Answer 29

Vitelline duct disintegrates along with the yolk sac by week 4 to be replaced by the umbilical cord
However, if the vitelline duct does not disintegrate, then the intestinal loops and the vitelline duct will form a ligament called the Meckel’s diverticulum.

Question 30

Embryological development of the position of the small intestine

Answer 30

Around week 6, the growth of the intestinal loops in the midgut herniate anteriorly towards the umbilical cord to occupy more space. It makes three 90 degree anticlockwise turns which makes the cranial limb posterior to the caudal limb. This results in the adult duodenum being posterior to the transverse colon. At week 10, the abdominal cavity in the midgut enlarges enough and creates an inward suction force to bring back the intestinal loops.

Question 31

Exomphalos

Answer 31

Exomphalos is a congenital condition where the intestines are protruding through the belly button. It has a high survival rate but can lead to pulmonary hypoplasia (small lungs) which can affect breathing and heart function because there is not enough space for the thoracic cavity.

Question 32

Gastroschiasis

Answer 32

Lateral folding of the embryo does not close which allows the intestinal loops to herniate out of the yolk sac. There is no protective peritoneum.

Question 33

Sphlancic mesoderm

Answer 33

The sphlancic mesoderm surrounds the endoderm and forms the mucosal layers surrounding the abdominal organs (mucosa, submucosa, musclaris externa) and it forms the visceral mesogastrium

Question 34

Primary retroperitoneal organs

Answer 34

Developed outside the peritoneum. This includes the Abdominal aorta, IVC, kidneys, adrenal glands, ureter and lower rectum.

Question 35

Secondary retroperitoneal

Answer 35

Secondary retroperiotneal organs were once intraperitoneal but became retroperitoneal. It includes part of the duodenum, the descending colon, ascending colon and the head and body of pancreas. These are attached to the abdominal wall via the adventitia.

Question 36

Development of the stomach

Answer 36

Gut tube rotates longitudinally and anteroposteriorly rotating, (around the axis) , there is a 90 degree anticlockwise rotation. The ventral edge where the liver and stomach is located moves to the right and becomes the lesser curve of the stomach. The dorsal edge where the spleen and stomach are located moves to the left and becomes the greater curve. The different sizes is due to assymetrical growth which is faster left dorsal edge than the right ventral edge.

Question 37

Development of pancreas

Answer 37

Pancreas lies partially in both the ventral and dorsal mesogastrium as separate structures which rotates and fuse to become one gland. The duodenum development pushes it against the posterior abdominal wall and makes it secondary retroperitoneal.

Question 38

What is the composition of the mesentery?

Answer 38

The mesentery is formed of a double serous membrane of simple squamous epithelia and loose areolar tissue which allow vessels to vascularise and drain the organs that the mesentery suspend in the abdominal cavity via its attachment to the abdominal wall.

Question 39

Ventral mesogastrium

Answer 39

Liver

Question 40

Dorsal mesogastrium

Answer 40

Spleen

Question 41

Abdominal pain

Answer 41

Visceral pain is poorly localised and refers to the dermatome of the spinal nerve innervation. If this affects the parietal peritoneum surrounding the organ, there is a greater localisation.