Embryology of GI tract Flashcards
Pharyngeal arch 1
Tuberculum impar, lateral lingual swellings, Jaw, muscles of mastication and Maxillary artery
Pharyngeal Arch 2
Copula and Hyoidal artery innervated by Facial nerve
Pharyngeal Arch 3
Copula, Hyoid bone, Common carotid artery and distal internal carotid
Pharyngeal Arch 4
Epiglottal swellings, Copula, Cricothyroid, levator veli palatini and pharyngeal constrictor muscles, subclavian artery and aortic arch
Tuburculum ampar
Tuberculum ampar gives rise to the anterior part of the tongue. From pharyngeal arch 1
Lateral lingual swellings
Lateral lingual swellings give rise to the anterior 2/3 of the tongue. From pharyngeal arch 1
Copula
Copula of the tonuge gives rise to the tongue root. From pharyngeal arch 2, 3, and 4
Epiglottal swelling
Epiglottal swelling gives rise to the epiglottis. From pharyngeal arch 4.
How does the lingual frenulum form?
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
Embryological origin of the tongue muscles
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.
How does the gut form?
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.
Mesentery
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.
Portal triad development
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.
Greater sac and lesser sac
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
Omenta
Sheets of visceral peritoneum which connect organs to organs
Greater omentum
Extends from the greater curvature of the stomach to attach to the transverse colon. It is composed of 4 layers of peritoneum.
Lesser omentum
Attaches the lesser curvature of the stomach to the liver. It is composed of only 2 layers of peritoneum.
What organs are in the foregut?
Oesophagus to the superior duodenum , proximal to the ampulla of Vater. Supplied by the coeliac trunk
What organs are in the midgut?
Descending duodenum to the 2/3 of the transverse colon. Supplied by the superior mesenteric artery
What organs are in the hindgut?
Distal 1/3 of the transverse colon to end where the anal canal begins. Supplied by the inferior mesenteric artery.
What does the cloaca give rise to?
Anal canal and bladder
Intraembryonic caecum
A cavity in the centre of the embryo, derived from mesoderm which forms the thoracic and abdominal cavities.
Dorsal mesentery
Lines the entire gut tube
Ventral mesentery
Lines only the foregut, leaving a free edge for the portal triad to enter.
Stomach in development
Dorsal mesentery attaches stomach to posterior wall. Ventral mesentery attaches stomach to anterior wall. It forms a right and left sac.
Left sac
Left sac formed by the dorsal and ventral mesentery attachments to the stomach becomes the greater sac.
Right sac
Right sac becomes the lesser sac.
Meckel’s diverticulum
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.
How does the umbilical cord form?
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.
Embryological development of the position of the small intestine
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.
Exomphalos
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.
Gastroschiasis
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.
Sphlancic mesoderm
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
Primary retroperitoneal organs
Developed outside the peritoneum. This includes the Abdominal aorta, IVC, kidneys, adrenal glands, ureter and lower rectum.
Secondary retroperitoneal
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.
Development of the stomach
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.
Development of pancreas
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.
What is the composition of the mesentery?
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.
Ventral mesogastrium
Liver
Dorsal mesogastrium
Spleen
Abdominal pain
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.
