1. Asist. Univ. Dr. Tulin Raluca
Embryology Year 2- LP1
Asist. Univ. Dr. Tulin Raluca

2. The development of the digestive tract Covered topics
I. The formation of serous cavities of the trunk -LECTURE
II. The development of the digestive tube: foregut, midgut, hindgut. Separation of the cloaca- abnormalities. – LECTURE
III. The development of the liver and portal system. The development of the pancreas. – abnormalities. LECTURE
L.P Formation of the omental bursa, greater omentum and transverse mesocolon.
2. Development of the gall bladder- malformations.
3. Physiological hernia- abnormalities.
4. Development of the spleen- abnormalities.
5. Clinical implications of the most frequently occurring digestive tract malformations.

3. Development of the diaphragm
Separation of the peritoneal cavity from the pleural cavity (they are both derived from the intra-embryonic coelom)
Develops from 4 sources:
Septum transversum (mesoderm)—central tendon
Incompletely separates the two cavities, leaving 2 pericardioperitoneal canals on either side of the foregut
Pleuropericardial folds- contain the phrenic nerves
Mesentary of the esophagus- the crura of the diaphragm
Myoblasts from thoracic wall (somites C3-C5)

5. Malformations of the diaphragm
Congenital diaphragmatic hernia
1/2000 births, commonly postero-laterally
More frequently unilateral, on the left (foramen of Bochdalek)
If the pericardioperitoneal canals are not closed by W10 when the physiological hernia retracts, the intestinal coils (less frequently the stomach, colon, rectum) will ascend into the thoracic cavity and impede normal ventilation.
Congenital hiatal hernia
Rare, organs herniate through an enlarged esophageal hiatus. Usually occurs during adulthood
Parasternal hernia (retrosternal) – Morgagni
Rare, between then sternum and the sterno-costal surface of the diaphragm

6. Clinical implications
The uneven growth of the lateral body walls pushes the diaphragm inferiorly from the cervical region (origin of the phrenic nerves) into the thorax
Irritation of the diaphragm may produce pain in the shoulder or neck (both innervated by nerves of the cervical or brachial plexus- referred pain.
Their common origin from mesenchyme explains the close contact between the diaphragm and the pericardium
Similarly, the common origin of the liver and the diaphragm from the septum transversum explains the close contact between the two structures

7. IVC +nn. Phrenic (T8)
Esophagus+ nn. Vagi (T10)
Aorta+ thoracic duct (T12)
Sympathetic chain – medial arcuate ligaments

8. Development of the digestive system

9. Foregut- derivatives Pharynx- larynx- respiratory system Esophagus
Stomach
Superior half of duodenum
Liver and bile ducts
Pancreas

10. Esophagus Esophageal atresia (and/or tracheoesophagial fistula)
Polyhydramnios in uterus
Surgical treatment
Esophageal stenosis
Narrowing of the lumen Ingustarea lumenului
Incomplete recanalization
Vascular abnormalities

12. Development of the stomach and formation of the omental bursa

14. Mesenteries Ventral mesogastrium (liver)
Lesser omentum (liver- duodenum + stomach) – hepatoduodenal ligament contains portal triad (bile duct, portal vein, hepatic artery), forms the superior margin of the foramen of Winslow, which allows passage into the omental bursa
Falciform ligament (liver-anterior body wall) contains ombilical vein which will become the round ligament of the liver (ligamentum teres)
Dorsal mesogastrium (spleen) – grows over the transverse colon and the coils of the small intestine
Greater omentum (4 peritoneal sheets)
Transvere mesocolon (4 periotneal sheets)

16. Bursa omentala

18. Stomach malformations
Pyloric stenosis
Circular muscle in the region of the pylorus hypertrophies
Passage of food is obstructed + frequent vomiting

19. Development of pancreas

20. Pancreas malformations
Annular pancreas
Occasionally associated with obstruction of the duodenum
Accessory pancreatic tissue (ectopic)
In the stomach
In Meckel’s diverticulum

21. Midgut- derivaties Forms inferior half of duodenum Jejunum Ileum Cecum
Apendix
Ascending colon
Proximal 2/3 of transverse colon

22. Physiological hernia During S6-S10 Primary intestinal loop (midgut)
cephalic limb
caudal limb
Uneven elongation of cephalic and caudal limbs
270 degree counterclockwise rotation (90 degrees while herniated degrees when returned inside abdominal cavity)

25. Small intestine
Age
Length (cm)
20W
125 30
200
TERM
275
1 year
380
10 years
500
20 years
575
Elonagation of small intestine is proportional until 3rd trimester
Length doubles in last trimester
Elongation continues post-natally but slows after 1 year
Duodenum
25 cm
Jejunum
1,4 m
Ileum
3,5 m
Apendix
2-20 cm
Ascending colon

26. Migration of neural crest cells into the developing GI tract
W5- neural crest cells migrate to midgut. W7- they colonize entire length of primitive gut (anterior-posterior)
Auerbach myenteric plexus- between the circular and longitudinal muscle layers – motor and secretory innervation to both (sympathetic + parasympathetic)
Meissner submucous plexus – forms 2-3 days after the myenteric plexus. Innervates the muscularis mucosa
Interstitial cells of Cajal- possess intrinsic pacemaker property, located between smooth muscle cells. Derived from mesoderm.

27. Malformations Omphalocoel Gastroschisis Enlarged umbilicus
Herniated intestinal coils are contained within a sac (amniotic membrane)
2,5/10,000 births
Physiological hernia does not return into abdominal cavity
Mortality rate 25%
Gastroschisis
Abdominal wall defect, lateral to umbilicus
Herniated organs are not contained within sac
1/10,000 births (associated with consumption of cocaine)
High survival rate

29. Meckel’s diverticulum
Present in 2-4% of all adults
Approximately cm from ileocecal (Bauhin) valve, on the antimesenteric border of ileum
Usually asymptomatic
May contain gastric mucosa or pancreatic tissue
May form direct communication between umbilicus and intestinal tract- vitelline fistula

31. Development of the liver
2 origins
Outgrowth of endoderm gives rise to liver bud (inferior limit of the of the foregut)
Hepatocytes
Hepatic sinusoids (formed by fragmentation of vitelline and umbilical veins)
Mesoderm of septum transversum
Hematopoietic cells
Kupffer cells
Connective tissue (Glisson capsule)

33. Clinical implications
W10- liver makes up 10% of body weight and carries out hematopoietic function (synthesis of formed elements in blood )
M7- hematopoietic function stops
At birth- liver makes up 5% of body weight
W12 – biliary secretion begins (cystic duct, bile duct, gall bladder are already formed) into GI tract

34. Hematopoiesis
Initially- yolk sac and para-aortic sac in splanchnopleura (aorto-gonado-mesonephros) AGM
W5 –liver (main site until W8)
W8- SPLEEN- is never a main site (as in mice) –M8
W12- bone marrow
W15- thymus
PERIPHERAL BLOOD – IMPORTANT SOURCE OF STEM CELLS (PRENATALLY)

35. Hematopoiesis

36. Malformations of liver and bile ducts
Variations in hepatic lobulations- not clinically significant
Accessory hepatic ducts
Duplication of the gall bladder
Extrahepatic biliary atresia
1/15,000 live births, most frequently in Asia
Treatment- liver transplant
Jaundice, dark colored urine, colorless stool
Intrahepatic atresia/stenosis
1/100,000 live births
Fetal infections
May be lethal

37. Liver lobes

38. Extrahepatic biliary atresia

39. Hindgut Forms Distal 1/3 of transverse colon Descending colon
Sigmoid colon
Rectum (anal canal- superior part, up to pectinate line)
Clinical implications
The different origins of the 2 parts of the transverse colon (proximal 2/3 and distal 1/3) explains there different blood supplies
The different origins of the rectum explains the different blood supplies, innervation and lymphatic drainage of this structure

41. Cloaca- division W6 Clinical implications
Superior
Inferior– last 2 cm of anal canal
Origin
Endoderm
Ectoderm
Blood supply
Inferior mesenteric artery
Internal iliac arteries (middle and inferior rectal arteries)
Venous drainage
Superior rectal veins (venous plexus)
Inferior and middle rectal veins--- IVC
Lymphatic drainage
Internal iliac lymph nodes
Inguinal lymph nodes
Innervation
Visceral sensory
Somatic sensory

42. Clinical implications
The different lymphatic drainage of the anal canal explains the different types of metastasis above or below the pectinate line
The different innervation explains the absence of perceived pain from lesions above the pectinate line

43. Hirschsprung’s Disease
Congenital megacolon
Absence of parasympathetic ganglia from the intestinal wall (normally derived from neural crest cells)
Rectum and sigmoid colon are frequently affected (sacral nerve supply)
The entire colon is rarely affected (Vagus nerve is effective guide for migrating neural crest cells- this condition rarely occurs proximal to splenic flexure)

44. Ano-rectal abnormalities
Due to abnormal division of the cloaca
Imperforate
Anal membrane fails to break down
Rectouteral or rectovaginal fistulas
1/5000 births