Download LP1 - Embriologie

Embryology
Year 2- LP1
Asist. Univ. Dr. Tulin Raluca
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.
1. 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.
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)
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
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
IVC +nn. Phrenic
(T8)
Esophagus+ nn.
Vagi (T10)
Aorta+ thoracic
duct (T12)
Sympathetic chain
– medial arcuate
ligaments
Development of the digestive system
Foregut- derivatives
•
•
•
•
•
•
Pharynx- larynx- respiratory system
Esophagus
Stomach
Superior half of duodenum
Liver and bile ducts
Pancreas
Esophagus
• Esophageal atresia (and/or tracheoesophagial
fistula)
• Polyhydramnios in uterus
• Surgical treatment
• Esophageal stenosis
• Narrowing of the lumen Ingustarea lumenului
• Incomplete recanalization
• Vascular abnormalities
Development of the stomach and
formation of the omental bursa
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)
Bursa omentala
Stomach malformations
• Pyloric stenosis
– Circular muscle in the region of the pylorus
hypertrophies
– Passage of food is obstructed + frequent vomiting
Development of pancreas
Pancreas malformations
• Annular pancreas
– Occasionally associated with obstruction of the
duodenum
• Accessory pancreatic tissue (ectopic)
– In the stomach
– In Meckel’s diverticulum
Midgut- derivaties
•
•
•
•
•
•
•
Forms inferior half of duodenum
Jejunum
Ileum
Cecum
Apendix
Ascending colon
Proximal 2/3 of transverse colon
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 + 180 degrees when
returned inside abdominal cavity)
Small intestine
• Elonagation of
small intestine is
proportional
until 3rd trimester
• Length doubles
in last trimester
• Elongation
continues postnatally but slows
after 1 year
Age
Length (cm)
20W
125
30
200
TERM
275
1 year
380
10 years
500
20 years
575
Duodenum
25 cm
Jejunum
1,4 m
Ileum
3,5 m
Apendix
2-20 cm
Ascending colon
25 cm
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.
Malformations
• Omphalocoel
– 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
Meckel’s diverticulum
• Present in 2-4% of all adults
• Approximately 40-60 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
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)
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
Hematopoiesis
• Initially- yolk sac and paraaortic sac in
splanchnopleura (aortogonado-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)
Hematopoiesis
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
Liver lobes
Extrahepatic biliary atresia
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
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
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
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)
Ano-rectal abnormalities
• Due to abnormal division of the cloaca
• Imperforate
– Anal membrane fails to break down
• Rectouteral or rectovaginal fistulas
– 1/5000 births