Download Objectives Derivatives of the yolk sac,

Objectives
• Primordium of various areas of digestive system,
• Morphological events including herniation and rotation of gut,
• Clinical significance of morphological deviations,
• Correlation of knowledge of embryology in the significance of
maternal / foetal clinical problems,
• Correlation of embryological knowledge in foetal imaging.
Primordium of various areas of digestive system,
• Stomodeum and Proctodeum
• Yolk sac,---Epithelium and the out growths of
– Foregut
– Midgut
– Hindgut and Cloaca
• Mesenchyme of the corresponding region including mesenchymal
condensation in its dorsal mesentery (spleen)
Stomodeum and proctodeum
• Stomodeum appears as a slight depression of surface ectoderm,
forming the ectoderm of lips,
• Separated from the cavity of the primordial pharynx by a
bilaminar membrane--- oropharyngeal membrane that is formed
during 3rd wk,
• The inner aspect of the oropharyngeal membrane is composed of
endoderm,
• Rupture of oropharyngeal membrane at about 26th day of
gestation, brings the primordial pharynx and foregut into
communication with the amniotic cavity.
Derivatives of the yolk sac,
•
Foregut,
•
Midgut,
•
Hindgut.
•Primordial gut forms during the 4th wk as the embryonic folding incorporates
the dorsal part of the yolk sac into the embryo,
•The endoderm of the primordial gut gives rise to most of the epithelium and
glands of the digestive tract.
•Muscle, connective tissue and other layers of the wall of the digestive tract
are derived from the splanchnic mesenchyme surrounding the primordial gut.
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Midgut derivatives
Foregut derivatives
Epithelium of
• Primordial pharynx and its derivatives,
Epithelium of
• Duodenum distal to the major duodenal papilla,
(oral cavity, tongue, Pharynx, tonsils, salivary glands and
• Jejunum,
the laryngo-tracheal diverticulum),
Oesophagus ,
• Ileum,
•
Stomoch,
• Caecum with vermiform appendix,
•
Duodenum up to the major duodenal papilla,
• Proximal 2/3 rd of transvers colon,
•
Epithelial derivatives; parenchyma of the liver and pancreas
•
Note;
Mesenchymal condensation in the dorsal mesogastrium= spleen.
(not a derivative of foregut)
Hindgut derivatives
Derivative of Proctodium
Epithelium of
Caudal end of digestive tract is lined by ectoderm– proctodeum
-Distal 1/3rd of transverse colon
Anal canal distal to the pectinate line derives from proctodeum.
-Descending colon,
- Sigmoid colon,
-Distal part of the hindgut is the cloacathat gives rise to
* Rectum,
* Anal canal up to the pectinate line.
Morphological events during the development of digestive system.
Arteries of Digestive system
In the abdomen
The tongue;
Branches of ;
•
External carotid
Subclavial arytery
Thoracic aorta
Foregut
Coeliac artery
Superior Mesenteric arteryr
Superior mesenteric
]
Midgut
Inferior Mesenteric artery
Internal pudendal artery
]
]
Hindgut
Proctodeum
Anterior 2/3rd
– Mucosa – foregut
– Mesenchyme of 1 st pharyngeal arch – lateral lingual swellings and
median lingual swelling ( tuberculum impar) which forms no
recognizable part of the adult tongue,
• Posterior 1/3rd
– Mucosa – foregut
– The copula (eventually disappears) – fusion of ventromedial part of
2nd pharyngeal arch
– The hypobranchial eminence – from the ventromedial part of the 3 rd
and 4 th pair of pharyngeal arches,
• The line of fusion of the two areas is roughly indicated by
sulcus terminalis
• Most of the tongue Muscles are derived from
the occipital myotomes
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Morphological events during the development of
digestive system.
Pharynx
•
Mucosa – foregut
•
Connective tissue, muscles and glands –
will be delt with in another lecture.
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Rathke’s pouch
Morphological events,contd.
•
Laryngo-Tracheal diverticulum; begins to form during the 4th wk of
development, just distal to the primordial pharynx.
•
Seperation of the L-T tube from the distal part of the pharynx, occurs by the
following events;
– Tracheo-oesophagealfold
– T- o groove
– T- o septum
– L- T tube
Morphological events, contd.
Oesophagus
• Develops from foregut immediately distal to the primordial pharynx
•
Partitioning of trachea from the oesophagus by tracheo-oesophageal septum
•
Oesophagus is initially short
•
Then elongates rapidly, mainly because of the growth and descent of the heart
and lungs until 7th wk of embryogenesis
Morphological events ,contd
Oesophagus, contd.
• Striated muscle of oesophagusderives from the mesenchyme of the
lower pharyngeal arches
branchial arches -----
The Stomach
Drives from mucosa of foregut and mesenchyme-- goes through the following
events;
- Acquires dorsal and ventral meso-gastria
• Smooth muscle derives from the surrounding splanchnic
mesenchyme
- Dilatation,
- Differential elongation of lesser and greater curvatures
• Filure of the events in the development of trachea and oesophagus
results in tracheooesophageal fistula and oesophageal atrecsia.
- 90° rotation to the right( clockwise), turning
lesser curvature to the right and
greater curvature to the left, thus forming the lesser sac
- Original left and right surfaces become anterior and posterior surfaces
respectively
- Cranial and caudal ends are slightly to the left and right of mid line
respectively
Also leads to rotation of duodenum to the right to form a C- shaped loop
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Morphological events, contd.
• Duodenum derives from;
-Up to the entrance of
major duodenal papilla---- from foregut mucosa and the
mesenchyme
-Distal to that ----- from midgut mucosa and mesenchyme
• Epithelial proliferation followed by
• Vacuolation
• Re-canalization
Failure of recanalize results in
Duodenal atresia or stenosis
Morphological events, contd.
Liver and biliary apparatus arise as a ventral outgrowth called
hepatic diverticulum from the caudal part of the foregut.
– The epithelium of a larger part of the diverticulum continues to
proliferate into the septum transversum, forming the hepatic cells
around the endothelial lined spaces,primordia of hepatic sinusoids
– The septum transversum gives rise to the connective tissue elements
of the liver including heamopoitic tissue, Kupffer cells and the
capsule of the liver.
– A smaller part of the hepatic diverticulum becomes the gallbladder
and the extra hepatic duct system
– Duct system goes through epithelial proliferation and recanalization
Morphological events , contd
Pancreas develops from caudal part of foregut as ;
• Dorsal and Ventral pancreatic buds
• ventral bud is carried dorsally with ratation of duodenum and fuses with
the dorsal bud, forming part of the head of pancreas and uncinate
process,--- their ducts anastomose.
Mainduct = ventral duct and distal part of the dorsal duct
Acssessory duct = proximal part of the dorsal duct
• Connective tissue = from splanchnic mesenchyme,
• Insulin secretion begins at about 10th wk of IUL
• Glucagon secretion = at about 15thwk of IUL
• Pancreatic tissue may be located in the Meckel’s diverticulum
• Reversed rotation of Ventral bud can produce anular pancreas
The Spleen
•
Derives from a mass of mesenchymal cells in the dorsal mesogastrium
•
Begins to develop during the 5th wk
•
Lobulated in the foetus , but fuses before birth
•
Grooves of lobulation are represented as the notches on the border of adult
spleen
•
Hematopoitic center in foetus ,--- retains the potential even in adults
•
Accessory spleen;
– One or more in number
– Present in 10 % of normal individuals.
Aspleenia is a known but rare entity
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Morphological events, contd
Physiological herniation, reduction of herniation and the Rotation of
midgut
Jejunum and ileum develops from the midgut part of yolk sac (connection
may be retained as Meckel’s diverticulum, vitallo-intestinal fistula or a
fibrous string ) and also from the mesenchyme
•
Epithelial proliferation,
•
During the period of physiological herniation;
– The midgut rotates anticlockwise by 90° around the axis of superior
mesenteric artery
– Cranial loop of midgut goes to the right
– Caudal loop goes to the left
•
Vacuolation,
•
Canalization,
•
Elongation,
•
Physiological herniation, starts at 5th wk and
•
Returning of midgut to abdominal cavity at 10th week
•
Simultaneous rotation of the midgut occurs, as the gut returns to
abdominal cavity.
•
During the time of the reduction of physiological hernia (10th wk);
– Craneal limb that forms most of the small intestine returns to the
abdomen first
– occupies central position
– As the caudal loop that forms small part of small intestine and the large
intestine returns to the abdomen it undergoes 180°anticlockwise rotation
– Caecum at first is at a higher level then occupies the lower position.
Morphological events, contd.
Morphological events, contd
• Rotation of the gut
The colon
•
derives partly from midgut , partly from hindgut and the mesenchyme
•
Epithelial proliferation
•
Recanalization
•
Rotation and partial fixation.
Morphological events ,contd
•
Rectum and anal canal up to pectinate line---from cloaca
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Anal canal distal to the pectinate line -------from
from proctodeum
Will discuss the development of rectum and anal canal in gross anatomy lecture .
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Clinical significance of morphological deviations
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Frenulum lingula superioris and inferioris-- Ankylosis
Pharyngeal diverticulum
Laryngeal web, agenisis of lung/lungs
Oesophageal atresia and tracheo-oesophageal fistula
Pyloric stenosis an pyroric web
Duodenal stenosis and
Duodenal atresia
Anular pancreas
Jejunal atresia/ stenosis
Ilial atresia
Meckel’s diverticulum
Colonic atresia
Rectal agenisis
Anal agenisis/Stenosis/covered anus/recto-vaginal fistula
Situs inversus
Malrotation
Internal herniation
Duplications
etc.
Correlation of embryological knowledge to foetal imaging
Polyhydramnias
Correlation of knowledge of embryology in the significance of
maternal / foetal clinical problems,
.
End of topic
Physiological umbilical hernia
G.I atresia / obstruction at different levels
Aganglianosis
Diaphragmatic hernia
Keep antenatal clinical picture in mind at evaluation of
the new born baby.
Duplications
Any intra - abdominal mass
etc.
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