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![Page 1: Embryology: Development of digestive system. Embryo folding – incorporation of endoderm to form primitive gut. Outside of embryo – yolk sac and allantois.](https://reader035.fdocuments.in/reader035/viewer/2022081514/56649f225503460f94c3b2bb/html5/thumbnails/1.jpg)
Embryology:Development of digestive system
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Embryo folding – incorporation ofendoderm to form primitive gut. Outside of embryo – yolk sac andallantois. Vitelline duct
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Stomodeum (primitive mouth) the oral cavity + the salivary glands
Proctodeum primitive anal pit
Primitive gut whole digestive tube + accessory glands
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pharynx
forgut
midgut
hindgut
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• The epithelium and glandular cells of associated glands of the gastrointestinal tract develop from endoderm
• The connective tissue, muscle tissue and mesothelium are derived from splanchnic mesoderm
• The enteric nervous system develops from neural crest
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primitive gut
foregut midgut hindgut pharyngeal above ductus cloacal membrane omphalomesentericus membrane
and yolk sack
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Derivatives of
forgut – pharynx, esophagus (+ respiratory diverticul), stomach, cranial part of duodenum
midgut – caudal part of duodenum (+ liver, gall bladder, pancreas), small intestine and part of large intestine (to the flexura coli sin.)
hindgut – large intestine (from flexura coli sin.), rectum, upper part of anal canal
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Oral cavity• primitive mouth pit
– stomodeum• lined with ectoderm• surrounded by:
- processus frontalis
(single) - proc. maxillares (paired)
- proc. mandibulares (paired)
• pharyngeal membrane (it ruptures during the 4th week, primitive gut communicates with amnionic cavity
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Pharyngeal (branchial) apparatus
Pharyngeal arches• appear in weeks 4 - 5• on the ventral side
of the pharyngeal gut. • each arch has cartilage,
cranial nerve, aortic arch artery and muscle
• pharyngeal clefts and pouches are located between the arches
• membrana obturans
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Ectodermal pharyngeal clefts
(grooves)
Endodermal pharyngeal pouches
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Fate of pharyngeal pouches and clefts
early development later development
Sinus cervicalis
+ tympanic cavity
Tympanic nenbrane
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Structures derived from Arches
ARCH Nerve MusclesSkeletal
StructuresLigaments
1 (maxillary/mandib
ular)trigeminal (V) malleus, incus
ant lig of malleus, sphenomandibular ligament
2 (hyoid)
facial (VII)
stapes, styloid process, lesser cornu of hyoid, upper part of body of hyoid bone
stylohyoid ligament
3glossopharyngeal
(IX)
greater cornu of hyoid, lower part of body of hyoid bone
4 & 6
superior laryngeal and recurrent
laryngeal branch of vagus (X)
thyroid, cricoid, arytenoid, corniculate and cuneform cartilages
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Structures derived from PouchesEach pouch is lined with endoderm and generates specific structures.
POUCHOverall Structure Specific Structures
1 tubotympanic recesstympanic membrane, tympanic cavity, mastoid antrum, auditory tube
2 intratonsillar cleftcrypts of palatine tonsil, lymphatic nodules of palatine tonsil
3 inferior parathyroid gland, thymus
4superior parathyroid gland, ultimobranchial body
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primitive pharynx
thyroid gl.
laryngotracheal diverticle(respiratory divertcle)
esophagus
Esophagus developmentbelow respiratory diverticle,behind larynx and trachea
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Esophagus development
• differentiation of epithelium from endoderm
• during the 2nd month endoderm proliferates and temporarily closes esophageal lumen
• other tissues and structures in the wall arrise from splanchnic mesoderm
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mesoesophageum dorsale gives rise to dorsal mediastinum and mediastinal pleura
mesoesophageum ventrale disappears
esophagus
Mesenteries – suspensory duplicature derived from mesoderm and mesenchyme (a fold of tissue that attaches organs to the body wall)
mesooesophageum
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in the 4th week – spindle dilatation of distal forgut endoderm – epithelium and glandular cells splanchnic mesoderm – other tissues of stomach wall
Stomach development
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Rotation around longitudinal axis: - left side → ventrally, - right side → dorsally.
Uneven growth of ventral and dorsal wall: - curvatura minor (to the right), - curvatura major (to the left).Rotation around sagital axis : - curvatura minor (cranial position), - curvatura major (caudal position).
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Sagital rotation axis
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The liver bud (hepatocystic diverticcle) appears at the distal end of the foregut (week 4) and divides into hepatic and cystic diverticles, later ventral pancreatic bud and dorsal pancreatic bud (week 5). Both pancreatic buds meet and fuse (week 6).
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liver
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The midgut is divided into two regions at the viteline duct: the cranial and caudal limbs.
The derivatives of the cranial limb - the distal duodenum, jejunum, and proximal ileum.
The derivatives of the caudal limb - the distal ileum, cecum, appendix, ascending colon, and proximal 2/3 of transverse colon.
the midgut grows faster than that of the embryo, creating: - duodenal loop- umbilical loop
Midgut
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Duodenal loop and umbilical loop
Umbilical loop herniates into the umbilical cord (physiologic herniation, in week 6-10)
Flexuraduodenojejunalis
forgut
midgut
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Duodenum development
• Duodenal loop – 2 limbs: upper limb (from forgut) lower limb (from midgut)
• On top of loop – diverticles (for liver, gallbladder, pancreas)
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Due to rotation of umbilical loop, duodenal loop changes its position (from front to the right) and becomes retroperitoneal organ (together with pancreas)
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Intestines development
• Umbilical loop – 2 limbs: cranial – jejunoileal limb (jejunum, major part of ileum) caudal – ileocecal limb (rest of ileum, caecum + appendix, colon ascendens and 2/3 of colon transversum)
• A. mesenterica sup. – axis of rotation• week 6 – physiologic herniation into the umbilical
cord, week 10 – reposition into abdominal cavity
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Umbilical loop rotation
• The midgut loop rotates 90° counter-clockwise in the umbilical cord around the axis of the superior mesenteric artery
• Upon returning, the gut undergoes another 180° counterclockwise rotation, placing the cecum and appendix near the right lobe of the liver.
• The total rotation of the gut is 270°.
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90º
180ºafter 270ºrotation
º
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The distal end of the hindgut – the cloaca.
Derivatives of the hindgut: the distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum and upper part of anal canal (above the pectinate line).
Hindgut
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Division of the cloaca - urorectal septum divides the cloaca into a ventral primitive urogenital sinus and a dorsal primitive anorectal canal.
The cloacal membrane breaks down in the 7th week.
Distal to the pectinate line (site of the former cloacal membrane), the epithelium of the anal canal is derived from ectoderm of proctodeum (primitive anal pit)
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Mesenteries
• double layer of peritoneum enclosing organs and connecting them to the body wall
Ventral mesentery exists only in region of distal part of esophagus, stomach (lesser omentum) and upper part of duodenum
Dorsal mesentery forms dorsal meso- gastrium (greater omentum), dorsal mesoduodenum, mesentery proper (jejunum, ileum)
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Face development
• During 2nd month i.u.• Stomodeum• Mesenchymal processes covered with
ectoderm - processus frontonasalis - processus mandibulares - processus maxillares
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The head and neck of a human embryo 32 days old, seen from the ventral surface. The floor of the mouth and pharynx have been removed.
Stomodeum
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Frontonasal process
Maxillar process
Mandibular process
Stomodeum
Intermaxillary segment(intermaxillare)
Nasal placode (plate)
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Frontal view of an embryo at 4 to 5 weeks of age. Observe the branchial arch formation and the ruptured buccopharyngeal membrane.
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Developing face
week 4 4-5 5 -6 6-7
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stage 15 (8.0-mm), ×52. stage 17 (11.7-mm), 57x stage 17 (11.7-mm), 14x
Scanning electron micrograph (SEM): human embryo
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Nasal placodes
Nasal pits
Nasal canals
Proc. frontalis
Proc. nasalismedialisetlateralis
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Palate development 3 ectoderm-mezenchymal plates:
a) medial palatine plate (1) – from processus nasalis medialis (intermaxillare) primary palate
b) lateral palatine plates (2) – from medial side of maxillary processes secondary palate
Fusion of plates = raphe palati
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Clefts ofClefts of maxilla and palatemaxilla and palate
MaxillaCleft between lateral incisivus and caninus
Uni- or bilateral
(cheilognathoschisis unilateralis, cheilognathoschisis bilateralis)
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PalateUni- or bilateral
Single or combined (cheilo – gnatho – palatoschisis)
1: 2500
heredity- autosomal dominant
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Clefts of primary palateVentrally from foramen incisivum
One or both lateral plates don‘t fuse with primary palate
Clefts of secondary and primary palatesVentrally and dorsaly from foramen incisivum
Lateral palatine plates are not fused with primary palate
Nasal septum is free
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Clefts of secondary palate (palatoschisis)behind foramen incisivum
Nonfused palatine plate in middle plane (completly – soft and hard palate and uvula)
staphyloschisis (uvula bifida)
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H – fissura orbitofacialis bilat.
Transverse cleftsJ – macrostomiaK - microstomia
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Pharyngeal arches, pouches and clefts
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Pancreas – ducts and parenchyma development (from endoderm)
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Ectodermal pharyngeal clefts
(grooves)
primitive pharynx
Endodermal pharyngeal pouches
Thyroid gl.
Laryngotracheal diverticle
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Pharyngeal arches, pouches and clefts
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At 6 weeks, the pancreatic buds meet and fuse.
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