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GIS > GIS08 Development Of The Digestive System > Flashcards

GIS08 Development Of The Digestive System Flashcards

1
Q

Revision: Gastrulation

A

Day 16-18

  • Epiblast cells migrate through primitive streak (inwards and from caudal towards cephalic)
  • Definitive endoderm cells (from epiblast) displace hypoblast
  • Mesoderm spread between endoderm and ectoderm
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2
Q

Formation of primitive gut tube: Day 16

A
  • Developing endoderm initially open to yolk sac
  • Cardiac primodia formed cephalically
  • Longitudinal (cephalic-caudal) folding at both ends bring endoderm inside and form gut tube
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3
Q

Formation of primitive gut tube: Day 18

A

Longitudinal folding creates:

  • Anterior intestinal portal (future foregut)
  • Posterior intestinal portal (future hindgut)
  • Cardiac region brought to ventral side of gut tube
  • ***Oropharyngeal membrane: future mouth
  • ***Cloacal membrane: future anus
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4
Q

Formation of primitive gut tube: Day 22

A
  • **Stomodeum: **Ectodermal depression at head end of embryo –> front part of mouth
  • Gut associated organs: forms bud from endoderm
  • Midgut opening to yolk sac progressively narrows
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5
Q

Formation of primitive gut tube: Day 30

A
  • **Stomach bulge + **Dorsal pancreatic bud become visible

- Connection of midgut to yolk sac reduced to Yolk stalk

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6
Q

Invagination of lateral body wall

A
  • folding of embryo to enclose endoderm layer –> forms gut tube
  • Lateral folding –> embryo with a gut suspended by dorsal mesentery (***Splanchnic mesoderm)
  • ***Somatic mesoderm –> lines body cavity –> muscles and CT
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7
Q

Subdivision of gut tube and and their derivatives

A

Foregut:

  • esophagus
  • stomach
  • liver + gallbladder
  • pancreas
  • proximal duodenum (up to major duodenal papilla)

Midgut:

  • lower duodenum
  • small intestine
  • large intestine (cecum, appendix, ascending colon)
  • right half to 2/3 of transverse colon

Hindgut:

  • 1/3 left transverse colon
  • descending colon
  • sigmoid colon
  • rectum
  • upper part of anal canal
  • epithelium of urinary bladder and urethra
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8
Q

Development of foregut derivatives: Septum transversum

A

Portions of gut tube and derivatives are suspended from ventral + dorsal body wall by ventral + dorsal mesenteries (***mesodermal tissue)

  • **Septum transversum (future diaphragm):
  • formed by aggregation of ***mesenchyme tissue that develops within caudal part of ventral mesentery of foregut
  • between
  • -> Primitive thoracic cavity
  • -> Abdominal cavities
  • contributes to formation of **CT in liver and **central tendon of diaphragm
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9
Q

Esophagus formation

A
  • ***Respiratory diverticulum (lung bud) at ventral wall of foregut (4 weeks)
  • -> ***Tracheoesophageal septum partitions diverticulum from dorsal foregut
  • -> esophagus grows in length to keep up with descent of heart and lungs

Foregut:

  • -> ventral: trachea, lung buds
  • -> dorsal: esophagus
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10
Q

Stomach formation

A
  • Dorsal wall grows faster than ventral wall
  • -> greater and lesser curvatures
  • stomach rotates 90o clockwise (around longitudinal axis)
  • -> ***left side face anteriorly
  • -> **left vagus nerve –> innervates **anterior wall (vice versa)
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11
Q

Omental bursa / Lesser sac formation

A

Stomach attached to dorsal abdominal wall by ***dorsal mesogastrium (mesentery) (vice versa)

  • -> rotation around longtudinal axis
  • -> pull dorsal mesogastrium to the left (vice versa)
  • -> formation of Omental bursa / Lesser sac (pouch of peritoneal cavity / potential space behind stomach)

5th week:
Spleen primordium appears as ***Mesodermal proliferation between 2 leaves of dorsal mesogastrium

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12
Q

Congenital malformations of stomach

A

Pyloric stenosis:
- one of most common abnormalities in newborn

  • Circular (mainly) + Longitudinal musculature of stomach in pylorus enlarges (hypertrophy)
  • -> extreme narrowing of pyloric lumen
  • -> obstruct passage of food
  • -> severe projectile vomiting
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13
Q

Duodenum formation

A
  • forms at junction of foregut and midgut
  • as stomach rotates, duodenum takes on form of ***C-shaped (anterior) loop and rotates to the right
  • duodenum rotation + pancreas growth
  • -> swings duodenum from midline position to the right and lie against dorsal wall
  • **dorsal mesoduodenum (mesentery) fuses with back body wall leaving main portion of duodenum in retroperitoneal position (only anterior covered with mesentery) —> **secondarily extraperitoneal
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14
Q

Liver and gallbladder formation

A

Liver, Biliary system, Pancreas:
appear as outgrowth of **endodermal epithelium at **distal foregut (4th week)

  • connection between liver bud and duodenum narrows
  • -> forming bile duct
  • -> give rise to gallbladder and cystic duct

Formation of liver:
Liver bud grows and penetrates ventrally from duodenum into septum transversum (plate between pericardial cavity and yolk stalk)
–> invade entire **septum transversum
–> portion of septum transversum / mesentery between **liver and foregut / stomach
–> becomes membranous
–> ***Lesser omentum

  • -> portion of septum transversum / mesentery between ***liver and ventral abdominal wall
  • -> becomes membranous
  • -> ***Falciform ligament
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15
Q

Pancreas formation

A

Outgrowth of dorsal + ventral endodermal lining of duodenum
–> Dorsal + Ventral pancreatic anlage

Rotation of duodenum

  • -> ventral anlage moves dorsally
  • -> lie below and behind dorsal anlage
  • **fusion of ducts from dorsal, ventral anlagen
  • -> formation of ***Main pancreatic duct
  • -> enter duodenum together with bile duct at site of ***major duodenal papilla

original duct of dorsal anlage

  • -> ***accessory pancreatic duct
  • -> exit at ***minor papilla

dorsal anlage –> body and tail of pancreas

ventral anlage –> head and uncinate process

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16
Q

Pancreatic divisum

A
  • most common congenital anomaly of pancreas
  • failure of fusion of dorsal and ventral pancreatic anlages
  • -> drainage of fluid from **main pancreatic duct via **minor papilla
17
Q

Rotation of midgut (6-8th week)

A
  • rapid elongation of midgut and mesentery –> formation of ventral U-shaped midgut loop
  • ***Superior mesenteric artery forms axis of rotation (dorsoventral axis 穿向前) and herniates into umbilical cord (physiological umbilical herniation)
  • U-shape mid gut loop rotate ***90o anticlockwise
  • -> ***Small intestine loop (jejnum, ileum) become on the right
  • -> ***Cecal diverticulum become on the left (primordium of cecum and appendix)
  • Yolk stalk / Vitelline duct attached to apex of midgut loop where two limbs join (small intestine loop, cecal diverticulum)
18
Q

Rotation of midgut (10th week)

A

Abdominal cavity larger: midgut return into abdominal cavity (sequential manner)

  • small intestine loop first
  • then cecal diverticulum

Midgut loop further rotate ***180o anticlockwise

  • -> small intestine loop now on the left (lower left)
  • -> cecal diverticulum now on right (upper right)
  • Displacement of cecum and appendix caudally (向下)
  • -> places them in right lower quadrant
  • -> ascending colon on right

Both ascending colon and descending colon back mesenteries fuse with back wall –> Retroperitoneal

19
Q

Gut rotation defects

A

Rotate 90o anticlockwise **without further 180o rotation
–> **left and right reverse

Rotate 90o **clockwise (in 1st rotation) (with subsequent 180o rotation)
–> Duodenum **in front of transverse colon

–> may result in twisting of bowel (volvulus) and compromise blood supply

20
Q

Omphalocele

A
  • Failure of herniated gut to return to abdominal cavity
  • herniated gut covered by amnion
  • associated with other malformations e.g. heart / neural tube defects / chromosomal abnormalities
21
Q

Remnants of vitelline duct

A
  • Vitelline duct regresses between 5-8th week and later obliterates into ***fibrous cord and degenerate completely
  • -> ***Umbilicus

Not degenerate completely:

  • ***Meckel’s diverticulum (outpouch at ileum)
  • Vitelline cyst
  • Vitelline fistula (remain patent)
22
Q

Cecum and appendix development

A

midgut: cecal diverticulum
- -> cecal bud
- -> cecum + appendix (posterior to cecum)

23
Q

Development of hindgut

A

Partitioning of cloaca (by ***Urorectal septum —> Mesoderm)
- separate region between Allantois and Hindgut

  • -> anterior: Urogenital sinus
  • -> posterior: Anorectal canal
  • Hindgut enter posterior region of cloaca –> future anorectal canal
  • Allantois enter anterior region –> future urogenital sinus

Primitive urogenital sinus –> bladder, pelvic urethra, definitive urogenital sinus

24
Q

Anal canal

A
  • upper 2/3 of anal canal from endoderm of hindgut

Invagination of ectoderm in region of Proctodeum
–> lower 1/3 of anal canal + anal pit

  • degeneration of anal membrane (cloacal membrane)
  • -> establish continuity between upper and lower anal canals
  • -> leftovers: ***Pectinate line
25
Q

Congenital hindgut malformations

A
  • **Imperforate anus: failure of cloacal membrane to break down
  • -> rectum cannot connect with anus

Imperforate anus with rectal atresia

  • -> urorectal septum cannot separate allantois and hindgut
  • -> ***urorectal fistula (rectum connect with urethra)

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