Anatomy - GI Development Flashcards by Anna Farrell

During week 4, the primitive gut tube is incorporated into embryo with

embryonic folding

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The gut tube forms from

dorsal (upper) portion of the endoderm lined yolk sac

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Longitudinal folding results in a

blind tube forming at the cranial and caudal ends
- foregut and hindgut

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As folding progresses, opening of gut tube into the yolk sac narrows to form the

vitelline (yolk) stalk/duct

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the vitelline (yolk) duct will do what prior to birth

degenerate

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Deep depressions start to form in the surface of the ectoderm, what are the cranial and caudal ends called

cranial end - stomodeum
caudal end - proctodeum

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Bilayered membranes at the stomodeum and proctodeum

cranial end - oropharyngeal membrane
caudal end - cloacal membrane

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the gut tube is lined with

endoderm

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the gut tube extends from

the oropharyngeal membrane to the cloacal membrane

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what ruptures early in week 4?

oropharyngeal membrane

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what contributes to forming the muscular and connective tissue components of the gut

splanchnic mesoderm

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what are the exceptions to the regions that are supplied by the celiac trunk

pharynx, respiratory tract, thoracic esophagus

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what makes up the ventral mesentery

lesser omentum
falciform ligament

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what makes up the dorsal mesentery

greater omentum
mesentery proper
transverse mesocolon
sigmoid mesocolon

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what gives rise to the stomach in week 4

the caudal foregut

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what does the stomach do in week 4

enlarges and rotates 90 degrees CLOCKWISE around a longitudinal axis

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original dorsal surface and original ventral surface of the stomach becomes what surfaces

dorsal = left
ventral = right

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what portion of the stomach grows fastest

dorsal portion grows faster than the ventral portion

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which directions do the caudal and cephalic portions move

caudal = upward
cephalic = downward

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due to the 90 degree clockwise rotation, what do the vagus nerves become?

left vagus nerve - anterior vagal trunk
right vagus nerve - posterior vagal trunk

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Stomach is suspended from the dorsal wall by _______ and from ventral wall by _________

dorsal mesentery (mesogastrium)
ventral mesentery (mesogastrium)

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the dorsal mesogastrium is carried to the ______ side of the peritoneal cavity

left side

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the dorsal mesogastrium forms the

greater omentum

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the ventral mesogastrium is carried to the _____ side the peritoneal cavity

right side

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the ventral mesogastrium forms the

lesser omentum and falciform ligament

Left side of the peritoneal cavity is stretched to form the _________

greater peritoneal sac

Right side of the peritoneal cavity is pushed behind the stomach/lesser omentum to form the ___________

lesser peritoneal sac

Spleen is not derived from the ?

gut tube

when does development of the primordial spleen begin

week 5

what does development of the primordial spleen appear as

mesodermal proliferation

what does the primordial spleen develop between

layers of dorsal mesogastriun

Duodenum is derived from the _____ and ________

caudal foregut and cranial midgut

What is the dual blood supply of the duodenum

celiac trunk - foregut SMA - midfut

what is the dual sympathetic innervation of the duodenum

greater splanchnic - foregut lesser splanchnic - midgut

regarding the duodenum, the two segments grow rapidly, forming a C-shaped loop that projects ________ toward the umbilical cord

ventrally

Rotation of the ________ rotates the duodenal loop __________

stomach clockwise 90°

regarding the duodenum, the initially ventrally projecting C-shaped loop is now projecting on the _____- side of body

right

Reduction of the _______ will push duodenum into a ______________ position

midgut secondarily retroperitoneal

After reduction of the midgut, what happens to the dorsal mesoduodenum and the duodenum ?

Dorsal mesoduodenum is absorbed, remains attached to a portion of the 1st part of the duodenum, remains INTRAPERITONEAL The duodenum (all of the 2nd, 3rd, and 4th portions become fixed; retroperitoneal)

During weeks 5-6, duodenum lumen becomes

progressively smaller

during weeks 5-6 of duodenum formation, the duodenal epithelium is _________ and ________ the lumen

proliferating occluding

during weeks 8-9 of duodenum formation, ________ occurs and what degenerates?

recanalization occurs occlusion is breaking down as epithelial cells degenerate

what 2 things happen if recanalization is incomplete or fails to occur?

duodenal stenosis duodenal atresia

lumen is narrowed due to failed recanalization

duodenal stenosis

lumen is occluded due to failed recanalization

duodenal atresia

what is associated with in-utero polyhydramnios due to low intestinal reabsorption of amniotic fluid

duodenal atresia

what 2 endodermal foregut outgrowths does the pancreas develop as

dorsal and ventral pancreatic bud

dorsal pancreatic bud grows between

dorsal mesentery

dorsal pancreatic bud is connected to the foregut by a

dorsal pancreatic duct

the ventral pancreatic bud grows between

ventral mesentery

ventral pancreatic bud is connected to foregut by a

ventral pancreatic duct

Stomach/duodenum rotation carries the ___________ posteriorly to dorsal bud

ventral pancreatic bud

the ventral and dorsal pancreatic buds fuse into single pancreas during

week 6

the ventral bud contributes to the

inferior portion of head uncinate process

the dorsal bud contributes to the

superior portion of head, neck, body, and tail of pancreas

what forms the main pancreatic duct

distal part of dorsal pancreatic duct entire ventral pancreatic duct

what forms the accessory pancreatic duct

proximal part of the dorsal pancreatic duct

Rotation of the _____________- places pancreas into a posterior position

stomach/duodenum

Reduction of the midgut will push pancreas into a

secondarily retroperitoneal position

what occurs when components of the ventral pancreatic bud fail to fuse and rotate around the duodenum

annular pancreas

during the middle of week 3: the liver, gallbladder, and biliary duct system develop from the

hepatic diverticulum (ventral endodermal outgrowth) cranial and caudal portions of the outgrowth

Larger cranial portion develops into the liver --> it grows rapidly during weeks __ to __ and fills most of the _______

weeks 5 to 10 fills most of the abdomen

By week 10, the liver is approximately _____ of the total embryonic weight

10%

hematopoiesis begins in week

bile production begins in week

by birth the liver is only ____ of total body weight

the larger cranial portion develops into the liver and grows between the

ventral mesogastrium layers

what 2 parts does the ventral mesogastrium layers divide into

lesser omentum component falciform ligament component

Portion of liver in contact with the ___________- becomes the bare area of the liver

septum transversum

Smaller caudal portion of the hepatic diverticulum develops into the ______ and _______

gallbladder cystic duct

Connection between hepatic diverticulum and gut tube narrows forming the

common bile duct

the midgut is supplied by the

SMA

In a 5-week embryo, midgut openly communicates with the _______ via the _______

yolk sac yolk stalk (vitelline duct)

what reduces the communication to the yolk stalk to a narrow yolk stalk (vitelline duct) and it is lost when?

embryonic folding by birth

Midgut forms a ventral U-shaped loop around the _____ 90 degrees _____

axis of the SMA, counter-clockwise

Dorsal mesentery attaches the midgut to the

posterior body wall

Midgut loop herniates into the

primitive umbilical cord space

when does physiological umbilical herniation occur

between weeks 6 and 10

physiological umbilical herniation --> midgut limbs (loops) --> what are the 2 called?

cranial and caudal limb

the cranial limb develops into the

small intestine (distal duodenum, jejunum, more proximal ileum)

the caudal limb develops into the

distal ileum, cecum, ascending, and proximal 2/3rds of transverse colon

Midgut ends rotation with the cranial limb on the _____ side of abdominal cavity

right

Midgut ends rotation with the caudal limb on the _____ side of abdominal cavity

left

Cranial limb grows rapidly forming many

intestinal loops

when does reduction of the midgut hernia occur

during week 10

reduction of the midgut hernia causes intestines to return to

embryonic body

reduction of the midgut occurs because of which 3 reasons

Expansion in the size of peritoneal cavity Decrease in relative size of the liver Regression of mesonephric kidneys

The midgut rotates another 180° counter-clockwise around the

SMA

after the midgut rotates another 180 degrees counter-clockwise around the SMA, _______ is the first to re-enter abdominal cavity

the cranial limb

_____ is the last part to enter and settles in the right upper quadrant

Cecal bud (adult cecum)

what will the cecal bud (adult cecum) descend into eventually

right iliac fossa

The distal end of the cecal bud forms a _____ at week ___

small diverticulum or pouch that will be the appendix week 8

Inferior portion of anal canal develops from

ectoderm

Expanded caudal portion of the hindgut is called the

cloaca (‘sewer’)

the cloaca is lined with

endoderm

the cloaca receives

embryonic urinary and digestive products

Cloacal membrane lies at the _____ boundary of the cloaca

ventral

cloacal membrane boundary composed of endoderm of ______ and ectoderm around the ______

hindgut proctodeum

Cloaca is partitioned by the _____

urorectal septum (layer of mesoderm)

ventral derivative - urogenital sinus what components?

urinary system (bladder/urethra)

dorsal derivative - anorectal canal what components?

anorectal canal (rectum and superior anal canal)

as the embryo grows and folds, the urorectal septum reaches the

cloacal membrane

the cloacal membrane divides into

urogenital membrane (more anterior) anal membrane (more posterior)

Ectoderm around the proctodeum starts to proliferate and invaginates to form the ____

anal pit

During week 7, the anal membrane ruptures, bringing what into communication with each other?

the lower anal canal into communication with the upper (superior) anal canal

What marks the transition in germ layer, blood supply/drainage, innervation, and lymphatic drainage

pectinate line

Absence of parasympathetic ganglia in the intestine wall due to a failure of neural crest cell migration leads to what disease?

Hirschsprung’s Disease (congenital megacolon)