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Anatomy Exam 2 > Development of the Digestive System > Flashcards

Development of the Digestive System Flashcards

1
Q

Describe how body folding plays a role in forming the primitive gut.

A
  • body folding occurs during week 4
  • it encorporates endoderm from the dorsal portion of the yolk sac into the embryo
    • endoderm forms the inner most lining of the primative gut tube
      • epithelial lining
      • glands of the GI tract

Note: cranio-caudal folding

  • foregut forms during head fold
  • hindgut forms during tail fold
  • midgut forms during lateral folding
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2
Q

Identify components of the foregut and include the main artery that supplies this region.

A

components:

  • Pharynx
  • Lower respiratory system
  • Esophagus
  • Stomach
  • Proximal ½ of duodenum (up until just after entrance of pancreatic & bile ducts)
  • Associated organs (liver, gall bladder, biliary system, pancreas)

main artery:

  • celiac trunk a.
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3
Q

Identify the components of the midgut and include the main artery that supplies this region

A

Components:

  • Distal ½ duodenum (just after major duodenal papilla)
  • Jejunum
  • Ileum
  • Cecum & appendix
  • Ascending colon
  • Proximal 2/3 transverse colon

Main artery:

  • Superior mesenteric a. (SMA)
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4
Q

Identify the components of the hindgut and include the main artery that supplies this region

A

Components:

  • Distal 1/3 transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
  • Superior portion of anal canal

Note: rectum and superior portion of anal canal are derived from posterior portion of the cloaca after it is partitioned by the urorectal septum

Main artery:

  • Inferior mesenteric a. (IMA
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5
Q

List the contributions of endoderm to the gastrointestinal tract.

A
  • GI epithelial lining
  • GI glands
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6
Q

List the contributions of mesoderm to the gastrointestinal tract. (Include the role of mesoderm in forming peritoneum and mesenteries.)

A

splanchnic mesoderm :

  • smooth muscle and CT of GI tract
  • mesentary
  • visceral peritoneum

somatic mesoderm:

  • parietal peritoneum
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7
Q

List the contributions of neural crest to the gastrointestinal tract.

A
  • aka endoderm contribution
  • Neural crest cells migrate into walls of G.I. tract to form the enteric nervous system
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8
Q

What condition may result from the failure of neural crest cells to migrate to the walls of the GI tract? How will aganglionic segments of the bowel appear vs. normal segments?

A
  • Hirschsprung’s Disease (Aganglionic Megacolon)
    • Affects variable portions of the bowel (usually sigmoid colon and/or rectum)
    • Aganglionic portion constricts, bowel distends proximal to constriction, can lead to severe constipation / failure to thrive
  • Aganglionic segments are more constricted than normal segments
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9
Q

Describe how peritoneum and mesentery are organized in the body.

A
  • mesentery suspends organs from the body wall
  • peritoneum lines the abdominal cavity and organs
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10
Q

Define peritoneum

A
  • the serous membrane lining the abdominal cavity (parietal) & organs (visceral)
  • arises from somatic and splanchnic mesoderm
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11
Q

Define mesentery

A
  • a double-layer of peritoneum that suspends an organ from the body wall (can contain CT, blood vessels, lymphatics, nerves)
  • created by lateral folding
  • from splanchic mesoderm
  • ventral mesentery
    • reabsorbed inferior to foregut
  • dorsal mesentery
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12
Q

Describe the formation of the lower respiratory tract.

A
  • occurs in the foregut
  • Esophagus develops as the portion of the foregut immediately caudal to the pharynx
  • Week 4: a respiratory diverticulum appears on ventral side of foregut
    • becomes the trachea, respiratory tree & lungs
    • slide 23
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13
Q

Describe the growth and rotation of the stomach.

A

Growth:

  • in foregut
  • Week 4
    • A portion of foregut caudal to esophagus begins to dilate uniformly.
    • As the stomach enlarges, it’s dorsal side expands faster than the other sides
      • becomes the greater curvature.
    • The ventral face of stomach will become the lesser curvature.

Rotation:

  • Starts on day 35 ends around day 56
  • Stomach undergoes 90° clockwise rotation (if looking from superior view)
  • Ventral side (lesser curvature) ends up on the right
  • Dorsal side ends up on the left
  • Right vagus n. now supplies dorsal stomach
  • Left vagus n. now supplies ventral stomach
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14
Q

How does stomach rotation reposition the right and left vagus nerves?

A

After rotation:

  • Right vagus n. supplies dorsal stomach,
  • left vagus n. supplies ventral stomach
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15
Q

How does stomach rotation reposition the dorsal mesogastrium?

A
  • As stomach rotates, the dorsal mesogastrium is carried to the left.
  • This enlarges the omental bursa into a sizeable recess between the stomach & posterior abdominal wall.
  • Spleen forms between 2 leaves of dorsal mesogastrium (week 5)
    • spleen is carried to the left with the dorsal mesogastrium
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16
Q

What is the omental bursa?

A
  • lesser sac of peritoneum
  • becomes a sizeable recess between the stomach & posterior abdominal wall as stomach rotates
17
Q

Describe the development of the liver, gall bladder and bile ducts as diverticula of the foregut

A
  • Hepatic diverticulum emerges ventrally from endoderm of distal foregut (week 4),
  • grows superiorly toward septum transversum
  • gives rise to liver, gall bladder, and bile ducts
  • The liver, gall bladder, biliary tree, and pancreas all develop as endodermal diverticula from the distal foregut.
18
Q

How does an annular pancreas develop, and around what structure does it form?

A
  • If the 2 ventral buds of the pancrease fail to fuse prior to rotation
  • If they fail to fuse, each portion may wrap oppositely around the duodenum and fuse with the other, forming an obstructive ring.
19
Q

Explain what it means for an organ to be retroperitoneal vs. intraperitoneal.

A

Retroperitoneal: Behind the peritoneum. Organs aren’t supported by mesentery and lie between the parietal peritoneum(anterior side) and abdominal wall

Intraperitoneal: surrounded by peritoneum, within the intraperitoneal space, within the confines of the parietal peritoneum

20
Q

Be able to identify portions of the GI tract and associated organs that are retroperitoneal

A

primarily retroperitoneal:

  • Kidneys (midgut)

secondarily retroperitoneal

  • Distal duodenum (midgut)
  • Pancreas (foregut)
  • Ascending colon (midgut)
  • Descending colon (hindgut)
21
Q

What structure serves as the axis of rotation for the midgut?

A
  • Superior mesenteric artery (SMA)
22
Q

Describe normal midgut rotation

A

Normal rotation:

  • 1st rotation occurs at week 6
    • 90 degree counter clockwise rotation
    • loop is in proximal umbilical cord
  • 2nd rotation occurs at week 10
    • intestines return to abdomen
      • cranial limb returns first
      • week 11 cecum descends
    • 180 degree counter clockwise rotation
      • brings intestines to normal postion

Note: direction of rotation is assuming an anterior view and the axis of rotation is SMA

23
Q

When and why does a physiological umbilical herniation occur?

A
  • Occurs during weeks 6-10
  • Occurs because of insufficient room in the abdominal cavity
    • it’s a temporary herniation of midgut loop into the proximal umbilical cord
24
Q

Describe an omphalocoele, and explain how this condition differs from gastrochisis.

A
  • Congenital Omphalocoele
    • Persisting umbilical hernia
    • Viscera covered by amnion & within proximal umbilical cord
    • Often associated with chromosomal abnormalities and other severe malformations, so mortality rate is high (25%)
  • Gastrochisis
    • Doesn’t involve umbilical cord
    • Hernia of small intestine and occasionally other abdominal viscera through anterior body wall
      • Exposure to amniotic fluid can damage viscera
25
Q

Describe the role of recanalization in normal and abnormal gut formation.

A

Normal gut formation

  • Intestines become temporarily occluded by epithelial cells at week 6
  • Should recanalize by the end of week 8

Abnormal gut formation

  • lumen fails to recanalize by week 8
  • leads to stenosis or atresia
26
Q

Describe an ileal (Meckel’s) diverticulum

A
  • Most common GI malformation; occurs in 2-4% of the population
    • male predominance
  • A remnant of the vitelline duct persists as a finger-like outpouching of the ileum
    • ~40-60 cm from ileocecal junction
  • Diverticulum may contain pancreatic tissue/gastric mucosa that secretes acid,
    • causes ulcers & bleeding
27
Q

Describe possible remnant variations of an ileal (Meckel’s) diverticulum

A
  • Vitelline fistula
  • Vitelline cyst
  • Vitelline ligament
28
Q

How does the urorectal septum play a role in separating the urinary tract from the GI tract?

A
  • urorectal septum grows inferiorly toward the cloacal membrane (week 4)
  • divides it into urogenital and anal membranes (week 6)
  • partitions the cloaca into the urogenital sinus (ventrally) and the anorectal canal (dorsally). (week 7)

Fistulas can result if the urorectal septum fails to completely separate the hindgut from the urogenital sinus or if the cloaca is too small

This occurs during hidgut development

29
Q

What structure temporarily connects the midgut to the yolk sac (umbilical vesicle)?

A

The vitelline (omphaloenteric) duct

30
Q

Describe the development of the pancreas as diverticulum of the foregut

A
  • As stomach rotates, duodenum twists with it in a CW direction.
  • The distal duodenum and pancreas become pressed against posterior abdominal wall
    • their dorsal mesenteries fuse w/parietal peritoneum and are lost.
    • These organs are secondarily retroperitoneal.
  • Pancreas emerges from distal foregut as two endodermal buds
    • one dorsal bud
    • one ventral bud
  • As duodenum rotates, ventral bud swings with it in CW direction until aligning & fusing with dorsal bud
  • Ventral bud becomes uncinate process + inferior portion of head of pancreas
  • pancreatic ducts fuse
31
Q

Describe the pancreatic ducts

A

Main pancreatic duct : distal portion of dorsal bud duct + ventral bud duct

Accessory pancreatic duct: proximal dorsal bud duct

Note: these duct fuse as the pancreas forms

32
Q

Be able to identify portions of the GI tract and associated organs that are intraperitoneal.

A
  • Stomach (foregut)
  • Proximal duodenum (foregut)
  • Jejunum (midgut)
  • Ileum (midgut)
  • Transverse colon (midgut/hindgut)
  • Sigmoid colon (hidgut)
33
Q

Describe nonrotation and reversed rotation of the midgut.

A

Nonrotation

  • Normal first midgut rotation no second midgut rotation
  • Caudal limb returns first and occupies the left side of abdominal cavity,
    • results in a left-sided colon

Reversed rotation

  • Normal first rotation, reversed second rotation (180 CW instead of CCW)
  • Net rotation is 90 ° CW
    • midgut & hindgut in normal positions
    • except duodenum is ventral to TVC (doesn’t become retroperitoneal)

Note: Abnormal rotation may cause intestinal loop to twist around mesenteric attachment site. Can result in bowel obstruction/compromised blood flow leading to stenosis/atresia/ischemia/necrosis

34
Q

Define stenosis

A
  • the abnormal narrowing of a lumen/orifice (tubular organ or structure)
  • poor vacuoles, narrow lumen

Possible Causes: failure to recanalize following a temporary epithelial plug, adequate blood supply fails to develop, accidents that compromise blood flow, mechanical obstruction

35
Q

Define atresia

A
  • the condition in which a body lumen or orifice is abnormally closed or absent
  • no vacuoles, no lumen

Possible Causes: failure to recanalize following a temporary epithelial plug, adequate blood supply fails to develop, accidents that compromise blood flow, mechanical obstruction

36
Q

Describe the arterial supply to gut regions

A
  • Pharynx: Pharyngeal arch aa.
  • Foregut: Celiac trunk (a.)
  • Midgut: Superior mesenteric a. (SMA)
  • Hindgut: Inferior mesenteric a. (IMA)
37
Q

Describe midgut development

A
  • forms a U shape
  • vitelline duct
  • physiological umbilical herniation
  • midgut rotation
38
Q

Define fistula

A
  • an abnormal passageway between two organs/vessels or between an organ and the external environment

Anatomy Exam 2 (13 decks)

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