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Embryology > Lect. 4: GI System > Flashcards

Lect. 4: GI System Flashcards

1
Q

What is the blood supply to the foregut?

A

celiac trunk

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2
Q

What is the blood supply to the midgut?

A

superior mesenteric artery

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3
Q

What is the blood supply to the hindgut?

A

inferior mesenteric artery

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4
Q

What provides parasympathetic innervation to the foregut?

A

vagus nerve

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5
Q

What provides parasympathetic innervation to the midgut?

A

vagus nerve

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6
Q

What provides parasympathetic innervation to the hindgut?

A

pelvic splanchnic nerves (S2-S4)

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7
Q

What provides sympathetic innervation to the foregut?

A

Preganglionics: greater thoracic splanchnic (T5-T9)
Postganglionics: celiac and superior mesenteric ganglia

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8
Q

What provides sympathetic innervation to the midgut?

A

Preganglionics: lesser thoracic splanchnic (T10-11)
Postganglionics: celiac and superior mesenteric ganglia

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9
Q

What provides sympathetic innervation to the hindgut?

A

Preganglionics: lumbar splanchnics (L1-L2)
Postganglionics: inferior mesenteric ganglia

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10
Q

What are the adult derivatives of the foregut (primitive gut tube)?

A

1) pharynx
2) esophagus
3) stomach
4) 1st and 2nd parts of duodenum
5) liver
6) pancreas
7) biliary apparatus
8) gallbladder

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11
Q

What are the adult derivatives of the midgut (primitive gut tube)?

A

1) 2nd, 3rd, and 4th part of duodenum
2) jejunum
3) ileum
4) cecum
5) appendix
6) ascending colon
7) transverse colon (proximal 2/3)

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12
Q

What are the adult derivatives of the hindgut (primitive gut tube)?

A

1) transverse colon (distal 1/3) to splenic flexure
2) descending colon
3) sigmoid colon
4) rectum
5) anal canal (above pectinate line)

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13
Q

The primitive gut tube is made of what primary germ layer?

A

endoderm (inner wall of gut tube)

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14
Q

What marks the transition between the foregut and midgut?

A

ampulla of Vater

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15
Q

What marks the transition between the midgut and the hindgut?

A

splenic flexure

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16
Q

Where do the lateral body folds fuse?

A

ventral midline (at linea alba)

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17
Q

Is the amniotic cavity dorsal or ventral on the week 4 embryo?

A

dorsal

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18
Q

Is the yolk sac dorsal or ventral on the week 4 embryo?

A

ventral

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19
Q

What is pulled into the body of the embryo to form the gut tube? What lines this?

A

part of the endoderm-lined yolk sac is pulled into the body of the embryo forming the gut tube

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20
Q

What is the name of the closed captured space that surrounds the gut tube?

A

coelom (forerunner of cavities)

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21
Q

What are the future divisions of the coelum?

A

1) pleural cavity
2) pericardial cavity
3) peritoneal cavity

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22
Q

What is the consequence of head to tail body folding in the development of the gut tube?

A

folding at the head and tail makes posterior recess and anterior recess that divide the gut tube into its 3 parts: foregut, midgut, and hindgut

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23
Q

What maintains a connection between the yolk sac and midgut?

A

vitelline duct

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24
Q

How long does the connection exist between the yolk sac and the midgut?

A

around the 9th-10th week, the vitelline duct closes and the gut sac gets excluded from the embryo

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25
Q

Describe the rotation of the foregut.

A

Rotates 90 degrees to the right (clockwise) along the longitudinal axis

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26
Q

Describe the characteristics of the midgut.

A

midgut is represented by gut loop (very simple structure that will grow over 20 feet)

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27
Q

Describe the rotation of the midgut.

A

Rotates 270 degrees to the left (counterclockwise)

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28
Q

What is the important landmark of the colon (dilated sac in hindgut)?

A

cloaca

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29
Q

Where does the vitelline duct extend?

A

patent diverticulum that connects midgut loop to umbilical ring/stalk

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30
Q

Describe the herniation of the midgut.

A

there is not enough room in the abdominal cavity for both the foregut and midgut, so the midgut is forced to move out of abdominal space into the connecting stalk for around 4 weeks (and 90 degrees of the 270 degree rotation occurs at this time)

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31
Q

When does the midgut retract back in?

A

at 10th week, abdominal space is large enough for the midgut to retract back in (and the rest of the rotation (180 degrees) occurs at this time)

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32
Q

Does hindgut rotate?

A

NO, it septates

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33
Q

What is the outermost, continuous, single layer of peritoneum around the body wall/periperty called?

A

parietal peritoneum

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34
Q

What is found somewhere in the course of the parietal peritoneum?

A

a reflection off the dorsal body wall and formation of visceral peritoneum

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35
Q

Other than location, what is different about parietal and visceral peritoneum?

A

visceral refections are 2-4 layers, parietal peritoneum is only 1 layer

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36
Q

What is significant about the multiple layers of visceral reflections?

A

double layered extension is conduit for arteries/nerves/veins/lymphatic extensions to come off the dorsal body wall and come into contact with viscera

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37
Q

Does the parietal peritoneum change names?

A

NO

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38
Q

Does the visceral peritoneum change names?

A

yes, named by location (ex. omenta, mesocolon, etc.)

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39
Q

What is the visceral peritoneum of the stomach?

A

omenta

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40
Q

What is the visceral peritoneum of the colon?

A

mesocolon

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41
Q

Do adults have a large coelom?

A

NO, peritoneal cavity (coelom) is not very developed in humans, in development in coelom is filled with organs and viscera, the parietal and visceral layers will become opposed (very close together)

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42
Q

What does retroperitoneal mean?

A

between parietal and inner layers of body wall (transversalis fascia, etc.) (external to parietal peritoneal)

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43
Q

What is similar about the duodenum and pancreas?

A

4 parts each, and 1 part is intra, other parts are retro
duodenum (1st part)
pancreas (tail)

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44
Q

From what primary germ layer does the spleen develop?

A

mesoderm* different, only foregut derivative that is from mesoderm and not endoderm

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45
Q

Name the retroperitoneal organs.

A 
Suprarenal glands
Aorta and IVC
Duodenum (2nd, 3rd,4th parts)
Pancreas (head, neck and body)
Ureters
Colon (ascending and descending)
Kidneys
Esophagus
Rectum
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46
Q

After body foldings, the foregut is suspended by what?

A

dorsal AND ventral embryonic mesentery** remember this

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47
Q

Mesentery wise, how are the foregut and midgut/hindgut different?

A

the midgut and hindgut only have a dorsal embryonic mesentery (ventral dissipates)

48
Q

What structures develop within the ventral mesentery?

A

liver and biliary system

49
Q

Describe the development of the liver.

A

liver buds off of the endoderm of the foregut and pushed down into ventral embryonic mesentery

50
Q

What adult structure (derived from ventral embryonic mesentery) attaches the liver to the anterior body wall?

A

falciform ligament

51
Q

What adult structure (derived from ventral embryonic mesentery) attaches the liver to the stomach?

A

Lesser omentum

52
Q

What 2 ligaments are a part of the lesser omentum?

A

1) hepatoduodenal

2) hepatogastric

53
Q

Why is the hepatoduodenal ligament significant?

A

transports the portal triad

54
Q

Describe the development of the spleen.

A

develops from mesoderm and within the dorsal embryonic mesentery

55
Q

What two adult structures are developed from dorsal embryonic mesoderm?

A

1) splenorenal ligament

2) gastrosplenic ligament

56
Q

What organ also moves into the dorsal embryonic mesoderm?

A

pancreas

57
Q

After the foregut rotates 90 degrees to the right, what occurs?

A

the liver moves to the right (with ventral mesentery) and the spleen and pancreas move to the left (with dorsal mesentery)

58
Q

Rotation of foregut splits the peritoneal cavity into what 2 parts?

A

lesser (omental bursa) and greater sacs

59
Q

What is the opening of the omental bursa?

A

epiploic foramen

60
Q

What is the greater omentum derived from?

A

dorsal embryonic mesentery (outpocketing of gastrocolic ligament)

61
Q

What are the boundaries of the omental bursa?

A
  • Ant: lesser omentum, posterior surface of stomach, gastrocolic ligament
  • Inf: transverse colon and transverse mesocolon
  • Sup: left lobe of liver
  • Post: parietal peritoneum over pancreas and left kidney
62
Q

What 3 visceral systems are developed as buds of foregut endoderm?

A

1) lung and lower respiratory tract
2) liver and biliary tract
3) pancreas

63
Q

From what part of the foregut endoderm is the lung and lower respiratory tract derived?

A

upper esophageal lining endoderm

64
Q

From what part of the foregut endoderm is the liver/pancreas derived?

A

endoderm lining of the first part of the duodenum

65
Q

What is the lower respiratory system originally (at 4th week)?

A

single anterior endodermal bud that divides into single respiratory diverticulum

66
Q

What separates the foregut from the trachea?

A

tracheoesophageal septum

67
Q

How does the respiratory tree develop from the single respiratory diverticulum?

A

goes around 12 divisions to deelop an elaborate respiratory tree (from trachea to respiratory bronchioles)

68
Q

On the timeline of lung development, what weeks are critical for survival?

A

minimally 25-28th week (before the 25th week, infant cannot survive)

69
Q

Why can infants not survive if born before the 25th week of gestation?

A

you need enough development of type 2 pneumocytes (needed for sufactant produciton)

70
Q

What is the most common of all respiratory newborn defects?

A

Tracheoesophageal (TE) fistula

71
Q

What is a TE fistula?

A

TE septum does not properly develop– upper esophagus ends in a blind sac, lower end of the esophagus hooks into the trachea (slightly above slit)

72
Q

What are the signs of a TE fistula?

A

1) esophageal atresia
2) polyhydramnios (increased volume of amniotic fluid)
3) regurgitation of milk with gagging/cyanosis after feeding
4) abdominal distention after crying
5) Reflex of gastric contents into lungs causing pneumonitis

73
Q

Why does polyhydramnios occur with TE fistula?

A

because cannot circulate via ingestion, so it builds up in amniotic cavity

74
Q

When does the pancreas develop?

A

pancreas develops in 5th and 6th weeks

75
Q

What does the pancreas develop from?

A

from endodermal buds (2 of them, ventral and dorsal sides of the gut tube) ventral bud rotates posteriorly behind the duodenum to insert underneath the dorsal bud and fuses (ducts fuse too)

76
Q

What portions of the pancreas come from the ventral bud?

A

head and uncunate process

77
Q

What portions of the pancreas come from the dorsal bud?

A

neck, body and tail

78
Q

What is annular pancreas?

A

ventral bud splits and forms a ring around the duodenum instead of rotating cleanly around. This causes a duodenal constriction.

79
Q

What is a symptom of annular pancreas?

A

polyhydramnios (build-up of amniotic fluid)

80
Q

Name the 2 connections between the GI tract and the umbilicus. What exactly do these connect?

A

1) viteline duct: connects midgut with umbilicus

2) allantois: connects cloaca (future bladder) with umbilicus

81
Q

What are the fibrous remains of the allantois called?

A

urachus (median umbilical ligament)

82
Q

When should the viteline duct close?

A

8th-10th week

83
Q

When should the allantois close?

A

around 9th-12th week (a week or 2 after the viteline duct closure)

84
Q

What happens if the viteline duct stays patent at birth?

A

vitelline fistula: leakage of digestive material (meconium)out of umbilical stump

85
Q

What happens if the allantois stays patent at birth?

A

uracheal fistula: leakage of urine out of umbilical stump

86
Q

What types of mucosa do Meckel’s Diverticulum contain?

A

gastric and pancreatic mucosa

87
Q

What is Meckel’s diverticulum?

A

a 2 inch long remnant part of the vitelline duct that is around 2 feet from the ileocecal junction that occurs in 2% of the population (and is most common GI defect)

88
Q

What is interesting about a vesicouracheal diverticulum?

A

it is a continuation of the allantois into adulthood that usually closes down, but does not close down tightly, it can push open later in life with increased pressure in the bladder due to prostate problems

89
Q

When does the 270 degree rotation of the midgut occur?

A

6th -10th week

90
Q

The midgut starts out as a simple loop around what artery?

A

superior mesenteric artery

91
Q

What are the two portions of the simple midgut loop?

A

1) cephalic limb

2) caudal limb

92
Q

What does the cephalic portion of the midgut loop form?

A

distal duodenum
jejunum
proximal ileum

93
Q

What does the caudal portion of the midgut loop form?

A

distal ileum
cecum
ascending colon
proximal 2/3 of the transverse colon

94
Q

Which portion of the loop has the most growth?

A

cephalic portion of the loop

95
Q

Describe the 4 steps of the midgut retraction.

A

1) jejunum returns first and lies to the left side of the abdomen
2) ileum follows and lies to right of abdomen
3) cecum enters last and passer to upper right quadrant and movement of cecum pulls transverse colon across upper abdomen
4) sinks to lower right quadrant, forming descending colon

96
Q

What is hypertrophic pyloric stenosis? What part of the gut does this effect?

A

narrow pyloric lumen (foregut) that does not allow proper drainage from stomach to duodenum

97
Q

What is associated with hypertrophic pyloric stenosis?

A

polyhydramnios

98
Q

What is the presentation of a patient with hypertrophic pyloric stenosis?

A

child that will take a normal feeding then experience PROJECTILE, NONbilous (clear) vomiting

99
Q

What is duodenal atresia? What part of the gut does this effect?

A

lumen of duodenum (midgut) fails to recanalize (constriction of duodenum)

100
Q

What is associated with duodenal atresia?

A

polyhydramnios

101
Q

What is the presentation of a patient with duodenal atresia?

A

distended stomach and bile-containing (streaks) vomit (because distal to bile duct)

102
Q

What is omphalocele?

A

defect of herniation, midgut gets captured in umbilical stalk and won’t come back in at 10th week. Occurs at the umbilical ring and the gut is covered by a sac of amnion

103
Q

What is gastroschisis?

A

defect in body folding (typically weakness in right fold), occurs to the side of the umbilical ring and is NOT covered by sac of amnion

104
Q

Why does omphalocele have such a high mortality rate?

A

because it is associated with other respiratory, CV, etc. problems

105
Q

What is volvulus?

A

twisting of the intestine causing an obstruction

106
Q

What is malrotation of the midgut?

A

when the normal 270 degree rotation is not complete and the cecum/appendix lie in the upper abdomen (commonly associated with volvulus)

107
Q

What must occur in the hindgut during development?

A

urorectal septum, mass of mesoderm from caudal end of dorsal body wall grows from dorsal to ventral and divides original cloaca space into ventral and dorsal side

108
Q

What is developed on the dorsal side of the urorectal septum?

A

anorectal canal (until pectinate line)

109
Q

What is developed on the ventral side of the urorectal septum?

A

urogenital sinus (with urinary bladder, lower vagina and urethra in females, and prostate gland and all of male urethra except penile urethra)

110
Q

What is the “plug” of the anorectal canal that breaks down at the pectinate line in development?

A

anal membrane

111
Q

What is an imperforate anus?

A

most common defect of hindgut due to failure of the anal membrane to properly break down (misdirected urorectal septum going slightly dorsal), so no complete opening at anal membrane

112
Q

What primary germ layer does the anal canal BELOW the pectinate line come from?

A

ectoderm

113
Q

What is colonic aganglionosis?

A

Hirschsprung Disease

114
Q

What happens in Hirschsprung Disease?

A

failure of neural crest cells to form the myenteric plexus–usually in the hindgut (so it does not have parasympathetic innervation to pelvic splanchnics)

115
Q

What are the symptoms of Hirschsprung Disease?

A

loss of peristalsis, fecal (merconium) retention, and abdominal distention of the gut proximal to the usual lesion site (at transverse colon)

116
Q

What is anal agenesis?

A

lack of anal opening as a result of improper formation of the urorectal septum (may cause rectovesical, rectovaginal, or rectourethral fistula)

Embryology (6 decks)

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