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GI 2016 > Embryology of the GI tract > Flashcards

Embryology of the GI tract Flashcards

1
Q

Formation of Intraembryonic Body Cavity

A

A. Forms within the lateral plate mesoderm; divides lateral plate mesoderm into parietal (somatic) and visceral (splanchnic) mesoderm.

a. Parietal mesoderm will form parietal serous membranes.
b. Visceral mesoderm will form visceral serous membranes and muscles/ct of organs.

B. Body folding causes fusing of body wall ventrally. This process incorporates the intraembryonic cavity fully into the embryo. However, it retains its connection to the extraembryonic cavity in the region of midgut until week 12.

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2
Q

Body wall defects

A

Body wall defects are caused when the ventral body wall fails to fuse and viscera herniate through the defect.

a. Ectopic cordis
b. Gastroschisis
c. Bladder/cloacal exstrophy
d. Cantrell’s pentology
a. Cleft sternum
b. Ectopic cordis
c. Gastroschisis
d. Diaphragmatic hernia (anterior)
e. Congenital heart defects

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3
Q

Mesenteries definition

A

Double layer of peritoneum; provide pathway for vessels, nerves to organs.

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4
Q

Dorsal Mesentery (definition and derivatives)

A
  1. Suspends gut tube to posterior body wall.
  2. Extends from caudal foregut to hindgut.
  3. Derivatives:
    a. Mesoesophagus
    b. Greater omentum (gastrocolic, gastrosplenic, gastrophrenic ligaments)
    c. Splenorenal ligament
    d. Phrenicosplenic ligament
    e. Phrenicocolic ligament
    f. Mesentery proper
    g. Mesoappendix
    h. Transverse mesocolon
    i. Sigmoid mesocolon
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5
Q

Ventral mesentery

A
  1. Suspends gut tube to anterior body wall.
  2. Extends from caudal foregut to proximal duodenum.
  3. Derivatives
    a. Lesser omentum (hepatogastric, hepatoduodenal ligaments)
    b. Falciform ligament
    c. Coronary and triangular ligaments
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6
Q

Primarily retroperitoneal

A

kidneys, ureters, bladder, etc.

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7
Q

Secondarily retroperitoneal

A

duodenum; ascending, descending colon; pancreas.

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8
Q

Peritonealized stuff

A

stomach, spleen, parts 1 and 4 of the duodenum, jejunum, ileum, transverse and sigmoid colon.

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9
Q

Partitioning of Intraembryonic Body Cavity

A

septum transversum and Pleuropericardial and pleuroperitoneal membranes

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10
Q

Septum transversum

A
  1. Plate of mesoderm which separates thoracic and peritoneal cavities.
  2. Will form bulk of diaphragm; muscle and central tendon of diaphragm.
  3. Septum transversum does not completely separate thoracic and abdominal cavities; leaves openings on either side of the foregut called pericardioperitoneal canals.
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11
Q

Pleuropericardial and pleuroperitoneal membranes

A
  1. Pleuropericardial membranes will separate pleural and pericardial cavities.
  2. Pleuroperitoneal membranes will separate pleural and peritoneal cavities.
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12
Q

4 sources contribute to formation of the diaphragm

A
  1. Septum transversum: central tendon + muscle

2. Pleuroperitoneal membranes: central tendon

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13
Q

Positional changes of diaphragm

A
  1. The muscle of the diaphragm forms from cervical somites 3-5.
  2. Differential growth of the body leads to a descent of the diaphragm into the thorax.
  3. By week 8; diaphragm is at level of 1st lumbar vertebra.
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14
Q

Motor and Sensory innervation of diaphragm

A
  1. Motor – phrenic nerve

2. Sensory – phrenic nerve to central tendon; intercostal nn to muscular diaphragm.

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15
Q

Congenital diaphragmatic hernias

A
  1. Posterolateral defect (Bochdalek hernia)

2. Parasternal hernia (Morgagni hernia)

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16
Q

Posterolateral defect (Bochdalek hernia)

A

a. Incomplete formation of pleuroperitoneal membranes; most often on left.
b. Small intestine, and/or other viscera, herniate through defect into pleural cavity.
c. The lungs and heart are compressed ; common cause of pulmonary hypoplasia.

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17
Q

Parasternal hernia (Morgagni hernia)

A

a. Anterior defect in muscular portion of diaphragm.

b. Small, sometimes not detected until child is several years old.

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18
Q

Eventration of the diaphragm

A
  1. Weakness (usually unilateral) of diaphram due to failure of myotome migration.
  2. Allows abdominal visceral to ‘‘ballon’’ into the thoracic cavity.
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19
Q

Germ layer contributions to gut

A
  1. Endoderm: epithelium and glands
  2. Mesoderm: connective tissue and smooth muscle
  3. Ectoderm: epithelium at ends of tube (mouth, lower 1/3 of anal canal)
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20
Q

The rostral and caudal ends of the gut tube are originally …

A

closed by the oropharyngeal and cloacal membranes, respectively. Rupture during 4th and 7th weeks, respectively.

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21
Q

derivatives and artery of the foregut

A

a. Pharynx (described with pharyngeal arches), esophagus, stomach, parts one and two of duodenum; liver, gallbladder and pancreas, spleen
b. Celiac artery supplies abdominal portion of foregut

22
Q

derivatives and artery of the midgut

A

a. Part three and four of duodenum, small intestine, cecum, appendix, ascending colon and proximal (right) 2/3s of transverse colon
b. Superior mesenteric artery

23
Q

derivatives and artery of hindgut

A

a. Distal 1/3 of transverse colon to upper anal canal

b. Inferior mesenteric artery

24
Q

Esophagus development

A
  1. Originally very short, but lengthens with growth of thorax.
  2. Also, lumen becomes partly obliterated during 5th week, recanalizes by week 8.
25
Q

Esophageal atresias and stenoses

A

a. Can be caused by malformation of tracheoesophageal septum.
b. Can also be caused by incomplete recanalization of distal esophagus
a. During week 5, the entire gut tube undergoes a process call canalization in which the endoderm proliferates very rapidly and produces an epithelial plug.
b. By week 8, the gut tube will recanalize.
c. If this process of recanalization is incomplete = stenosis
d. If this process of recanalization if completely absent = atresia.

26
Q

congenital hiatal hernia

A

esophagus fails to elongate, pulls stomach through diaphragm.

27
Q

Rotation of the stomach

A

a. Stomach rotates 90° clockwise around longitudinal axis. Dorsal part (greater curvature) is now to left, ventral part (lesser curvature) is now to right.
b. Stomach also rotates around its anteroposterior axis – the pyloric part moves upward and to the right; the cardiac portion moves downwards and to the left.

28
Q

Omental bursa

A

a. As the stomach rotates, it stretches the dorsal mesentery. The omental bursa comes to lie inferior and posterior to stomach.
b. During later development, the layers of the greater omentum fuse.

29
Q

Pyloric stenosis

A

– hypertrophy of smooth muscle around pyloric sphincter; present with forcible vomiting of stomach contents after eating.

30
Q

Spleen

A
  1. Forms from mesenchymal cells within the two layers of dorsal mesogastrium.
  2. Rotation of gut results in spleen being situated on left side of abdominal cavity.
31
Q

Hepatic diverticulum

A

outgrowth from second portion of duodenum.

32
Q

Development of liver

A

a. Endoderm gives rise to parenchyma; mesoderm gives rise to stroma.
b. Functions as a hematopoietic organ during 2nd month.
c. Bile formation begins during 12th week.

33
Q

Gallbladder and cystic duct development

A

a. Forms from an evagination of bile duct.

b. Because of rotation of the foregut, bile duct passes posterior to duodenum.

34
Q

Pancreas development

A
  1. Arises from two endodermal outgrowths from the duodenum (dorsal, ventral buds). Rotation of duodenum causes fusion of buds. Most of pancreas is derived from the dorsal bud; ventral bud forms lower portion of head and uncinate process.
  2. Main pancreatic duct derived from ventral pancreatic duct + distal dorsal pancreatic duct.
  3. Accessory pancreatic duct is derived from proximal part of dorsal pancreatic duct.
35
Q

accessory pancreatic tissue

A

can result from abnormal migration of tissue during gut rotation. Usually asymptomatic, but can degrade surrounding tissue.

36
Q

annular pancreas

A
  1. Bifid ventral pancreatic bud ; during rotation the bifid bud encircles the duodenum.
  2. After fusion of the pancreas, the annular tissue can constrict the duodenum.
37
Q

a result of gestational diabetes…

A

fetal insulin-secreting cells are exposed to high levels of maternal glucose. As a result, insulin-secreting cells hypertrophy and increase rate of insulin secretion.

38
Q

development of duodenum

A
  1. Arises from the caudal end of the foregut (parts 1 and 2) AND the rostral end of the midgut (parts 3 and 4); (how does this correlate to blood supply ?).
  2. As stomach rotates, it pulls the duodenum superiorly and to the right; together with the rapid growth of the pancreas, results in a C-shaped duodenum.
  3. During the 2nd month, the lumen of the duodenum is obliterated, but is recanalized shortly thereafter by apoptosis.
39
Q

duodenal stenosis

A

most often caused by failure to recanalize; mostly affects 3rd and 4th portions; digested food + bile are forcibly vomited (green-colored); distended epigastrium due to overfilled stomach. Due to fact that infant is not swallowing amnionic fluid, mother often presents with polyhydramnios.

40
Q

midgut development

A

A. Midgut remains in communication with the yolk sac via the vitelline duct until about week 10.

B. Physiological herniation occurs during week 6 as space within the abdominal cavity becomes much reduced. As a result, the gut around the superior mesenteric artery herniates though the umbilical ring into the extraembryonic cavity.

C. Midgut rotation

  1. The primary intestinal loop undergoes a rotation of 270 degrees counterclockwise.
  2. As a result of rotation, the mesentery proper becomes twisted and the ascending/descending colon become secondarily retroperitoneal.

D. Retraction of herniated loops

  1. The herniated intestinal loops return to abdominal cavity during week 10.
  2. The jejunum returns first and comes to lie on left side.
  3. The cecum returns last and lies in upper right quadrant; the cecum then descends to lie in the lower right quadrant. The appendix forms after the midgut returns to the abdomen as the cecum is descending (thus retrocecal postion).
41
Q

omphalocele

A

results from failure of midgut to return to abdominal cavity. Tissue protrudes through umbilicus and is covered by the amniotic membrane.

42
Q

gastroschisis

A

results when gut herniates through weakness in body wall; typically occurs lateral to umbilicus (to right). Usually results from incomplete fusion of ventral body wall during folding. Herniated bowel is not covered by amniotic membrane; bathed in amniotic fluid.

43
Q

Umbilical hernia

A

results when gut herniates into umbilical cord after returning to abdominal cavity. Loops of bowel herniate through an imperfectly closed umbilicus; along midline. Herniated tissue covered by skin, subcutaneous tissue.

44
Q

Meckel’s (ileal) diverticulum

A

results from a persistence of the vitelline duct. Rule of 2’s: Occurs in 2% of population; 2x more likely in males; found within distal 2 feet of ileum; usually about 2 inches long; 2% become symptomatic usually before the age of 2; 2 types of tissue (gastric, pancreatic).

45
Q

malrotation of the gut can lead to…

A

may result in volvulus and potential loss of blood supply.

46
Q

Stenoses and atresias may occur

A

anywhere along intestine resulting from vascular compromise or failure to re-canalize.

47
Q

Failure of ascending colon to become retroperitoneal results in

A

a long mesocolon which may allow for abnormal movements and potentially volvulus of the colon. Retrocolic hernia (entrapment of small intestine behind colon) may also result.

48
Q

hindgut development

A

A. Cloaca – distal most portion of gut tube; endoderm lined cavity which will contribute to formation of the hindgut and urogenital system.

B. Urorectal septum divides cloaca into urogenital sinus and anorectal canal.

C. Cloacal membrane ruptures during week 7.

D. Pectinate Line – marks division between ectoderm/endoderm.

49
Q

Hirschsprung’s disease

A

(congenital megacolon) – failure of neural crest cells to migrate into caudal large intestine or rectum; absence of parasympathetic ganglia. (–> paralyzed bowel)

50
Q

Fistulas and atresias involving the cloaca result from

A

improper formation of urorectal septum. Rectourethral and rectovaginal fistulas result from an anterior displacement of the hindgut. Rectoanal atresias result from loss of vascular supply or failure of recanalization.

51
Q

Imperforate anus

A

failure of cloacal membrane to degenerate.

GI 2016 (13 decks)

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