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Histology / Embryology Unit 3 > Development of the Digestive System > Flashcards

Development of the Digestive System Flashcards

1
Q

What does the foregut give rise to in the thorax?

A

pharynx, larynx, trachea, lungs, and esophagus

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2
Q

What does the foregut give rise to in the abdominal cavity? What artery supplies it?

A

stomach, proximal half of duodenum (up to entrance of bile duct), liver, gallbladder, bile & hepatic duct system, pancreas, and spleen

Blood supply: Celiac artery only

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3
Q

What does the midgut give rise to and what artery supplies it?

A

Distal half of duodenum (past pile duct), jejunum ileum, cecum & appendix, ascending colon, and proximal 2/3 of transverse colon

All supplied by superior mesenteric artery

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4
Q

What does the hindgut give rise to and what artery supplies it?

A

Distal 1/3 of transverse colon, descending colon, sigmoid colon, and rectum up to the pectinate line. It also gives rise to urinary bladder and urethra.

Blood: Inferior mesenteric artery

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5
Q

What is the primary control over which division of the primordial gut develops where?

A

Retinoic acid gradient released by visceral mesoderm, increasing in concentration from oropharyngeal membrane to cloacal membrane.

This riggers regional expression of specific transcription factors within the endoderm.

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6
Q

What is the reciprocal control of gut differentiation?

A

Endoderm which has been induced to make transcription factors also produces sonic hedgehog, which induces expression of nested HOX genes within neighboring mesoderm

HOX gene expression within mesoderm is the final determinant of development

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7
Q

What does the endoderm become in the GI tract?

A

epithelium and glands

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8
Q

What does splanchnic mesoderm give rise to in the GI tract?

A

Lamina propria, muscularis mucosae, submucosa, blood vessels, lymphatics, and adventitia (visceral peritoneum)

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9
Q

What does the somatic mesoderm give rise to?

A

Musculature and skeletal components of body wall, has nothing to do with gut tube. Lines abdominal and pelvic cavities with parietal peritoneum

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10
Q

What do neural crest cells give rise to in the GI tract?

A

submucosal and myenteric nervous plexus

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11
Q

What is the dorsal mesentery / where does it form? What is at its base? What is special about early on?

A

It is the structure which suspends the primordial gut off the body wall inferior to the thoracic diaphragm, and is derived by splanchnic mesoderm. Within it, there are blood vessels, lymphatics, connective tissues, and autonomic input.

The descending aorta is positioned at its base.

Early on in development, EVERYTHING is peritoneal.

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12
Q

What are the four divisions of the dorsal mesentery? What do they contain?

A
  1. Dorsal mesogastrium - celiac artery
  2. Dorsal mesoduodenum - suspends duodenum
  3. Mesentery proper - all SMA derivatives
  4. Dorsal mesocolon - all IMA derivatives
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13
Q

What structures other than the stomach does the dorsal mesogastrium give rise to?

A

Dorsal pancreas and spleen, gastrosplenic and splenorenal ligaments. Also greater omentum

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14
Q

What is the ventral mesentery? Where is it attached to the anterior body wall?

A

Double-layered mesothelium that is derived from septum transversum of developing thoracic diaphragm. It is shorter than the dorsal mesentery and suspends esophagus, stomach, and 1/2 duodenum as they develop.

Attachment: Diaphragm to umbilicus

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15
Q

What ligaments does the ventral mesentery give rise to?

A
  1. Lesser omentum - between liver and stomach
  2. Falciform ligament - Between ventral surface of liver and anterior abdominal wall
  3. Coronary and triangular ligaments - suspend liver off inferior surface of thoracic diaphragm
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16
Q

What gives rise to the posterior mediastinum?

A

The esophagus as it elongates behind pleural and pericardial cavities, and it is invested by connective tissues from splanchnic mesoderm. Will contain trachea, right + left vagal nerves, roots of lungs, esophagus, and phrenic nerves

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17
Q

What creates the esophageal opening of the adult thoracic diaphragm?

A

When the esophagus is approached by the pleuroperitoneal folds and the septum transversum

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18
Q

What is the first developmental shift of the stomach?

A

Since it is attached by dorsal and ventral mesogastrium, it is flanked by right and left vagal trunks.

First shift: Rotates 90 degrees clockwise about its longitudinal axis (From cranial view). This includes distal half of esophagus + proximal duodenum.

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19
Q

What happens from the first rotation of the stomach?

A

Left side of stomach becomes ventral surface, with left vagal trunk.

Right side becomes dorsal surface, with right vagal trunk.

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20
Q

What forms the greater and lesser curvature of the stomach?

A

Prior to the 90 degree rotation, the dorsal surface of the developing stomach grows faster than the ventral surface. Thus, with 90 degrees rotation, the right surface becomes the lesser curvature, and the left surface becomes the greater curvature.

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21
Q

What is the second rotation of the stomach?

A

55-60 degree rotation along its anterior/posterior axis, causing distal end of stomach to move upward and right, and cardiac portion of stomach to be displaced slightly downward and to the left.

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22
Q

What are the regional transcription factors for GI development?

A 
Respiratory - TBX4
Esophagus + stomach - SOX
Duodenum - PDX1
Jejunum and ileum - CDXC
Large intestine + rectum - CDXA
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23
Q

What is the space between the dorsal mesogastrium and the dorsal surface of the stomach?

A

The omental bursa, i.e. the lesser sac of the peritoneal cavity. Forms greater omentum

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24
Q

What happens to dorsal mesogastrium that comes in contact with the parietal peritoneum of the body wall?

A

They fuse together. The posterior sheet will degenerate, leaving only the anterior sheet of dorsal mesogastrium covering the posterior abdominal wall

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25
Q

What causes the duodenum to become related to the posterior abdominal wall? What structure does the ventral mesoduodenum give rise to?

A

Rotation of stomach via rotation of primary intestinal loop. Duodenum gives rise to hepatic diverticulum

Stomach + intestinal turning gives rise to C-shape of duodenum

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26
Q

What is the hepatic diverticulum and what induces it? What side does it originally start?

A

Bud which gives rise to liver, hepatic / bile system, gall bladder + cystic duct, and ventral pancreatic bud. It forms off of mid-duodenum, induced by release of local fibroblast growth factors (FGF) from cardiac mesoderm early on

Starts on ventral side of duodenum before clockwise stomach rotation allows bile duct on the inferior right side of the duodenum

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27
Q

What forms the liver parenchyma(Germ layer + where)?

A

Endoderm in the foregut region of future mid-duodenum branching from hepatic diverticulum.

Liver hepatocytes proliferate within the right septum transversum.

28
Q

What forms liver sinusoids?

A

Intermingling of vitelline and umbilical veins

29
Q

What part of the liver is actually formed by the mesoderm of the septum transversum?

A

Hematopoietic cells, Kupffer cells, and connective tissues in the liver.

30
Q

What forms the anterior and posterior coronary ligaments?

A

Mesoderm from septum transversum which makes the visceral peritoneum covering the anterior, posterior, and inferior surfaces of the developing liver (does not include bare area which is directly attached to diaphragm

31
Q

What are the two subdivisions of the ventral mesogastrium after the liver enlarges?

A
  1. Falciform ligament

2. Lesser omentum

32
Q

What does the ventral pancreatic bud give rise to?

A

Off of the hepatic diverticulum within the confines of the ventral mesoduodenum, it gives rise to main pancreatic duct, uncinate process, and dorsal half of head of the pancreas.

33
Q

What bud forms in the dorsal mesoduodenum and what does it give rise to?

A

The dorsal pancreatic bud. Gives rise to ventral half of pancreatic head, the body and tail of pancreas, and the accessory pancreatic duct.

34
Q

What happens to the two pancreas segments on rotation?

A

They both become positioned on the medial surface of the duodenum, where they fuse and the accessory pancreatic duct degenerates. It only remains functional in about 10% of people.

35
Q

What causes most of pancreas and duodenum to be retroperitoneal?

A

Rapid growth of overlying colon and rotation of intestinal loop

36
Q

What gives rise to the spleen and what holds it off the posterior body wall to keep it peritoneal?

A

It is formed by mesenchymal cells located between the two mesothelial layers of the dorsal mesogastrium (mesoderm derived).

It is held off the posterior abdominal wall by the splenorenal ligament, and attached to the stomach by the gastrosplenic ligament.

37
Q

What forms the primary intestinal loop, and what is at its center dorsally and ventrally?

A

Rapidly growing midgut

Dorsally: centered around superior mesenteric artery + mesentery off posterior abdominal wall
Ventrally: Vitelline duct which extends to the yolk sac, located in the extraembryonic cavity of the umbilical cord on anterior abdominal wall

38
Q

What causes the first rotation of the intestinal loop and what is this turn about its axis around the vitelline duct?

A

Causes by rapid growth of portion of midgut between distal half of duodenum and vitelline duct (the anterior half of the loop)

It rotates 180 degrees counterclockwise about its front axis, making the cecal bud and transverse colon ventral to the developing duodenum.

39
Q

What happens in the final 90 degrees of rotation for the intestinal loop?

A

From the accelerated growth of jejunum and ileum, it rotates to a total of 270 degrees so the cecal bud lies to the right side underneath the developing liver.

40
Q

What happens to the yolk sac?

A

It remains in direct communication to the midgut via the vitelline duct, and becomes incorporated in the serous-lined sac of the extraembryonic cavity, continuous with umbilical vessels

41
Q

What is the physiological herniation?

A

When the jejunum and ileum is extruded into extraembryonic cavity of umbilical cord in order to accommodate the rapid growth of the intestines which cannot be held by the abdominal cavity.

42
Q

When does the physiological herniation start to retract, and what is the pattern? What is the last part to re-enter the abdominal cavity?

A

Starts right after the 270 degree rotation completes. Starts with proximal jejunum and coils from left to right in a repeated fashion from proximal to distal. Last part to re-enter in the cecal bud, which defines the proximal part of the large intestine

43
Q

How are the ascending colon and appendix formed?

A

After cecum is located in the RUQ following the physiological herniation, the ascending colon is displaced inferiorly and forms the narrow diverticulum called the appendix during the descent

44
Q

What are the hepatic and splenic flexures, respectively, and what structure remains intact in between?

A

Hepatic flexure: transition from retroperitoneal ascending colon to intraperitoneal transverse colon
Splenic flexure: transition from intraperitoneal transverse colon to retroperitoneal descending colon

Transverse mesocolon remains intact in between these two, as it is unaffected by the 270 degree rotation.

45
Q

What does the peritoneum of the transverse mesocolon fuse with?

A

The superior surface of the transverse mesocolon fuses with the inferior / horizontal surface of the greater omentum

46
Q

Are the cecum and appendix intraperitoneal or retroperitoneal?

A

Intraperitoneal - they maintain their corresponding mesenteries

47
Q

Why are the ascending and descending colons retroperitoneal?

A

Their dorsal mesentery fuses with the peritoneum of the posterior abdominal wall

48
Q

What is the urorectal septum?

A

It is visceral mesodermal connective tissue between the two parts of the cloaca which separates the developing urogenital system from the rectum, which is retroperitoneal

49
Q

What is the cloaca and its two parts?

A

The enlarged region at the terminal end of the hindgut. Anterior part: Forms urogenital system, where the allantois enters the cloaca
Posterior part: Forms the future anal opening

50
Q

What is the cloacal membrane? What does it form?

A

The membrane formed on the inside by the endothelium of the hindgut, and on the outside by the ectoderm. Forms the proctodeum (primitive anal canal, opposite of stomodeum)

51
Q

What happens when the urorectal system fuses with cloacal membrane?

A

The urogenital tract and alimentary tracts are finally partitioned. The cloaca membrane is subdivided into anterior urogenital membrane and posterior anal membrane.

52
Q

What forms the perineal body?

A

The part of the urorectal septum which comes in content with the cloacal membrane, between the urogenital membrane and posterior anal membrane.

53
Q

What happens when the urogenital and anal membranes rupture?

A

The anal opening for the hindgut and the opening to the urogenital sinus are made.

54
Q

What is the pectinate line and what forms it above and below?

A

Pectinate line divides the upper 2/3 of the anal canal from the lower 1/3.

Upper 2/3: Derived from endoderm of hindgut
Lower 1/3: Derived from ectoderm of proctodeum

Upper gets superior + middle rectal arteries
Lower gets inferior rectal arteries

55
Q

What is the difference in sensation above and below the pectinate line?

A

Above pectinate line is still gut derived, so it can only sense distension and pressure

Below pectinate line is ectoderm, below which you can feel touch, temperate, and pain

56
Q

Why can atresia occur in the alimentary tract?

A

As the endoderm of the gut tube grows, the lumen is filled with cells. It must be recanalized via apoptosis. If this fails anywhere, you will have an atresia (blockage of this region of digestive tube).

57
Q

What is an omphalocele?

A

Failure of small intestines and sometimes liver to return to abdominal cavity following physiological herniation. Mostly genetically related, very rate but high mortality.

58
Q

What is gastroschisis?

A

A defect in anterior abdominal wall away from the umbilical cord (usually right side) that results in abdominal viscera protruding out of the abdominal cavity and into amniotic cavity. Less serious than omphalocele.

59
Q

What is Meckel’s diverticulum and why is it called the disease of twos?

A

Incomplete degeneration of vitelline duct. Can just be leading to the umbilicus by a ligament, surrounded by two ligaments (a cyst), or a complete fistula that allows fecal discharge through the umbilicus.

Twos:
Two feet away from ileocecal junction in adults
Two inches long
2% of the population has this

60
Q

What is accessory pancreatic tissue?

A

No symptoms under normal conditions, pancreatic tissue can appear anywhere from distal end of esophagus to vitelline duct

61
Q

What is annular pancreas?

A

Ventral pancreatic bud becomes bifid, where one rotates posteriorly and one rotates anteriorly, creating a ring of pancreatic tissue around the duodenum. Can be a problem if pancreas tissue becomes inflamed and will block digestion of food.

62
Q

What happens in nonrotation of the gut?

A

When midgut does not rotate when it re-enters the abdomen following physiologic herniation, thus the most upper left thing that enters is the caudal end of the intestinal loop. Cecum + ileum start on top left until jejunum at bottom right up to the duodenum.

63
Q

What happens in over-rotation of the gut?

A

Midgut causes cecum to become fixed in upper right posterior abdominal wall, resulting in over-rotation of the mesentery, which can lead to strangulation or narrowing/atresia of this section of intestine

64
Q

What is the problem with reverse rotation of gut?

A

Mesentery and duodenum will actually pass overtop of the transverse colon, which can lead to atresia of the transverse colon.

65
Q

What is oddly grouped as incomplete rotation of gut?

A

Subphrenic or subhepatic cecum / appendix, as cecal bud and ascending colon are not displaced down right side of posterior abdominal wall. Asymptomatic

66
Q

What is an internal hernia?

A

When intestines twist and ultimately cause retroperitoneal structures like duodenum and pancreas to become peritoneal again (since there is a plane of fusion). Can happen from birth to old age, and may lead to blood loss / necrosis

67
Q

What is a midgut volvulus?

A

Sometimes from a reverse rotation the cecum and ascending colon will remain intraperitoneal, If the cecum twists around the transverse colon it can strangle the overlying duodenum, leading to duodenal atresia

Histology / Embryology Unit 3 (9 decks)

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