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Semester 3 > GI Embryology > Flashcards

GI Embryology Flashcards

1
Q

What does lateral embryonic folding in week 4 cause in the GI tract?

A

Creates a ventral body wall

Primitive gut becomes tubular

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2
Q

What does craniocaudal embryonic folding in week 4 do to the GI tract?

A

Creates cranial and caudal pockets from yolk sac endoderm beginning primitive gut development

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3
Q

Where is the opening in the gut tube at the beginning of its formation?

A

In the midgut - foregut and hindgut are blind ended diverticula

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4
Q

What is the stromatodeum?

A

Future mouth

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5
Q

What is the proctodeum?

A

Future anus

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6
Q

What is the internal lining of the gut derived from?

A

Endoderm (future epithelial linings)

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7
Q

What is the external lining of the gut derived from?

A

Slanchnic mesoderm (future musculature and visceral peritoneum)

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8
Q

How is the primitive gut tube held in place?

A

Suspended in intraembryonic coelom by a double layer of splanchnic mesoderm

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9
Q

What are the adult derivatives of the foregut?

A

Oesophagus

Stomach

Pancreas, liver and gall bladder

Duodenum (prox to entrance of bile duct)

Blood supply by celiac trunk

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10
Q

What are the adult derivatives of the midgut?

A

Duodenum (distal to entrace of bile duct)

Jejunum

Ileum

Cecum

Ascending colon

Prox 2/3 transverse colon

Blood supply by superior mesenteric artery

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11
Q

What are the adult derivatives of the hindgut?

A

Distal 1/3 transverse colon

Descending colon

Sigmoid colon

Rectum

Upper anal canal

Internal lining of bladder adn urethra

Blood supply by Inferior mesenteric artery

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12
Q

How does the arterial blood supply of the gut reflect embryonic development?

A

Each embryonic segment receives blood supply from a distinct branch of the abdominal aorta

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13
Q

What are the exceptions in the gut that have dual blood supply?

A

Dudodeum - proxial to bile duct by coeliac trunk and distal, by superior mesenteric artery

Pancreas - by both coeliac trunk and superior mesenteric artery

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14
Q

What are the body cavities formed from?

A

Intraembryonic coelom

Begins as one large cavity. Later subdivided by the future diaphragm into abdominal and thoracic cavities.

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15
Q

What is the peritoneal membrane and cavity?

A

Membrane lines the abdominal cavity and invests the viscera. During development it grows, changes shape and specialises.

Cavity is a potential space but under normal conditions it should contain nothing

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16
Q

What are mesenteries and what are their purpose?

A

Double layer of peritoneum suspending the gut tube from the abdominal wall. Allows a conduit for blood and nerve supply and mobility where needed.

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17
Q

How are mesenteries formed?

A

From a condensation of the splanchnic mesoderm surrounding the primitive gut in the intraembryonic coelom

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18
Q

Where are the mesenteries?

A

Dorsal mesentery suspends the entire gut from the dorsal body wall

Ventral mesentery only in the region of the foregut

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19
Q

What does the attachment of the dorsal and ventral mesenteries to the foregut mean?

A

Divides the cavity into left adn right sacs/ greater and lesser sacs respectively.

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20
Q

Where does teh lesser sac lie?

A

Behind the stomach

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21
Q

What are omenta?

A

Specialised regions of the peritoneum

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22
Q

Describe the formation of the greater omentum

A

Formed from the dorsal mesentery

First structure seen when the abdominal cavity is opened anteriorly

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23
Q

Describe the formation of teh lesser omentum.

A

Formed from the ventral mesentery

Free edge conducts the portal triad

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24
Q

How are the greater and lesser sacs and omenta formed?

A

Rotation of the stomach

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25
Q

How does the primitive stomach rotate?

A

2 diretions:

Around teh longitudinal axis adn around the anteroposterior axis

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26
Q

What is the result of stomach rotation?

A

Greater and lesser curvature come to lie first on the right and left side then cardia and pylorus move horizontally, pushing greater curvature inferiorly

27
Q

How does rotation of the stomach and growth of the liver effect the right/lesser sac?

A

Moves it round to become posterior/dorsal to the left/greater sac

28
Q

How does rotation of the stomach change the location of the vagus nerves?

A

Moves them to lie anterior and posterior instead of left and right

29
Q

What is a peritoneal reflection?

A

A change in direction from parietal peritoneum to mesentery, from mesentery to visceral peritoneum etc…

30
Q

What does “retroperitoneal” mean?

A

Were never in the peritoneal cavity and never had a mesentery

31
Q

What does ‘secondarily retroperitoneal’ mean?

A

Began development invested by peritoneum, had a mesentery but, with successive growth and development, the mesentery is lost through fusion at posterior abdominal wall parietal peritoneum due to massive expansion of GI tract during development. Produces fusion of fascia

Eg duodenum (except duodenal cap) and pancreas

32
Q

Where does the foregut extend from?

A

The lung bud to the liver bud

33
Q

Describe the formation ofthe lung bud in relation to the foregut.

A

In the 4th week a respiratory diverticulum forms in teh ventral wall of teh foregut at the junction with the pharyngeal gu t- respitatory primordium (ventrally) and oesophagus (dorsally) separated by the tracheoesphageal septum

34
Q

What are some abnormal positioning of the tracheosophageal septum?

A

Proximal blind-end oesophagus

Tracheoesophageal fistula

35
Q

Why does the dorsal border create a greater curvature than the ventral?

A

Faster growth

36
Q

What foregut-derived glands are formed in the ventral mesentery?

A

Liver

Biliary system

Part of pancreas (uncinate process and inferior head)

37
Q

What foregut derived gland(s) are formed in the dorsal mesentery?

A

Pancreas - superior head, neck, body and tail

38
Q

Describe the deveolpment of the liver

A

Earliest associated GI tract gland

Develops from a hepatic bud withhin the ventral mesentery

Occupies a large proportion of the abdomen during development

Surrounded by the falciform ligament anteriorly and the lesser omentum posteriorly. Bare area superiorly

39
Q

Describe the formation of the duodenum.

A

In 5th and 6th week lumen is obliterated, then recanalised by the end of the embryonic period

Rotation of the stomach pushes it to the right, then against the posterior abdominal wall

40
Q

Why does the primary intestine loop?

A

Elongates enormously and runs out of space

41
Q

Describe the primary intestinal loop.

A

SMA axis

connected to the yolk sac by the vitilline duct

Has cranial and caudal limbs

42
Q

How does physiological herniation occur in development?

A

During 6th week, growth of the primary intestinal loop is very rapid - elongation

Liver is also growing rapidly - abdominal cavity is too small to accommodate both

Intestines herniate into the umbilical cord

43
Q

What structures are seen in the umilical cord at week 6 of development?

A

Umbilical vein

Umbilical artery (x2)

Allantois

Intetine

Amnion covering cord

44
Q

How many times does the midgut rotate?

A

3 x 90 degrees around superior mesenteric artery

90 during herniation

90 to twisting intestine around itself

90 so cranial limb returns to abdominal cavity first, moving to the left side

45
Q

After rotation, where does the cecal bud lie?

A

Just under the liver - must descend

46
Q

What are the derivitives of the cranial limb of the midgut?

A

Distal duodenum

Jejunum

Proximal ileum

47
Q

What are the derivitives of teh caudal limb of the midgut?

A

Distal ileum

Cecum

Appendix

Ascending colon

Proximal 2/3 transverse colon

48
Q

What are the 2 type od malrotation of teh midgut?

A

Incomplete - midgut lopp makes only 90 degree rotation - left sided colon

Reversed - midgut loop makes a 90 degree rotation clockwise - transverse colon passes posterior to the duodenum

49
Q

What are the major complications of the midgut defects?

A

Volvulus - strangulation/ischaemia

50
Q

What abnormailities can result from a persistant yolk sac?

A

Vitelline cyst - vitelline duct forms fibrous strands

Vitelline fistula - Direct communication betwen the umbilicus and intestinal tract

Meckel’s diverticulum - AKA ileal diverticulum, most common GI anomaly

51
Q

What is recanalisation?

A

In some gut structures, cell growth becomes so rapid that the lume is partially or completely obliterated - oesophagus, bile duct, small intestine

Recanalisation occurs to restore the lumen

52
Q

What happens if recanalisation is wholly or partially unsuccessful?

A

Atresia - lumen obliterated

Stenosis - lumen narrowed

Most occur in duodenum

Vascular accidents may also contribute to these conditions (common contribution in the lower duodenum)

53
Q

What is pyloric stensosis and what is the cause?

A

Hypertrophy of the circular muscle in the region of the pyloric sphincter - NOT a recanalisation failure

Common abnormality of the stomach in infants - causes characteristic projectile vomiting

54
Q

What is gastrochisis?

A

Failure of closure of the abdominal wall during folding of the embryo

Leaves gut tube and derivatives outside the body cavity

55
Q

What is Omphalocoele/exomphalos and how does it differ from a hernia?

A

Persistance of physiological herniation

Differs from umilical hernia because hernias have covering of skin and subcut. tissue

ie. Hernia, gut had complete physiological herniation sequence.

56
Q

What deos teh hindgut give rise to?

A

Distal 1/3 transverse colon

Descending colon

Rectum

Superior part of anal canal

Epithelium of urinary bladder

57
Q

What divides the anal canal histologically?

A

Pectinate line - indicates differences in arterial supply, venous and lymphatic drainage and innervation

Above (endoderm origination) - IMA, S2-4 parasympathetic, columnar epithelium, lymph drainage = internal iliac nodes. Only sensitive to stretch sensation

Below (ectoderm origination) - pudenal A, S2-4 pudenal nerve, stratified spitheliu, lymph drainage = superficial inguinal nodes. Sensitive to temperature, touch and pain sensation

58
Q

How is the anal canal formed?

A

At 6 weeks, the hindgut ends in the cloaca

Separated from teh outside by the cloacal membrane

The cloaca is subject to anteroposterior subdivision

A wedge of mesoderm grows down into the cloaca dividing it into the urogenital sins anteriorly and the anorectal canal posteriorly.

59
Q

What makes up the cloacal membrane?

A

Endoderm adn ectoderm

60
Q

What hindgut abnormalities can occur?

A

Imperforate anus - failure of anal membrane to rupture

Anal / anorectal agenesis

Hindgut fistulae

61
Q

What mid and hindgut derivatives retain mesenteries?

A

Jejunum

ileum

appendix

transverse colon

sigmoid colon

62
Q

What sturctures of the mid/hindgut have fused mesenteries?

A

Duodenum

Ascending colon

Descending colon

Rectum (no peritoneal covering in distal 1/3)

63
Q

What deos teh dorsal mesentery become?

A

Greater omentum

Gastrolienal ligament - stomach to spleen

Lienorenal ligament - spleen to kidney

Mesocolon

Mesentery proper - Jejunal and ileal loops

Semester 3 (19 decks)

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