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GI lectures > development of the foregut > Flashcards

development of the foregut Flashcards

1
Q

where does foregut start and end

A

starts from the distal oesophagus

ends halfway along the duodenum (proximal end)

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2
Q

where does midgut start and end

A

starts from the distal half of the duodenum

ends at the last 1/3rd of the transverse colon

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3
Q

where does hindgut start and end

A

starts from distal 1/3rd of the
transverse colon

ends at the upper anal canal

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4
Q

blood supply of foregut

A

celiac arterty

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5
Q

components of foregut (4)

A
  • pharynx
  • oesophagus
  • stomach
  • proximal half of duodenum and the derivative (liver, biliary apparatus & the pancreas)
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6
Q

blood supply of midgut

A

superior mesenteric artery

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7
Q

components of midgut

A
  • distal half of the duodenum
  • jejunum
  • ileum
  • caecum
  • appendix
  • ascending colon
  • right 2/3rds of the transverse colon
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8
Q

blood supply of hindgut

A

inferior mesenteric artery

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9
Q

components of hindgut

A
  • left 1/3 of the transverse colon
  • descending colon
  • sigmoid colon
  • rectum
  • anal canal
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10
Q

what is embryonic folding

A

during the 4th week of development the embryo begins to fold and change shape from a flat trilaminar disc into a
cylinder

this process is known as embryonic folding

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11
Q

what are the 2 planes of embryonic folding

A

the horizontal & medial planes
or
longitudinal & transverse folding

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12
Q

why does embryonic folding occur in 2 planes

A

due to the differing rates of growth of the embryonic structures

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13
Q

what does folding in the horizontal plane result in

A

the formation of the two lateral body folds - transverse

lateral folding

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14
Q

what does folding in the medial plane result in

A

the formation of the cranial & caudal folds - longitudinal

cephalo-caudal folding

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15
Q

does folding in both planes occur simultaneously or separately

A

simultaneously

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16
Q

what is mainly responsible for the development of the GI tract

A

the endoderm

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17
Q

what happens as embryonic folding continues

A

the endoderm moves towards the midline and fuses
- incorporating the dorsal part of the yolk sac to form the primitive gut tube

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18
Q

what is the primitive gut-derived from

A

the endoderm and the visceral mesoderm

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19
Q

what does the endoderm give rise to

A
  1. Epithelial lining of digestive tract
  2. Hepatocytes of the liver
  3. Endocrine and exocrine cells of the pancreas
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20
Q

what does the visceral mesoderm give rise to

A
  1. Muscle, connective tissue & peritoneal components of the wall of the gut
  2. Connective tissue for the glands
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21
Q

what does the primitive gut tube differentiate into

A

the foregut, midgut & hindgut

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22
Q

where is the foregut

A

on the cranial end of the embryo and is temporarily closed by the oropharyngeal membrane which at the end of the 4th week of development ruptures to form the mouth

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23
Q

where is the midgut

A

lies between the fore and hindgut
and remains connected to the yolk sac until the 5th week of development

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24
Q

where is the hindgut

A

lies at the caudal end of the embryo, it is temporarily closed by the cloacal membrane, which during the 7th week of development, ruptures to
form the anus

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25
Q

what is the vitelline duct

A

as embryonic folding continues, the connection to the yolk sac narrows into a stalk called the vitelline duct - an embryonic structure providing communication from the yolk sac to the midgut during fetal development

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26
Q

sympathetic innervation of foregut from ANS

A

greater splanchic nerve (T5-T9)

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27
Q

parasympathetic innervation of foregut from ANS

A

vagus

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28
Q

sympathetic innervation of midgut from ANS

A

lesser splanchnic nerve (T10-T11)

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29
Q

parasympathetic innervation of midgut from ANS

A

vagus

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30
Q

sympathetic innervation of hindgut from ANS

A

least splanchnic nerve (T12 +/- L1)
and lumbar splanchnic nerves

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31
Q

parasympathetic innervation of hindgut from ANS

A

pelvic splanchnics

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32
Q

where is foregut visceral pain felt

A

epigastric region

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33
Q

where is midgut visceral pain felt

A

umbilical region

34
Q

where is hindgut visceral pain felt

A

suprapubic region

35
Q

where does bilaminar disc develop from

A

the inner cell mass

36
Q

describe gastrulation process (5 steps)

A
  1. primitive streak forms on epiblast
  2. epiblast cells migrate to primitive streak and invaginate through it
  3. some cells displace the hypoblast and form the endoderm
  4. some cells create a new layer between the epiblast and endoderm = mesoderm
  5. epiblast = ectoderm
37
Q

what are the 3 germ layers

A

ectoderm

mesoderm

endoderm

38
Q

describe muscle of upper 2/3 of oesophagus

A

striated muscle

39
Q

describe muscle of lower 1/3 of oesophagus

A

smooth muscle

40
Q

what is upper 2/3 of oesophagus innervated by

A

vagus nerves

41
Q

what is lower 1/3 of oesophagus innervated by

A

splanchnic nerves

42
Q

what happens to oesophagus in the 4th week

A

at the end of the pharynx and the beginning of the oesophagus, at
the ventral wall of the foregut - respiratory diverticulum (lung buds) appear

43
Q

how is the foregut divided in the 4th week

A

the trancheoesophageal septum develops and separates the respiratory
diverticulum from the dorsal part of the foregut

  • in this way the foregut is divided
    into the ventral respiratory primordium & the dorsal oesophagus
44
Q

what is the foregut divided into in the 4th week

A
  1. the ventral respiratory primordium
  2. the dorsal oesophagus
45
Q

describe length of oesophagus

A

initially it is short but it lengthens rapidly with the descent of the heart and lungs

46
Q

what are mesenteries

A

double layers or peritoneum that surround an organ and connect
it to the body wall,

such an organ is called intraperitoneal

parts of the gut tube are suspended from the dorsal & ventral body walls by
mesenteries

47
Q

what is a retroperitoneal organ

A

when an organ is sitting directly on the posterior abdominal wall and covered by peritoneum on its anterior surface only

48
Q

what are ligaments

A

double layers of peritoneum which pass from one organ to another or from one organ to the body wall

49
Q

what do mesenteries and ligaments provide

A

pathways for blood vessels, lymphatics & nerves to go to and come from the abdominal viscera

50
Q

what are the 2 mesenteries of the foregut

A

dorsal mesentary

ventral mesentary

51
Q

where does dorsal mesentery extend from

A

extends from the lower part of the oesophagus to the cloacal region (rectum)

52
Q

what does dorsal mesentery do in 5th week

A

by the 5th week the lower part of the foregut, midgut & major part of the hindgut are suspended from the posterior abdominal wall by dorsal mesentery

53
Q

where is the ventral mesentery

A

only in the region of the foregut -

terminal part of the oesophagus,

the stomach

and the upper part of the duodenum

54
Q

which mesenteries does the foregut have

A

both ventral and dorsal

55
Q

which mesenteries do the midgut and hindgut have

A

only a dorsal mesentary

56
Q

what is the ventral mesentery derived from

A

the septum transversum

57
Q

what does the free lower margin of the ventral mesentery contain (3)

A

the hepatic artery

portal vein

bile duct

58
Q

where does the liver develop

A

in the ventral mesentery

59
Q

what does the liver divide the ventral mesentery into

A

into the lesser omentum

& the falciform ligament

60
Q

when does the foregut begin to dilate into the stomach

A

week 4

the stomach appears as a fusiform (spiral-shaped) dilation in the foregut in the 4th week

61
Q

why does the appearance and position of the stomach change

A

it changes greatly as a result of the different rate of growth in various
regions of its wall

62
Q

how is the developing stomach attached to the body walls

A

by the dorsal & ventral mesenteries

63
Q

which are nerves are on the sides of the stomach

A

left side of developing stomach = left vagus nerve

right side of developing stomach = right vagus nerve

64
Q

effect of the dorsal wall of the stomach growing faster than the ventral wall

A

this differential growth forms the greater & lesser curvatures
of the stomach

65
Q

what does the stomach do in the 7th week

A

the stomach rotates 90 degrees CLOCKWISE about a longitudinal axis -

this rotate produces a space behind the stomach called the lesser sac

66
Q

what happens to the greater and lesser curvature in the 7th week

A

the greater curvature (on the embryonic dorsal side) now faces
the left of the body

the lesser curvature (on the embryonic
ventral side) faces the right

67
Q

what happens to the left and right vagus nerve in the 7th week

A

the left vagus is now on the anterior side of the stomach

the right vagus is located on the posterior side

thus they are now called the anterior & posterior vagal trunks

68
Q

what does the stomach do in the 8th week

A

the stomach and duodenum ROTATE about a ventrodorsal axis, pulling the end of the stomach upwards, they pull the duodenum into a C-shape

results in the thinning of the dorsal
mesentery, which now hangs from the greater curvature of the stomach - it is now called the greater omentum

the ventral mesentery is now attached to the developing liver and has formed the lesser omentum

69
Q

effect of the development of the omen and the rotations of foregut structures

A

produces distinct spaces of
the peritoneal cavity

70
Q

what is the lesser sac

A

the space posterior to the stomach

71
Q

what is the greater sac

A

the space anterior to the stomach

72
Q

how do the greater and lesser sacs communicate

A

via a small opening (located near the hilum of the liver) called the epiploic foramen

73
Q

what do the anterior and posterior folds of the greater omentum do during the fetal period

A

they FUSE to form one THICK sheet formed from 4 layers of peritoneum

74
Q

where does the liver grow from

A

liver bud is an outgrowth from the distal foregut (endotherm epithelium)

75
Q

when does liver begin to develop

A

week 3

76
Q

how does the liver deveelop

A
  1. cells proliferate - grow into the septum transversum
  2. connection between the liver bud and foregut (duodenum) narrows > bile duct
  3. small outgrowth from the bile duct > gallbladder
  4. as the liver grows the remaining mesoderm either side becomes membraneous > falciform ligament and lesser omentum
77
Q

how does the pancreas develop

A
  1. dorsal and ventral buds arise from the duodenum
  2. dorsal bud develops in the dorsal mesentary
  3. rotation of the stomach swings the ventral bud posteriorly
  4. dorsal and ventral buds fuse
78
Q

derivatves of the foregut

A

liver

pancreas

79
Q

what determines how regions of the gut tube develop

A

differential expression of transcription factors and genes along the tube

80
Q

when does the gut tube start to differentiate

A

whilst lateral folding is bringing the ventral body wall together

GI lectures (9 decks)

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