Development of the Midgut and Hindgut Flashcards Preview

ESA 3 - Gastrointestinal System > Development of the Midgut and Hindgut > Flashcards

Flashcards in Development of the Midgut and Hindgut Deck (125):
1

What does the midgut give rise to? 

  • Small intestine, including most of the duodenum post bile duct entry
  • Caecum and appendix
  • Ascending colon
  • Proximal 2/3 or transverse colon 

 

2

Draw a diagram illustrating the position of the midgut in an embryo

3

What causes the midgut to make a loop? 

It elongates enormously, and quickly runs out of space due to the large size of the developing liver 

4

What does the loop made by the midgut have at its axis? 

The superior mesenteric artery 

5

What is the loop made by the midgut connected to? 

The yolk sac

6

How is the midgut loop connected to the yolk sac? 

By the vitelline duct 

7

What are the limbs of the midgut loop called? 

Cranial and caudal limbs 

8

Label this diagram 

  • A - Cranial limb 
  • B - Superior mesenteric artery at axis 
  • C - Caudal limb 
  • D - Vitelline duct to yolk sac

 

  1. SMA
  2. Cranial 
  3. Caudal 

 

9

What are the derivatives of the cranial limb? 

  • Distal duodenum 
  • Jejunum 
  • Proximal ileum 

 

 

10

What are the derivates of the caudal limb? 

  • Distal ileum 
  • Cecum 
  • Appendix
  • Ascending colon 
  • Proximal 2/3 of transverse colon

 

11

What happens to the primary loop during the 6th week of development? 

It elongates very rapidly 

12

What happens to the liver during the 6th week of development? 

It grows very rapidly 

13

What is the problem with the rapid growth of both the liver and the primary loop? 

The abdominal cavity is too small to accomodate both

14

What is the result of the abdominal cavity being too small too accomodate the primary loop and the liver? 

Physiological herniation 

15

What is physiological herniation? 

Where the intestines herniate into the proximal umbilical cord, alongside the umbilical vessels 

16

What are the stages in rotation of the midgut loop? 

  1. First rotation 
  2. Second rotation 

 

17

By how much is the first rotation of the midgut loop? 

90 degrees

18

By how much is the second rotation of the midgut loop? 

180 degrees 

19

What happens in the first rotation of the midgut loop? 

During herniation into the umbilical cord, the midgut rotates around the axis formed by the SMA in a counter clockwise direction (cranial limb moves to back, caudal to the front) 

20

Draw a diagram illustrating what happens in the first rotation of the midgut loop? 

21

Does elongation of the small intestinal lumen continue during rotation? 

Yes 

22

What is the result of the elongation of the small intestinal loop continuing during rotation? 

The jejunum and ileum form a number of coiled loops 

23

What happens to the large intestine during rotation? 

It lengthens, but does not participate in the coiling phenomenon

24

When does the second rotation of the midgut loop occur? 

When it returns into the abdominal cavity, around week 10 

25

In what direction does the second rotation of the midgut loop occur? 

Turns 90 degrees counter-clockwise twice 

26

Draw a diagram illustrating the second rotation of the midgut loop 

27

In total, by how much does the midgut loop rotate? 

270 degrees counter-clockwise 

28

Which limb returns to the abdomen first? 

The cranial limb 

29

In what direction does the cranial limb move on return to the abdomen? 

To the left hand side 

30

What returns to the abdomen last following rotation? 

The cecal bud 

31

What happens once the cecal bud has returned to the abdomen? 

It descends, moving the ceacum to the right lower quadrant 

32

What does the rotation of the midgut loop account for? 

The positions of the small and large intestines, and the twisted apperances of the mesentery of the small intestine 

33

Are abnormalities of rotation common? 

Yes 

34

What do abnormalities of rotation cause? 

Abnormal positioning of the midgut derivatives, e.g. the appendix on the left 

35

What happens in incomplete rotation? 

The midgut only makes one 90 degree rotation 

36

What is the consequence of incomplete rotation? 

Left sided colon

37

Draw a diagram showing the consequence of incomplete rotation

38

What happens in reversed rotation? 

The midgut makes one 90 degree rotation clockwise 

39

What is the consequence of reversed rotation? 

The transverse colon passes posterior to the duodenum, and can wrap arround and occlude 

40

Draw a diagram showing the consequences of reversed rotation

41

What does incomplete or reversed rotation lead to? 

Hypermobile guts 

42

What is a volvulus? 

A bowel obstruction where a loop of bowel has abnormally twisted in on itself

43

What makes a volvulus more likely? 

Hypermobile guts 

44

What can a volvulus lead to? 

  • Strangulation 
  • Ischaemia 

45

What does the hindgut give rise to? 

  • The distal 1/3 transverse colon 
  • Descending colon 
  • Rectum 
  • Superior part of anal canal 
  • Epithelium of the urinary bladder 

 

46

Draw a diagram illustrating the position of the hindgut

47

What happens to the hindgut at 6 weeks? 

It ends in the cloaca 

48

What separates the cloaca from the outside? 

The cloacal membrane 

49

What does the cloaca undergo after formation? 

An anteroposterior division 

50

What happens in cloacal partitioning? 

 A wedge of mesoderm grows down into the cloaca

51

What is the cloaca divided into in partitioning? 

  • The urogenial sinus anteriorly 
  • The anorectal canal posteriorly 

 

52

Draw a labelled diagram illustrating the progression of cloacal partitioning 

53

What is the anal canal derived from? 

  • The superior part is derived from the hindgut 
  • The inferior part is derived from the endoderm 

 

54

What is the pectinate line? 

The line at which the two parts fo the anal canal meet 

55

Draw a diagram illustrating the formation of the anal canal 

56

Label this diagram 

 

  • A - Rectum 
  • B - Pectinate line 
  •  C - 'White' line 
  • D - Anal pecten 
  • E - Anal aperture 

 

57

What is the blood supply for the anal canal above the pectinate line? 

Inferior mesenteric artery 

58

What is the blood supply for the anal canal below the pectinate line? 

Pudendal artery 

59

What is the innervation of the anal canal above the pectinate line? 

S2/3/4 pelvic parasympathetic 

60

What is the epithelia in the anal canal above the pectinate line? 

Columnar 

61

What is the lymph drainage of the anal canal above the pectinate line? 

Internal iliac nodes 

62

What is the blood supply of the anal canal below the pectinate line? 

Pudendal A. 

63

What is the innervation of the anal canal below the pectinate line? 

S2/3/4 Pudendal N. 

64

What is the epithelia of the anal canal below the pectinate line? 

Stratified squamous (non-keratinised)

65

What is the lymph drainage of the anal canal below the pectinate line? 

Superficial inguinal nodes 

66

Why do the two different parts of the anal canal vary in several ways?

Because they have different origins 

67

What sensation is possible above the pectinate line? 

Stretch 

68

What sensation is possible below the pectinate line? 

  • Temperature 
  • Touch
  • Pain 

 

69

Why is the tissue below the pectinate line sensitive to temperature, touch, and pain? 

Due to its somatic innervation by the Pudendal nerve (S2/3/4)

70

What are some common congital defects of the GI tract? 

  • Vitelline duct 
  • Meckel's Diverticlum
  • Vitelline cyst
  • Vitelline fistula 
  • Recanalisation problems
  • Pyloric stenosis 

 

71

What is the most common GI abnormality? 

Meckel's Diverticulum

72

What is the problem with a vitelline duct? 

It can persist, resulting in a number of different abnormalities 

73

What is Meckel's Diverticulum also known as? 

Ilieal diverticulum 

74

What does Meckel's Diverticulum follow? 

A rule of 2's 

75

What is the rule of 2's followed by Meckel's diverticulum?

  • 2% of population affected
  • 2 feet from ileocecal valve
  • 2 inches long
  • Usually detected in under 2's 
  • 2:1 male:female 

 

76

Can Meckel's Diverticulum be asymptomatic?

Yes 

77

What does Meckel's Diverticulum cause?

Ulceration 

78

Why does Meckel's Diverticulum cause ulceration? 

Because the diverticulum can contain ectopic gastric or pancreatic tissue. The ectopic tissue will secrete enzymes and acids into the tissue not protected from them, causing ulceration 

79

Draw a diagram illustrating Meckel's diverticulum

80

What is a vitelline cyst? 

When the vitelline duct forms fibrous strands at either end 

81

Draw a diagram illustrating a vitelline cyst? 

82

What is a vitelline fistula? 

When there is direct communication between the umbilicus and the intestinal tract 

83

What is the result of a vitelline fistula? 

Faecal matter coming out of the umbilicus 

84

Draw a diagram illustrating a vitelline fistula 

85

Why is recanalisation required in the embryo?

The primitive gut tube is a simple tube. In some gut stuctures, cell growth becomes so rapid that the lumen is partially or completely obliterated. Recanalisation occurs to restore the lumen 

86

What structures can cause the obliteration of the lumen in the primitive gut tube? 

  • Oesophagus
  • Bile duct
  • Small intestine 

 

87

What happens if recanalisation is wholly or partially unsuccessful? 

Atresia or stenosis of the stucture can occur 

88

When does atresia of the gut tube structure occur?

When there is a complete loss of the lumen 

89

When does stenosis of the gut tube structures occur? 

When there is a narrowing of the lumen 

90

Where does most atresia/stenosis occur?

In the duodenum 

91

What is the most likely cause of atresia/stenosis in the duodenum?

Incomplete canalisation, but 'vascular accidents' can also contribute 

92

What is meant by a 'vascular accident'?

Where there is a loss of blood supply and that part of the gut dies 

93

Where does atresia occur more, the duodenum or the jejenum?

Duodenum

94

Where does atresia/stenosis occur more, the jejenum or the ileum?

The same

95

Where does atresia/stenesis occur more, the ileum or the colon? 

Ileum 

 

96

What are atresias most often due to in the upper duodenum? 

Recanalisation failure

97

What are atresias most commonly due to in the lower duodenum? 

A vascular accident 

98

What can cause a vascular accident in the lower duodenum? 

  • Malrotation
  • Volvulus
  • Body wall defects

 

 

99

What is pyloric stenosis?

A narrowing of the exit from the stomach

100

Where is pyloric stenosis common?

In infants

101

What does pyloric stenosis result in?

Characteristic projectile vomiting 

102

What causes pyloric stenosis?

Hypertrophy of the circular muscle in the region of the pyloric sphincter 

103

What are some defects of the abdominal wall?

  • Gastroschisis
  • Omphalocoele

 

104

What is gastroschisis?

The failure of closure of the abdominal wall during folding of the embryo, leaving the gut tube and its derivatives outside the body cavity 

105

What happensto the gut tube/derivates in gastroschisis?

There is no covering over them as they herniate through the abdominal wall directly into the amniotic cavity 

106

What is omphalocoele? 

The persistance of physiological herniation 

107

What physiological herniation persists in omphalocoele?

A part of the gut tube fails to return to the abdominal cavity following normal herniation into the umbilical cord 

108

Is there a covering in omphalocoele? 

Yes 

109

Why is there a covering in omphalocoele? 

Since the umbilical cord is covered by a reflection of the amnion, this epithelial layer covers the defect 

110

What are some hindgut abnormalities?

  • Imperforate anus
  • Anal/anorectal agenesis 
  • Hindgut fistulae 

 

111

What is an imperforate anus? 

Failure of the anal membrane to rupture 

112

Draw a diagram of an imperforate anus 

113

What is anal/anorectal agenesis?

Failure of development 

114

Draw a diagram illustrating anal/anorectal agenesis?

115

What is a hindgut fistulae? 

An abnormal connection within the hindgut 

116

Draw a diagram illustrating hindgut fistulae

117

What are the mesenteries retained by? 

  • Jejenum
  • Ileum 
  • Appendix
  • Transverse colon
    Sigmoid colon 

 

118

What structures of the midgut/hindgut are fused with mesenteries?

  • Duodenum
  • Ascending colon 
  • Descending colon 
  • Rectum (no peritoneal covering in distal 1/3)

 

119

What happens, regarding gut development, in week 3? 

Tubular gut begins to form

120

What happens, regarding gut development, in week 4? 

  • Primordia of liver, pancreas, and trachea
  • Buccopharyngeal membrane ruptures 

 

121

What happens, regarding gut development, in week 5? 

  • Expansion and early rotation of the stomach
  • First intestinal loop appears 
  • Caecum and bile duct develop

 

122

What happens, regarding gut development, in week 6?

  • Increased liver growth
  • Herniation of intestinal loop
  • Appendix develops 
  • Cloacal partioning begins - urorectal septum appears 

123

What happens, regarding gut development, in week 7?

  • Pancreatic buds fuse
  • Clocal partioning complete
  • Rupture of clocal membrane 

 

124

What happens, regarding gut development, in week 8?

  • Counterclockwise rotation of herniated loop
  • Recanalisation

125

What happens, regarding gut development, in week 10?

  • Return of herniated loop
  • Adult disposition achieved