Development of the GI tract Flashcards

1
Q

When is folic acid needed?

A

→ In the first trimester

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2
Q

What is folic acid used for?

A

→helps with the fusion and the closure of the spinal cord.

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3
Q

What is spina bifida?

A

→when the spinal cord herniates out of the back.

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4
Q

When are the primary germ layers formed?

A

→ During the process of gastrulation

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5
Q

What happens at the beginning of the third week?

A

→embryo has implanted into the uterine wall

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6
Q

What is the structure of the embryo at 3 weeks?

A

→The embryo is a flat disc comprised of two cell layers
→Epiblast
→Hypoblast

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7
Q

What do the epiblast cells in the midline of the embryo start to do?

A

→ Begin to ingress starting from the caudal end

→Visible as the primitive streak

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8
Q

What do ingressing cells differentiate into and what do they surround?

A

→differentiate into Mesoderm

→Surrounding muscles, connective tissue, mesentery and blood vessels

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9
Q

What does the epiblast give rise to?

A

→Ectoderm

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10
Q

What does gastrulation give rise to?

A

→three primary germ layers
→ Ectoderm
→ mesoderm
→endoderm

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11
Q

How is the gut tube formed?

A

→by folding of sheets of cells in two directions

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12
Q

What are the two ways in which the gut tube folds?

A

→Folding towards the midline along the cranial-caudal axis

→Folding towards the yolk sac at the cranial and caudal ends

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13
Q

What does the buccopharyngeal membrane form?

A

→ mouth and throat

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14
Q

What does the cloacal membrane form?

A

→ urogenital tract

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15
Q

What is the septum tranversum?

A

→ area where the diaphragm is

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16
Q

What does the somatic mesoderm form?

A

→ The muscles

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17
Q

What does the Splanchnic mesoderm form?

A

→ autonomic nervous system

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18
Q

What is the mesentery and what does it do?

A

→ a folded membrane that anchors the GI tract to the posterior abdominal wall.
→It prevents the organs falling due to gravity.

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19
Q

What is the primary gut tube made up of?

A

→sheet of endoderm, which makes the epithelia and glands

→surrounding mesoderm, which makes muscle and connective tissue (including mesentery)

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20
Q

How is part of the yolk sac cavity enclosed?

A

→Part of the yolk sac cavity is enclosed within the embryo by pinching-off the yolk sac to form a yolk stalk and balloon-like yolk sac.

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21
Q

What makes up the foregut?

A
→Pharynx 
→Oesophagus 
→Stomach
→Cranial half of duodenum 
→Ampulla of Vater (joining of bile ducts and pancreatic duct)
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22
Q

What makes up the midgut?

A
→Caudal duodenum 
→Jejunum 
→Ileum
→Caecum 
→Appendix 
→Ascending colon
→Proximal ⅔ of transverse colon
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23
Q

What makes up the hindgut?

A

→Distal ⅓ of transverse colon
→Descending colon
→Rectum

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24
Q

What artery supplies the foregut?

A

→ Celiac artery

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25
Q

What artery supplies the midgut?

A

→ Superior mesenteric artery

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26
Q

What artery supplies the hindgut?

A

→ Inferior mesenteric artery

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27
Q

What is the gut surrounded by?

A

→plexus of blood vessels joining vitelline (relating to or associated with the yolk of an egg) vessels to aorta

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28
Q

What does the plexus resolve to form?

A

→Plexus resolves to form the arteries that supply the GI tract from the aorta

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29
Q

How many arterial branches are there to the thoracic oesophagus?

A

→5

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30
Q

What innervates the foregut?

A

→ celiac ganglion

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31
Q

What innervates the midgut?

A

→ superior mesenteric ganglion

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32
Q

What innervates the hindgut?

A

→ inferior mesenteric ganglion

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33
Q

How does the stomach arise?

A

→ expansion

→rotation

34
Q

What is the stomach initially?

A

→concave ventral

→convex dorsal

35
Q

What happens at week 4?

A

→at the level where the stomach will form the tube begins to dilate, forming an enlarged lumen

36
Q

What establishes the curvature of the stomach?

A

→90o turn about craniocaudal axis

→The dorsal border grows more rapidly than ventral, which establishes the greater curvature of the stomach

37
Q

How is the dorsal wall of the stomach attached?

A

→Attached to body by mesentery

→The dorsal mesogastrium (will form greater omentum)

38
Q

How is the ventral wall of the stomach attached?

A

→attached by ventral mesentery, which includes the liver (will form lesser omentum)

39
Q

What is the longest nerve in the body?

A

→ Sciatic nerve

40
Q

What does the sciatic nerve follow?

A

→ Most of the oeosophagus

41
Q

What is the peritoneum for?

A

→ Membrane designed to protect organs

42
Q

What are the two types of peritoneum?

A

→Parietal and visceral peritoneum

43
Q

What does the falciform ligament do?

A

→falciform ligament keeps the liver in place

44
Q

What does the omentum do?

A

→Omentum protects the bowel from getting inflamed

45
Q

What happens as the stomach rotates?

A

→ The dorsal mesogastrium is drawn with it

46
Q

What does the mesogastrium enclose?

A

→ a space

→ the omental bursa

47
Q

What does the folded mesogastrium do?

A

→ Grows to form the greater omentum

→The folds fuse and obliterate the bursa

48
Q

What are retroperitoneal structures?

A

→oesophagus
→ rectum
→ kidney

49
Q

Where does the greater omentum extend from?

A

→ Greater curvature

50
Q

Where does the lesser omentum come from?

A

→ Lesser curvature

51
Q

What is the epiploic foramen?

A

→ passage between the greater and lesser sac

→ allows communication

52
Q

What is gastric outlet obstruction caused by?

A

→ Smooth muscle hypertrophy

53
Q

What happens with pyloric stenosis?

A

→Projectile vomiting shortly after feeding

→Pyloric channel elongation ‘railroad track’

54
Q

What does the pylorus do?

A

→ Controls what can enter the duodenum

55
Q

What are the dimensions in pyloric stenosis?

A

→L > 16mm
→Wall > 4mm
→Diameter > 14mm

56
Q

What is the inducing signal for the liver?

A

→heart to ventral gut endoderm

57
Q

Where does the hepatic diverticulum grow?

A

→grows into mesenchyme of septum transversum

58
Q

What parts of the liver proliferate?

A

→ Chords of hepatic endoderm
→ Bile drainage ducts
→ Blood vessels: arranged as sinusoids

59
Q

How does the liver expand?

A

→ Liver exceeds size of septum transversum and expands into ventral mesentery.

60
Q

What does the remaining ventral mesentery give rise to?

A

→Falciform ligament between liver and body wall

→Lesser omentum between liver and stomach

61
Q

What are the two pancreatic buds and what are they induced by?

A

→Dorsal from duodenal endoderm (induced by notochord)

→Ventral from hepatic diverticulum (induced by hepatic mesoderm)

62
Q

What happens as the duodenum rotates?

A

→ventral and dorsal buds meet and fuse

63
Q

How does annular pancreas occur?

A

→develops from bi-lobed ventral buds that migrate in opposite directions.

64
Q

What can an annular pancreas do?

A

→Annular pancreas can constrict the duodenum

65
Q

How are the intestines attached?

A

→Attached throughout length by dorsal mesentery

66
Q

What leads to the folding of the gut?

A

→Mesentery and gut grow at different rates, leading to folding of the gut

67
Q

What branch of the aorta supplies the midgut?

A

→Ventral branch of the aorta supplies the midgut : superior mesenteric artery

68
Q

What do the intestines rotate around?

A

→With a rapid increase in length the intestines rotate around the SMA

69
Q

Why do the intestines herniate?

A

→Abdomen is too small to accommodate so it herniates into the umbilical stalk at 6-7 weeks

70
Q

When do the intestines return?

A

→By 10 weeks the abdomen is bigger and the intestines

return.

71
Q

What is umbilical hernia?

A

→Intestines return normally but rectus abdominis fails to fuse around umbilicus : gut covered in skin

72
Q

What is omphalocele?

A

→Failure of intestinal loops to return into abdomen (associated with obesity, alcohol/tobacco or SSRI)

73
Q

What is gastroschisis?

A

→Failure of ventral body wall to fuse : no covering

74
Q

What is the persistence of the yolk duct?

A

→Most common intestinal abnormality

→Yolk duct attached to ileum near ileocecal junction - apex of midgut loop

75
Q

What can Meckel’s diverticulum cause?

A

→Gut rotation causes volvulus

→Can form umbilical fistula

76
Q

What can Meckel’s diverticulum contain and what does this cause?

A

→ ectopic gastric cells : ulceration and lower GI bleeding

77
Q

What is Hirschsprung’s disease?

A
→Aganglionic megacolon (no ganglia) 
→Primarily affects the hindgut
→Absence of parasympathetic ganglia
→Caused by lack of neural crest cells
→Ganglia present in dilated/hypertrophic region 
→Aganglionic segment shows contraction
78
Q

What does Hirschsprung’s disease cause?

A

→Dilatation of sections of the colon, with lack of tone and peristalsis, leading to profound constipation

79
Q

What is the cloacal membrane?

A

→ Transient common end of the digestive and urogenital systems including the base of the allantois (urogenital sinus)

80
Q

What is the cloaca covered by?

A

→Covered by cloacal (proctodeal) membrane over ectoderm depression

81
Q

What is the cloaca split by and what does this give rise to?

A

→Split by the urorectal septum

→This gives rise to the urogenital membrane and anal membrane (perforate at 7-8 weeks)

82
Q

What can imperforate anus be?

A

→Persistence of anal membrane

→Atresia of anal canal, rectum or both