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SGUL - Physiology 1 > Development of the GI Tract > Flashcards

Development of the GI Tract Flashcards

1
Q

What is the significance of gut tube formation?

A

Organs and glands are produced by budding from the gut tube.

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2
Q

Describe primary germ formation.

A

Formed during gastrulation.
- At the beginning of the third week, embryo has implanted into uterine wall and appears as a flat disc made up of 2 layers.

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3
Q

What two layers does the embryo consist of?

A

Epiblast and hypoblast

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4
Q

What happens to epiblast cells in the mid-line of the embryo?

A

Ingress, starting from the caudal end - visible as the primitive streak.

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5
Q

What do ingressing cells differentiate into?

A

Mesoderm

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6
Q

What does the mesoderm give rise to?

A
  • Surrounding muscles
  • Connective tissue
  • Blood vessels
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7
Q

What does the epiblast give rise to?

A

Ectoderm

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8
Q

What is the importance of the neural crest?

A

Provides innervation to the gut - enteric NS

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9
Q

What does the hypoblast give rise to?

A

Endoderm

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10
Q

What does the endoderm differentiate to form?

A
  • Epithelium
  • Gut tube
  • Glands
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11
Q

Briefly describe the directions of the formation of the gut tube.

A

Formed by the folding of sheets of cells in two directions:
- folding towards the midline along the cranial-caudal axis
- folding towards the yolk sac at the cranial and caudal ends

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12
Q

The gut tube doesn’t form as a tube the first time round. Describe this phenomenon.

A
  • Cells will grow to the point where there’s no lumen
  • Gut needs rearrangement (scaffolding).
  • Recanalisation occurs - cells die forming a diameter within the tube
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13
Q

What can occur if the middle part of the gut does not recanalise?

A
  • Duodenal atresia (if short term)
  • Jejunal atresia (if long term)
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14
Q

How can duodenal atresia affect new borns?

A
  • Projectile vomiting
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15
Q

What are the subdivisions of the gut?

A

FOREGUT
MIDGUT
HINDGUT

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16
Q

Outline the parts of the foregut

A
  • Pharynx
  • Oesophagus
  • Stomach
  • Cranial half of duodenum
  • Ampulla of Vater
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17
Q

Outline the parts of the midgut

A
  • Caudal duodenum (From duodenal papilla )
  • Jejunum
  • Ileum
  • Caecum
  • Appendix
  • Ascending colon
  • Proximal 2/3 of transverse colon
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18
Q

Outline the parts of the hindgut

A
  • Distal 1/3 of transverse colon
  • Descending colon
  • Rectum
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19
Q

What are the blood supplies to the different parts of the gut?

A

FOREGUT - coeliac artery
MIDGUT - superior mesenteric artery
HINDGUT - inferior mesenteric artery

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20
Q

Where do the sympathetic ganglia develop?

A

Next to the major branches of the aorta

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21
Q

What do post-ganglionic sympathetic axons innervate?

A
  • The same tissues that the arteries supply with blood
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22
Q

What is the innervation of the gut?

A

FOREGUT - celiac ganglion
MIDGUT - superior mesenteric ganglion
HINDGUT - inferior mesenteric ganglion

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23
Q

Describe the rotation of the stomach.

A
  • Tube begins to dilate, forming an enlarged lumen.
  • Makes a 90° turn about the craniocaudal axis, so the dorsal border grows more rapidly than the ventral border, establishing the greater curvature of the stomach.
  • Anterior part becomes the right, and the posterior becomes the left.
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24
Q

What genes determine the position (of the structures) along the cranio-caudal axis?

A

Homeotic (HOX) genes.

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25
Q

What fixes the mature gut in place?

A

Fusion of the mesentries with the posterior abdominal wall

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26
Q

Describe pyloric stenosis.

A
  • Gastric outlet obstruction caused by smooth muscle hypertrophy (ie. the smooth muscle forming the pyloric sphincter overgrows).
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27
Q

How can pyloric stenosis be spotted in newborns?

A

Will start projectile vomiting shortly after feeding

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28
Q

Describe the formation of the liver, budding from the gut tube. PART 1

A
  • Hepatic diverticulum grows into the mesenchyme of the septum transversum.
  • Cords of the hepatic endoderm, bile drainage ducts, and blood vessels proliferate, arranged as sinusoids.
  • Liver exceeds the size of the septum transversum, and expands into the ventral mesentery.
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29
Q

Describe the formation of the liver, budding from the gut tube. PART 2

A

The remaining ventral mesentery gives rise to:
- falciform ligament between the liver and the body wall
- lesser omentum between the liver and stomach

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30
Q

Describe the formation of the pancreas, budding from the gut tube.

A

TWO PANCREATIC BUDS
- dorsal, from the duodenal endoderm (induced by the notochord)
- central, from the hepatic diverticulum (induced by the hepatic mesoderm)

As the duodenum rotates, the dorsal and ventral buds fuse.

31
Q

Describe annular pancreas

A
  • Develops from bi-lobed ventral bud that migrates in separate directions, coming around and fusing to constrict the duodenum.
32
Q

Describe the development of the intestines.

A
  • Mesentery and the gut grow at different rates, leading to folding of gut.
  • Abdomen is too small to accommodate this, so the gut herniates into the umbilical stalk at 6/7 weeks.
  • By 10 weeks, the abdomen is bigger, and the intestines return.
33
Q

Describe an umbilical hernia.

A
  • Intestines return normally
  • Rectus abdominis fails to fuse around the umbilicus, leading to gut covered in skin.
34
Q

Describe an omphalocele.

A
  • Failure of the intestinal loops to return to the abdomen - ends up as a hernia covered in amnion.
  • Associated with maternal obesity, alcohol/ tobacco
35
Q

Describe gastroschisis.

A
  • Defect in the abdominal wall, a failure of the ventral body wall to fuse.
  • No covering of the gut as it sits outside the body.
  • Association with young maternal age, low maternal BMI, and recreational drugs (especially cocaine).
36
Q

Describe Hirschsprung’s disease. PART 1

A
  • Person has an aganglionic megacolon.
  • Primarily affects the hindgut.
  • Absence of parasympathetic ganglia, caused by a lack of neural crest cells.
37
Q

Describe Hirschsprung’s disease. PART 2

A
  • Dilation of sections of the colon, with a lack of tone and peristalsis, leading to profound constipation.
  • Because of the failure of the development of enteric ganglia, there is a section of the gut that is completely absent of ganglia.
38
Q

In anal development, what is the cloaca?

A
  • Transient common end of the digestive and urogenital systems, including the base of the allantois (urogenital sinus).
  • Covered by the cloacal (proctodeal) membrane over the ectoderm depression, the proctodeum.
39
Q

What are the cloaca split by?

A
  • Split by the urorectal septum - gives rise to the urogenital membrane and anal membrane (that perforate at 7-8 weeks).
40
Q

What could cause an imperforate anus?

A
  • Persistence of the anal membrane
  • Atresia of the anal canal, rectum or both
41
Q

When does GI tract development occur?

A

During 3rd to 12th weeks embryonic age

42
Q

What are the regionalised changes in the gut tube caused by?

A

Rotation, swelling, elongation

43
Q

What is the purpose of gastrulation?

A

Generates the three primary germ layers

44
Q

Give an overview of formation of the gut tube. PART 1

A
  • Embryo initially a solid flat disk attached to the hemispherical yolk sac
  • 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
45
Q

Give an overview of formation of the gut tube. PART 2

A
  • Cranial and caudal intestinal portals extend the tube towards the mouth and anus, delimited by the prochordal and cloacal plates
46
Q

What is the primary gut tube made out of?

A
  • Sheet of endoderm, which makes the epithelia and glands
  • Surrounding mesoderm, which makes muscle and connective tissue (including mesentery)
47
Q

What is the gut surrounded by?

A

Plexus of blood vessels, joining vitelline vessels to aorta.

48
Q

What does the plexus resolve to form?

A

Arteries that supply the GI tract from the aorta

49
Q

How many arterial branches lead to the thoracic oesophagus?

Where do these branches derive from?

A

5 branches
- derive from descending aorta

50
Q

What does the dorsal wall of the stomach attach to and form?

A

Attached by dorsal mesogastrium - will form greater omentum (from greater curvature)

51
Q

What does the ventral wall of the stomach attach to and form?

A

Attached by ventral mesentery, which includes the liver - will form lesser omentum (from lesser curvature)

52
Q

Describe the mesenteric attachments from the stomach to the liver

A

Mesenteric arteries - arteries of the small intestine
- Connects the liver and the stomach

53
Q

Describe the foregut development

A
  • As the stomach rotates, the dorsal mesogastrium is drawn with it
  • Mesogastrium encloses the omental bursa (lesser sac)
  • Folded mesogastrium grows to form the greater omentum, the folds fusing to obliterate the bursa
54
Q

What is peritoneum?

A

Serous double membrane lining the cavity of the abdomen and covering the abdominal organs.

55
Q

What occurs as a result of pyloric stenosis?

A
  • Pyloric channel elongation
  • Length >16mm, diameter >14mm due to hypertrophy
56
Q

What occurs in persistence of the yolk duct?

A
  • Yolk duct attached to ileum, near ileo-cecal junction - apex of midgut loop (about 2 feet from ileocaecal junction)
57
Q

What occurs in Meckel’s diverticulum?

A
  • May contain ectopic gastric cells: ulceration and lower GI bleeding
  • Can be connected to umbilicus by ligament
  • Gut rotation causes volvulus
  • Can form umbilical fistula
58
Q

What does the buccopharyngeal membrane form?

A

Mouth and throat

59
Q

What is the septum tranversum?

A

Area where the diaphragm is

60
Q

What does the somatic mesoderm form?

61
Q

What does the splanchnic mesoderm form?

A

Autonomic NS

62
Q

What is the mesentery and what does it do?

A
  • Folded membrane that anchors the GI tract to the posterior abdominal wall.
  • Prevents the organs falling due to gravity.
63
Q

How does the stomach arise?

A

Expansion and rotation

64
Q

What is the stomach initially?

A
  • concave ventral
  • convex dorsal
65
Q

What is the longest nerve in the body?

A

Sciatic nerve

66
Q

What does the sciatic nerve follow?

A

Most of the oesophagus

67
Q

What are the two types of peritoneum?

A
  • Parietal and visceral peritoneum
68
Q

What does the falciform ligament do?

A

Keeps the liver in place

69
Q

What does the omentum do?

A

Protects the bowel from getting inflamed

70
Q

What are retroperitoneal structures?

A
  • oesophagus
  • rectum
  • kidney
71
Q

What is the epiploic foramen?

A

Passage between the greater and lesser sac

72
Q

What does the pylorus do?

A

Controls what can enter the duodenum

73
Q

How are the intestines attached?

A

Attached throughout length by dorsal mesentery

SGUL - Physiology 1 (68 decks)

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