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PHYSIOLOGY > Development of GI tract > Flashcards

Development of GI tract Flashcards

1
Q

When does GI tract development occur

A

During 3rd to 12th week of embryonic age

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2
Q

In chronological order what is formed

A

Primary germ layer first
Then the gut tube formation
Then regionalised changes caused by rotation, swelling and elongation

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3
Q

How are organs and glands produced

A

By budding from the gut tube

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4
Q

What is the blastocyst made up of

A

Outer layer of cells = TROPHECTODERM/TROPHOBLAST

Middle = INNER CELL MASS (ICM)

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5
Q

What can the inner cell mass differentiate into

A

Epiblast

Hypoblast

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6
Q

Embryo is a flat disc comprised of 2 cell layers

A

Epiblast

Hypoblast

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7
Q

When are the primary layers formed

A

In grastulation

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8
Q

Ingressing cells give rise to

A

Mesoderm

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9
Q

Epiblast give rise to

A

Ectoderm

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10
Q

Hypoblast give rise to

A

Endoderm

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11
Q

How is the gut tube formed

A

Folding of sheets of cells in 2 directions

1) Folding towards the midline along the cranial caudal axis
2) Folding towards the yolk sac at the cranial caudal ends

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12
Q

What mesoderms surround the gut

A

Somatic mesoderm

Splanchnic mesoderm

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13
Q

Steps for the formation of gut tube

A

1) Embryo initially a solid flat disk attached to hemispherical yolk sac
2) Part of yolk sac cavity enclosed within the embryo by pinching off the yolk sac to form a yolk stalk and balloon like yolk sac
3) Within the embryo, the cranial and caudal intestinal portals extend the tube towards the mouth and anus, delimited by the prochordal and cloacal plates
4) The primary gut tube made up of :
A sheet of endoderm which makes up the epithelia and glands. And surrounding mesoderm which makes muscle and connective tissue

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14
Q

Regions in foregut

A

Pharynx to Ampulla of Vater

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15
Q

Regions in midgut

A

Caudal duodenum to Proximal 2/3 of transverse colon

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16
Q

Regions in hindgut

A

Distal 1/3 of transverse colon to rectum

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17
Q

Where is the foregut arterial supply from

A

Celiac artery

18
Q

Where is the midgut arterial supply from

A

Superior mesenteric artery

19
Q

Where is the hindgut arterial supply from

A

Inferior mesenteric artery

20
Q

What innervates the foregut

A

Celiac ganglion

21
Q

What innervates the mid gut

A

Superior mesenteric ganglion

22
Q

What innervates the hind gut

A

Inferior mesenteric ganglion

23
Q

Abnormality of foregut development - Pyloric stenosis

A

Gastric outlet obstruction
Caused by smooth muscle hypertrophy - smooth muscle forming the pyloric sphincter overgrows
Causes projectile vomitting

24
Q

Foregut stomach development

A
  • Stomach arises by expansion and rotation
  • During week 4 at the level where the stomach will form the tube begins to dilate, forming an enlarged lumen
  • Initially concave ventral, convex dorsal
  • 90 degree turn about cranio-caudal axis
  • The dorsal border grows more rapidly than ventral, which establishes the greater curvature of the stomach
  • Dorsal wall of stomach attached to body by mesentery: the dorsal mesogastrium (will form greater omentum)
  • Ventral wall attached by ventral mesentery, which includes the liver (will form lesser omentum)
25
Q

Mesogastrium

A
  • As stomach rotates the dorsal mesogastrium is drawn with it
  • This mesogastrium encloses a space, the OMENTAL BURSA (lesser sac)
  • The folded mesogastrium grows to form the greater omentum, the folds fusing to obliterate the bursa
26
Q

Bursa

A

Protective layer, contains WBC to prevent infection if any gastric intestinal fluid spillages

27
Q

Organ budding from the foregut - forming of the liver

A
  • Inducing signal: heart to ventral gut endoderm
  • Hepatic diverticulum grows into mesenchyme of septum transversum
  • Cords of hepatic endoderm, bile drainage ducts, and blood vessels proliferate, arranged as sinusoids
  • Liver exceeds size of septum transversum, expands into ventral mesentery
  • Remaining ventral mesentery gives rise to:
  • falciform ligament between liver and body wall
  • lesser omentum between liver and stomach
28
Q

Organ budding from foregut - forming of the pancreas

A
  • Two pancreatic buds
    1) Dorsal from duodenal endoderm (induced by notochord)
    2) Ventral from hepatic diverticulum (induced by hepatic mesoderm)
  • As duodenum rotates, ventral and dorsal buds meet and fuse
  • If ventral bud bifid (bi-lobed), and one rotates around duodenum, annular pancreas forms, which can obstruct duodenum
29
Q

Formation of midgut intestines

A
  • Attached throughout length by the dorsal mesentery – mesentery and gut grow at different rates leading to stereotypical folding of the gut
  • Ventral branch of the aorta supplies the mid gut – superior mesenteric artery (SMA)
  • Intestines rotate by 90 degrees around the SMA
  • Abdomen is too small to accommodate, so herniates into umbilical stalk at 6 or 7 weeks – They rotate by 180 degrees
  • By 10 weeks, the abdomen is bigger, and intestines return
30
Q

3 kinds of hernia that can occur in new borns

A

Umbilical hernia
Omphalocele
Gastroschisis

31
Q

Umbilical hernia

A

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

32
Q

Omphalocele

A

Failure of intestinal loops to return to abdomen, hernia covered in amnion

33
Q

Gastroschisis

A

Failure of the ventral body to fuse, no covering

34
Q

Examples of more abnormalities of intestinal development

A

Persistence of yolk duct
Meckel’s diverticulum
Hirschprung’s disease

35
Q

Persistence of yolk duct

A

Most common intestinal abnormality

Yolk duct attached to ileum, near ileo-cecal junction - apex of midgut loop

36
Q

Meckel’s diverticulum

A
  • Usually asymptomatic
  • May contain ectopic gastric cells: ulceration and lower GI bleeding
  • Can be connected to umbilicus by ligament:
  • Gut rotation causes volvulus - strangulation
    Can form umbilical fistula - contents leak out
37
Q

Hirschprung disease

A 
Aganglionic megacolon
Primarily affects the hindgut
Dilatation of sections of the colon, with lack of tone and peristalsis, leading to profound constipation
Absence of parasympathetic ganglia
Caused by lack of neural crest cells
38
Q

Neural crest cells

A
  • Neural crest cells populate developing gut and give rise to enteric ganglia
  • Neural crest cells from occiptocervical region populate the entire gut
  • Neural crest cells from sacral region populate the distal gut
39
Q

Anal development - the CLOACA

A
  • Cloaca – transient common end of the digestive and urogenital systems, including the base of the allantois (urogenital sinus)
  • Covered by the cloacal membrane over an ectoderm depression, the proctodeum
  • Split by the urorectal septum – give rise to urogenital membrane and anal membrane
  • Imperforate anus can be:
  • Persistence of an anal membrane
  • Artesia of anal canal, rectum or both
40
Q

3 steps to forming of the anal

A

1) Invagination
2) Septum formation
3) Separation

PHYSIOLOGY (28 decks)

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