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GI BLOCK > Development > Flashcards

Development Flashcards

1
Q

What is Gastrulatikn?

A

Formation of three layers of embryo

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2
Q

Which layer form the GÌ tube?

A

Endodermal layer

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3
Q

What other tissue comes from the splanchnic mesoderm?

A

●Connective tissue in the glands (stromal cells)
●Muscle tissue
●Connective tissue
●Peritoneal tissue

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4
Q

What structures of the GÌ for, from the enedoderm?

A

●Lining of GI is endodermal

●Functional cells that make up the glands in the pancreas and liver are also endodermal (parenchymal cells)

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5
Q

How is the GUT tube formed?

A

●Gut tube is closed at either end to start with: oropharyngeal membrane and cloacal membrane
●Oropharyngeal membrane breaks down at approximately 22 days-35d

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6
Q

What are the regions of the tube?

A

●Pharyngeal gut (pharynx)
Oropharyngeal membrane to the respiratory diverticulum
●Foregut
Respiratory diverticulum to the liver bud
●Midgut
Below (caudal) liver bud to junction of the Right and Left thirds of the adult transverse colon (R ⅔ , L ⅓)
●Hindgut
L ⅓ of colon to the cloacal membrane (anus)

●Cloaca separates into bladder and rectal regions to allow intestine to join the rectum

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7
Q

HOW IS THIS REGIONALISATION SET UP?

A

●Regionalisation = specification or patterning
●Concentration gradient of Retinoic Acid (RA)

RA, FGF and Wnt gradient causes the expression of different transcription factors, which further specify the gut tube.

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8
Q

What happens for further specification?

A

Mesoderm, epithelia and enteric NS interact to fix this regionalisation. Modified throughout life
●Shh is expressed throughout the gut endoderm and sets up further specification.

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9
Q

How does SHH expresses further specification?

A

Shh stimulates mesodermal expression patterns through BMP4

Interaction determines epithelial layers and

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10
Q

What happens when Shh signalling I’d disrupted?

A

Disruption: bowel dysfunction, epithelial cancers

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11
Q

How is the pharynx formed?

A

●Top part is ectodermal
●Only forms with no RA
●Lower is endodermal
●Pharyngeal pouches form from this tissue, within the pharyngeal arches:
1st pair: auditory cavities and Eustachian tubes
2nd pair: tonsils
3rd pair: Thymus (T-lymphocyte production) and parathyroid gland
4th pair: parathyroid gland

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12
Q

What is the important e of mesenteries in the formation of the GÌ tract?

A

●Allows nerves, blood vessels and lymphatic system access to the gi tract
●Initially fully covered, but by 5 weeks, dorsal mesentery covers only the:
Caudal foregut
Midgut
Most of hindgut

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13
Q

What are mesenteries?

A

●Gut tube suspended by mesenteries attached to the body wall.
●Fully surrounded by a double layer of peritoneum (Intraperitoneal)

●Comes from caudal region of septum transversum.

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14
Q

What is the ventral mesentry?

A

●Upper part of GI tract
●End of oesophagus
●Stomach
●Upper duodenum

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15
Q

What is the function of the ventral mesentry?

A

As the liver grows, it splits the ventral mesentery into the lesser omentum and falciform ligaments

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16
Q

What happens at the dorsal mesentry ever the stomach ?

A

Becomes dorsal mesogastrium/ greater omentum

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17
Q

What does the ventral mesentry at the oesophagus, stomach, upper duodenum become?

A

Lesser omentum

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18
Q

What does the dorsal mesentry of the duodenum become?

A

Mesoduodenum

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19
Q

What does the ventral mesentry of the stomach become?

A

Ventral mesogastrium

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20
Q

What does the dorsal mesentry of the colon become?

A

Dorsal mesocolon

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21
Q

What does the ventral mesentry of the liver to liver body wall become?

A

Falciform ligament

22
Q

What does the dorsal mesentry over the jejenum la and ideal loops become?

A

Mesentry proper

23
Q

The connection of the gut to the mesentry is essential for what?

A

Development of both the mesentry structures and the position of the GI tract itself

As the embryo and the GI twists and grows, it stretches and moves the mesentery

24
Q

How is the stomach formed?

A

●Stomach forms by rotation and differential growth rates
●Greater curvature: Posterior axis → faster growth
●Rotation means that left and right vagus nerves are carried round too

25
Q

How do rotation and movements of stomach occur?

A

Rotation and movement of the stomach moves the duodenum to the right.
It takes the pancreas with it, moving the pancreas to the back (dorsal position)

Duodenum is blocked in the 2nd month as cells proliferate. Canalisation reopens the lumen.

26
Q

Duodenum is blocked in the 2nd month as cells proliferate.

What reopens the lumen?

A

Canalisation

27
Q

How the midgut formed?

A

●Rapid elongation and looping.
●Body cavity is too small for this process, so physiological herniation occurs
- Gut extends outside the body cavity and into the umbilical cord (week 6)
- Rotation occurs around the mesenteric artery:
* First rotation is 90◦ CCW
* 2nd is 180◦

●Rotation means that the small intestine will sit below caecum and transverse colon
●Retraction gives final position and occurs around 10 weeks

28
Q

What are the final positions during formation of the GI tract?

A

●Jejunum and ileal loops formed during extension are retracted into the back of the cavity and left side of the cavity, but will move towards the right later.
●Transverse colon pushed straight back
●Cecal bud grows at 6 weeks. Last to enter into R quadrant. Grows downwards to right iliac fossa. Appendix forms from cecal diverticulaum

29
Q

What is the hindgut and where is it located?

A 
●Distal ⅓ of transverse colon
●Descending colon
●Sigmoid colon
●Rectum
●Upper part of anal canal
30
Q

Where Is the anal canal a?

A

●Upper part from hindgut

●Lower ⅓ from ectoderm around the proctodeum

31
Q

How is the anal canal formed?

A

●Cells on the surface of cloaca proliferate and invaginate to make an anal pit

●Cloacal membrane

  - Boundary of hindgut and cloaca
   - Degenerates at 7 weeks
    - Bladder and gut now open
32
Q

How are liver, pancreas and gall bladder (accessory organs) formed?

A

All endodermal in origin (lining)

Hepatic diverticulum gives rise to the gall bladder and remains to function as the hepatic duct.

The liver endoderm interacts with mesoderm to branch and grow to form the glandular portion of the liver

33
Q

How is the liver formed?

A

●Induced by proximity to the heart
●Grows into the septum transversum
●Gut next to the notochord won’t form liver
Two cell types
●Hepatocytes are specified by Hepatocyte Growth Factor (HGF) and glucocorticoids
●Cholangiocytes (bile duct cells) are specified by the TGFβ family. Bile forms at 12 weeks

34
Q

When is Bile formed ?

A

At 12 weeks

35
Q

What are the 2 types of cells in the liver?

A

●Hepatocytes are specified by Hepatocyte Growth Factor (HGF) and glucocorticoids

●Cholangiocytes (bile duct cells) are specified by the TGFβ family. Bile forms at 12 weeks

36
Q

How is pancreas formed?

A

●Forms from 2 buds- dorsal and ventral that rotate with the duodenum and fuse
●Ventral pancreas becomes the uncinated process (inferior part of the head of the pancreas)
●Islets of Langerhans form in 3rd month and is functional in the 5th month

●Pancreas induced by notochord and inhibited by heart
●Forms where the main veins are closest to the foregut endoderm

37
Q

When are the Islets of Langherans formed and when are they functional?

A

In the 3rd month and is functional in the 5th month

38
Q

What does the maturation of pancreas involve?

A

Pancreas is an exocrine gland and has two important , functional cell types :

●endocrine cells
β,δ α , PP cells in islets of Langerhans

●exocrine cells
Ductal and acinar cells

●Same progenitor
●Hierarchy of gene expression and mutual inhibition determines the fate of the cells

39
Q

How is constant regeneration pf the intestine maintained?

A

●The intestine works hard and turnover of cells is high due to high throughput
●Population of stem cells to replace intestinal absorptive cells (every 2-3 days)
●Cells move up the villus and undergo anoikis

Anoikis: programmed cells death through loss of attachment

40
Q

What is Anoikis?

A

programmed cells death through loss of attachment

41
Q

How do bacterial help differentiation of the gut?

A

Gut bacteria (up to 1011 /ml) from mother
●picked up during birth from birth canal after amnion bursts
●Bacteria also help with differentiation of the gut
●Mice with no bacteria have undifferentiated intestines
●Some bacteria affect proliferation of intestinal stem cells
●Some affect gene expression

42
Q

What does it mean when there are no bacteria present during differentiation of the gut?

A

No bacteria: no brush enzymes, decreased vascularisation, decreased cell number and no goblet cells

43
Q

What is necrotising enterocolitis?

A

Inflammation of the intestine results in perforation and leakage of bacteria and intestinal content into the abdomen

First few days postnatal, premature, SGA . 3:1000 in neonatal ICU

Green vomit, tenderness, bloody stool, general signs of infection.

Non specific signs at start

44
Q

What abnormalities/ congenital disorders are present in the lumen?

A

●Atresias
Interruptions of the lumen
Detectable by polyhydramnios (excessive amniotic fluid), or absent stomach bubble in ultrasound
Postnatally: frothy white bubbles at mouth, coughing or choking when feeding

●Stenosis: Narrowing of the lumen
Types:
- Duodenal stenosis
- Pyloric stenosis- muscle overgrowth, obstructing the lumen
Forceful vomiting (projectile), vomited milk is curdled, reduced amount of faeces.
Males more than females. Develops about 6 weeks.
Can feel a hard lump on RH of stomach.
Treatment is a pyloromyotomy

45
Q

What is meckel’s diverticulum?

A

●One of the most common disorders (2% of population)
●Persistence of the vitelline duct
●Generally asymptomatic. May release acid , causing ulceration, bleeding and infection. May lead to peritonitis.
●Treatment by laparoscopy if required and no food until stomach and bowel are healed

46
Q

What is MALROTATION (abnormal rotation) disease?

A

Volvulus

●Twisting of gut, causing an obstruction
●Caused by mesentry not fixing to duodenojejunal flexure or ileocaecal regions
●Can cut blood supply leading to necrosis

47
Q

What are the 3 types of malrotaion?

A

Midgut volvulus
Caecal volvulus
Sigmoid volvulus

48
Q

What is Herniation?

A

External herniation like Gastroschisis or Omphalocele are associated with problems in development.

49
Q

What is Gastroschisis?

A

MSK defect.

Body wall does not reform properly following physiological herniation or later disruption.

Abdomen contents herniate into the amniotic fluid which is corrosive.

Danger of dehydration and heat loss from exposure.

Operation required to repair damaged tissue. Prognosis good.

50
Q

What is Omphalocoele (exomphalos))?

A

Abdomen contents protrude through the umbilical ring (herniation extends into the umbilical cord).

Protected by the umbilical tissue so no degradation of abdominal tissues.

Generally associated with other major congenital conditions so prognosis not as positive

GI BLOCK (13 decks)

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