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Gastro-intestinal System > Embryology > Flashcards

Embryology Flashcards

(78 cards)

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1
Q

How does embryonic folding help development of the GI tract?

A

Creating a ventral body wall

Creating a tube within a cavity

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2
Q

In which week does the embryo fold?

A

4th

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3
Q

When the GI tube first develops, what does it look like?

A

A simple tube with 2 blind ends

1 opening at the umbilicus (midgut continuous with the yolk sac)

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4
Q

Where does the primitive gut tube run from and to?

A

Stomatodeum (future mouth) to the proctodeum (future anus)

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5
Q

What is the internal lining of the gut tube derived from?

A

Endoderm

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6
Q

What is the external lining of the gut tube derived from?

A

Splanchnic mesoderm

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7
Q

Which parts of the GI tract are derivatives of the foregut?

A 
Oesophagus 
Stomach 
Pancreas
Liver
Gall bladder
Duodenum (to duodenal papilla)
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8
Q

Which parts of the GI tract are derivates of the midgut?

A 
Duodenum (after duodenal papilla)
Jejunum 
Ileum 
Caecum 
Ascending colon 
Proximal 2/3 of the transverse colon
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9
Q

Which parts of the GI tract are derivatives of the hindgut?

A 
Distal 1/3 of the transverse colon 
Descending colon 
Sigmoid colon 
Rectum 
Upper anal canal 
(Internal lining of the bladder and urethra)
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10
Q

What is the blood supply to each embryonic division?

A 
Foregut = coeliac trunk 
Midgut = superior mesenteric artery 
Hindgut = inferior mesenteric artery
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11
Q

Describe the blood supply to the duodenum

A

Proximal to duodenal papilla = gastroduodenal and superior pancreaticoduodenal (from the coeliac trunk)
Distal to duodenal papilla = inferior pancreaticoduodenal (from SMA)

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12
Q

Describe the blood supply to the head of the pancreas

A 
Superior pancreaticoduodenal (coeliac trunk)
Inferior pancreaticoduodenal (SMA)
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13
Q

Describe the intraembryonic coelom

A

Begins as one large cavity
Later subdivided by the future diaphragm into the abdominal and thoracic cavities
Peritoneal membrane lines the abdominal cavity

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14
Q

What is a mesentery?

A

A double layer of peritoneum suspending the gut tube from the abdominal wall
Allows a conduit for nerve and blood supply
Allow mobility where needed

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15
Q

How is the mesoderm formed?

A

Condensation of splanchnic mesoderm

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16
Q

Describe the greater omentum

A

Formed by the dorsal mesentery
Suspended by the greater curve of the stomach
First structure seen when the abdominal cavity is opened

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17
Q

Describe the lesser omentum

A

Formed by the ventral mesentery

Free edge of the portal triad

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18
Q

The rotation of the stomach contributes to the formation of the …

A

Greater and lesser sacs

Omenta

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19
Q

How is the lesser sac formed?

A

The right hand sac pushed posterior to the stomach due to the enlargement of the liver
(Left and right sac formed due to having a dorsal and ventral mesentery at the foregut)

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20
Q

Describe the rotation of the stomach

A

Around the longitudinal axis and then around the anterior-posterior axis
Puts the vagus nerve anterior and posterior to the stomach
Shifts cardia and pylorus from midline
Contributes to moving lesser sac behind the stomach
Creates the greater omentum

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21
Q

Describe secondary retroperitoneal

A

Began development invested by peritoneum

Mesentery is lost through fusion at the posterior abdominal wall

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22
Q

When and where does the respiratory diverticulum form?

A

4th week
Forms in the ventral wall of the foregut at the junction with the gut where the pharyngeal will form
(Lungs and bronchial tree derived from the foregut)

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23
Q

How do the respiratory primordium and the oesophagus separate?

A

Tracheoesophageal septum grows

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24
Q

How often do we get abnormal positions of the tracheoesophageal septum?

A

1 in 3000 live births

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25
Describe the development of the stomach
Week 4 a slight dilation of the distal foregut occurs (stomach primordium) Faster growth at the dorsal border creates the greater curve Rotation - changes position of mesenteries
26
What structures are formed in the ventral mesentery?
Liver Biliary system Part of the pancreas (uncinate process and inferior head)
27
What structures are formed in the dorsal mesentery?
Superior head, neck, body and tail of the pancreas
28
Where is the lesser omentum?
Attaches the liver to the lesser curve of the stomach
29
What happens in the duodenum in the 5th-6th weeks?
Lumen is obliterated due to the rapid growth of the length and lining Recanalised by the end of the embryonic period
30
Why does the duodenum become retroperitoneal?
Rotation of the stomach pushes the duodenum to the right and then against the posterior abdominal wall (Secondary retroperitoneal)
31
Which structures are secondary retroperitoneal?
Duodenum (except cap) | Pancreas
32
What is another name for the lesser sac?
Omental bursa
33
What is the sign, during embryonic life, of atresia of the oesophagus?
Polyhydramnios Prevents normal passage of amniotic fluid in the intestinal tract resulting in accumulation of excess fluid in the amniotic sac
34
How is the spleen suspended?
Splenorenal ligament - connecting spleen to posterior abdominal wall in the area of the left kidney Gastrosplenic ligament - connects the spleen to the stomach
35
What forms the roof of the epiploic foramen of Winslow?
Free edge (lesser omentum)
36
What is the gubernaculum?
Connects the developing testicle to the developing scrotum | Gets shorter and guides the testicle into place
37
What is the primitive gut a derivative of?
Definitive yolk sac (during folding)
38
What does the midgut make a loop around?
Superior mesenteric artery (axis)
39
Why does the midgut need to herniate?
Midgut elongates enormously Runs out of space because the abdominal cavity doesn't grow at the same rate Liver is also growing rapidly Not enough space
40
What attaches the midgut to the yolk sac?
Vitelline duct
41
How are the cranial and caudal limbs defined?
Above and below where the SMA enters
42
When does physiological herniation take place?
6th week
43
Where do the intestines herniate?
Into the umbilical cord
44
Describe midgut rotation
A series of 3 90 degree turns anticlockwise Starts with cranial limb (above SMA) 1st turn occurs during herniation 2nd and 3rd turns occur on returning to the abdominal cavity
45
Where do the limbs of the midgut come to lie?
Cranial limb = left side of SMA | Caudal limb = right side of SMA
46
What happens during the second rotation?
Get the crossing of the 2 limbs | Caudal limb lies in front of the cranial limb
47
What happens during the third rotation?
Cranial limb derivatives are pushed towards the left | Descent of caecal bud to create the ascending colon
48
What are the cranial limb derivatives?
Distal duodenum Jejunum Proximal ileum
49
What are the caudal limb derivatives?
``` Distal ileum Caecum Appendix Ascending colon Proximal 2/3 transverse colon ```
50
Describe incomplete rotation of the midgut
Midgut loop makes only one 90 rotation Left sided colon Limbs don't twist on each other - cranial limbs not pushed back in first
51
Describe reversed rotation
Midgut makes one 90 clockwise rotation Less crossing Caudal limb is not anterior to cranial limb Transverse colon passes posterior to the duodenum
52
When should the vitelline duct close?
After herniation resolves
53
Name some consequences of a persistent vitelline duct
Vitelline cyst Vitelline fistula Meckel's diverticulum
54
Describe a Meckel's diverticulum
Most common GI anomaly Small diverticulum of small intestine where the vitelline duct was May be free or attached to the abdominal wall Rule of 2s: affects 2% population, 2 feet from ileocaecal, 2 inches long, under 2s, 2:1 male:female
55
Which types of ectopic tissue can a Meckel's diverticulum contain?
Gastric | Pancreatic
56
Where in the GI tract does recanalisation have to occur?
In the oesophagus, bile duct and small intestine
57
What is the difference between atresia and stenosis?
``` Atresia = no lumen Stenosis = lumen narrowed ```
58
Stenosis in the duodenum is most likely to be a result of ...
Incomplete recanalisation
59
What is pyloric stenosis?
Due to hypertrophy of the smooth muscle (circular) in the region of the pyloric sphincter Not a recanalisation failure Common abnormality in infants - projectile vomiting
60
Where are atresia and stenoses most likely to occur?
Duodenum
61
What divides the anal canal?
Pectinate line (superior and inferior)
62
The urorectal septum divides the cloaca into the ...
Urogenital sinus | Anorectal canal
63
What is the proctodeum?
Anal pit Small depression of ectodermal tissue Comes up into the body to meet the endoderm tube
64
What is the perineal body?
Pyramidal fibromuscular mass in the midline of the perineum | At the junction between the urogenital triangle and the anal triangle
65
Describe the blood supply, innervation and lymphatic drainage of superior anal canal
Inferior mesenteric artery S2,S3,S4 - pelvic PNS Lymphatic drainage - internal iliac nodes
66
Describe the blood supply, lymphatic drainage and innervation of inferior anal canal
Pudendal artery S2, S3, S4 - pudendal nerve Lymphatic drainage = superficial inguinal nodes
67
Describe the epithelia difference between superior and inferior anal canal
``` Superior = columnar Inferior = stratified squamous ```
68
What is the sensation possible above the pectinate line?
Stretch | Poorly localised pain
69
What sensations can be felt below the pectinate line?
Temperature Touch Pain (localised)
70
Which type of innervation does the parietal peritoneum receive?
Somatic innervation
71
What is an imperforate anus?
Failure of anal membrane to rupture
72
What is anal/anorectal agenesis?
Failure of normal formation of anal canal | Absence of primordial tissue
73
What are mesenteries retained by?
``` Jejunum Ileum Appendix Transverse colon Sigmoid colon ```
74
Where do fused mesenteries occur?
Duodenum Ascending and descending colon Rectum
75
What structures are formed from the dorsal mesentery?
``` Greater omentum Gastrosplenic ligament Splenorenal ligament Mesocolon Mesentery proper ```
76
What does the ventral mesentery become?
Lesser omentum | Falciform ligament
77
What is the innervation to the midgut?
PNS - vagus nerve | SNS - superior mesenteric ganglion and plexus
78
What is the innervation to the hindgut?
PNS - pelvic (S2,3,4) | SNS - inferior mesenteric ganglion and plexus

Gastro-intestinal System (10 decks)

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