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Development of GI Flashcards

1
Q

What germ layer is the epithelium derived from, and what are the exceptions?

A

Endoderm

Except the Mouth and Anal canal

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2
Q

What germ layer is the mesenchyme layer derived from?

A

Splanchnic mesoderm

Also makes the smooth muscle and connective tissue

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3
Q

What tissue are derived from Neural Crest Cells?

A

The autonomic ganglia

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4
Q

What germ layer are the mouth and anal canal derived from?

A

Ectoderm

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5
Q

What are the divisions of the GI tract and what structure determines this layout?

A

Foregut
Midgut
Hindgut

Determined by where the Yolk sac attaches.
Above Yolk sac = Foregut
At Yolk Sac = Midgut
Below Yolk sac = Hindgut

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6
Q

What structures are part of the Foregut?

A 
Pharynx
Respiratory System
Esophagus
Stomach
Liver
Pancreas
Biliary Apparatus
Proximal Duodenum
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7
Q

What structures are part of the Midgut?

A 
Small intestine
Cecum
Appendix
Ascending Colon
Right Half of Transverse Colon
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8
Q

What structures are part of the Hindgut?

A 
Left Half of Transverse Colon
Descending Colon
Sigmoid Colon
Rectum
Superior Anal Canal
Epithelium of Urinary Bladder/Urethra
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9
Q

What structure separates the Foregut and Midgut?

A

The Major Duodenal Papilla (the opening in the 2nd part of the duodenum where the common bile duct and pancreatic duct meet the intestine)

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10
Q

What are the 3 blood vessels that supply blood to the 3 divisions of the GI tract respectively?

A

Celiac Trunk supplies the Foregut

Superior Mesenteric A. supplies the Midgut

Inferior Mesenteric A. supplies the Hindgut

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11
Q

What germ layer derives the Mucosa of the Esophagus?

A

Foregut endoderm

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12
Q

What’s special about the esophageal mesenchyme and what germ layers cause this?

A

Esophagus has skeletal and smooth muscle

Skeletal primarily in the superior portion

Smooth primarily in the inferior portion

Smooth Muscle is derived from Splanchnic Mesoderm

Skeletal Muscle is derived from Pharyngeal Arch Mesoderm (specifically arch 4 and 6)

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13
Q

What is a tracheal esophageal fistula?

A

An abnormal passage between the trachea and the esophagus (due to an failure of tracheoesophageal folds to properly form the tracheoesophageal septum; occurs in week 5)

Presenting signs and symptoms:

  • Prenatally: Polyhydramnios (too much amniotic fluid)
  • Birth: Coughing, gagging, cyanosis, vomiting, voluminous oral secretions, possible respiratory distress
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14
Q

What is Esophageal Atresia?

A

Blind end esophagus

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15
Q

When does the stomach begin to form?

A

4th week

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16
Q

How does the stomach form?

A

Starts as a swelling inferior to esophagus

Ventral side grows at a faster rate forming a pocket

Pocket rotates in transverse plane 90 degrees so that ventral pocket is facing left

Then it rotates in the coronal plane 90 degrees so that the greater curvature is below and the lesser curvature is above

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17
Q

What happens to the vagus nerves as the stomach rotations occur?

A

The Left vagus nerve becomes anterior while the Right Vagus nerve becomes posterior (clockwise rotation)

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18
Q

What is Hypertrophic Pyloric Stenosis?

A

Circular and some longitudinal muscles of the Pylorus become hypertrophied, constricted the Pylorus

Patient projectile vomits soon after eating, has smaller and fewer stools, failure to gain weight or may lose weight

Cause unknown; very common

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19
Q

What structure are formed from the hepatic diverticulum?

A

The liver, biliary system, and the ventral pancreatic bud

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20
Q

As the liver grows superiorly, it fuses with what structure?

A

Septum transversum (diaphragm)

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21
Q

When does bile production begin?

A

12th week

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22
Q

When does hematopoiesis in the liver begin?

A

Week 6-30

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23
Q

How is the pancreas formed?

A

There is a ventral and dorsal primordia of the pancreas
Ventral primordia is fromed from the hepatic diverticulum.

These structures eventually rotate and fuse

The ventral primordia forms some of the head of the pancreas, the uncinate process, and the main pancreatic duct

The dorsal primordia forms some of the head, the body, and the tail of the pancreas

24
Q

What is an Annular Pancreas?

A

Annular Pancreas occurs when the ventral pancreatic bud is bifid.

It then rotates in the opposite direction it should be rotating, fusing around the duodenum in a ring, causing a constriction of the gut.

Similar to Hypertrophic Pyloric Stenosus, but the vomiting with have bile in it.

2/3 of patients are asymptomatic

25
What germ layer is the Spleen derived from?
Mesoderm (it is still foregut though)
26
When does the spleen form?
Week 5
27
When does hematopoiesis occur in the Spleen?
Week 9-28
28
How does the midgut develop?
The mid gut along with the Superior Mesenteric A. herniates into the yolk stalk forming an elongated loop. The loop rotates 90 degrees clockwise so that the inferior half is on the left, and the superior portion is on the right. The right half (inferior) forms a bulge near the end that forms into the cecum. The left half (superior) becomes very convoluted (squiggly). Left half ultimately becomes the large intestine, while the right half forms the small intestine. The abdomen grows larger, and the right (superior/small intestine) portion returns to the abdomen first and PASSES UNDER the left (inferior/large intestine portion) to the left side of the abdomen. This results in the proximal duodenum being in a position posterior to the transverse colon
29
Why does the midgut herniate into the yolk stalk for development?
To make room for the massive liver (which is producing blood) and the large kidneys
30
When does the Midgut herniate into the yolk stalk?
Week 6
31
When does the midgut return to the abdomen from the yolk stalk?
Week 10
32
Where and how much are the 3 rotations?
Rotates 90 degrees in the yolk stalk Then the small intestine rotates 180 degrees when it returns to the abdomen Then the large intestine rotates 180 degrees when it returns to the abdomen Total rotation = 270 degrees
33
What is omphalocele?
Gut in umbilicus (with sac of peritoneum and skin surrounding guts Caused by failure of guts to return to abdomen at week 10 NOT AN UMBILICAL HERNIA
34
What is Gastroschisis?
Guts outside of abdomen without sac of peritoneum and skin Failure of body wall closure at week 4
35
What is Hirschprung Disease?
Also known as mega colon. Most common cause of neonatal obstruction Failure of neural crest, resulting in lack of autonomic ganglion cells (preventing motility of segment distal to dilated (clogged) section. Dilated (feces filled section) is normal; only distal part is affected.
36
What is Midgut Nonrotation?
Nonrotation is when the midgut returns to the abdomen from the yolk stalk, but fails to complete its final rotation This results in the small intestine lying in the Right side of the abdomen and the large intestine lying in the left side of the abdomen Fissures of the colon are tighter, and can cause constriction However, patients can also be asymptomatic
37
What is Midgut Reversed Rotation?
When the Midgut returns to the abdomen from the yolk stalk, it completes its final rotation in the wrong direction, resulting in the duodenum being anterior to the transverse colon. Duodenum can potentially cause a constriction of the transverse colon
38
How is the lumen of the gut tube formed?
At first the tube is hollow Then tube is occluded by endodermal proliferation Then Recanalization occurs via apoptosis
39
What can go wrong with lumen formation
Duplication can occur, where a pocket or pouch forms on the wall of the gut tube, which can collect material and occlude the gut Stenosis (narrowing of lumen due to failure of apoptosis) can occur, causing a constriction of the gut tube
40
What is Meckel's diverticulum?
Abnormailty of the vitelline duct (normally regresses) Causes a projection of the ileum to abdominal wall (essentially making a fork in the road with a dead end at the belly button) Leads to intestinal obstruction, gastrointestinal bleeding, bowel sepsis (presents similar to appendicitis) RULE OF 2's - Affects 2% of population - Approx. 2 feet form ileocecal junction - Pouch is 2 inches long - Conatins 2 types of ectopic tissue (pancreatic or gastric tissue) - Present at 2 years of age - Males 2x more than females Some can have Meckel's without symptoms
41
What is an Omphalomesenteric fistula?
One form of Meckel's Diverticulum Diverticulum leads straight through umbilicus resulting in Ileal contents to drip out of belly button
42
What is an Omphalomesenteric Cyst?
Bubble of fluid encased in a ligement remnant of the vitelline duct. Usually asymptomatic; rare
43
What is a Omphalomesenteric Ligament?
Ligament remnant of the vitelline duct that connects the ileum to the umbilicus Asymptomatic; rare
44
What developmental processes occur at the cloaca?
Urorectal septum grows toward the cloacal membrane and divides it into 2 The Urogenital Membrane - which forms into the Bladder The Anal Membrane - which forms into the anus Both are derived from ENDODERM AND ECTODERM
45
What germ layer forms the Urorectal Septum?
Mesoderm
46
Why does the cloacal membrane not have mesoderm?
Without mesoderm, the cloacal membrane is able to eventually rupture to form the open anus and urethra
47
How does the Anal Canal Develop?
The Proximal 2/3 of the Anal Canal is formed from Hindgut (endoderm) The Distal 1/3 of the Anal Canal is formed from the Anal Pit (formed from ectoderm proctodeum) The Pectinate Line is where the two portions are divided
48
What is the Blood Supply, Nerve Innervation, and Lymph flow for the Hindgut portion of the Anal Canal?
B: Inferior Mesenteric A. N: Autonomics L: Inferior Mesenteric Lymph nodes Cannot feel pain if hemorrhoid is present above the Pectinate Line
49
What is the Blood Supply, Nerve innervation, and lymph flow for the Anal Pit portion of the Anal Canal?
B: Middle Rectal Arteries and Inferior Rectal Arteries N: Pudendal Nerve (somatic; voluntary control) L: Superficial Inguinal Lymph Nodes Can feel pain if hemorrhoid is present below Pectinate Line
50
What are the two processes that must take place in order to correctly form the Anorectal structure?
The Urorectal septum must fully migrate and separate the cloaca The ENDODERM (hindgut) and the ECTODERM (anal pit) must meet at the correct place Failure of either of these events can cause a variety of complications
51
What germ layer is the septum transversum derived from?
Somatic layer of lateral plate mesoderm
52
How does closure of the Percardioperitoneal Canal Occur?
Septum transversum does not migrate all the way to the posterior wall, leaves the Pericardioperitoneal canals open The Pleuroperitoneal membrane migrates from the posterior wall to meet the septum transversum Then finally, tissue from the body wall is pulled into the diaphragm (forming the outermost portions of the diaphragm)
53
What specific part of the diaphragm is derived from the Septum Transversum?
Central Tendon (white part)
54
What part of the diaphragm is derived from the dorsal mesentery?
The Right and Left Crus
55
What is a mesentery?
Double layer of splanchnic mesoderm
56
What do somatic and splanchnic mesoderm form in the parietal cavity?
Somatic Mesoderm - Parietal Layer of peritoneum Splanchnic Mesoderm - Visceral Layer of Peritoneum

Colin GI (10 decks)

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