1. What arises from endoderm 2. What arises from visceral (splanchnic) mesoderm

1. Epithelial lining of GI tract and glands 2. Muscle, connective tissue, and peritoneal components of wall of gut (and stroma of glands)

Development Of Digestive System Flashcards by Michelle Slattery

What is the primitive gut

Part of endoderm-lined yolk sac cavity incorporated into the embryo

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3 parts of the primitive gut?

Foregut, midgut and hindgut

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Foregut and hindgut are blind ended, what about midgut

Temporarily connected to yolk sac by vitelline duct

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Two parts of the foregut

Pharyngeal gut and caudal to pharyngeal gut up to the hepatic diverticulum (so from proximal part of duodenum and up)

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Pharyngeal gut (part of foregut) extends from where to where

Oropharyngeal membrane to respiratory diverticulum

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Where does midgut begin and end

Caudal to liver bud and extends to junction of proximal and distal transverse colon

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Hindgut extends from where to where

Distal transverse colon to cloacal membrane

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What arises from endoderm

2. What arises from visceral (splanchnic) mesoderm

Epithelial lining of GI tract and glands

2. Muscle, connective tissue, and peritoneal components of wall of gut (and stroma of glands)

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Ventral mesentery exists for what 3 organs

Derived from?

Esophagus, stomach, and initial part of duodenum

Septum transversum (mesodermal plate between pericardial cavity and stalk of yolk sac)

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Function of tracheoesophageal septum

Completely separates esophagus from respiratory diverticulum

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What is esophageal atresia?

What does this cause

Distal esophagus becomes connected to trachea just above bifurcation

Accumulation of excess amniotic fluid (polyhydramnios)

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Where does esophageal stenosis usually occur

In lower 1/3

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What is a congenital hiatal hernia caused by

Failure of esophagus to lengthen causes stomach to be pulled up through esophageal hiatus of diaphragm

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What part of the stomach do both vagus nerves innervate

Right vagus nerve innervates posterior wall of stomach
Left vagus nerve innervates anterior wall of stomach

~left side of stomach becomes anterior side

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What creates the omental bursa/lesser peritoneal sac?

Rotation of stomach pulls dorsal mesogastrium to the left and ventral mesogastrium to the right creating a space behind stomach

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What causes ventral mesogastrium to divide into 2 regions

What are these regions

Development of liver

Liver to ventral body wall (forms falciform ligament) and stomach to upper duodenum to lover (forms lesser omentum)

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Free margin of lesser omentum contains what 3 things

Bile duct, portal vein, and hepatic artery (portal triad)

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What causes pyloric stenosis

What does it cause

When musculature of stomach (usually circular fibers) hypertrophies in the pyloric region

Obstructs passage of food resulting in severe vomiting

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What part of the gut is the duodenum

Terminal part of foregut and initial part of midgut

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Duodenum rotates __

What does this contribute to

To the right with the pancreas

Contributes to these two organs being retroperitoneal (fuse with posterior body wall)

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What forms the bile duct

Narrowing of connection between liver bud and foregut

Hematopoietic cells, Kupffer cells and connective tissues cells originate from?

Mesoderm of septum transversum

Cells of hepatic diverticulum give rise to?

Liver parenchyma (hepatocytes) and epithelial lining of biliary ducts

Importance of the liver between months 2-7 of development

Produces RBCs and WBCs

What is extrahepatic biliary atresia

Biliary ducts fail to recanalize leading to death unless liver transplant. Few of these cases result in a patent proximal ducts which is correctable without transplant

What is the communication between the primitive gut and the yolk sac

Vitelline duct

Location of septum transversum (made of mesoderm)

Between pericardial cavity and vitelline duct

What is the pancreas formed by

Ventral and dorsal pancreatic buds that originate from endodermal lining of duodenum

What forms the main pancreatic duct Fate of proximal part of dorsal pancreatic duct

Distal part of dorsal pancreatic duct and entire ventral pancreatic duct Either obliterated or becomes accessory pancreatic duct

What forms pancreatic connective tissue

Visceral mesoderm surrounding pancreatic buds

What is annular pancreas What happens if it is compressed

Pancreatic tissue that surrounds the duodenum Causes complete obstruction of duodenum

What is the physiological umbilical herniation

Abdominal cavity becomes temporarily too small to accommodate the rapidly growing intestines, so they enter umbilical cord during 6th week-10th week (gives abdominal cavity time to grow)

What is the last part of the midgut to reenter the abdominal cavity

Cecal bud

As cecal bud descends into right iliac fossa, what does it cause

The ascending colon to be on the right side of abdominal cavity

What is an omphalocele

Herniation of abdominal viscera through an enlarged umbilical ring (Failure of the organs to return to the abdominal cavity) - high fatality rate because usually have chromosomal abnormalities as well

What is gastroschisis?

Protrusion of intestinal loops into the amniotic cavity (so on the outside of umbilical cord) due to abnormal closure of body wall

Other differences between omphalocele and gastroschisis

Omphalocele- high mortality rate; herniated viscera is covered by amnion Gastroschisis- lower mortality rate because it is not associated with other abnormalities, common in babies of young moms who use cocaine during pregnancy; not covered by amnion so exposed and can be damaged easier

What is/what causes Meckel’s/ileal diverticulum Symptoms?

Small portion of vitelline duct persists forming outpocket of ileum- usually asymptomatic Can cause ulcers/bleeding; symptoms mimic appendicitis

What is enterocystoma/vitelline cyst What can it cause

When both ends of vitelline duct transform into fibrous cords and middle portion forms a cyst (can compromise blood supply)

What is a vitelline fistula Symptom

Vitelline duct remaining patent which forms a communication between umbilicus and intestinal tract Fecal discharge may be found at umbilicus

1. If primary intestinal loops only rotate 90 degrees COUNTERCLOCKWISE what happens 2. What happens if 90 degrees CLOCKWISE

1. Cecum and colon will end up on left side instead of right side; jejunum and ileum will be on left side 2. Transverse colon will pass behind duodenum and lie behind SMA

Where in the midgut are you most likely to have atresias and stenoses?

Duodenum

1. Atresia’s in upper part of duodenum are most likely from? | 2. Distal duodenum and other parts of midgut?

1. Lack of recanalization | 2. Vascular accidents (will lead to blood loss and eventual transformation into a fibrous cord)

Hindgut endoderm gives rise to

Internal lining of urinary bladder and urethra

Caudal end of hindgut is called __ This is connected to

Cloaca Allantois (which connects to umbilical cord)

Cloacal membrane is derived from

Ectoderm and endoderm

Urorectal septum divides cloaca into

Primitive urogenital sinus (anteriorly) and anorectal canal (posteriorly) (These both rupture to form anal opening)

What can cause rectourethral/rectovaginal fistulas?

Abnormalities in formation of cloaca and/or urorectal septum

Most likely causes of rectoanal atresia?

Vascular accidents (may leave fistula, or cause loss of segment of rectum/anal canal)

What causes an imperforate anus

Failure of anal membrane to breakdown

What causes congenital megacolon (aka aganglionic megacolon/Hirschprungs disease) How does it present

Scarce or absent parasympathetic neurons in distal colon (leaves this region permanently constricted - and causes proximal region to be dilated Hypertrophy of sigmoid and descending colon, constipation, abdominal distention