Hy Embryology 07 Part 2

Front 1

What germ layer is the pancreas formed from?

Back 1

The ventral pancreatic bud and dorsal pancreatic bud are direct outgrowths of the foregut endoderm

Front 2

Describe the formation of the exocrine pancreas

Back 2

Within both pancreatic buts (ventral and dorsal), endodermal tubules surrounded by mesoderm branch repeatedly to form acinar cells and ducts (ie, exocrine pancreas)

Front 3

Describe the formation of the endocrine pancreas

Back 3

Isolated clumps of endodermal cells bud from the endodermal tubules in the pancreatic buds and accumulate within the mesoderm to form islet cells (ie endocrine pancreas)

Front 4

Describe the formation of the definitive adult pancreas

Back 4

1. The ventral pancreatic bud and dorsal pancreatic bud are direct outgrowths of foregut endoderm

2. Because of the 90 degree clockwise rotation of the duodenum, the ventral but rotates dorsally and fuses with the dorsal bud to form the definitive adult pancreas

Front 5

What portion of the pancreas does the ventral bud form?

Back 5

-Uncinate process
-A portion of the head of the pancreas

Front 6

What portion of the pancreas does the dorsal bud form?

Back 6

-A portion of the head
-Body
-Tail

Front 7

Describe the formation of the uncinate process of the pancreas

Back 7

From the ventral bud

Front 8

Describe the formation of the head of the pancreas

Back 8

A portion is from the ventral bud and a portion is from the dorsal bud

Front 9

Describe the formation of the body of the pancreas

Back 9

From the dorsal bud

Front 10

Describe the formation of the tail of the pancreas

Back 10

From the dorsal bud

Front 11

Describe the formation of the pancreatic duct

Back 11

Formed by the anastamosis of the distal 2/3 of the dorsal pancreatic duct (the proximal 1/3 regresses) and the entire ventral pancreatic duct (48% incidence).

Front 12

Describe the accessory pancreatic duct

Back 12

Develops when the proximal 1/3 of the dorsal pancreatic duct persists and opens into the duodenum through a minor papillae at a site proximal to the ampulla of Vater (33% incidence)

Front 13

Describe the pancreas divisum

Back 13

1. Occurs when the distal 2/3 of the dorsal pancreatic duct and the entire ventral pancreatic duct fail to anastomose and the proximal 1/3 of the dorsal pancreatic duct persists, thereby forming two separate duct systems

2. The dorsal pancreatic duct drains a portion of the head, body, and tail of the pancreas by opening into the duodenum though the major papillae

3. Patients with pancreas divisum are prone to pancreatitis especially if the opening of the dorsal pancreatic duct at the minor papillae is small

4. 4% incidence

Front 14

Describe annular pancreas

Back 14

1. Occurs when the ventral pancreatic bud fuses with the dorsal bud both dorsally and ventrally, thereby forming a ring of pancreatic tissue around the duodenum causing severe duodenal obstruction

2. Infants and newborns are intolerant of oral feeding and often have bilious vomiting

Front 15

Describe the development of the upper duodenum

Back 15

Develops from the caudal portion of the foregut

Front 16

What artery supplies the midgut derivatives

Back 16

Superior mesenteric artery

Front 17

Describe the formation of the lower duodenum

Back 17

1. The lower duodenum develops from the cranial-most part of the midgut

2. The junction of the upper and lower duodenum is just distal to the opening of the common bile duct

Front 18

Describe the changes in the midgut throughout development

Back 18

The midgut formats a U-shaped loop (midgut loop) that herniates through the primitive umbilical ring into the extraembryonic coelom (ie, physiological umbilical herneation) beginning at week 6

Front 19

Describe the divisions of the midgut loop

Back 19

The midgut loop consists of a cranial limb and a caudal limb

Front 20

What forms from the cranial limb of the midgut loop?

Back 20

-Jejunum
-Upper part of the ileum

Front 21

Describe omphalocele

Back 21

1. Occurs when abdominal contents herniate through the umbilical ring and persist outside the body covered variably by a translucent peritoneal membrane sac (a ligh-gray shiny sac) protruding from the base of the umbilical cord

2. Large omphaloceles may contain stomach, liver, and intestines

3. Small omphaloceles contain only small intestine

4. Omphaloceles are usually associated with other congenital anomalies (eg, trisome 13, trisomy 18, Beckwith-Wiedemann syndrome)

Front 22

Describe gastroschisis

Back 22

1. Occurs when there is a defect int he ventral abdominal wall usually to the right of the umbilical ring through which there is a massive evisceration of intestines (other organs may be involves)

2. The intestines are not covered by a peritoneal membrane, are directly exposed to amniotic fluid, and are thickened and covered with adhesions

Front 23

Describe ileal diverticulum (Meckel diverticulum)

Back 23

1. Occurs when a remnant of the vitelline duct persists, thereby forming an outpouching located on the antimesenteric border of the ileum

2. The outpouching may connect the umbilicus via a fibrous cord or fistula

3. A Meckel diverticulum is usually located about 30cm proximal to the ileocecal valve in infants and varies in length from 2-15cm

4. Heterotropic gastric mucosa may be present which leads to ulceration, perforation, or GI bleeding, especially if a large number of parietal cells are present

5. Associated clinically with symptoms resembling appendicitis and bright-red or dark-red stools (ie bloody)

Front 24

Describe nonrotation of the midgut loops

Back 24

1. Occurs when the midgut loop rotates only 90degrees counterclockwise, thereby positioning the small intestine entirely on the right side and the large intestine entirely on the left side

2. The cecum located either in the LUQ or the left iliac fossa

Front 25

Describe malrotation of the midgut loop

Back 25

1. Occurs when the midgut loops undergoes only partial counterclockwise rotation

2. Results in the cecum and appendix lying in a subpyloric or subhepatic location adn the small intestine syspended by only a vascular pedicle (ie, not a broad mesentery)

3. A major clinical complication of malrotation is volvulus (twisting of the small intestines around the vascular peduncle), which may cause necrosis due to compromised blood supply

Front 26

Describe the characteristic radiograph characteristic after a barium swallow in a patient with malrotation of the midgut loop

Back 26

Beak sign that occurs secondary to the twisting of the intestines and an early spiraling of the small intestine

Front 27

Describe reversed rotation of the midgut loops

Back 27

1. Occurs when the midgut loop rotates clockwise instead of counterclockwise, causing the large intestine to enter the abdominal cavity firsdt

2. This results in a large intestine being anatomically located posterior to the duodenum and the superior mesenteric artery

Front 28

Describe intestinal atresia and stenosis

Back 28

1. Atresia occurs when the lumen of the intestines is completely occluded

2. Stenosis occurs when the lumen of the intestines is narrows

3. The causes of these conditions seem to be both failed recanalization and/or an ischemic intrauterine event

4. Clinical findings of proximal atresia include polyhydramnios and bilious vomiting early after birth

5. Clinical findings of distal atresias include normal amniotic fluid levels, abdominal distention, later vomiting, and failure to pass meconium

Front 29

What are the clinical findings of proximal intestinal atresia?

Back 29

Polyhydramnios and bilious vomiting early after birth

Front 30

What are the clinical findings of distal intestinal atresia?

Back 30

Normal amniotic fluid levels, abdominal distention, later vomiting, and failure to pass meconium

Front 31

Describe duplication of the intestines

Back 31

1. Occurs when a segment of the intestines is duplicated as a result of abnormal recanalization (most commonly near the ileocecal valve)

2. The duplication is found on the mesenteric border

3. Its lumen generally communicates with the normal bowel and is lined by normal intestinal epithelium, but heterotopic gastric and pancreatic tissues has been identified

4. Clinical findings include an abdominal mass, bouts of abdominal pain, vomiting, chronic rectal bleeding, intussusception, and perforation

Front 32

Describe intussusception

Back 32

1. Occurs when a segment of bowel invaginates or telescopes into an adjacent bowel segment leading to obstruction or ischemia

2. This is one of the most common causes of obstruction in children younger than 2 years of age

3. Most often is idiopathic

4. Most commonly involves the ileum and colon (ie, ileocolic)

5. Clinical findings include acute onset of intermittent abdominal pain, vomiting, bloody stools, diarrhea, and somnolence

Front 33

Describe retrocecal appendix

Back 33

1. Occurs when the appendix is located on the posterior side of the cecum

2. This anomaly is very common and important to remember during appendectomies

Front 34

Describe retrocolic appendix

Back 34

1. Occurs when the appendix is located on the posterior side of the colon

2. This anomaly is very common and important to remember during appendectomies