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SF3- EXAM 3 (Camelita) > Development of GI Tract > Flashcards

Development of GI Tract Flashcards

1
Q

Midgut remains conencted to yolk sac by _________

A

Vitelline duct

NOTE: The foregut and hindgut are blind-end tubes

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2
Q

Aside from the primitive gut, what are the other portions of the endorderm-lined cavity?

A

Yolk sac; allantois

NOTE: Both structures remain outside of the yolk sac

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3
Q

Septum transversum develops into connective tissue of ___________.

A

Diaphragm

REMEMBER: The diaphragm separates the thorax from the abdomen

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4
Q

What contributions does the endoderm make to the gut?

A
  • Epithelial lining of the digestive tract
  • Gives rise to the specific cells (parenchyma) of glands, such as hepatocytes and exocrine and endocrine cells of pancreas
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5
Q

What contributions does the visceral mesoderm give to the gut?

A
  • Forms stroma (connective tissue) for glands
  • Muscle
  • Connective tissue
  • Peritoneal components of the wall of the gut
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6
Q

Why is a portion of the endoderm-lined yolk sac cavity incorporated into the embryo?

A

As a result of craniocaudal and lateral folding of the embryo

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7
Q

There is a retinoic acid gradient established during folding. What is that gradient in regards to the cranial and caudal ends? What is the function?

A
  • The cranial end is exposed to little or no retinoic acid, while the caudal end is exposed to a high concentration of retinoic acid
  • This gradient causes characteris transcription factors to be expressed at each region of the gut tube
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8
Q

List the transciption factors that are expressed as a result of the retinoic acid gradient. What does each transcription factor lead to the production of?

A
  • SOX2- Esophagus and stomach
  • PDX1- Duodenum
  • CDXC- Small intestine
  • CDXA- Large intestine, rectum
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9
Q

The epithelial-mesenchymal interaction is initiated by ____________ expression throughout the gut tube.

A

Sonic Hedgehog (SHH)

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10
Q

SHH expression upregulates factors in the ___________that then determine the type of structure that forms from gut tube, such as stomach, duodenum, small intestine.

A

mesoderm

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11
Q

Blood supply to the foregut

A

Celiac trunk

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12
Q

What are the derivatives of the foregut?

A
  • Distal esophagus
  • Stomach
  • First half of duodenum
  • Liver
  • Gallbladder
  • Pancreas

NOTE: Though the spleen is not a deriverative of the foregut, it shares the same blood supply as foregut organs.

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13
Q

Blood supply to the midgut

A

Superior mesenteric artery

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14
Q

Derivatives of the midgut

A
  • 2nd half of duodenum
  • Jejunum
  • Ileum
  • Cecum
  • Appendix
  • Ascending colon
  • Hepatic flexure of colon
  • Transverse colon (proximal 2/3rd)
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15
Q

Blood supply to the hindgut

A

Inferior mesenteric artery

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16
Q

Derivatives of the hindgut

A
  • Distal third of the transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
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17
Q

Mesentery

A

Folds of peritoneum; double layers of peritoneum that enclose an organ and conenct it to the body wall

NOTE: Mesenteries provide pathways for vessels, nerves, and lymphatics to and from abdominal viscera

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18
Q

The entire abdominal gut tube is suspended from the posterior wall by a __________.

A

Dorsal mesentery

NOTE: By the 5th week, the caudal part of the foregut, the midgut, and a major part of the hindgut are suspended from the abdominal wall by the dorsal mesentery.

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19
Q

Dorsal mesentery of the jejunal and ileal loops forms the ___________.

A

Mesentery proper

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20
Q

The ventral mesentary is derived from the ___________.

A

Septum transversum

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21
Q

Where does ventral mesentery exist?

A

Only in terminal part of esophagus, stomach, and upper part of the duodenum

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22
Q

Growth of the liver divides the ventral mesentery into:

A
  • Lesser omentum
  • Falciform ligament
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23
Q

What are the boundaries of the pharynx?

A
  • Oropharyngeal membrane to respiratory diverticulum

NOTE: This is the first part of the foregut, the remainder of the foregut lies caudal to the pharyngeal tube and extends as far caudally as liver outgrowth

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24
Q

What is another name for the respiratory diverticulum?

A

Trachea-bronchial diverticulum

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25
Q

Trachea becomes partitioned from the esophagus by formation of the ____________.

A

Tracheoesophageal septum

*This leaves them connected only at the larynx

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26
Q

__________ prevents swallowing of amniotic fluid.

A

Atresia

NOTE: Esophageal atresia causes the esophagus to end in a blind-ended pouch rather than connecting normally to the stomach.

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27
Q

In esophageal atresia, amniotic fluid is not able to flow from the amniotic sac to the intestinal tract, causing a build up of excess fluid in the amniotic sac called ___________.

A

Polyhydramnios

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28
Q

Tracheoesphogeal fistula

A

An abnormal connection between the trachea and esophagus that allow regurgitated contents to contaminate lungs and abdomen with distend air.

REMEMBER: The tracheoesophageal septum is supposed to form between trachea and esophagus

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29
Q

How can positional changes of the stomach be explained?

A

By assuming that it rotates around a longitudinal and an anteroposterior axis.

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30
Q

How are the greater and lesser curvatures of the stomach formed?

A
  • The stomach rotates 90 degrees clockwise around its longitudinal axis, causing its left side to face anteriorly and its right side to face posterior.
    • During rotation, the original posterior wall grows faster than the anterior portion.

NOTE: The anterior portion forms the lesser curvature and the posterior portion forms the greater curvature

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31
Q

As a result of rotation of the stomach, the left vagus nerve innervates the ___________ of the stomach and the right vagus nerve innervates the _________ of the stomach.

A

Anterior wall; posterior wall

32
Q

During rotation of the stomach, the caudal or pyloric part moves _____________, and cephalic or cardiac portion moves __________.

A

To the right and upward; to the left and slightly downward

33
Q

Free margin of of the falciform ligament contains the _________.

A

Umbilical vein

NOTE: The umbilical vein is abloterated after brith to form the roud ligament of the liver

34
Q

The round ligament is also known as the ________.

A

Ligamentum teres hepatis

35
Q

What are the components of the hepatoduodenal ligament?

A
  • Bile duct
  • Portal vein
  • Hepatic artery
36
Q

The epiploic foramen joins which two structures?

A

The greater and lesser sac (omental bursa)

37
Q

The 4-layered greater omentum fuses with the dorsal mesentery of the transverse colon, forming the ___________.

A

transverse mesocolon

38
Q

The spleen forms within, and from, the _________.

A

dorsal mesentery

NOTE: During rotation of the stomach in the 5th week of development, the spleen appears as a mesodermal proliferation between the two leaves of dorsal mesogastrium.

39
Q

The spleen is connected to the body wall in the region of the left kidney by the ___________ and to the stomach by the _________.

A

Lienorenal ligament; gastrolienal ligament

40
Q

What is the landmark that separates the parts of the duodenum into foregut and midgut?

A
  • Proximal to the bile duct: duodenum is considered foregut (supplied by the celiac trunk)
  • Distal to the bile duct: Duodenum is considered midgut (supplied by the superior mesenteric artery)
41
Q

How is a duodenal atresis diagnosable before birth?

A

Presents as a “double bubble” in ultrasound, along with polyhydramnios

NOTE: The duodenum undergoes a solid stage and then later recanalizes. Failure to recanalize produces a duodenal atresia

42
Q

Components of the liver are derived from both the endoderm and mesoderm. Which parts respectively?

A

Endoderm: Hepatocytes

Mesoderm (of septum transversum): Sinusoids and hematopoietic tissue and central diaphragm

43
Q

Liver and gall bladder connect to the duodenum via _________.

A

Bile duct

44
Q

How is the diphragm formed?

A
  1. Septum transversum leaves two pericardio-peritoneal canals posteriorly
  2. These canals are gradually closed by the pleuroperitoneal membranes (folds)

NOTE: The left closes later than the right and is more often deficient.

45
Q

The left pleuroperitoneal canal closes later than the right and is more often deficient. What can this result in?

A

Diaphragmatic herniation of the intestines into the lung space, causing pulmonary hypoplasia (incomplete development of the lungs)

46
Q

Anything that decreases volume of the thoracic cavity may result in ____________.

A

Pulmonary hypoplasia

NOTE: Normal growth of the fetal lung depends on it being filled with adequate fluid, secreted by pulmonary epithelium.

47
Q

What are the causes of pulmonary hypoplasia?

A
  • Congenital diaphragmatic hernia
  • Oligodramnios (bilateral reanl agenesis)
48
Q

What signs will a newborn with severe diaphragmatic herniation present with?

A
  • Severe dyspnea
  • Bowel sounds over the chest
  • Flattened abdomen
49
Q

How is the final position of the pancreas determined?

A

Lengthening and fusion of dorsal mesogastrium to posterior body wall

50
Q

How does the tail end up in a different region than the rest of pancreas?

A
  • Initially, the pancreas grows into dorsal mesoduodenum, but eventually its tail extends into the dorsal mesogastrium
  • Since this portion of the dorsal mesogastrium fuses with the dorsal body wall, the tail of the pancreas lies against this region
51
Q

Which position does the pancreas reside in, intraperitoneal or retroperitoneal?

A

Retroperitoneal

52
Q

When the duodenum rotates the dorsal and ventral pancreatic buds fuse to form the ___________.

A

Uncinate process

53
Q

Main pancreatic duct is fusion of both ducts; proximal portion of orginal dorsal duct may persist as an __________.

A

Accessory pancreatic duct

54
Q

Both exocrine and endocrine pancreatic cells derive from _________.

A

Endoderm

55
Q

Pancreas divisum

A

Failure of ducts to fuse, resulting in small, separate duct systems that can lead to pancreatis

56
Q

Annular pancreas

A

Ventral bud may migrate in both anterior and posterior directions around duodenum, creating a ring that may obstruct the duodenum

NOTE: Annular pancreas may be difficult to distinguish from duodenal atresia

57
Q

Midgut and colon development

A
  1. Growth of GI exceeds the volume of the abdominal cavity, whichs causes the tube to herniate through the umbilicus
  2. While herniated, gut undergoes primary rotation
  • This corresponds with rotation of the stomach
  • Results in positioning of appendix to the left
  • Brings the right vagus to the front, changing name to anterior vagus nerve

​3. With growth of embryo, abdominal cavity expands thus drawing gut tube back within abdominal cavity and causing secondary rotation

  • Appendix is then positioned to the right

_​_4. Once in the abdominal cavity, colon continues to grow in length, pushing appendix to its final position in the lower right quadrant

​

58
Q

The site of the vitelline duct is in ______.

A

Distal ileum

59
Q
A
60
Q

Nonrotation can result in____

A

Entire small intesine on the right side

61
Q

Malrotation can result in..

A
  • Cecum remains subhepatic
    • Subhepatic appendix makes it difficult to diagnose appendicitis
  • Mesentary is deficient and may twist; leading to necrosis
62
Q

Reversed rotation can result in…

A
  • Midgut rotates in opposite direction, so large intestine enters abdomen first, positioning the colon posterior to the duodenum
63
Q

Omphalocele

A
  • Herniation through enlarged umbilical ring
  • Organs lie within cord, covered with amnion
  • Associated with serious chromosomal defects and other malformations
64
Q

Gastroschisis

A

Bowel herniates through body wall lateral to umbilicus

*Organs are not covered with membrane

65
Q

Umbilical hernia

A

Protrusion of bowel through umbilical ring, but covered with skin

*Usually closes with maturation

66
Q

Merkel’s Diverticulum is usually found on ___________

A

Ileum

67
Q

Merkel’s Diverticulum

A

If vitelline duct persists, it may form a ligament, a cyst or a fistula

68
Q

In cases of merkel’s diverticulum, intestinal loops may be caught by ligament, causing ________.

A

Volvulus

69
Q

The cloaca is divided into ___ and ____.

A

Urogenital sinus; anorectal canal

70
Q

What is the mesoderm between the allantois and the hindgut called?

A

Urorectal septum

71
Q

Rupture of the ________ forms the anal canal.

A

Anal membrane

72
Q

Mechanism by which hidgut is partioned

A
  1. Hindgut initially enters the cloaca.
  2. Mesoderm between the allantois and hindgut grows toward the cloacal membrane and divides it into urogenital sinus and anorectal canal.
73
Q

The anal canal is divided into superior and inferior portions. Where do they join?

A

At the pectinate line

*•demarks junction between different types of epithelium and different blood and nerve supplies

74
Q

What is each portion of the anal canal derived from?

A
  • Superior portion: Endoderm (since it comes from the cloaca)
  • Inferior portion: Ectoderm (from the proctodeum)
75
Q

Hindgut abnormalities

A
  • Urorectal fistula
  • Rectovaginal fistula
  • Rectoperineal fistula
  • Imperforate anus
76
Q

What is Hirschsprung Disease?

A

Hirschsprung’s disease is a birth defect in which nerves are missing from parts of the intestine. The most prominent symptom is constipation.

77
Q

Cause of Hirshsprung Disease

A

Results from failure of neural crest cells to migrate to form enteric ganglia

NOTE: Without ganglia, the wall fails to relax and comes constricted. The area proximal to the aganglionic area becomes distended.

SF3- EXAM 3 (Camelita) (23 decks)

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