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BLOCK 2 - Embryology (Grace) > Digestive System > Flashcards

Digestive System Flashcards

1
Q

The primitive gut tube is formed from the incorporation of the dorsal part of the yolk sac into the embryo as a result of what two types of folding in the embryo?

A

craniocaudal folding

lateral folding

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2
Q

Week 4: The primordial gut is closed at its cranial and caudal ends by what membranes?

A

cranial = oropharyngeal membrane

caudal = cloacal membrane

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3
Q

What tissue of the primordial gut gives rise to most of the epithelium and glands?

A

endoderm

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4
Q

What part of the adult G.I. tract is derived from endoderm and has a lamina propria and muscularis mucosae?

A

Mucosa

epithelial lining and glands

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5
Q

What 3 parts of the acult G.I tract are derived from visceral mesoderm?

A

submucosa

muscularis externa

adventitia or serosa

*(lamina propria + muscularis mucosa are also mesoderm)

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6
Q

In early development the epithelial lining of the gut proliferates and obliterates the lumen. What precess reverses this later?

A

recanalization

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7
Q

The epithelium of the cranial and caudal end of the gut is derived from what primordial tissue type?

A

ectoderm of the stomodeum and proctodeum

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8
Q

The primordial gut is divided in what three sections?

A
  • foregut
  • midgut
  • hindgut
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9
Q

The Foregut:

What are the derivitives?

A

Primordial pharynx (+ derivatives)

Lower respiratory system

Esophagus and stomach

Duodenum, distal to the opening of the bile duct

Liver, biliary apparatus (hepatic ducts, gallbladder + bile duct)

Pancreas

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10
Q

The foregut derivatives are supplied by the what artery/branch?

A

celiac trunk

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11
Q

The foregut is divided into the esophagus dorsally + trachea ventrally by what folds?

These fuse to form what structure?

The esophagus reaches its final length by what week?

A
  • tracheoesophageal folds
  • tracheoesophageal septum
  • week 7
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12
Q

The epithelium and glands of the esophagus are derived from what primordial tissue?

It proliferates and obliterates the esophageal lumen. By what week does recanalization occur?

A

endoderm

  • week 8
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13
Q

Esophagus: superior third

A
  • striated muscle forms muscularis externa
  • derived from mesenchyme in caudal pharyngeal arches
  • innervated by CN X
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14
Q

Esophagus: inferior two thirds

A
  • smooth muscle
  • derived from splanchnic mesenchyme
  • innervated by CN X
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15
Q

Esophageal Atresia

A

incomplete separation of the esophagus from the trachea

  • results from deviation of tracheoesophageal septum in a posterior direction
  • associated w. tracheoesophageal fistula (TEF) - 85% of cases
  • other congenital defects associated with the VACTERL syndromes - 33% of cases
  • can not swallow amniotic fluid = polyhydramnios
  • Inability to pass a catheter through esophagus into stomach
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16
Q

V.A.C.T.E.R.L. syndromes/associations

A

V = vertebral defects

A = anal atresia

C = cardiovascular defects

T/E = tracheoesphageal fistula

R = renal defects

L = upper limb defects

*syndrome = all defects; association = only some*

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17
Q

Esophageal Stenosis

A

narrowing of the lumen (usually in midesophagus)

  • week 8 = recanalization process is incomplete, or blood vessels did not develop in this region= atrophy of segment
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18
Q

Esophageal duplication

A

usually a congenital esophageal cyst

**(usually lower esophagus) **

  • cysts may lie on posterior aspect of the esophagus protruding into the posterior mediastinum
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19
Q

Vascular Compression of the Esophagus

A

abnormal origin of one of the vessels derived from the pharyngeal arteries (usually right subclavian artery)

  • anomalous artery passes behind the esophagus and may cause dysphagia (difficulty swalling)
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20
Q

The foregut is initially a simple tubular structure. At week 4, a slight dilation becomes ____________?

A

primordium of the stomach

(oriented in the median plane)

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21
Q

Rotation of the Stomach

A

90 degrees clockwise

  • lesser curvature (ventral) moves right; greater

curvature (dorsal) moves left

  • cranial region moves left + slightly inferiorly; caudal region moves right + superiorly
  • Final position = long axis almost transverse
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22
Q

Due to rotation, the dorsal mesentery is carried to the left and eventually forms …?

What nerves innervates the ventral and dorsal surfaces of the stomach?

A

** greater omentum**

ventral = left vagus nerve (CN X)

dorsal = right vagus nerve (CN X)

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23
Q

Regarding the stomach, which cells are derived from endoderm?

A

Surface mucous cells lining the stomach

mucous neck cells

parietal cells

chief cells

enteroendocrine cells of the gastric glands

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24
Q

Regarding the stomach, which layers are derived from visceral meesoderm?

A

lamina propria

muscularis mucosae

submucosa

outer longitudinal layer

middle circular layer

inner oblique layers of smooth muscle of muscularis externa

serosa of the definitive stomach

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25
Q

Congenital Hypertrophic Pyloric Stenosis

A

thickening of the pylorus

  • circular + longitudinal muscles in the pyloric region are hypertrophic causing a narrow pyloric lumen that obstructs food passage
  • treatment = pyloromyotomy

Results in:

  • distended stomach (palpated @ R. costal margin)
  • projectile vomiting (no bile)
  • * increased incidense in infants treated with erythromycin*
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26
Q

The duodenum develops from what primordial sections?

A
  • caudal part of foregut
  • cranial part of the midgut
  • splanchnic mesenchyme of these regions
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27
Q

What vessels supply the duodenum?

When does recanalization occur?

A

branches of celiac + superior mesenteric arteries

  • recanalization = end of embryonic period
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28
Q

Duodenal Stenosis

A

incomplete recanalization

stenosis of stomach’s contents = projectile vomiting

(USUALLY with bile)

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29
Q

Duodenal Atresia

A

Complete occlusion of duodenal lumen

  • occurs at junction of bile + pancreatic ducts (hepatopancreatic ampula)
  • vomiting starts a few hours after birth (ALWAYS contains bile)
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30
Q

What structures arise from the distal part of the foregut and form the hepatic diverticulum?

Where does the diverticulum extend to?

A

- liver

- gallbladder

- biliary duct system

diverticulum extends into the septum transversum

(mass of splanchnic mesoderm b/t developing heart +midgut

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31
Q

The tremendous growth of the liver causes what?

A
  1. liver bulges into abdominal cavity = stretches septum transversum

= ventral mesentery (falciform ligament + lesser omentum)

32
Q

falciform ligament

A
  • contains the left umbilical vein (after birth = ligamentum teres)
33
Q

lesser omentum

A
  • divided into the hepatogastric ligament + hepatoduodenal ligament
  • hepatoduodenal ligament = bile duct, portal vein, and hepatic artery (i.e., portal triad)
34
Q

What are important developmental features of the liver at:

* week 5-10?

* week 6?

* week 12?

A

week 5-10 = fast hepatic growth; liver fills lg. part of peritoneal cavity

**week 6 = hematopoiesis **begins (liver is bright reddish color)

**week 12 = **bile formation by hepatic cells start

35
Q

What does the connection between the hepatic diverticulum and the foregut create?

An outgrowth from this structure gives rise to _______ and ________.

A

bile duct

  • gallbladder rudiment + cystic duct
36
Q

The cystic duct divides the bile duct into the ________ an _______?

A

common hepatic duct + common bile duct

*(closure & recanalization of the lumen occur)

37
Q

At Week 13, what gives the meconium (intestinal contents) a dark green color?

A

** bile** entering the duodenum through the bile duct

38
Q

Biliary Atresia

A

obliteration of extrahepatic and/or intrahepatic ducts

  • ducts are replaced by fibrotic tissue due to acute and chronic inflammation
  • Clinical symptoms = progressive neonatal jaundice, white clay-colored stool (acholia), and dark-colored urine
  • average survival time w/o treatment = 12 to 19 months (100% mortality rate)
  • treatment = Kasai hepatoportoenterostomy (surgical procedure) or liver transplantation
39
Q

What primordial structures arise from endoderml cells in pancreatic development?

A

dorsal + ventral pancreatic buds

(rotation of the duodenum causes these buds to eventually fuse)

40
Q

ventral pancreatic bud

A

= uncinate process

= head of the pancreas

41
Q

dorsal pancreatic bud

A

= accessory pancreatic duct

= body of pancreas

= tail of pancreas

42
Q

The main pancreatic duct and common bile duct form a single opening into the duodenum called what?

Where is this opening located?

A

hepatopancreatic ampulla of Vater

  • at the tip of a major papilla (hepatopancreatic papilla)
43
Q

Acinar cells, islet cells, and simple columnar or cuboidal epithelium lining the pancreatic ducts are derived from what type of tissue?

A

endoderm

(Surrounding connective tissue + vascular components = visceral mesoderm)

44
Q

1. Insulin secretion starts at what week in the pancreas?

  • Glucagon + somatostatin-containing cells develop before differentiation of insulin-secreting cells.*
    2. Endodermal cells from tubules accumulate within mesoderm to form islet cells:

name 4 types.

A

Week 10

  • alpha cells (glucagon)
  • beta cells (insulin)
  • delta cells (somatostatin)
  • PP cells (pancreatic polypeptide)
45
Q

What causes an Annular Pancreas?

What is raiological sign of this?

A

ventral pancreatic bud fuses with dorsal bud both dorsally + ventrally

(= ring of pancreatic tissue around duodenum; severe duodenal obstruction)

Radioraphy shows:

duodenal obstruction + “double bubble” sign (dilation of stomach + distal duodenum)

46
Q

This pathology occurs when the distal two thirds of the dorsal pancreatic duct + the entire ventral pancreatic duct fail to anastomose (dorsal pancreatic duct persists; two separate duct systems)?

These patients are prone to…?

A

Pancreas Division

  • prone to pancreatitis
47
Q

Hyperplasia of Pancreatic Islets

A
  • fetal islets exposed to high blood glucose levels in infants of diabetic mothers
  • glucose stimulates fetal islet hyperplasia + insulin secretion = increased fat + glycogen deposition in fetal tissues
  • results in increased birth weight at term (macrosomia) + episodes of hypoglycemia in the postnatal period.
48
Q

The spleen is derived from what tissue type?

A

a mass of mesenchymal cells (b/t layers of dorsal mesogastrium)

  • capsule, connective tissue + parenchyma of spleen differentiate from mesenchyme
49
Q

What does the splenorenal ligament form from?

A

fusion of mesogastrium + peritoneum over the left kidney

50
Q

The spleen functions as a hematopoietic organ during what part of fetal life?

A

approx. week 3 -> late fetal life (month 5)

51
Q

Midgut

Its derivatives are:

A
  • small intestine
  • distal duodenum
  • cecum
  • appendix
  • ascending colon
  • part of the transverse colon
52
Q

The midgut is supplied by what artery?

A

superior mesenteric artery

53
Q

physiologic umbilical hernia

A

As the intestine grows it forms a midgut loop that projects into the umbilical cord; important for the shape the intestine will form

  • communicates with umbilical vesicle through omphaloenteric duct (yolk sac) until week 10
  • midgut rotates counter clockwise arouns SM artery = forms intestinal loops
54
Q

What are the 2 limbs of the midgut loop of intestine?

A

cranial limb and caudal limb

(suspended by an elongated mesentery)

cranial limb:

  • grows fast
  • forms small intestinal loops

caudal limb:

  • goes through little change
  • forms the cecal sweelings (primordium of cecum), + appendix
55
Q

During rotation of the midgut, which limb elongates and forms intestinal loops (primordia of the jejunum and ileum)?

A

the cranial limb

56
Q

When & how do the intestines return to the midgut?

A

Week 10

  • 1st: small intestine returns to abdomen
  • 2nd: as large intestine returns, it rotates 180 degrees counterclockwise. (comes to occupy right side of abdomen)
  • 3rd: ascending colon becomes recognizable as the posterior abdominal wall elongates
57
Q

Fixation of the Intestines

(occurs as intestines enlarge, lengthen, and assume their final positions)

A
  • their mesenteries are pressed against the posterior abdominal wall
  • ascending colon becomes retroperitoneal (looses its peritoneum)
  • fan shaped mesentery of small intestines attaches to the dorsal abdominal wall by a new line of fixation that passes from the duodenojejunal junction
58
Q

At what week does the cecal swelling appear?

What does it become?

A

week 6

  • primordium of cecum and appendix
  • appears as an elevation of the border of the caudal limb
  • after birth, wall of cecum grows unequally; 64% of people the appendix is located retrocecally
59
Q

Congenital Omphalocele

A

herniation of abdominal contents through umbilical ring

  • covered by a translucent peritoneal membrane sac protruding from the base of the umbilical cord
  • abdominal cavity is small; surgical repair is required, often these infants present pulmonary + thoracic hypoplasia

*** Associated with: congenital anomalies such as **trisomy 18 (Edward’s Syndrome) + 21 (Down Syndrome)*

60
Q

Umbilical Hernia

A

intestines return to the abdomen, but then herniate through a faulty umbilicus

  • protruding mass is covered by subcutaneous tissue + skin
  • hernia protrudes during crying, or coughing
  • can be easily reduced through the fibrous ring at the umbilicus (slowly, over time)
61
Q

Gastroschisis

A

Congenital abdominal wall defect; Extrusion of abdominal viscera without involving the umbilical cord.

  • viscera float in the amniotic fluid
  • intestines are not covered by a peritoneal membrane( thickened + covered with adhesions)
62
Q

Ileal Diverticulum (Meckel’s Diverticulum)

A

remnant of the vitelline duct (joins yolk sac to midgut)

  • outpouching of the ileum = common anomaly of the digestive system
  • wall of the diverticulum contains all layers of the ileum + may contain gastric and pancreatic tissues
  • ectopic gastric tissue may secrete acid = ulceration + bleeding.
  • appears on antimesenteric border of ileum, 40 to 50 cm from ileocecal junction
63
Q

Hindgut

Its derivatives are:

A
  • left half of transverse colon
  • descending colon
  • sigmoid colon
  • rectum + part of the anal canal
  • epithelium of urinary bladder
  • most of the urethra
64
Q

hindgut and its derivatives are supplied by what artery?

A

the inferior mesenteric artery

65
Q

What is the expanded terminal part of the hindgut lined by endoderm?

Where does it contct surface ectoderm?

A

Cloaca

(receives the allantois ventrally, which is a fingerlike diverticulum)

  • contacts surface ectoderm @ cloacal membrane
66
Q

The cloaca is divided into dorsal and ventral parts by what?

What are these 2 divisions?

A

the urorectal septum (mesenchyme)

(develops b/t allantois + hindgut)

Dorsal: rectum + part of the anal canal

Ventral: urogenital sinus

67
Q

What occurs at week 7, in regards to the urorectal septum?

A

fuses with cloacal membrane

  • divided into anal membrane and a larger ventral urogenital membrane

- perineal body results from this fusion

68
Q

urorectal septum:

divides the cloacal sphincter into anterior and posterior parts. What are these parts?

A

posterior = external anal sphincter

anterior = superficial transverse perineal, bulbospongiosus, and ischiocavernosus muscles.

69
Q

proctodeum (anal pit):

A

formed by mesenchymal proliferation in the surface ectoderm around the

anal membrane

70
Q

The Anal Canal:

The anal membrane ruptures by week …?

This allows communication between what 2 structures/areas?

A

week 7

  • communication b/t digestive tract + amniotic cavity
71
Q

Anal Canal

A

superior canal = derived from hindgut (superior rectal a.)

inferior part = develops from proctodeum (inferior rectal aa.)

(divided by pectinate line)

  • approx. 2 cm superior to the anus = anocutaneous line (white line)

(epithelium changes from columnar to stratified squamous)

  • anus = keratinized epithelium; continuous with external skin
72
Q

Hirschsprung Disease (Congenital Megacolon)

A

- failure of neural crest cells to migrate into wall of colon = no development of parasympathetic ganglion in Auerbach and Meissner plexuses

  • lack autonomic ganglion cells (aganglionosis) in myenteric plexus distal to dilated segment of colon
  • enlarged colon or megacolon= normal number of ganglion cells

** *most common cause of neonatal obstruction of the colon***

treatment:
rescect the affected area; probably prepare an ostomy
until distal portion of colon can connect to anal canal

73
Q

Imperforate Anus

A

Abnormal development of urorectal septum

= incomplete separation of the cloaca into urogenital +anorectal portions

  • sometimes it’s obvious, sometimes there’s a “blind opening” when an entrance exists but only goes a few cm.
74
Q

Anal Agenesis

(with or without fistula)

A

most common type of anorectal anomaly

  • anal canal may end blindly; may be an ectopic anus or an anoperineal fistula opening into perineum (or into vagina or urethra)
  • rectum ends superior to puborectalis muscle
  • usually a fistula to the bladder (rectovesical) or to the vagina (rectovaginal)
  • passage of meconium or flatus (gas) in the urine is diagnostic of rectourinary fistula.
  • Higher rates of fecal incontinence.
75
Q

Anal Stenosis

A

anus is in normal position, but the anus + anal canal are narrow

Due to a deviation of the urorectal septum

76
Q

Membranous Atresia of Anus

A
  • thin layer of tissue separates anal canal from the exterior
  • anal membrane appears blue from meconium superior to it

Due to imperforation of the membrane at week 8.

77
Q

Rectal Atresia

A
  • anal canal + proximal rectum are present but separated
  • sometimes two segments are connected by fibrous cord (remnant of an atretic portion of the rectum)
  • cause may be abnormal recanalization of the colon or more likely defective blood supply

BLOCK 2 - Embryology (Grace) (5 decks)

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