Development of GI System (Brauer) Flashcards
1
Q
- cranio-caudal folding of the embryo creates the primitive gut tube which is comprised of these structures:
- around week 4, the midgut’s connection to the yolk sac narrows, creating this structure:
A
- cranio-caudal folding of the embryo creates the primitive gut tube which is comprised of these structures: foregut, midgut, hindgut
- around week 4, the midgut’s connection to the yolk sac narrows, creating this structure: vitelline duct
2
Q
GI structures derived from endoderm:
A
- mucosal epithelium
- GI glands (except lower 1/3 of anus)
3
Q
GI structures derived from splanchnic mesoderm:
A
- connective tissue
- vasculature
- smooth muscle wall
4
Q
GI derivatives derived from ectoderm:
A
- enteric ganglia, nerves, and glia (via neural crest cells)
- epithelium of lower 1/3 anus
5
Q
What are the structures of the foregut and what is the arterial supply?
A
- structures: esophagus, stomach, liver, gallbladder, pancreas, upper duodenum
- BS: celiac trunk
6
Q
What are the structures of the midgut and what is the arterial supply?
A
- structures: lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon
- BS: superior mesenteric artery (SMA)
7
Q
What are the structures of the hindgut and what is the arterial supply?
A
- structures: distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, upper anal canal
- BS: inferior mesenteric artery (IMA)
8
Q
What is the function of peritoneum within the abdomen and what are the different types of peritoneum?
A
- peritoneum: thin membrane that lines the abdominal and pelvic cavities, and covers most abdominal viscera; composed of layer of mesothelium supported by a thin layer of connective tissue
- parietal peritoneum: the portion that lines the abdominal and pelvic cavities (also known as the peritoneal cavity)
- visceral peritoneum: covers the external surfaces of most abdominal organs, including the intestinal tract
9
Q
GI structures derived from dorsal mesentary:
A
- greater omentum: gastrosplenic, gastrocolic, splenorenal ligaments
- small intestine mesentery
- mesoappendix
- transverse mesocolon
- sigmoid mesocolon
10
Q
GI structures derived from ventral mesentery:
A
- lesser omentum: hepatoduodenal and hepatogastric ligaments
- falciform ligament of liver
- coronary ligament of liver
- triangular ligament of liver
11
Q
- organs that are suspended by mesentery
- stomach, tail of pancreas, first five cm and the fourth part of the the duodenum, jejunum, ileum, cecum, appendix, transverse colon, sigmoid colon, and upper third of the rectum
A
intraperitoneal organs
12
Q
- organs that are excluded from peritoneal cavity
- mnemonic: SAD PUCKER
Suprarenal (adrenal) gland
Aorta/IVC
Duodenum (2nd and 3rd part)
Pancreas (except tail)
Ureters
Colon (ascending and descending)
Kidneys
(o)Esophagus
Rectum
A
retroperitoneal organs
13
Q
- organs that were initially suspended within mesentery that later fused w/ body wall
- ascending/descending colon, duodenum, bulk of pancreas
A
secondarily retroperitoneal organs
14
Q
Mnemoic SAD PUCKER is used to recall:
A
retroperitoneal organs
S - suprarenal (adrenal) glands
A - aorta/IVC
D - duodenum (2nd and 3rd parts)
P - pancreas (except tail)
U - ureters
C - colon (ascending/descending)
K - kidneys
E - (o)esophagus
R - rectum
15
Q
GI structures derived from foregut:
A
- esophagus
- stomach
- liver and gallbladder
- pancreas
- upper duodenum (proximal bile duct)
16
Q
When the stomach (foregut) rotates during development, what anatomical changes occur and what structures develop?
A
- stomach is attached to body wall by peritoneum (mesentery) both ventrally and dorsally
- stomach rotates 90 degrees wherein left side moves ventrally and right side moves dorsally
- ventral mesentery > lesser omentum (located on lesser curve of stomach)
- dorsal mesogastrium > greater omentum (located on greater curve of stomach)
- lesser sac located behind stomach
- vagus nerve (LARP): left vagus nerve > anterior; right vagus nerve > posterior
17
Q
How do the greater and lesser omentums develop?
A
- ventral mesentery > lesser omentum
- dorsal mesogastrium > greater omentum
- lesser omentum located between lesser curve of stomach and liver
(epiploic foramen: opening to lesser sac between liver and top of duodenum)
- greater omentum grows downward in a double fold in front of transverse colon
- greater omentum superior to transverse colon comes together w/ transverse mesocolon (attaches colon to pancreas and body wall) and duplicated layers are absorbed > greater omentum becomes stuck to transverse colon while also hanging below it
18
Q
How do the greater and lesser sacs develop?
A
(side note: liver develops in ventral mesogastrium and spleen develops in dorsal mesogastrium)
- rapid and large growth of liver causes lesser sac to develop
- lesser sac: located behind lesser omentum, stomach, and gastrocolic ligament (part of the greater omentum)
- greater sac: larger portion of the peritoneal cavity; divided by the transverse mesocolon into supracolic and infracolic compartments
- epiploic foramen: opening within lesser omentum from greater sac to lesser sac
19
Q
- thickened muscle causing narrowing of opening between stomach and duodenum
- etiology: faulty migration of neural crest cells > ganglion cells of enteric nervous system not properly populated which causes inability of sphincter to relax; or narrowing of pyloric lumen due to hypertrophy of muscularis externa in this region
- presentation: occurs within a few months after birth, palpable mass (“olive”) at right costal margin, projectile non-bilious vomiting after feeding, fewer and smaller stools, failure to gain weight (may lose weight)
- incidence: 1:500
A
hypertrophic pyloric stenosis
20
Q
How does the liver develop?
A
- during week 4, begins as hepatic diverticulum from gut endoderm
- connection of diverticulum to foregut > common bile duct
- endoderm > hepatocytes, bile ducts, and hepatic ducts
- splanchnic mesoderm > stromal, Kupffer, and stellate cells
- takes over hematopoiesis in utero by week 10
- congenital anomalies are rare
21
Q
Describe the development of the gallbladder and bile duct:
A
- around week 4, begins as cystic diverticulum (outgrowths from cystic endoderm)
- gallbladder develops as a secondary out-pouching from hepatic diverticulum (common bile duct) that grows into ventral mesentery, the connection between the two is the cystic duct
- around the end of week 5, recanalization of bile duct occurs
- around the end of week 6, the common duct and ventral pancreatic bud rotate 180° clockwise around the duodenum so that the gallbladder remains situated inferior to the liver
- beginning week 12, bile is formed by hepatic cells
22
Q
- blockage of the ducts that carry bile from the liver to the gallbladder
- both congenital and adult forms of condition
- etiology: obliteration of bile duct, or inflammation replaces duct w/ fibrotic tissue
- presentation: immediate onset of progressive jaundice in infants, white/clay colored stool, dark urine, poor prognosis (12-19 month lifespan)
- incidence: extrahepatic (1:15,000) and/or intrahepatic (1:100,000)
A
biliary atresia
23
Q
Describe the development of the pancreas:
A
- around week 4, begins as two additional endodermal buds sprouting from the foregut, inferior to cystic diverticulum
- ventral pancreatic bud derivatives: uncinate process (grows into ventral mesentery)
- dorsal pancreatic bud derivatives: pancreatic head, body, and tail (grows into dorsal mesentery)
- buds develop w/ both exocrine and endocrine portions
- around week 5, ventral pancreas migrates around posteriorly to fuse w/ dorsal pancreas (ventral and dorsal ducts also fuse)
- ventral pancreatic duct > main pancreatic duct (connection to duodenum)
- dorsal pancreatic duct > accessory pancreatic duct
24
Q
- developmental variation within pancreas where there is an additional pancreatic duct (Duct of Santorini) that occurs within 33% of people
- can be functional or non-functional and may open separately into the second part of the duodenum which is dorsal and usually (in 70%) drains into the duodenum via the minor duodenal papilla
- in the other 30% it drains into the main pancreatic duct, which drains into the duodenum via the major duodenal papilla
- the main pancreatic duct and this additional duct both eventually—either directly or indirectly—connect to the second part (‘D2’, the vertical segment) of the duodenum
A
accessory pancreatic duct
(left side of photo)
25
- developmental variation of pancreas that occurs in 4% of people where the ventral and dorsal parts fail to fuse by week 8
- mostly asymptomatic
- patients prone to abdominal pain/pancreatitis
pancreas divisum
| (right side of photo)
26
- condition where pancreas forms a ring around duodenum
- **etiology**: poor migration of pancreas (the ventral pancreas migrates both anteriorly and posteriorly) \> pancreatic ring around 2nd part of duodenum
- **presentation**: duodenal obstruction/stenosis, bilious vomiting (if the annulus develops inferior to bile duct), low birth weight
annular pancreas
27
Describe the development of the spleen:
- around week 4, begins as **mesenchymal condensation** that forms in the **dorsal mesogastrium**
- by week 5 the spleen is fully formed
- derived from **mesoderm** not endoderm
28
Describe the general development and derivatives of the midgut:
- midgut begins as U-shaped loop of gut w/ vitelline duct extending from it to definitive yolk sac
- major occurences of development are **rotation** and **elongation**
- midgut herniates out of umbilicus at week 6 and returns to abdomen by week 10 (physiological herniation)
- **derivatives**: lower duodenum (distal to bile duct), jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 transverse colon
- **blood supply**: superior mesenteric artery (axis for rotation)
29
Describe the process of midgut rotation:
**TLDR: midgut herniates out of umbilicus at week 6 and returns to abdomen by week 10, all while making a ~270° counterclockwise turn**
- at week 6, midgut loop makes a 90° ccw rotation; **proximal portion** lies on the **right** and becomes **convoluted**, **distal portion** lies on the **left** and develops a buldge (**cecum**)
- at week 10, **proximal portion** of loop **returns to abdomen**, passing under distal portion to make a second 90° ccw turn; brings cecum to upper right quadrant and ascending colon is anterior to duodenum
- at week 11, **distal portion** of loop **returns to abdomen**, making a third 90° ccw turn; cecum descends to lower right quadrant, carrying ascending colon to end up on right side of abdomen
- the originally proximal part of the midgut, distal duodenum, ends up posterior to an originally distal part of the midgut, the proximal transverse colon
30
Where are midgut structures located anatomically due to rotation?
- **proximal (cephalic) loop** rotates inferiorly to become distal duodenum, jejunum, and part of the ileum
- **distal (caudal) loop** rotates superiorly becoming rest of the ileum, cecum, appendix, ascending colon, and most of the transverse colon
31
- **presentation**: herniation of midgut through umbilicus, covered by parietal peritoneum
- **etiology**: herniated bowel does not fully retract during development
- **incidence**: 2.5/10,000 births, increased risk w/ trisomy 13 or 18
omphalocele
32
- defect of the abdominal wall causes infant's intestines to be found outside the body, exiting through a hole beside the belly button
- **etiologies**: abnormal lateral body folding \> creates wall weakness that allows bowel to herniate; or connective tissue of skin and hypaxial musculature of body wall do not form normally \> wall weakness
- not covered by parietal peritoneum
- **incidence**: 1:10,000 births
gastroschisis
33
- an outpouching or bulge in the lower part of the small intestine, which is congenital and is a leftover of the umbilical cord
- **etiology**: failure of yolk stalk (vitelline duct) connection to the midgut to regress, midgut remains connected to umbilicus
- **presentation**: usually asymptomatic; can lead to abd swelling, intestinal obstruction, bowel sepsis, and GI bleeding
- **rule of 2's**: 2% of population, 2x more likely in males, 2% have symptoms, 2 feet proximal to ileocecal valve, 2 in long, presents in year 2 of life
Meckel's diverticulum
34
- **etiology**: midgut completes first 90° ccw rotation but does not complete remaining 180° ccw rotations
- **presentation**: left-sided colon and right-sided small intestines; formation of fibrous Ladd bands \> volvulus, duodenal obstruction
- **incidence**: 1:500 births
malrotation/non-rotation of midgut loop
35
- midgut completes initial 90° ccw rotation, but then completes a 180° cw rotation
- results in a net 90° cw rotation
- duodenum results **anterior** to transverse colon
reverse gut rotation
36
- **etiology**: twisting of bowel around its mesentery, increased risk w/ gut rotation anomalies
- **presentation**: acute abd pain, vomiting, GI bleeding
- **complications**: bowel obstruction, infarction
- "coffee bean sign" seen on diagnostic imaging
volvulus
37
GI structures derived from hindgut:
- distal 1/3 of transverse colon
- descending colon
- sigmoid colon
- rectum
- superior 2/3 of anal canal (to pectinate line)
(BS by **inferior mesenteric artery**)
38
Describe development of the hindgut:
- **cloaca**: portion of hindgut in early embryo that separates into the **rectum** and **urogenital sinus**
- **urorectal septum** (mesoderm between vitelline duct and allantois) develops fork-like extensions of the cloacal walls that grow inward to partition the cloaca into: **ventral (anterior) urogenital sinus** (becomes bladder and urethra) and the **dorsal (posterior) anorectal canal**
- urorectal septum meets outside of body at **perineal body**, a CT structure that divides cloacal membrane into **anal membrane** and **urogenital membrane**
- **"cloacal membranes"** eventually rupture to open both to the exterior
39
Describe the development of the anal pit and pectineal line:
- anal rectal lumen temporarily closed by endodermal epithelial anal plug and **anal membrane** (eventually opens via apoptosis)
- mesoderm surrounding anal opening proliferates outward (invaginates) to form a circular **anal pit** (lined by **ectooderm**) that meets rectum and connects to it as membrane ruptures
- **pectineal line** divides origin of hindgut and anal pit within the anal canal: **superior 2/3's** (endodermal epithelium, separate BV supply and innervation of hindgut); **lower 1/3** (ectodermal epithelium, separate BV and innervation of anal pit)
40
What is the germ layers and vasculature to the rectum and anus?
- **rectum**: germ layer **endoderm**; vasculature **superior rectal (IMA)** and **middle rectal (internal iliac A.)** arteries, veins of hindgut
- **anus**: germ layer **ectoderm**; vasculature **inferior rectal** arteries (**prudendal A.**) and veins
41
- opening to anus is missing/blocked due to persistent anal membrane
- low, intermediate, or high distinction - relative to levator ani muscles and pelvic bony landmarks
- incidence: 1:5000 births
imperforate anus
42
What are the different types of abnormal urorectal septum development?
- **rectovaginal**: occurs in females born w/ a persistent cloaca; a common chamber is present receiving urethra, vagina, and rectum
- **rectovesical**: occurs in males; connection of rectum to bladder
- **rectourethral**: occurs in males; connection of rectum to urethra
(incidence of these abnormalities: 1:2000-5000)
43
- **etiology**: failure of neural crest cell migration \> absence of ganglionic plexus, causes lack of peristalsis (colon fails to relax)
- **presentation**: intestinal wall hypertrophy proximal to aganglionic segment, lack of peristalsis, abnormal colonic dilation or distension (megacolon), failure to pass meconium
Hirschsprung's disease
| (congenital aganglionic megacolon)
