Flashcards in Quiz 4 - Abdominal Embryology Deck (67):
during lateral and longitudinal folding, the endoderm is incorporated into the embryo as the _____
the gut tube will form...
epithelial lining of the gut and its associated organs
once the gut tube is incorporated into the body of the embryo, it can be subdivided into 3 regions...
1. foregut: cranial blind-ended portion that is capped by oropharyngeal membrane
2. midgut: portion that remains temporarily connected to the yolk sac thru the vitelline duct
3. hindgut: caudal blind-ended portion that is capped by the cloacal membrane.
-a small diverticulum of the hindgut that extends into the connecting stalk
gut tube is surrounded by the ________
visceral layer of lateral plate mesoderm, which will form the smooth muscle, connective tissue, and visceral peritoneum of the gut and its associated organs
as the gut tube is being incorporated into the body of the embryo, it moves away from the ____ body wall and becomes "suspended" into the intraembryonic coelem
initially, the gut tube is suspended from the dorsal body wall by a ______
mesentary; a mesentary is a double layer of visceral peritoneum that connects an organ to the body wall. Vessels and nerves travel to the gut tube between these layers of visceral peritoneum.
-remains in the regions of the abdominal portion of the foregut, midgut, and hindgut
-regions of the dorsal mesentary are named according to the organs they connect to the posterior body wall
-develops in the region of the abdominal portion of the foregut as a caudal downgrowth from the septum transversum
what does the ventral mesentery form?
-falciform ligament (formed by the division of the ventral mesentery by the growing liver)
organs that are suspended in the abdominal cavity by a mesentery are referred to clinically as _____
organs that lie against the posterior body wall and are covered by peritoneum only on their anterior surface are considered _____
-an organ that is never suspended by a mesentery
-an organ that is initially suspended by a mesentery, but is pushed against the body wall during development
-visceral and parietal layers of the peritoneum meet, fuse, and be reabsorbed
-the organs are now only covered by peritoneum on their anterior surface
which structures/organs are primarily retroperitoneal?
-rectum (technically SUBperitoneal)
which structures/organs are secondarily retroperitoneal?
which structures/organs are intraperitoneal?
-liver & gallbladder
general features of gut development
-MOST organs develop as outgrowths of the gut tube
-gut tube rotations force some organs to change orientation
-each region of the gut tube is associated with particular vessels and nerves
blood supply of gut tube
3 major branches (celiac trunk, superior mesenteric artery, inferior mesenteric artery) of the abdominal aorta supply the gut tube. In general, an organ derived from a particular region of the gut tube will be supplied by the artery that was associated with it in the embryo.
celiac trunk supplies ___
superior mesenteric artery (SMA) supplies ___
inferior mesenteric artery (IMA) supplies ___
which nerve supplies embryonic foregut?
Sympathetic: greater splanchnic nerve (T5-T9) via celiac ganglion
Parasympathetic: vagus nerve (CN X)
which nerve supplies embryonic midgut?
Sympathetic: lesser and least splanchnic nerves (T10-T12) via superior mesenteric ganglion
Parasympathetic: vagus nerve (CN X)
which nerve supplies embryonic hindgut?
Sympathetic: lumbar splanchnic nerves (L1-L2) via inferior mesenteric ganglion
Parasympathetic: pelvic splanchnic nerves (S2-S4)
derivatives of the foregut
-pharynx and derivatives
-trachea, bronchi, lungs (lower resp system)
-proximal 1/3 of duodenum
-liver & gallbladder
how does the stomach form?
-as an expansion of the caudal portion of the foregut
-the dorsal border of the stomach grows faster than the ventral border, creating the greater curvature of the stomach
-the stomach rotates 90* clockwise around its longitudinal (AP) axis, moving the ventral border (lesser curvature) to the right, and the dorsal border (greater curvature) to the left. Rotation also pulls fundus left & inferior, and pylorus right & superior.
what produces the spaces of the peritoneal cavity?
-rotation of the stomach and development of the greater and lesser omenta
from where does the spleen develop?
-mesoderm in the dorsal mesentery in the stomach
-swings to the left with the rotation of the stomach
what divides the ventral mesentary into the falciform ligament and the lesser omentum?
-the developing liver
what divides the dorsal mesentery of the stomach (dorsal mesogastrium) into the splenorenal ligament and the gastrosplenic ligament?
-the developing spleen
lesser sac (omental bursa)
-a portion of the peritoneal cavity that is "walled off" posterior to the stomach after the rotation of the stomach and the development of the omenta.
(the remaining peritoneal cavity is the greater sac)
how do the greater and lesser sacs communicate?
-thru a small opening near the hilum of the liver called the epiploic foramen
-the portion of the dorsal mesentery that "hangs down" from the greater curvature of the stomach following rotation
-formerly a part of the ventral mesentery, but after rotation extends between the stomach/1st part of the duodenum and the developing liver
where does the dorsal mesentery hang from after rotation of the stomach?
-from the greater curvature of the stomach, where it becomes enlarged to form the greater omentum
initially, the lesser sac is continuous with ____
-the space between the layers of the greater omentum (it's like a pouch within a pouch kind of)
-but eventually, the two layers of the greater omentum fuse, leaving 4 total layers of peritoneum and limiting the inferior extent of the lesser sac.
-the mesentery of the transverse colon also fuses with a portion of the greater omentum
development of duodenum
-also due to rotation of stomach
-proximal (1st) part of duodenum develops from the terminal portion of the foregut
-the foregut ends just caudal to the origin of the common bile duct at the apex of the duodenal loop
-the rotations of the stomach pull the duodenum into a C-shape around the head of the developing pancreas
-the duodenum becomes pressed against the dorsal body wall, becoming secondarily retroperitoneal
the pancreas forms from 2 different outgrowths of the foregut. what are they?
-ventral pancreatic bud (in the ventral mesentery, which is an outgrowth of the bile duct)
-dorsal pancreatic bud (in the dorsal mesentery, which is an outgrowth of the foregut)
-with rotation of the stomach and duodenum, the ventral bud rotates dorsally behind the duodenum and fuses to the dorsal bud. The ducts of the pancreatic buds also fuse, normally forming one pancreatic duct which opens into the duodenum at the major duodenal papilla
-pressed against the dorsal body wall, so secondarily retroperitoneal
what does the ventral pancreatic bud give rise to?
-uncinate processes of the pancreas
what does the dorsal pancreatic bud give rise to?
-tail of the pancreas
formation of liver and gallbladder
-form as outgrowths of the ventral foregut in the region of the developing duodenum
-arises cranial to the developing pancreas
-grows into the septum transversum
-differentiates into the liver parenchyma (liver cells)
-as the liver bud grows, its connection to the foregut narrows, forming the bile duct
from what are the connective tissue, hematopoietic cells, and Kupffer cells of the liver derived?
-mesoderm of the septum transversum
...as an outgrowth of the bile duct
what does the growing liver divide the ventral mesentery into?
annular pancreas (AP)
-rare congenital abnormality; usu non-symptomatic
-results in a ring of pancreatic tissue that can partially or completely constrict the descending duodenum
-if symptoms do occur, they can do so at any age
-typical symptoms: abdominal pain, nausea, lack of appetite, vomiting
-surgical intervention = treatment
derivatives of the midgut
-small intestines (EXCEPT for 1st and 2nd parts of duodenum = foregut)
-cecum & appendix
-proximal 2/3 of transverse colon
when does the midgut elongate?
-5th week, forming a U-shaped midgut loop
cranial limb of the midgut loop
-will form most of the small intestine
caudal limb of the midgut loop
-will form most of the large intestine
how is the apex of the midgut loop connected to the yolk sac?
-by the vitelline duct, which lies within the umbilical cord
what happens in the 6th week, when the midgut loops grows faster than the abdominal cavity?
-the midgut loop herniates into the abdominal cord
-as herniation occurs, the loop undergoes a 90* CCW rotation around the superior mesenteric artery
-this rotation brings the cranial limb (small intestine) to the right side of the body, and the caudal limb (large intestine) to the left side of the body
-the loop continues to elongate and the caudal limb (large intestine) develops an enlarged cecal bud (future cecum)
what happens in re: to the midgut by the 11th week, when the abdominal cavity has increased in size?
-the cavity can reincorporate the intestines
-as the loop is retracting, it undergoes an additional 180* CCW rotation
-the cranial limb (small intestine) retracts first, and as it does so, it becomes located more towards the left side of the abdominal cavity.
-the caudal limb (large intestine) becomes situated to the right
initially the cecum and the ascending colon rest under the liver. how do they move to their final positions?
-the ascending colon elongates and the cecum descends until the cecum and appendix lie in the LRQ.
when does the vitelline duct disappear?
once the final position of the intestines is attained
**results in the ascending colon and descending colon becoming secondarily retroperitoneal
derivatives of the hindgut
-distal 1/3 of transverse colon
-superior part of anal canal
-urinary bladder and urethra
endoderm --> embryonic folding --> ?? --> ??
--> gut tube --> foregut, midgut, hindgut
foregut --> ??
--> esophagus, stomach, liver, gallbladder, pancreas, proximal duodenum
stomach --> rotations --> ??
--> greater & lesser sacs & spleen swing left; distal duodenum and pancreas become secondarily retroperitoneal
growth of dorsal mesentery of stomach --> ??
--> greater omentum
hepatic diverticulum --> ??
--> bile duct + liver
bile duct --> ?? --> ??
--> cystic diverticulum --> gallbladder
ventral pancreatic bud + dorsal pancreatic bud --> dorsal rotation of ventral pancreatic bud --> ??
--> secondarily retroperitoneal pancreas
midgut --> midgut loop --> herniation into umbilical cord --> 270* total CCW rotation --> ??
--> small intestines + ascending t/v colon; ascending colon and descending colon become secondarily retroperitoneal
hindgut --> ??
--> descending colon + sigmoid colon + rectum + proximal anus