Term
The beginning of the gut
¡The primordial gut begins at week (2, 3, 4)
¡It is closed at week 4 by the (oropharyngeal or cloacal) membrane at its cranial end and by the (oropharyngeal or cloacal) membrane at its caudal end
¡Eventually, both ends open and the cranial end has a (stomodeum or proctodeum) and the caudal end has a (stomodeum or proctodeum)
§Both are derived from (endoderm or ectoderm) |
|
Definition
4
oropharyngeal, cloacal
stomodeum, proctodeum, ectoderm |
|
|
Term
Lateral body wall folding and formation of the gut tube
¡Lateral body wall folds help to close the (dorsal or ventral) body wall and form the gut tube.
¡As the gut tube forms, its connection to the yolk sac becomes smaller.
¡Lateral plate mesoderm (which splits to form somatic and splanchnic mesoderm) lines the body cavity (parietal) and the outside of the gut tube (visceral), and these layers become the parietal and visceral peritoneum, respectively. |
|
Definition
|
|
Term
Lateral body wall folding and formation of the gut tube
¡Gut tube is made from (endoderm or ectoderm).
¡The mesoderm thins posteriorly to suspend the gut tube from the dorsal body wall by the (dorsal or ventral) mesentery
¡Dorsal mesentery is where the visceral layer reflects off the gut onto the posterior wall and is (continuous or separate) with the parietal layer and represents a double layer of peritoneum. |
|
Definition
endoderm
dorsal
continuous |
|
|
Term
Lateral body wall folding and formation of the gut tube
¡A mesentery is defined as a double layer of peritoneum, and it allows blood vessels, nerves, and lymphatics to reach the organ between the two layers.
¡Both the visceral and parietal layers thin to form serous membranes, which secrete a serous (protein filled, watery) fluid for lubrication around organs and the body wall. |
|
Definition
|
|
Term
Positions
¡(Secondarily retroperitoneal OR Intraperitoneal OR Retroperitoneal) refers to an organ that is surrounded by a visceral layer of peritoneum and is suspended in the peritoneal cavity by a mesentery.
¡(Secondarily retroperitoneal OR Intraperitoneal OR Retroperitoneal) refers to an organ covered on one side by peritoneum and, therefore, without a mesentery, such as the kidneys.
¡(Secondarily retroperitoneal OR Intraperitoneal OR Retroperitoneal) refers to an organ that was once intraperitoneal, but then fused later to the posterior body wall and lost its posterior layer of peritoneum.
§ Examples include the pancreas, parts of the colon, etc. |
|
Definition
Intraperitoneal
Retroperitoneal
Secondarily retroperitoneal |
|
|
Term
¡Head and tail folds also help to form the gut tube and pinch it off from the (yolk sac or umbilical cord).
¡The yolk sac connection to the gut narrows to an area in the connecting stalk (umbilical cord). |
|
Definition
|
|
Term
Body Folding Closes the Gut Tube around the (Yolk Sac or Connecting Stalk) |
|
Definition
|
|
Term
¡The yolk sac is “pinched down” by body folding to a narrow connection to the midgut called the (bitelline or vitelline) (yolk sac) duct.
¡The connection remains until the 12th to 14th weeks of gestation. |
|
Definition
|
|
Term
The (Midgut or Hindgut) Remains Attached to the Yolk Sac Via the Vitelline Duct |
|
Definition
|
|
Term
¡The gut tube is divided into four regions:
§(Pharyngeal OR oropharyngeal) gut: from the oropharyngeal membrane to the (respiratory diverticulum or cloacal membrane).
§Foregut: from the lung bud diverticulum to the (bile or gall) duct.
§Midgut: from the bile duct to the first two-thirds of the (transverse or vertical) colon.
§Hindgut: from the last third of the transverse colon to the cloacal membrane. |
|
Definition
Pharyngeal, respiratory diverticulum
bile
transverse |
|
|
Term
¡The cloaca ( latin for sewer) is an (endoderm or ectoderm) derivative that receives connections from the hindgut and primitive urogenital structures.
¡The vitelline duct connects to the midgut through the (cloacal or umbilical) region
|
|
Definition
|
|
Term
Mesenteries of the gut
-A (dorsal or ventral) mesentery extends from the lower end of the esophagus to the (cloaca or oropharnx).
¡A (dorsal or ventral) mesentery only forms from the caudal end of the esophagus to the (bile or vitelline) duct.
¡Ventral mesentery forms from thinning of (mesoderm or ectoderm) in the septum transversum. |
|
Definition
dorsal, cloaca
ventral, bile
mesoderm |
|
|
Term
Mesenteries of the Gut
¡Growth of the (stomach or liver) into the septum transversum (which contributes (connective or muscle) tissue for liver cells) separates the ventral mesentery into two parts: the lesser omentum (from the esophagus and stomach to the (stomach or liver) and the falciform ligament (from the liver to the (ventral or dorsal) body wall).
¡Note that the bile duct lies in the caudal-free border of the (lesser omentum or falciform ligament). |
|
Definition
liver, connective, liver, ventral
lesser omentum |
|
|
Term
Organ buds forming from foregut (endoderm or ectoderm)
--Foregut endoderm from the pharynx down to the liver bud (bile duct) proliferates to form outpocketings called buds or diverticula.
¡In the pharynx, these buds form (glands or vesicles) in the neck and thorax.
¡In the rest of the foregut, they form the lungs, liver, gallbladder, and pancreas.
¡Lung development begins as a proliferation of (endoderm or mesoderm) at the caudal end of the pharynx that forms the respiratory diverticulum (lung bud). |
|
Definition
|
|
Term
¡ There are different gut tube regions. Each region (like the esophagus region) is affected by transcription factors expressed in these regions.
¡This is started by expression of sonic hedgehog (SHH) gene in the gut tube, resulting in an additional expression of (HOX or BOX) genes in the (endoderm or mesoderm).
¡The HOX genes then instruct the endoderm as to what it should become: small intestine, liver, large intestine, pancreas, etc. |
|
Definition
|
|
Term
Differentiation of the Gut Tube Is Regulated by Interactions between Gut Endoderm and the Surrounding (Mesoderm or Ectoderm)
|
|
Definition
|
|
Term
Layout
¡Esophagus
¡Liver and pancreas
¡Stomach
¡Intestines
¡Anus
¡Septation of Urinary System from GI system |
|
Definition
|
|
Term
¡The esophagus develops from the foregut immediately caudal to the (larynx or pharynx)
¡Esophagus is separated from the trachea by the treoesophageal septum.
¡The esophagus is short at first but it becomes longer rapidly because of the growth of the heart and lungs.
¡Its epithelium and glands are derived from (mesoderm or endoderm) |
|
Definition
|
|
Term
¡The striated muscle surrounding some of the esophagus is from (mesoderm or endoderm)
¡The smooth muscle in parts of the esophagus are from (splachnic or somatic) mesenchyme.
¡The outer esophageal wall has 1/3 (striated or smooth) muscle at the cranial end, 1/3 mixed smooth and striated muscle in the middle, and 1/3 (striated or smooth) muscle at the caudal end just before it enters the stomach
¡It is innervated by cranial nerve X (vagus) |
|
Definition
mesoderm
splachnic
striated, smooth
|
|
|
Term
Development of the liver and gallbladder
¡The liver begins as a proliferation of gut (endoderm or mesoderm) called the liver bud.
¡The (gallbladder or intestines) forms from a bud off of this initial outgrowth.
¡The liver cells grow into (endoderm or mesoderm) off of the septum transversum.
¡Endoderm forms (connective tissue or hepatocytes); mesoderm forms (connective tissue or hepatocytes) and blood vessels |
|
Definition
endoderm
gallbladder
mesoderm
hepatocytes, connective tissue |
|
|
Term
--As the liver grows into the (septum transversum or gall bladder), mesoderm of the septum transversum thins to form the central tendon of the diaphragm and the ventral mesentery (falciform ligament and lesser omentum).
¡Note that the heart (pericardial sac) and liver are connected to the central tendon of the diaphragm because of their relationships to the septum transversum. |
|
Definition
|
|
Term
Round ligament of the (liver or stomach)
¡Within a week of birth, the infant's umbilical vein is completely obliterated and is replaced by a fibrous cord called the round ligament of the (liver or stomach).
¡ It extends from the umbilicus to the transverse fissure, where it joins with the ligamentum venosum to separate the left and right lobes of the liver. |
|
Definition
|
|
Term
Molecular regulation of liver induction
¡Liver bud outgrowth is induced by secreted factors from (cardiac or pleural) mesoderm and from the septum transversum.
¡Later, hepatocyte-specific genes regulate liver cell differentiation. |
|
Definition
|
|
Term
Formation of the pancreas
¡Two pancreatic buds form, dorsal and ventral, on opposite sides of the gut tube by proliferations of gut (endoderm or mesoderm).
¡Note that the ventral bud forms at the (base or apex) of the liver bud. |
|
Definition
|
|
Term
Fusion of the pancreatic buds
¡The (ventral or dorsal) pancreatic bud moves around to lie beneath the (ventral or dorsal) pancreatic bud.
¡This change in position is caused by gut rotation and differential growth between the two sides of this region of the gut tube.
¡Fusion of the 2 buds produces the definitive pancreas, with the (ventral or dorsal) bud contributing the uncinate process and part of the head and the remainder (head, body, and tail) derived from the (ventral or dorsal) pancreas. |
|
Definition
ventral, dorsal
ventral, dorsal
|
|
|
Term
Fusion of the Pancreas
¡Fusion also occurs in the ducts from the two buds.
¡The main pancreatic duct is formed by the distal portion of the dorsal bud and the proximal portion of the ventral bud with its connection to the duodenum with the bile duct at the (major or minor) papilla. |
|
Definition
|
|
Term
Mesenteries attached to the stomach
Mesenteries attached to the stomach include
---the (dorsal or ventral) mesentery of the gut tube (dorsal mesogastrium)
---the part of the (dorsal or ventral) mesentery from the gut tube to the liver,
---the lesser omentum.
¡Portions of the gut tube rotate causing major changes in the orientation of these mesenteries. |
|
Definition
|
|
Term
-The stomach rotates around two axes:
§Ninety degrees clockwise around a longitudinal axis that brings the posterior part to the left side and the anterior part to the right side.
§This explains why the left and right vagus nerves come to lie anteriorly and posteriorly, respectively.
§Ninety degrees clockwise around the anterior-posterior axis. This movement causes the stomach to assume a more transverse position. |
|
Definition
|
|
Term
¡In addition, the left side grows (faster or slower) than the right, which results in formation of the greater and lesser curvatures.
¡Because the mesenteries are attached to the posterior (dorsal) and anterior (ventral) surfaces, their positions will be rearranged by these rotations |
|
Definition
|
|
Term
¡As the stomach rotates around its longitudinal axis, the dorsal mesentery is pulled to the (left or right), while the ventral mesentery is pulled to the (left or right). |
|
Definition
|
|
Term
Rearrangements of the mesenteries due to stomach rotation
¡The (spleen or liver) is forming at this time by proliferation of mesoderm in part of the dorsal mesentery.
¡This creates new attachment sites for this mesentery:
§a part from the spleen to the dorsal body wall which is also continuous with peritoneum over the kidney (lienorenal ligament)
¡Mesentery running from the spleen to the stomach called the gastrolienal ligament. (lieno=spleen) |
|
Definition
|
|
Term
Formation of the greater and lesser omenta (aprons)
¡Rotation of the stomach around its anterior-posterior axis pulls the dorsal mesentery into a horizontal position hanging from the (greater or lesser) curvature.
¡The dorsal mesentery starts to grow and it hangs down over the intestines forming the greater omentum. |
|
Definition
|
|
Term
Relationship of the mesenteries after stomach rotation
¡The (greater or lesser) omentum, it is double-layered creating a space in between the layers (the omental bursa [sac]).
¡The entire omental bursa lies posterior to the lesser omentum and posterior to the stomach and extends downward between the layers of the greater omentum.
¡The layers of the greater omentum fuse with each other, obliterating this part of the sac. |
|
Definition
|
|
Term
¡The opening into the omental bursa is through the epiploic foramen , which is located posterior to the free margin of the lesser omentum
¡ the free margin of the lesser omentum is the hepatoduodenal ligament |
|
Definition
|
|
Term
¡The greater omentum is attached to the greater curvature of the stomach and drapes over the transverse (colon or rectum) and small intestines like an apron.
¡The greater sac is formed by the peritoneal cavity, and the epiploic foramen represents the connection between the greater and lesser sacs
¡Two different things |
|
Definition
|
|
Term
Effects of gut rotation on positioning of the pancreas
¡Rotation of the stomach about its longitudinal axis twists the duodenum
¡ this causes the pancreas to shift to the (left or right) and fuse with the posterior body wall.
¡ the pancreas was at one time covered by peritoneum inside the peritoneal cavity
§ the shift makes it secondarily retroperitoneal. |
|
Definition
|
|
Term
Formation of the primary intestinal loop
¡The midgut undergoes rotation.
¡Initially, this rotation is 90 degrees counterclockwise and forms the primary intestinal loop.
¡The axis for the rotation is the superior mesenteric artery
¡ The point of the loop is connected to the (yolk sac or vitellin duct) by the (yolk sac or vitellin duct). |
|
Definition
|
|
Term
Formation of the primary intestinal loop
¡As this loop forms in the (sixth or seventh) week, it herniates into the (umbilical cord or connecting stalk), a process called “physiological umbilical herniation.”
¡ Loops of bowel will start to return to the abdominal cavity in the 10th week. |
|
Definition
|
|
Term
Growth of the (midgut or hindgut) and its herniation into the umbilical cord
¡The (midgut or hindgut) will differentiate into part of the duodenum, jejunum, ileum, ascending colon, and two-thirds of the transverse colon.
¡It lengthens rapidly. |
|
Definition
|
|
Term
Return of the intestinal loops to the abdominal cavity
¡Loops begin returning in the (9th or 10th) week and by 12 weeks have assumed their permanent position.
¡As the loops return, they rotate an additional 180 degrees, for a total of 270 degrees.
¡Both the ascending and descending parts of the colon will fuse to the (posterior or anterior) wall and become retroperitoneal. |
|
Definition
|
|
Term
Fixation of the Intestines
¡Rotation of the stomach and duodenum causes the duodenum and pancreas to fall to the (right or left).
¡The colon presses the duodenum and pancreas against the posterior abdominal wall
¡Most of the duodenal mesentery is absorbed and most of the duodenum is (secondary retroperitoneal or retroperitoneal).
¡The remaining small intestine is intraperitoneal |
|
Definition
|
|
Term
¡The allantois is an (endodermal or ectodermal) evagination of the developing hindgut which becomes surrounded by the (mesodermal or ectodermal) connecting stalk.
¡The connecting stalk forms the umbilical cord
¡ The fetal bladder is connected to the allantois via the urachus (which removes nitrogenous waste from the fetal bladder) |
|
Definition
|
|
Term
¡The caudal part of the hindgut is divided by the urorectal septum into the urogenital sinus and rectum.
¡The rectum and the superior anal canal are separated from the outside by the anal membrane (the membrane breaks down by week (8 or 9))
¡The inferior part of the anal canal develops from the proctoderm (ectoderm) |
|
Definition
|
|
Term
Formation of the urorectal septum and hindgut formation
¡The hindgut ends in the posterior portion of the cloaca (sewer)
§the anterior portion will form the urinary bladder.
¡The surface of the cloaca is covered by the cloacal membrane, (mesoderm or endoderm)
¡ external to this cloacal membrane is a layer of ectoderm.
¡Together these layers constitute the cloacal plate. |
|
Definition
|
|
Term
Formation of the urorectal septum and hindgut formation
¡The cloacal plate sits at the bottom of an indentation called the (proctodeum or urorectal septum).
¡The (proctodeum or urorectal septum) is a proliferation of mesoderm on the floor of the pelvic cavity that grows caudally to separate the hindgut from the the new bladder (the urogenital sinus ). |
|
Definition
| proctodeum, urorectal septum |
|
|
