Lecture 24: Abdomen I Flashcards
Digestive Tube components, from top to bottom
Mouth, pharnynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum/appendix, colon, rectum, anal canal, anus)
Accesory organs to digestive tract
teeth, salivary glands, liver, pancreas
Signals for induction of endoderm
Fibroblast Growth Factor-4 (FGF-4), Activins
When does primordial gut tube form, what is it made of?
Beginning of fourth week, head, caudal, and lateral fold incorporate dorsal part of the yolk sac into the body. The gut tube/yolk sac is made of endoderm that gives rise to most of the digestive tract.
Stomodeum
pre-cursor of the mouth
proctodeum
pre-cursor of anal pit
What is the epithelium near the stomodeum and proctodeum made of?
ectoderm of those areas
What encloses the gut tube at either end
Cranially by the oropharyngeal membrane, caudally by the cloacal membrane
What are the derivatives of the primordial pharynx
oral cavity, pharynx, tongue, tonsils, salivary glands, upper respiratory system
What are the derivatives of the foregut?
It includes the primordial pharynx and all of its derivatives (oral cavity, pharynx, tongue, tonsils, salivary glands, upper respiratory system), the lower respiratory system (bronchi and lungs), esophagus and stomach, liver, pancreas, biliary apparatus, duodenum proximal to the bile duct
Where does the esophagus develop, what is it derived from?
From the fore-gut immediately caudal to the pharynx. The glands and epithelia are derived from the endoderm of the foregut. The striated muscle in the superior 1/3 are derived from the mesenchyme in the caudalpharyngeal arches, and the smooth muscle in the inferior 2/3 are derived from the surrounding splanchnic mesoderm
What separates the esophagus from the foregut during development.
The T-E septum, which eventually separates the esophagus from the trachea
How does the esophagus lumen change during development?
The canal is obliterated by proliferating epithelium, re-canalizes by the end of the eighth week. Can incompletely recanalize leading to a thin lumen, called esophageal stenosis.
The two causes of esophageal stenosis
Incomplete re-canalization at the end of the eight weeks or the failure of esophageal blood vessels to develop leading to atrophy of the esophagus.
Where does the stomach develop?
Distal part of the foregut, first develops as slight dilation in the median plane (which is the sagittal plane that goes right down the naval)
What attaches the stomach to the posterior abdominal wall
The dorsal mesentary, or the dorsal mesogastrium
What creates the greater curvature of the stomach, and where does it point towards initially?
While broadening dorsally and ventrally, the stomach (oriented in the medial plane) widens faster dorsally, creating the greater curvature pointing towards the vertebral column. The lesser curvature is then initially ventral, and points towards the anterior abdominal wall.
How does the stomach rotate?
It rotates 90 degrees clockwise, so the ventral lesser curvature moves right and the dorsal greater curvature moves left. Now lesser –> body right, and greater –> body left.
How does stomach rotation affect stomach innervation?
The original left side is now ventral and the original right side is now dorsal. The left vagus nerve supplies the anterior wall and the right vagus nerve supplies the posterior wall. The left vagus nerve is now renamed the anterior vagal trunk, and the right vagus nerve the posterior vagal trunk.
What happens to the dorsal mesentary during stomach rotation
Is carried to the left, creating the omental bursa, or the lesser sac of the peritoneum to the right of the dorsal mesentary
Ventral mesogastrium attaches to?
Suspends the stomach and duodenum to liver and ventral abdominal wall.
The purpose of the omental bursa, and it’s other name
Facilitates movement of the stomach. Also called lesser sac
Position of the omental bursa
Sits between the stomach and the posterior abdominal wall.
What makes up the greater omentum
the anterior and posterior fold layers of an elongated dorsal mesogastrium that fuse together by folding in on itself. There was an inferior recess within the fold, but that disappears during the fusing process.
What are the borders of the omental bursa in a mature body
In mature human the borders are anteriorly the liver, stomach and hepatoduodenal ligament. Posteirorly the pancreas, the dorsal mesogastrium, the greater omentum and the duodenum
Entrance to the lesser sac, and its location
The omental foramen/epiploic foramen, found posterior to the hepatoduodenal ligament. Connects the greater and lesser sacs
After rotating 90 degrees clockwise, how and when does the stomach rotate next?
The stomach rotates about a ventrodorsal axis, the bottom part coming superior and to the right. The top of the duodenum is also pulled up, creating a c-curve in the duodenum. This happens during the eighth week.
Congenital pyloric stenosis
Greater in males than in females, stenosis of pyloric canal (sphinctoric region that runs between stomach and duodenum), leads to obstruction of food and projectile vomiting. Can be treated surgically.
What perfuses the duodenum?
The celiac artery and superior mesenteric artery. Because it was derived from the foregut.
Orientation of the duodenum
Originally is a loop that projects ventrally, after rotation points to the right. It forms a c-shaped curve. Eventually is retroperitoneal.
Duodenal stenosis
Caused when lumen (which is filled with epithelium weeks 5-6) only partially recanalizes, leads to vomiting of the stomach’s contents (including bile).
Duodenal atresia
Similar to duodenal stenosis, but complete closure of duodunal tube. 20-30% of cases are associated with downs. Can be diagnosed prenatal with ultrasound, see two separate bubbles for stomach and duodenum.
Where does the hepatic diverticulum arise
as a ventral outgrowth from the caudal part of the foregut early in the fourth week, and extends into the septum transversum. In this region the septum transversum makes up the ventral mesentary.
Is induced by Fibroblast Growth Factors (FGFs) released by the heart.
What arises from the hepatic diverticulum
The liver, gall-bladder, and biliary duct system
The larger cranial and lower caudal part of the hepatic diverticulums are each premordial of?
The liver –> cranial
The gall-bladder –> caudal
The stalk of the diverticulum –> cystic duct, which connects the gall-bladder to the bile duct.
The endodermal cells of the hepatic diverticulum give rise to what part of the liver?
Give rise to the hepatic cords that separate the sinusoids of the liver. These sinusoids are spaces that will hold blood.
The surrounding mesenchyme of the transversum septum gives rise to?
Kuppfer cells (macrophages of the liver) and hematopoietic tissue. The liver is responsible for blood cell formation until the bone marrow develops and matures.
Which lobe of the liver is larger?
The right
When does hematopoiesis start?
Six weeks
When does bile formation start?
Twelve weeks
Location and orientation of bile duct.
Connects the hepatic and cystic ducts to the duodenum. Initially connects ventrally to duodenum, but after rotations is connected dorsally.
Two parts of lesser omentum
The hepatogastric ligaments and hepatoduodenal ligament.
Ventral mesentary gives rise to
The hepatogastric ligament, the hepatoduodenal ligament (together the lesser omentum) and the falciform ligament.
The bare area of the liver
The liver is covered by peritoneum except for the bare area, which is in direct contact with the liver. The borders are the coronary ligaments and triangular ligaments laterally.
Accessory hepatic ducts
There can be additional hepatic ducts that can develop, and this is of surgical importance when cutting into the liver
extrahepatic biliary atresia
1/10,000 to 1/15,000, failure of bile ducts to canalize. Could be also caused by late fetal liver infection. Can be diagnosed by jaundice shortly after birth. Need surgical fix or liver transplant.
Where does the ventral pancreatic bud arise from?
It arises from the medial part of the hepatic diverticulum.
Where and when does the dorsal pancreatic bud arise from?
Directly off of the foregut, it develops first and slightly cranially to the ventral pancreatic bud.
How does the main pancreatic duct form?
From the fusion of the dorsal and ventral pancreatic ducts. Their ducts anastomose, and the main pancreatic duct arises from the ventral duct, and the distal part of the dorsal duct.
What induces the ventral pancreatic duct
FGF-2 secreted by the fetal heart, develops from the same bipotential endoderm tissue as the liver arises from.
What induces the dorsal pancreatic duct
Activins from the notochord and FGF-2 from heart.
What forms the exocrine acinar cells and ducts within the pancreas
Endodermal tubules surrounded by mesoderm branch out to form the acini and ducts
exocrine vs. endocrine gland formation pancreas
Exocrine –> endodermal tubules branch to form acini and ducts
endocrine –> clumps of cells from exocrine formation form islets
annular pancreas
There is an anormal bifid ventral pancreatic bud that grows around the duodenum on either side, can cause duodenal obstruction.
What does the spleen arise from?
It arises from the thickening of the dorsal mesogastrium at the tail of the pancreas,
Where is it oriented
It is carried to the left and behind the stomach, when the stomach rotates. Is in contact with the kidney, and above the pancreas.
gastrosplenic ligament
arose from dorsal mesentary, connects spleen to stomach
what do spleen mesenchymal cells differentiate into?
capsule, connective tissue, and parenchyma
what purpose does the spleen serve in embryo
hematopoiesis
Accessory spleen
Exists in 10% of people, fully functional, can exist in tail of pancreas or within gastrosplenic ligament
