Module 5: Development of the Digestive System, Heart, and Great Vessels Flashcards
Embryonic folding of the gut tube
-ventral folding at anterior and posterior ends forms a closed tube
Primary gut tube
-hollow cylinder of endodermal cells surrounded by mesoderm
3 distinct regions of the gut tube
-foregut
-midgut
-hindgut
Primitive foregut
-extends from oral cavity to initial part of duodenum
Primitive midgut
-extends from mid-duodenum to initial 2/3 of transverse colon
Primitive hindgut
-extends from distal 1/3 transverse colon to upper portion of anus
Blood supply of primitive foregut
-celiac artery
Blood supply of primitive midgut
-superior mesenteric artery
Blood supply of primitive hindgut
-inferior mesenteric artery
Mesentery
-double layer membrane formed by the fusion of the splanchnic mesoderm
Dorsal mesentery
-composed of mesogastrium, mesoduodenum, mesentery proper, and mesocolon
Ventral mesentery
-derived from the septum transversum and forms the falciform ligament of the liver and lesser omentum
Steps of the development of the esophagus
-elongation
-occlusion
-recanalization
Elongation of the esophagus
-after the trachea separates, esophagus continues to grow in length to keep up with overall growth
-also responsible for repositioning of stomach in abdomen
Occlusion time period
-week 5
Occlusion of esophagus
-proliferation of endoderm results in occlusion of esophagus
Recanalization of esophagus time period
-week 9
Recanalization of esophagus
-results in the formation of a hollow tube
Parts of the stomach
-cardia
-fundus
-body
-pylorus
Longitudinal rotation of the stomach
-rotates right 90 degrees about longitudinal axis
Differential growth of stomach
-there is differential growth along one border of the stomach which causes it to elongate more rapidly than the other
-this produces the greater and lesser curvature
Anteroposterior rotation of the stomach
-rotation about anteroposterior axis
-pylorus moves cranially and the cardia moves caudally
Omental bursa
-created by rotation of the stomach that pulls the mesogastrium to the left
What does the dorsal mesentery form
-forms the greater omentum and gastrosplenic and splenorenal ligaments
What does the ventral mesentery form
-forms the capsule and peritoneal coverings of the liver and ligaments of the liver
Ligaments of the liver
-lesser omentum
-triangular, coronary, and falciform
Development of liver and gallbladder steps
-hepatic diverticulum forms
-hepatic diverticulum divides
-hepatic duct forms
-hepatic duct outgrowth
-liver cords differentiate
-liver stroma forms
Hepatic diverticulum forms
-grows from distal end of foregut and penetrates the septum transversum
Hepatic diverticulum divides
-divides into a cranial part, which forms parachyma of liver, and caudal part which will later give rise to the gallbladder and cystic duct
Hepatic duct forms
-hepatic cells continue to penetrate septum transverum, and the connection between the diverticulum and foregut narrows, forming hepatic duct
Hepatic duct outgrowth
-from hepatic duct, outgrowth gives rise to gallbladder and cystic duct
-these then together form the bile duct
Liver cords differentiate
-epithelial liver cords differentiate into liver parenchyma and form the lining of the biliary
Liver stroma forms
-the connective tissue capsule of the liver is derived from the septum transversum
Development of the pancreas
-forms from 2 outgrowths of the gut tube endoderm
What are the outgrowths of the gut tube endoderm
-dorsal pancreatic bud
-ventral pancreatic bud
Dorsal pancreatic bud origin
-originates from the duodenum
Ventral pancreatic bud origin
-develops from the bile duct
Migration of the pancreas and duodenum
-ventral pancreatic migrates towards dorsal pancreatic bud, the proximal duodenum also rotates clockwise with pancreas
Union of the pancreas and duodenum
-ventral bud fuses with dorsal bud and becomes the uncinate process
What does dorsal pancreatic bud make up
-main body of pancreas
Steps of the development of the midgut
-elongation
-herniation and rotation
-retraction
When does elongation of the midgut occur
-week 5
What structure is formed by the elongation of the midgut
-primary intestinal loop
2 limbs of the midgut
-cephalic (cranial) limb
-caudal limb
Vitelline duct
-how the loop communicates with the yolk sac
Umbilical herniation of the midgut
-while looping continues, abdomen becomes too small for intestines and several intestinal loops are forced into the umbilical cord
Rotation of midgut
-intestinal loop rotates 90 degrees and axis of rotation is relative to the superior mesenteric artery
Retraction of the midgut
-intestinal loop returns into abdominal cavity later once there is space
-this loop is the small intestine
What does not participate in intestinal looping
-large intestine
Midgut volvulus
-improper rotation of small intestine
-rotates around axis of its own mesentery
Midgut volvulus symptoms
-improper flow of digestion
-intestinal blockages
-blocking of intestinal circulation
Hindgut derivatives
-caudal half of transverse colon
-descending colon
-rectum
-superior part of anal canal
Steps of hindgut development
-cloaca
-urorectal septum
-perineal body
-anal pit
Cloaca
-shared end of the hindgut and urogenital tract
-common chamber that intestinal, urinary, and genital tract opens into
Urorectal septum
-migrates to cloacal membrane, and separates hindgut from urinary system
Urogenital sinus
-forms the bladder and urethra
Perineal body
-between urogenital and anal membranes, where the anal canal begins to develop
Anal pit formation
-ectoderm invaginates cloaca
-establishes continuity of the anal canal and rectum
What is the proximal 2/3 anal canal derived from
-endoderm
What is the distal 1/3 of anal canal derived from
-ectoderm
Imperforate anus
-normal anal opening is absent at birth
-results from abnormal development of urorectal septum
Enteric nervous system parts
-myenteric plexus
-submucosal plexus
Myenteric plexus location
-located between inner circular and outer longitudinal muscle layers
Submucosal plexus location
-situated within submucosa layer
What is the enteric nervous system derived from
-autonomic nervous system
What are ENS neurons derived from
-derived from neural crest cells
Function of the enteric nervous system
-functions with smooth muscle cells and mucosal villi to control absorption and secretion of GI system, including small and large intestines
Formation of the heart tube steps
-progenitor cells
-migration
-heart field
When does formation of the heart tube begin
-week 3
What are progenitor cells derived from
-intraembryonic mesoderm and cranial 1/3 of primitive streak
Migration of progenitor cells
-leave primitive streak and become localized on either side of primitive streak
Heart field
-progenitor cells form a U shaped tube around notochord
-these merge to form endocardial tube
Longitudinal heart tube folding
-starts in front of oropharyngeal membrane
-ends up in the thorax
Lateral heart tube folding
-allows for endocardial tubes to fuse
-forming heart tube
Components of the heart tube
-bulbis cordis
-sinus venosus
Components of bulbis cordis
-truncus arteriosus
-conus cordis
-primitive ventricle
-primitive atrium
Truncus arteriosus
-outflow tracts of aorta and pulmonary arteries
Conus cordis
-outflow tracts of both right and left ventricles
Primitive ventricle
-trabeculated walls of the ventricles
Primitive atrium
-later divides into left and right atrium
-connected to sinus venosus
Sinus venosus
-derives from and is connected to venous system
Cardiac looping
-when heart grows it is restricted by the septum transversum and pericardium and must bend
Cardiac looping movements
-primitive atria moves posteriorly
-bulbus cordis and right primitive ventricle come to lie between primitive right and left atria
Why is the primitive heart different from the adult heart
-resembles it, but primitive heart is still one continuous tube
Interatrial septum
-separate right and left atria
Interventricular septum
-separate right and left ventricles
Formation of interatrial septum steps
-septum primum
-ostium secondum
-septum secundum
Septum primum
-cells from the roof of common atria grow caudally
-grows towards endocardial cushion but does not fuse
Ostium secundum
-when septum fuses with the endocardial cushion this second opening is created
Septum secundum
-second septum forms from roof of atria
-common atria is now divided into left and right atrium
Formen ovale
-oval shaped window that allows blood to pass between the atria
What is the foramen ovale covered by
-thin valve-like membranous flap from septum primum
First step of foramen ovale formation
-fetus receives oxygenated blood from the placenta via the umbilical vein, oxygenated blood enters the right atrium
Second step of foramen ovale formation
-since blood is already oxygenated, it does not need to be pumped to the lungs
Third step of foramen ovale formation
-foramen ovale allows blood to bypass the pulmonary circulation by shunting blood from right atrium to left atrium
Where does blood move from left atrium
-blood moves into left ventricle, and then through aorta to the rest of the body
Patent foremen ovale
-incomplete fusion of septum secundum and septum primum
-has been associated with increased risk of adverse events including strokes
-most are asymptomatic and do not require treatment
Embryonic arteries
-aortic sac
-ventral aorta
-aortic arches
-dorsal aorta
Aortic sac
-sits cranial to truncus arteriosus
Ventral aorta
-aortic sac branches into 2 horns, right and left ventral aorta
Aortic arches
-6 arteries branch off each ventral aorta, and wrap around the pharynx
What do aortic arches follow the pattern of
-pharyngeal arches
Dorsal aorta
-connects with the aortic arches and connect back with aortic sac
How many aortic arches are there
-6
Aortic arches 1, 2 and 5
-all regress
Arch 3 parts
-dorsal aortae
-ventral aortae
Arch 3 dorsal aortae
-forms the internal carotid arteries and common carotid arteries
Arch 3 ventral aortae
-external carotid arteries
Arch 4 parts
-right ventral aorta
-left ventral aorta
Arch 4 right ventral aorta
-forms right subclavian artery
Arch 4 left ventral aorta
-aortic arch
Arch 6
-forms right and left pulmonary arteries
-also forms ductus arteriosus which forms the ligamentum arteriosus at birth
Ductus arteriosus general function
-directs the flow of blood in the fetus
Ductus arteriosus prenatal function
-instead of entering underdeveloped lungs through pulmonary arteries, blood passes through the ductus arteriosus and enters aorta at aortic arch
Ductus arteriosus postnatal function
-lungs are now developed and blood must travel through pulmonary arteries
What is formed when the ductus arteriosus obliterates
-ligamentum arteriosum
-separates the pulmonary and systemic circulation
Patent ductus arteriosus
-condition where ductus arteriosus does not fully close and there is still a connection between pulmonary and systemic circulation
-small openings may be asymptomatic
-larger openings are closed with ligation
When do embryonic veins develop
-week 4
Embryonic veins
-vitelline veins
-umbilical veins
-cardinal veins
Vitelline veins function
-drain the yolk sac
Umbilical veins function
-come from chorionic villi and carry oxygenated blood to embryo
Cardinal veins function
-drain the body of the embryo
Vein remodelling
-left veins tend to regress while right veins enlarge and give rise to great veins
