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Questions and Answers
What is the primary purpose of the College of Medicine's mission?
What is the primary purpose of the College of Medicine's mission?
Which layer is NOT part of the inner cell mass or embryoblast?
Which layer is NOT part of the inner cell mass or embryoblast?
What is the role of the College of Medicine's values?
What is the role of the College of Medicine's values?
Which sequence correctly describes the stages from fertilization to the formation of a blastula?
Which sequence correctly describes the stages from fertilization to the formation of a blastula?
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What is gastrulation primarily responsible for in embryonic development?
What is gastrulation primarily responsible for in embryonic development?
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Which value emphasizes the importance of transparency and belonging in the College of Medicine?
Which value emphasizes the importance of transparency and belonging in the College of Medicine?
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In what form does the embryo develop immediately after fertilization?
In what form does the embryo develop immediately after fertilization?
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Which of the following defines the hypoblast layer?
Which of the following defines the hypoblast layer?
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What is the primary origin of the germ layers during embryonic development?
What is the primary origin of the germ layers during embryonic development?
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During which developmental process do the germ layers originate from the epiblast?
During which developmental process do the germ layers originate from the epiblast?
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Which layer is NOT derived from the epiblast?
Which layer is NOT derived from the epiblast?
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What is the fate of the epiblast in the early stages of embryonic development?
What is the fate of the epiblast in the early stages of embryonic development?
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Which of the following statements accurately describes the relationship between the epiblast and germ layers?
Which of the following statements accurately describes the relationship between the epiblast and germ layers?
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What is the main process through which the epiblast contributes to organogenesis?
What is the main process through which the epiblast contributes to organogenesis?
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Which layer forms directly from the epiblast during the later stages of embryonic development?
Which layer forms directly from the epiblast during the later stages of embryonic development?
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Which option describes an incorrect statement about the ectoderm?
Which option describes an incorrect statement about the ectoderm?
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Study Notes
Introduction to Embryology
- The presentation covers the development of the Gastrointestinal Tract (GIT)
- The different parts of the GIT are the foregut, midgut, and hindgut
Vision and Mission of College of Medicine
- The College of Medicine aims to become a leading model for medical education, research, and promoting community health in the Kingdom
- Their mission is to provide high-quality education and produce excellent healthcare professionals through research and collaboration
Values of College of Medicine
- Responsible citizenship
- Interdisciplinary integration
- Innovative knowledge creation and application
- Respecting diverse ideas, opinions, and backgrounds
- Promoting transparency, fairness, and belonging
- Empowering expertise and capabilities
Development of the GIT
- Blastula: Forms when sperm and egg fuse and implant on the uterine wall
- Gastrula: Develops next, with three germ layers forming: endoderm, mesoderm, and ectoderm
- The epiblast is the source for all germ layers during gastrulation
- The developing embryo forms the amniotic cavity from the epiblast
- The hypoblast lines the blastocyst cavity to form the yolk sac
- The mesoderm doesn't form in two midline areas (oropharyngeal and cloacal membrane)
- The septum transversum is the primordium of the diaphragm. This structure connects to the allantois, an important part of the connecting stalk to the umbilical cord.
- The yolk sac is lined by the endoderm and the visceral layer of the intra-embryonic mesoderm
- The GIT folds to further form the foregut, midgut, and hindgut
- The vitellointestinal duct (connecting the yolk sac to the developing gut) shrinks during development
- The foregut, midgut, and hindgut areas develop on the ventral aspect of the embryo.
- The foregut is closed by the oropharyngeal membrane.
- The midgut connects ventrally, to the yolk sac
- The hindgut is closed by the cloacal membrane. It connects ventrally to the allantois.
- The primitive gut is covered with endoderm covered by a visceral layer of the intra-embryonic mesoderm
- Endoderm forms lining cells of the gut/GIT and parenchyma/functional part
- The surrounding mesoderm produces the muscles and connective tissue of the GIT and its stroma
- The body wall and primitive gut are connected by peritoneal folds
- The peritoneal folds are named based on the gut structure, such as the ventral mesogastrium (stomach area) and dorsal mesogastrium (stomach/diaphragm/body wall area), the dorsal mesoduodenum (duodenum area) and dorsal Mesocolon.
- The upper part of the primitive peritoneal cavity divides into right and left halves, with ventral and dorsal mesogastrium
- The lower part of the primitive peritoneal cavity incompletely divides into right and left halves, with dorsal mesenteries/mesoduodenum/mesocolon
- The GIT is divided into foregut, midgut, and hindgut based on its embryonic origin.
- Foregut consists of the lower end of the esophagus, stomach, upper half of duodenum, liver, spleen, and most of the pancreas
- Midgut includes the lower half of the duodenum, the lower part of the pancreas head/uncinate process, ascending colon, cecum, appendix, right two thirds of the transverse colon
- Hindgut consists of the left third of the transverse colon, splenic flexure, descending colon, sigmoid (pelvic) colon, rectum, and anal canal.
- The esophagus and respiratory diverticulum (lung bud) are formed from the foregut
- Initially there's a communication between the regions forming trachea and esophagus (which is later separated)
- The esophagus is short and lengthens with the descent of heart and lungs
- Anomalies may occur due to recanalization failure of the lumen (at fetus 8th week), resulting in atresia of esophagus or stenosis
- The stomach develops and rotates from the cranial, to the caudal aspect of the fetus
- The liver, develops from the ventral mesogastrium
- The spleen from the dorsal mesogastrium
- During the fifth and sixth weeks, the stomach rotates with the greater curvature moving left and the lesser curvature right
- The cranial part of the stomach develops faster than the caudal part
- The primordial stomach is located in the median plane of the embryo, and expands in a ventrodorsally fashion
- Ligaments are formed to connect the stomach, liver, and diaphragm
- The duodenum originates from the union between foregut and midgut.
- The duodenum rotates to the right with the rotation of the stomach
- The primary pancreatic duct (Wirsung) is formed from the tail of the pancreas
- An accessory pancreatic duct (Santorini) may persist
- The pancreas develops as two pancreatic buds, one from The caudal end of the foregut and the other from the cranial end of the midgut
- The ventral pancreatic bud develops into to the lesser part of the head and the uncinate process of the pancreas.
- The most definitive pancreas is the dorsal bud
- The midgut develops through elongation and herniation from the lateral side
- The midgut folds to return to the umbilical cavity, which is completed by the end of the 11th week where the ascending colon and cecum are formed
Anomalies of the GIT
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Defects in the GIT development are rare but important clinically, such as hypertrophic pyloric stenosis (thickening of pylorus), complete duodenal atresia (absence of the duodenal lumen), and midgut anomalies
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Detailed information about the variations (atresia and/or fistula) of the different parts of the GIT may be presented
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These are due to abnormal rotation or failure (at fetus 8th week) in recanalization
References
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Include the following references:
- The Developing Human: Clinically Oriented Embryology-10th edition (2015)
- Langman's Medical Embryology-14th edition (2018)
- Netter's atlas of human anatomy
- Gray's Anatomy – 39th edition
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Description
Explore the fascinating stages of embryonic development, focusing on the Gastrointestinal Tract (GIT) formation through its three primary divisions: foregut, midgut, and hindgut. Additionally, understand the vision and mission of the College of Medicine and its commitment to community health and medical education.