Digestive System 1 Flashcards
What are the adult derivatives of the primordial gut tubes?
Foregut
- Pharynx and its derivatives
- Lower respiratory tract
- Esophagus, stomach
- Duodenum up to the major duodenal papilla
- Liver, Biliary apparatus and Pancreas
Midgut
- Duodenum distal to the major duodenal papilla
- Jejunum & Ileum; Cecum & Appendix
- Ascending colon & right 2/3 of transverse colon
Hindgut
- Left 1/3 of transverse colon
- Descending colon, sigmoid colon & rectum
- Anal canal up to the pectinate line
- Urinaary bladder & most of urethra
Describe parts of the primitive gut
After the embryonic folding, intra-embryonic part of the yolk sac is divided into the foregut [within head fold]; Midgut & Hindgut [within tail fold]
-Yolk stalk/ vitellointestinal duct connects midgut with the yolk sac vesicle
Give the overview of the primordial gut
Suspended in the peritoneal cavity by dorsal and ventral mesenteries
- Epithelial lining & glands- from yolk sac endoderm
- Smooth muscle & connective tissue- from the splachnic mesoderm
Explain organogenesis of the foregut
Foregut
Arterial supply- celiac trunk
Structures- esophagus, stomach, duodenum (1st and 2nd), liver, biliary apparatus, and pancreas (also pharynx and lower respiratory system)
The spleen is not an outgrowth of foregut. It develops in the dorsal mesentary from mesenchyme
Rotation due to differential growth: the spleen migrates to the left, the stomach rotates so that the left side faces anteriorly and the right side posteriorly (e.g. left vagus innervates anterior wall) //lesser curve faces right, greater faces left
Summarize foregut rotation
- Longitudinal axis rotation
- Ventraldorsal rotation axis rotation
Pyloric stenosis- the smooth muscle in the pyloric region of the stomach hypertrophied
-The passage of foods and liquids is obstructed, and can cause severe vomiting
Summarize rotation of the biliary and pancreatic ducts
- Abdominal accessory organs arise as foregut outgrowths
- Proximal duodenum rotates clockwise
- Ventral & dorsal pancreatic fuse-Bile and pancreatic ducts join to drain together at major papilla
Annular pancreas- left and right portions of ventral pancreatic bud wrap around the duodenum
-Can constrict/obstruct duodenal contents
Summarize the development of pancreas
Dorsal Pancreatic bud forms upper part of the head, body, and tail
Ventral pancreatic bud- lower part of the head and uncinate process
Summarize the steps in midgut development
- Herniation & 90 degree rotation
- Elongation & formation of jejunoileal loops
- Retraction & 1 degree rotation
- Final positions
Summarize the development of hindgut
- Cloaca is common end for hindgut and urogenital tract
- Urorectal septum grows towards cloacal membrane
- Perineal body separates urogenital and anal membranes
Give the key points of midgut development
- Primary intestinal loop elongates, outgrows abdominal cavity
- Rotates 90 degrees within umbilical cord
- Retracts, grows, and rotates an additional 180 degrees
- Gives rise to distal duodenum, jejunum, ileum, ascending colon and proximal 2/3 transverse colon
What are the key points of hindgut develop?
- Cloacal region differentiates to form separate urogenital and GI channels
- Gives rise to distal 1/3 transverse colon, descending, & sigmoidal colons, and proximal 2/3 anorectal canal
Describe organogenesis of Midgut
Arterial supply- Superior Mesenteric artery
- Rapid elongation of the gut and its mesentery resulting in the formation of the primary intestinal loop
- The Cephalic limb of the primary loop —> distal duodenum, jejunum, and some ileum
- The Caudal limb of the primary loop—> lower ileum, cecum, appendix, ascending colon, and 2/3rds of the transverse colon
Explain organogenesis of the hind gut
Arterial supply-Inferior mesentric artery
Structures- distal 1/3 rd of transverse colon, descending colon, sigmoid colon, rectum, and superior portion of the rectal canal
Develops from the caudal loop, it is the last part of the bowel to renter the body following rotation
Explain the role of the ileal diverticulum in the development of the midgut
A small portion of the umbilical vesicle [vitelline duct] may persist-ileal (Meckel’s) diverticulum (2-4% frequency)
-It is located 40-60 cm from the ileocecal valve on the anti-mesenteric border of the ileum. May be asymptomatic, may contain gastric or pancreatic tissue. May become infected —> symptoms resemble appendicitis but close to umbilicus
Explain the development of the anal canal
- Superior 2/3 derived from the hindgut
- Inferior 1/3 derived from proctodeum
- Pectinate line- junction of the epithelia derived from the ectoderm of the proctoderm and endoderm from the hind gut
Pectinate line is the former site of the anal membrane
