Development of the GI tract Flashcards
Week 1
Fertilization to implantation
Week 2
The bilaminar embryo (2 germ layers)
Week 3
The trilaminar embryo (3 germ layers)
Weeks 4–8
The embryonic period
Months 3–9
The foetal period
Week 3 - the 3 germ layers
- Endoderm
- Mesoderm
- Ectoderm
What occurs after gastrulation?
The formation of the foregut, midgut and hindgut.
Blastopore
Opening to the exterior / anus
Blastula ->
Gastrula
What does the endoderm layer become x4
- Digestive system
- Liver
- Pancreas
- Lung (inner layers)
What does the mesoderm layer become x4
- Circulatory system
- Lungs (epithelial layers)
- Skeletal system
- Muscular system
What does the ectoderm layer become x4
- Hair
- Nails
- Skin
- Nervous system
Foregut arterial
Coeliac trunk
Foregut arterial
Coeliac trunk
Midgut arterial
Superior mesenteric artery
Hindgut arterial
Inferior mesenteric artery
Coeliac trunk
- Ab. oesophagus
- Stomach
- Duodenum
- Liver
- Spleen
- Pancreas
- Gallbladder
Superior mesenteric artery organs
- Duodenum
- Small intestine
- Caecum
- Appendix
- Ascending colon
- Right 2/3 transverse colon
Inferior mesenteric artery supplies
- Left 1/3 of transverse colon
- Rectum
- Anal canal
- Descending colon
- Sigmoid colon
What occurs during week 3?
The flat trilaminar embryonic disk becomes a more cylindrical embryo that occurs as a result of embryonic growth forming body cavities.
What folding leads to the formation of the gut?
Dorsal / ventral and lateral folding of the embryo
What is the membrane that turns into the mouth?
Oropharyngeal (buccopharyngeal) membrane
What is the membrane that turns into the anus?
Cloacal membrane
What occurs at 22 days?
- Gut-associated organs begin to form as buds from the endoderm, including the thyroid, lung, liver, pancreas
- Midgut opening to the yolk sac progressively narrows
What occurs by the end of the first month? x 3
- The stomach bulge is visible
- Dorsal pancreas has begun to bud
- Connection of the midgut to the yolk sac is reduced to a yolk stalk
What does lateral folding of the embryo complete?
The gut tube via the formation of body cavities
What occurs at the lateral plate?
The mesoderm splits into splanchnic and somatic mesoderm
What does the splanchnic (visceral) mesoderm line?
Lines the gut continuous with yolk sac (viscera walls)
What becomes the mesentery?
Somatic mesoderm
What does the somatic mesoderm line?
The body cavity (body wall)
Where does the foregut extend from?
The buccopharyngeal membrane to the septum transversum
What is the buccopharyngeal membrane?
The septum between primitive mouth and pharynx
What is the septum transversum?
The precursor to diaphragm and ventral mesentery
Through what does the midgut communicate with the yolk sac?
Vitellein tube
Where does the hindgut extend to?
The cloacal membrane
Where is the cloacal
membrane? and what will it become?
Where ectoderm and endoderm are in contact – will become anus
What does the hindgut communicate with?
The allantoic diverticulum
What does the allantoic diverticulum become? x 2
The allantois, which becomes the urachus – medial umbilical ligament
What is the first functioning intra-embryonic blood vessel?
Dorsal aortae
What supplies the pharynx? (foetus)
Aortic arches
