Development Of Gut 1,2 Flashcards
What parts of GI make up the the;
- Foregut
- Midgut
- Hindgut
F: Oesophagus to Duodenum
M: Duodenum to Distal 2/3 of Transverse Colon
H: Distal 2/3 of Transverse Colon to Anus
What is the Vitelline duct?
What happens to it before birth
Connection between Midgut and Yolk Sac
Completely obliterates
List 2 abnormalities when the Vitelline Duct does not obliterate by birth
- Presence of a Meckel’s Diverticulum (Outpuch of Small Intestine)
- Connection between Midgut and Umbilicus (Fecal material comes out through Umbilicus)
What 2 types of folding occur in week 4?
What are the results of these?
Lateral:
- Creates ventral body wall (anterior body wall)
- Primitive gut becomes tubular (gut tube)
Craniocaudally:
- Creates cranial and caudal pockets/ head and tail ends (from yolk sac endoderm)
What is the Gut Tube that is made from Lateral Folding?
Where does it open? What is it covered by?
- An endoderm lined tube
- running the length of the body
- with blind pouches at head and tail ends
- Opens at Umbilicus
- Covered by Splanchnic (Visceral) Mesoderm
Compare the Splanchnopleuric and Somatopleuric mesoderm
What is the space between them called
- Splanchnopleuric: Combination of Splanchnic Mesoderm and Endoderm (of Gut tube)
- Somatopleuric: Combination of Somatic Mesoderm and Ectoderm
- Intraembryonic Coelom
What will the Intraembryonic Coelom eventually turn into?
How does it develop into this stage? (Very briefly)
- Begins as one large cavity
- Later divided by Diaphragm into Thoracic and Abdominal Cavities
Describe the Intraembryonic Coelom’s membrane
- 1 membrane lining whole cavity
- Specialises as cavities specialise into Pleura/ Pericardium/ Peritoneum and peritoneal cavity
What parts of the Peritoneum do the Somatic and Splanchnic Mesoderm develop into?
What is the space between called?
Splanchnic- Visceral
Somatic- Parietal
- Space between called the Peritnoneal Cavity (Is only a potential space, should be empty normally)
In the 4th week, what Membrane breaks, to effectively give us a “mouth”
Buccopharyngeal Membrane
In the 7th week, what membrane breaks, to effectively give us an “anus”
Cloacal membrane
What branches of the Abdominal Aorta supply each segment of the GI Tract?
Coeliac artery- Foregut
Superior Mesenteric- Midgut
Inferior Mesenteric- Hindgut
Name 1 non-GI derivative of the Foregut
Respiratory tract
What does the endoderm of the gut do in the 5th and 9th weeks?
5th: Proliferates rapidly, temporarily closing lumen
9th: Recanalises (Opens lumen again)
What happens in the Foregut in 4th week?
- A lung bud (respiratory diverticulum) forms ventrally
- A Tracheoesophageal Septum forms, separating Trachea and Oesophagus
Abnormal positioning of the Tracheoesophageal Septum occurs in about 1 in 3000 births and can lead to a variety of abnormalities
Name 2
- Blind end Oesophagus (Ends suddenly, doesn’t continue)
- Tracheoesophageal Fistula (Abnormal connection between the 2)
The stomach is simply a dilation of the foregut
Does it dilate more on the Anterior or Posterior aspect?
What happens next?
Posterior
Rotates by 90 degrees
What Mesenteries attach the Gut Tube to the body walls?
- Dorsal mesentery attaches ENTIRE gut tube to dorsal body wall
- Ventral mesentery attaches ONLY Foregut to ventral body wall
What is the Free Edge of the foregut?
The lower edge of the Ventral Mesentery of the Foregut
Which organs develop in the Ventral and Dorsal mesentery?
Ventral- Liver
Spleen- Dorsal
(Obviously the dorsal mesentery is rotated to the left and ventral to the right)
The liver develops as a bud off of the anterior foregut
What do the cranial and caudal portions of the bud develop into?
Cranial- Liver (Connection remains as Bile Duct)
Caudal- Gall bladder
The dorsal and ventral mesenteries of the foregut divide the peritoneal cavity into Left and Right Sacs (in this region only)
Which sac contributes to the Greater and Lesser sacs?
Left sac- Contributes to Greater sac
Right sac- Contributes to Lesser sac
Why is the Lesser sac much smaller than Greater?
Liver grows and takes up space
Which sacs lie Anterior and Posterior to stomach?
Lesser sac lies posterior to stomach
Greater sac lies anterior to stomach
What is the Foramen of Winslow/ Epiploic Foramen?
A small connection between Lesser and Greater sacs, formed by the Free Edge of the Foregut
The vagus nerves initially lie left and right to the stomach.
How does their position change after the stomach’s rotation?
Left vagus fibres lie anterior to stomach
Right vagus fibres lie posterior to stomach (In lesser sac)
Name and describe the 2 remnants of the Ventral Mesentery of the Foregut
(They are both double folds of Peritoneum)
- Falciform Ligament: From Anterior Abdominal wall to Liver
- Lesser Omentum: From Liver to Stomach
Name and describe the 2 remnants of the Dorsal Mesentery of the Foregut
(They are both double folds of Peritoneum)
- Gastro-splenic ligament: From Stomach to Spleen
2. Spleno-renal Ligament: From Spleen to Left Kidney
What are omenta?
Specialised regions of peritoneum
The Greater Omentum is formed from the Dorsal mesentery.
What structures does it connect together?
Stomach and transverse colon
Describe the development of the Pancreas
- Starts as a Smaller Ventral and Larger Dorsal Buds off of Foregut
- Ventral head rotates to become inferior to Dorsal Bud
Describe the development of the Duodeum
- Develops from Caudal Foregut and Cranial Midgut
- Stomach rotation pushes Duodenum to right, then against posterior abdominal wall
- It has now become Secondary Retroperitoneal
What is a Secondary Retroperitoneal structure?
- One that developed intraperitoneally
- whose mesentery was lost to fusion with Post. Ab Wall Parietal Peritoneum
- due to massive GI tract expansion during development
