S2 L2 Development of the Gut Flashcards
Embryology
- Layers in the trilaminar disc
- State the 3 parts of the middle layer
Following gastrulation, the trilaminar disc forms
3 sections of the mesoderm:
- Paraxial
- Intermediate
- Lateral plates
What tissues are derived from each layer?
Ectoderm: Epidermis and nerve tissue
Mesoderm:
Paraxial - Somites (Skeletal muscle, vertebra, cartilage, tendons)
Intermediate - Kidneys, gonads
Lateral plate - Somatic mesoderm becomes body wall, splanchnic mesoderm becomes viscera
What occurs next?
Folding:
- Cranial-caudal folding
- Lateral folding
Cranial-caudal folding
- Show what happens…
The 5th pic shows the 4 steps that occur
(pics 1-4 make it simpler, by adding one layer at a time)
In 1- Just concentrated on mesoderm (red)
In 2 - Add somatic lateral plate mesoderm to picture
In 3 - Added splanchnic lateral plate mesoderm to picture
In 4 - Added ectoderm layer
In 5 - Finally added endoderm layer (yellow)
- Can see ‘wrapping around’ of mesoderm
What does cranial-caudal folding produce?
This folding leads to the formation of a head end and tail end of the embryo
In detail - by the ‘end of cranio-caudal’ folding, what structures are produced?
What structures develop from:
- Foregut
- Midgut
- Hindgut
- What is the vitelline duct?
- What happens if the vitelline duct doesn’t disappear?
- Foregut: Oesophagus → Duodenum (where the bile duct joints)
- *- Midgut:** Duodenum → Distal ⅓ of transverse colon
- *- Hindgut:** Distal ⅔ transverse colon → Upper anal canal
Currently no openings at the moment
Vitelline duct:
Connection between the mid gut and yolk sac, this should disappear. If it doesnt, can get an outpouch…
Lateral folding
- When does this occur?
- What layers fuse?
- Occurs simulataneously to the cranial-caudal folding
- Fusion of many layers leads to: Aminotic cavity, ectoderm layer, gut tube, body wall…
Define and state where the following are ‘located’
- Splanchnopleuric mesoderm
- Somatopleuric mesoderm
- Intraembryonic coelom
- Parietal peritoneum
- Visceral peritoneum
- Splanchnopleuric mesoderm: Splanchnic portion of mesoderm and endoderm (froms viscera)
- Somatopleuric mesoderm: Somatic mesoderm and ectoderm (forms body walls and dermis)
- Intraembryonic coelom: Space between the splanchnopleuretic mesoderm and somatopleuretic mesoderm, gives rise to the thoracic and abdominal cavity
It is lined by serous membrane (peritoneum)
- Parietal peritoneum: Derived from the somatic potion of the lateral plate mesoderm
- Visceral peritoneum: Derived from the splanchnic portion of the lateral plate mesoderm
What happens after the folding process?
Formation of the holes (i.e. mouth and anus)
- *Mouth:** Bucopharyngeal membrane ruptures (in 4th week)
- *Anus:** Cloacal membrane ruptures around 7th week
Just been rotate 90 degrees
From the developing heart, aorta exits. 3 branches form to supply the different sections of the gut:
Blue: Foregut - Coeliac artery
Red: Midgut - Superior mesenteric artery
Green: Hindgut - Inferior mesenteric artery
Divisions of the gut
What structures arise from:
- Foregut
- Midgut
- Hindgut
How is the trachea formed? and when?
4th week:
- Lung bud develops ventrally (anteriorly) off foregut
(- Means trachae and oesphagus are seperate)
- The tracheaosophageal septum develops to seperate the oesophagus and trachea
How is the stomach formed?
A dilation in the foregut
When it dilates, it grows larger on dorsal aspect compared to ventral aspect
The foregut and stomach also rotate 90 degrees
- *Foregut rotation**
- Name the messenteries present at this stage of embryology
- Seperate into: Foregut, midgut, hindgut
Foregut: Ventral and dorsal messentery
Midgut: ONLY dorsal messentery (therefore, a free edge is created on the ventral side)
Hindgut: ONLY dorsal messentery
- *Foregut rotation -**
- How is the parietal peritoneum and visceral peritoneum formed?
- Talk about the nerve supply to the peritoneum and localisation of pain
Pic: blue = body wall, red = mesoderm, yellow = endoderm
White dashes = outlining the red lines (not an additional line!)
Parietal peritoneum = The mesoderm lining the body wall
Visceral peritoneum = The moment the mesoderm leaves the body wall, it is the visceral peritoneum
They are continuous with each other
Parietal peritoneum has a good sensory supply, so all irritation/pain is well localised
Visceral periotenum doesn’t have a well developed sensory supply, so pain from here is vague
- *Foregut rotation -**
- Where does the liver and spleen develop?
- How does the liver develop (brief)?
- What becomes the greater sac?
- How does the peritoneal cavity seperate into R and L
Liver develops in the ventral messentery. It develops from an anterior bud of the foregut. Cranial portion develops into the liver. The caudal portion develops into the gall bladder. Liver is connected to the ‘gut’ (i.e. duodenum) via the common bile duct.
The big space in the ventral side of the mid and hindgut in the pic
The ventral and dorsal messenteries split the peritonel cavity into left and right
- *Foregut rotation:**
- Another important ‘thing’ causing this forgut rotation
Visceral growth
Formation of the peritoneal sacs - Greater and Lesser
- How do they both form
- Where are the sacs compared to the other viscera?
-
Formed due to rotation
Pic - this section, the yellow is stomach
Have a space anterior and posterior to the stomach, due to visceral growth
What is the foramen of Winslow? What is it’s other name?
What 2 nerves have also been developing during this? Where do they ‘sit’ after the rotation seen?
Foramen of Winslow or Epiploic foramen
Due to only the forgut having two messenteries, this forms between the greater and lesser sac connection (very small space between them)
After rotation, the left vagal fibres form the anterior vagal trunk. The right vagal fibres form the posterior vagal trunk.
- *Peritoneal ligaments - Anterior to posterior**
- 4, name and locate
Anterior to posterior:
- Falciform ligament: Anterior wall of the abdomen to the liver
- Lesser omentum: Between liver and stomach
- Gastrosplenic ligament: Between stomach and spleen
- Splen-renal ligament: Between the spleen to posterior abdominal wall
Pancreas development
Two buds: Ventral bud (smaller) and dorsal bud (larger)
Rotation of the foregut, causes the ventral budy (that comes off the hepatic diverticulum) is forced around the back and inferior to the dorsal (larger bud)
They both fuse, forming the pancreas
