Embro Flashcards
(18 cards)
Development of the gut
- Layers of the gut within 14-15 days
- Epiblast (becomes ectoderm)
- Hypoblast (Becomes endoderm)
3.Mesoderm (at 16 days creates 3rd layer between the ectoderm and endoderm)
2 main structures of VERY early gut
AND what disc does the gut go from/transform into
Amnion
yolk sac
Bilaminar disc to trilaminar disc
Two types of folding and describe what that looks like
Longitudal
Lateral
Lateral Folding
-general process with the layers
- what cells in endoderm and mesoderm
Ectoderm and mesoderm fold laterally and ventrally
This closes off the endoderm creating a seperated gut tube structure
Endoderm- forms epithelial cells lining the tube
mesoderm - gives rise to supporting structures and smooth muscle
Longitudal folding
- what happens with specific membranes
-forms what structures
starts to draw the opening of gut tube to the yolk sack closed (like a purse string)
Divides into Ant. Intestinal portion (foregut) and Post. Intestinal portion (hindgut)
Midgut remains open to yolk sack
Label an early gut
Lecture slide
What is cranial and caudal end
- type of membrane
- what do they form when they rupture
Cranial End – Oropharyngeal membrane
Ectoderm of the stomodeum
Caudal End – Anal Membrane
Ectoderm of the anal pit
Describe the 3 stages in the lumen of the tube formation
A: Initially gut tube = patent (i.e. open)
B: As epithelium proliferates – plugs up the lumen of the gut tube
C: Recanalization occurs via cavity formation in the epithelial plug (vacules/cavity formation
Foregut: Esophagus
- development progression
There is a tracheophageal ridge
This ridge gets less wide up with the foregut tube behind.
The ridge closes forming the esophagus and trachea as two seperate organs.
-Immediately caudal to pharynx
-Trachea (ventral) partitions from the oesophagus (dorsal)
-Initially Oesophagus = short
Rapidly elongates
2 example of issues with foregut formation
- why it happens
- Tracheoesophageal Fistula / Atresia
Atresia = Blockage
Fistula = Connection
Both occur as result of incomplete partitioning
- Congenital Hiatal Hernia
(Short oesophagus)
- displaces stomach cranially
- herniates into thorax (through oesophageal hiatus)
Foregut: Stomach process of formation (3 stages)
Lecture Slide
Stage 1:
Gut tube starts to dilate
Stage 2:
- Dilation continues
- Rotation on long axis ~90° clockwise
- Anterior mesogastrium move to right, Posterior moves to left
Stage 3:
-Dilation continues
-Rotation on coronal axis ~90° clockwise
-Right boundary becomes superior (lesser curvature), Left boundary becomes inferior (Greater curvature)
How is greater omentum formed
Dorsal mesogastrium dragged round by rotation of stomach
Begins to hang down
Both sides of the hanging fold fuse together (making a 4 layered peritoneal structure)
The Greater Omentum is formed!
Transverse Colon fuses to underside
Foregut stomach:
Example of issue
and effects of it
- stomach
Congenital Hypertrophic Pyloric Stenosis
- Marked thickening of the muscular wall of the pylorus
- Blocks exit of stomach into 1st part of Duodenum
- Severe non-bilious vomiting!
Midgut
- what limbs
-process of formation
Shape & Elongation: U-Shape “Midgut Loop”
Cranial & Caudal limbs – named after relation to SMA
Herniation: Normal process – loop migrates through into umbilical cord
Rotation: Midgut loop begins to rotate counter-clockwise. (Rotation continues through 270°)
Return: Eventually herniation retracts
Midgut loop returns to abdominal cavity
Cecum & Appendix: rotate down to lower abdomen
Lecture Slide
Examples of Midgut: Congenital Malformations
-abnormal rotations
Abnormal Rotation:
A: Non-rotation (left-sided colon)
B: Mixed rotation and Volvulus (twisting)
C: Reversed rotation (transverse colon compressed by SMA overlaying)
D: Sub-hepatic cecum and appendix (failure for them to rotate and descend)
E: Internal hernia (e.g. Paraduodenal Hernia)
F: Midgut Volvulus (can obstruct duodenum)
Lecture Slide for images
Midgut: Congenital Malformations
- Umbilical Herniation/Fistula:
-Ileal (Meckel’s) Diverticulum
What happens
- Umbilical Herniation/Fistula:
Failure of umbilical cord to close properly
Gut herniates through weakened region in body wall - Ileal (Meckel’s) Diverticulum:
Remnant of the yolk stalk (Vitelline Duct)
Hindgut
- 2 aspects
Cloaca and Rectum/Anal canal
Cloaca:
- Expanded distal part of hindgut
- Divided into Dorsal and Ventral parts
- Mesenchymal Urorectal Septum
- As septum grows – separates rectum from urogenital sinus
Rectum/Anal canal:
- Boundary between outer ectoderm and inner endoderm
- Pectinate Line denotes boundary
-Blood supply to upper 2/3 = IMA
- Portal-Systemic Anastamosis
- Anal columns terminate at site of anal membrane
- Lymphatics change at Anocutaneous Line (White Line)
Below = superficial inguinal nodes
Hindgut: Congenital Malformations (3)
Imperforated Anus:
Failure of anal membrane to perforate
Rectal Atresia:
Anal canal and rectum are separated
- Fistulas may present
Megacolon:
Segment of colon is dilated
- Due to absence of ANS ganglion cells in wall of gut distal to it
- Failure of peristalsis in aganglionic part – cannot relax
- Prevents movement of intestinal contents
- Normally located around region of gut close to anus
