Flashcards in Week 4 - Development of mid/hindgut Deck (29):
Where is the midgut?
-From 2nd part of duodenum after bile duct enters to proximal 2/3 of transverse colon
Describe the midgut loop structure
-Has SMA at axis dividing into cranial and caudal limbs
-connected to yolk sac via vitelline duct
What is physiological herniation and why does it occur?
-During 6th week growth of loop so rapid and simultaneous to liver that the abdominal cavity is too small
-Intestines herniate into the umbilical cord
Explain midgut rotation during physiological herniation
-3x90 degree anticlockwise turns whilst herniating
-One when it is herniating, one whilst its herniated and one on the return
-Rotation 1 causes limbs to be side by side
-Rotation 2 causes cranial limb on bottom and to return first
-Rotation 3 causes limbs to be side by side and pulls remaining gut tube into body
-Achieves cranial limb returning first and being pushed to the left as others return -> correct anatomical position
How does the cecum come to lie in its correct anatomical position?
-The cecal bud descends from the transverse colon after physiological herniation
What are the derivatives of the cranial limb of midgut loop?
What are the derivatives of the caudal limb of midgut loop?
-Proximal 2/3 tranverse colon
What are 2 possible outcomes of malrotation?
-Incomplete rotation -> midgut loop makes one turn only -> left sided colon as cranial limb not pulled under caudal limb
-Reversed rotation -> one clockwise turn ->transverse colon passes posterior to duodenum
What is volvulus?
-Twisting of intestines due to mobile mesentery which can cause strangulation and ischaemia
Describe possible remnants of the yolk stalk (vitelline duct)
-Vitelline cyst as midportion on duct remains patent and fluid filled -> bowel abnormally tethered to anterior abdominal wall
-Vitelline fistula -> Patent duct resulting in spillage of intestinal contents out of umbilicus
-Meckel's diverticulum ->proximal segment is patent
Describe the rule of 2s and meckels diverticulum
-2% of pop
-2 feet from ileocecal valve
-2 inches long
-Usually detected in under 2s
-2 tissue types (ectopic gastric and pancreatic)
Describe recanalisation of gut tube. Give examples of structures to which this happens
-Cell growth becomes so rapid the lumen is obliterated
-Recanalisation restores the lumen
-Oesophagus, bile duct, small intestine
What is the result of incomplete recanalisation?
-Atresia or stenosis
What is the cause of pyloric stenosis? How does it commonly present?
-Hypertrophy of the circular muscle in the region of pyloric sphincter
-Presents with characteristic projectile vomiting
Which part of the intestines is atresia and stenosis most common?
What are the two main causes of duodenum atresia?
-Recanalisation failure (upper)
-Vascular accident (lower)
What is gastroschisis?
-Failure of closure of abdominal wall during folding
-Leaves gut tubes and derivatives outside body cavity
What is omphalocoele? How does it differ from umbilical hernia?
-Persistance of physiological herniation
-Differs from umbilical hernia as hernias have covering of skin and subcut ie physiological herniation had completed
-in exomphalos covered in peritoneu and amnion
Where is the hindgut?
-Distal 1/3 of transverse colon to pectinate line of anus
-Also includes epithelium of urinary bladder
What is the physiological difference superior and inferior to the pectinate line?
-Different arterial supply, venous and lymphatic drainage and innervation
How do the differences superior and inferior to the pectinate lines occur?
-The anorectal canal is formed by the cloaca and the cloacal membrane. The cloaca is endoderm whilst the cloacal membrane is ectoderm. These embryonic tissues have different innervation and supplies
Describe the epithelia, innervation and supply superior and inferior of pectinate line
-Superior -> IMA, Visceral innervtion, columnar epithelium
-Inferior -> Pudendal artery, somatic innervation, stratified epithelia
What significance does the differences in innervation above and below the pectinate line have?
-Above the pectinate line only sensation possible is stretch
-Below the pectinate line the tissue is temperature, touch and pain sensitive
Explain imperforate anus
-Failure of the anal membrane to rupture
Which structures of the mid and hind gut loose their mesentery and become retroperitoneal?
-Ascending and descending colon
Where is the gastrolienal ligament?
-Between stomach and spleen
What is the blood supply to midgut? hindgut?
-Midgut -> SMA
-Hindgut -> IMA
Describe the partitioning of the cloaca
-Urorectal septum grows down towards cloacal membrane
-Separates gut tube into urogenital sinus anteriorly and anorectal canal posteriorly
-Perineal body is where urorectal septum touches cloacal membrane