Week 4 Development Part 2 Flashcards
What is physiological herniation and when does it occur
During 6th week
As liver growing rapidly alongside midgut it pushes midgut loop into umbilical cord- covered by amnion
- physiological as normal development process that is resolved
How does the midgut rotate and what is happening at each stage?
3 90degree turns anti-clockwise
First turn leaves cranial on R and caudal on L
- cranial limb elongates much more- s.intestine
Second turn leaves cranial at bottom
- ceacal bud forms
last turn moves cranial to L first and then caudal to R- transverse colon ends up in front of duodenum
- ceacal bud continues to drop
What does the cranial and caudal limbs of the midgut loop develop into?
Cranial- s.intestines- distal duodenum, jejunum, ilium
Caudal- distal ilium, caecum, appendix, ascending colon, proximal 2/3 transverse colon
Congenital abnormalities- What types of malrotation can occur and what does this result in?
Incomplete rotation- only one 90degree turn- L sided colon
Reversed rotation- One 90degree clockwise turn- transverse colon passes posterior to duodenum
Results in:
Volvulus- twisted intestinal loop
Strangulation of bowel
Ischaemia- due to abnormal distribution of viscera
Congenital abnormalities- what abnormalities can arise as a result of remnants of the yolk stalk?
Vitalline duct can persist (patient uracus) resulting in;
Vitalline cyst- remained fluid filled and duct forms fibrous strands
Vitalline fistula- leakage of intestinal content into umbilicus
Meckels diverticulum- ileal diverticulum
- 2% of population, usually seen in under 2yrs, 2:1 male to female
- ilium can contain ectopic gastric and pancreatic tissue- not designed for proteolytic enzymes in it
What is Recanalisation and why does it occur?
Primitive gut tube is a simple tube- during development growth in some gut structures can become so rapid that the lumen is partly or completely obliterated
- oesophagus, bile duct, small intestine
Recanalisation occurs to restore the lumen
Congenital defect- what happens if Recanalisation is not completed and where does this most commonly occur?
if uwholly or partly unsuccessful =
atresia - total failure- no lumen
stenosis- partial failure- narrowed lumen
- most occurs in duodenum- upper part due to recanalisation failure
- lower part due to vascular accident- volvulus, malroatation or body wall defect
congenital abnormalities- what is pyloric stenosis, why does it occur?
hypertrophy of the circular muscle in the region of the pyloric sphincter
not a recanalisation failure
- common abnormality of the stomach in infants- narrowing of the stomach exit= projectile vomiting
What does the midgut give rise to?
Small intestine including most of duodenum, caecum and appendix, ascending colon, proximal 2/3 of transverse colon
congenital abnormalities (anterior abdo wall defects)- what is gsatroschisis and omphalocoele?
gastroschisis- intestinal loop outside body wall- failure of closure of abdominal wall during folding of embryo- leaves gut tubes outside
- picked up at 20week scan, isolated defect- prognosis good if bowel not damaged
omphalocoele- examphalos- persistence of physiological herniation- differs from umbilical hernias as they have covering of skin and tissue whereas this is covered only by amnion
- can be associated with other conditions
When the midgut elongates what is its axis, what duct connects it to the yolk sac
SMA
Vitelline duct
what does the hindgut give rise to?
distal 1,3 duodenum, descending colon, rectum, superior part of anal canal, epithelium of urinary bladder
what line is the anal canal divided by and what does this separate?
pectinate line separates histologically distinct superior and inferior parts
- different arterial, venous, nervous and lymphatic supply - affects pain
Describe the partitioning of the cloaca and the development of the anal canal
anteroposterior devision
- wedge of mesoderm grows down into cloaca dividing it into urogenital sinus anteriorly and anorectal canal posteriorly - end of 7th week
Describe what occurs after cloacal partitioning and what tissues make up each part?
Cloacal membrane is in a pit and contains endo and ectoderm layer
Perineal body formed where partition meets cloacal membrane which is in the pit
Ectoderm curves up inside the first part of anal canal
By what is the anal canal separated and describe each section- artery, nerve, lymph supply, epithelia?
By pectinate line
Above line:
- IMA- artery of hindgut
- S2,3,4 pelvic parasympathetics- splanchnic nerves
- columnar epithelia- derived from endoderm
- lymph drainage- internal iliac nodes
Below line:
- pudental artery
- S2,3,4 pudental nerve- somatic nerve
- stratified epithelia- from ectoderm
- lymph drainage- superficial inguinal nodes
What are the two sections of the anal canal sensitive to?
Above line- only sensation possible is stretch
Below line- temp, touch and pain sensitive- somatic innervation
Discuss the innervation and pain sensation to the peritoneum,
Visceral peritoneum- pain poorly localised- forgut=epigastrium, midgut=periumbilical, hindgut=suprapubic
- only sense stretch
Parietal peritoneum- has somatic innervation also so pain much more localised
Congenital abnormalities- discuss the hindgut abnormalities that may occur?
Imperforate anus- failure of anal membrane to rupture
Anal/ anorectal agenesis
Hindgut fistula
What structures are retained by mesentery and which have fused mesenteries?
Retained by- things could hold in dissection
jejunum, ilium, appendix, transverse and sigmoid colon
Fused mesenteries- duodenum, ascending and descending colon, rectum
What does the dorsal and ventral mesentery become?
Dorsal- greater omentum
- gastrolienal ligament- stomach to spleen
- lienorenal ligament- spleen to kidney
- mesocolon, mesentery proper- Jedinal and Ileal loops
Ventral- lesser omentum- foregut to liver
- falciparum ligament- liver to ventral body wall
State the blood supply and innervation of the midgut and hindgut
Midgut
Blood supply- SMA and SMV
Innervation- para s- vagus
- symp- superior mesenteric ganglion and plexus
Hindgut
Blood supply- IMA and IMV
Innervation- para s- pelvic- S2,3,4,
- symp- inferior mesenteric ganglion and plexus
