anatomy physiology of the anorectum Flashcards
describe the development of the primitive gut tube? from where and when does it occur?
Derived from the dorsal part of the yolk sac
Which is incorporated into the body of the embryo during folding of the embryo in the 4th week
what are the 3 germ layers?
endoderm
mesoderm
ectoderm
what layer of the yolk sac is the gut tube made from?
endoderm
what layer is the gut smooth muscle made from?
mesoderm
what are the sections of the primitive gut tube?
foregut
midgut
hindgut
what is the blood supply of the foregut, midgut and hindgut?
coeliac trunk
superior mesenteric artery
inferior mesenteric artery
what divides the trachea from the oesophagus?
tracheooesophageal septum
what is the result of failure of the tracheoesophageal septum to fully develop?
oesophageal atresia
tracheo-oesophageal fistula
what abnormalities can occur in the midgut?
duodenal atresia
Meckel’s diverticulum
malrotation
what causes duodenal atresia?
failed canalisation
what causes Meckel’s diverticulum?
when a remnant of the yolk sac (Vitelline duct) persists
what causes malrotation?
if the midgut does not complete the rotation prior to returning to the abdomen.
what develops from the cranial end of the hindgut?
Distal 1/3 of the transverse colon, descending colon and sigmoid colon
what does the upper anal canal divide?
develops from the terminal end of the hindgut with the urorectal septum
what does the upper anal canal divide and when?
dividing the upper anal canal and the urogenital sinus during 6th week.
how is the anal membrane formed?
in the 7th week the urorectal septum fuses with the cloacal membrane
what happens to the anal membrane in the 8th week and why?
The anal membrane ruptures during the 8th week allowing communication between the anal canal and the amniotic fluid.
what happens if the anal membrane doesnt rupture and why?
‘Imperforate anus’ or ‘anorectal malformation’ - failure of communication of the endodermal and ectodermal portions of anal canal).
describe the gut innervation
intrinsic NS - vagal and sacral NCC
extrinsic NS - parasympathetic NS (NCC and sacral NCC) and sympathetic (truncal NCC)
what modulates the ENS function?
extrinsic nerves
what is Hirschsprungs disease?
a birth defect characterized by the absence of enteric nervous system (ENS) in the terminal part of the intestine.
It causes the colon smooth muscle to be permanently contracted (no nNOS neurons to relax)
what are symptoms of Hirschsprung’s disease?
failing to pass meconiumwithin 48 hours
a swollen belly
vomiting green fluid (bile)
how is Hirschsprung’s disease treated?
failing to pass meconiumwithin 48 hours
a swollen belly
vomiting green fluid (bile)
what is normal faecal continence maintained by?
anal canal
pelvic floor musculature
rectum
what is the function of the rectum?
store or expel stool both of which require cortical sensory awareness acting in conjunction with intramural and spinal reflexes that ensure timely defaecation
what is the function of the anal canal?
helps to maintain faecal continence and control defecation
what is the purpose of the pelvic floor muscles?
divides abdominal cavity from perineum
what are the pelvic floor muscles
levator ani - puborectalis, pubococcygeus, iliococcygeus
coccygeus
what are the functions of puborectalis?
- surrounds the rectum, vagina and urethra
- supports the EAS and assists in creating the anorectal angle
what is the puborectalis?
passes from the back of puic symphysis to form a U-shaped loop from the rectum to the pbic
striated muscle
what muscles help to maintain the anorectal and urinary continence mechanism?
iliococcygeus and the ischiococcygeus
help the puborectalis
what is pubococcygeus divided into in men and women?
men - Pubourethralis, puborectalis
women - Pubovaginalis and puborectalis
what is the role of puborectalis?
maintain angle between anal canal and rectum
what is continence? what is it characterised by?
self control - the ability to hold it all in
Got to be full
Have to know that it is full
Got to squeeze it
what is faecal continence maintained by?
Anal sphincters Internal anal sphincter (IAS) External anal sphincter (EAS) Pelvic floor muscles Puborectalis muscle
