Anatomy- Faecal Continence Flashcards
what does the control of the excretion of faeces require?
a holding area (the rectum) to store faeces until appropriate to defecate
normal visceral afferent nerve fibres to sense the ‘fullness’ of the rectum
functioning muscle sphincters around the distal end of the GI tract to respond to this ‘fullness’
to appropriately contract, preventing defecation and to relax, allowing defecation
normal cerebral function to control the appropriate time to defecate
what can affect the control of the excretion of faeces?
- neurological pathology eg dementia, stroke, MS, trauma
- medications
natural age-related degeneration of nerve innervation of muscle - consistency of stool
where is the pelvic cavity?
within the bony pelvis
continuous with abdominal cavity above
lies between pelvic inlet and pelvic floor
where is the rectum located?
within the pelvic cavity
levator ani muscle
pelvic floor
purpose of pelvic floor
openings permit the distal parts of alimentary, renal and reproductive tracts to pass from the pelvic cavity into the perineum
where does the sigmoid colon become the rectum?
anterior to S3
recto-sigmoid junction
where does the rectum become the anal canal?
anterior to the tip of the coccyx just prior to passing through the levator ani muscle
where are the anal canal and the anus?
in the perineum
where is the rectal ampulla?
immediately superior to the levator ani muscle
what is the purpose of the rectal ampulla?
its walls can relax to accommodate faecal material
where does the prostate gland lie?
anterior to the inferior rectum
what covers the superior rectum?
peritoneum
what does the levator ani muscle form?
most of pelvic diaphragm together with fascial coverings
most of floor of pelvis
most of roof of perineum
what is the levator ani muscle made up of?
pubococcygeus
puborectalis
illiococcygeus
skeletal muscles
what is the purpose of the levator ani muscle?
provides continual support for the pelvic organs- tonically contracted most of the time
reflexively contracts further during increase in intra-abdominal pressure eg coughing, sneezing
must relax to allow defecation to occur
what nerve is the levator ani muscle supplied by?
‘nerve to levator ani’
a branch of the sacral plexus and pudendal (S2,3,4)
what is the importance of the puborectalis?
contraction of this muscle decreases the anorectal angle, acting like a sphincter
when the rectal ampulla is relaxed and filled with faeces, voluntary contraction of this muscle will help to maintain continence
what are the 2 anal sphincters?
1 internal sphincter (smooth muscle)
1 external sphincter (skeletal muscle)
what stimulates the contraction of the internal anal sphincter?
sympathetic nerves (ie sphincter is closed)
what inhibits contraction of the internal anal sphincter?
parasympathetic nerves
what stimulates contraction of the external anal sphincter?
pudendal nerve
what is the nerve supply of structures in the pelvis?
body cavity
sympathetic
parasympathetic
visceral afferents
what is the nerve supply of structures in the perineum?
body wall
somatic motor and somatic sensory
what is the role of sympathetic fibres from T12-L2?
contraction of internal anal sphincter
inhibit peristalsis
what is the course of sympathetic fibres from T12-L2?
travel to inferior mesenteric ganglia- synapse- then travel via periarterial plexuses around branches of IMA
what is the role of somatic motor from pudendal nerve (S2-S4) and nerve to levator ani (S3,S4) ?
contraction of external anal sphincter and puborectalis
what is the role of visceral afferents back to S2-S4?
run with parasympathetics
sense stretch, ischaemia etc
what is the role of parasympathetic fibres from S2-S4?
inhibit internal anal sphincter
stimulate peristalsis
what is the course of parasympathetic fibres from S2-S4?
via pelvic splanchnic nerves, synapse in walls of the rectum
describe the pudendal nerve
branch of sacral plexus
S2, S3, S4 anterior rami
supplies external anal sphincter
how does the pudendal nerve exit the pelvis?
via greater sciatic foramen
how does the pudendal nerve enter the perineum?
via lesser sciatic foramen and branches to supply structures of the perineum
what can happen to the pudendal nerve during labour?
branches of the pudenal nerve could be stretched
fibres within the puborectalis or external anal sphincter muscle could be torn
results in weakened muscle and may lead to faceal incontinence
what does the pectinate line mark?
the junction between the part of the embryo which formed to GI tract (endoderm) and the part that formed the skin (ectoderm)
what differs above and below the pectinate line?
arterial supply venous drainage lymphatic drainage nerve supply superior to line = visceral inferior to line = parietal
describe the supplies above the pectinate line
autonomic nerve supply
arterial supply from inferior mesenteric artery
venous drainage to hepatic portal system
lymphatic drainage to inferior mesenteric nodes
describe the supplies below the pectinate line
somatic and pudendal nerve supply
arterial supply from internal iliac artery
venous drainage to systemic venous system
lymphatic drainage to superficial inguinal nodes
describe the groups of lymph nodes draining the pelvic organs
Internal iliac (draining inferior pelvic structures)
External iliac (draining lower limb, and more superior pelvic structures)
Common iliac (drain the lymph from the external and internal iliac nodes)
Lymph draining through the common iliac nodes then drains to the lumbar nodes
what supplies the blood to the hindgut organs (to the proximal half of the anal canal)?
inferior mesenteric artery
what supplies blood to the remainder of the GI tract?
internal iliac artery (there is a degree of anastomoses)
what drains blood from the hindgut organs above the pectinate line?
inferior mesenteric vein
what drains blood below the pectinate line?
internal iliac vein to the systemic venous system
what causes rectal varices to form?
portal hypertension
what are rectal varices?
dilatation of collateral veins between portal and systemic venous systems
what are haemorrhoids?
prolapses of the rectal venous plexuses
what causes haemorrhoids?
raised pressure eg chronic constipation, straining, pregnancy
where do the ischioanal fossa lie?
on each side of the anal canal
what fills the ischioanal fossa?
fat and loose connective tissue
what is an infection within the ischioanal fossa called?
an ischioanal abscess
