Anatomy 4 (lecture 6) Flashcards
Purpose of the rectum?
To store faeces until it is appropriate to defecate
What type of nerves sense “fullness” of the rectum?
Normal visceral afferent nevre fibres
What is required to control the excretion of faeces?
A holding area (the rectum)
Normal visceral afferent nerve fibres
Functioning muscle sphincters
normal cerebral function (to control the appropriate time to defecate
(these can all be affected by a neurological pathology e.g. dementia, MS)
What factors, apart from neurological pathology, can affect faecal continence?
Medications
Natural age-related degeneration of nerve innervation of muscle
Consistency of stool
What does the pelvic cavity lie between?
Pelvic inlet and pelvic floor
What muscle forms the pelvic floor?
Levator ani muscle - forms the musculofascial inferior part of the pelvic cavity
Why must there be opening in the pelvic floor?
To permit the distal parts of the alimentary, renal and reproductive tracts to pass from the pelvic cavity into the perineum
At what vertebrae level does the sigmoid colon become the rectum?
What is this called?
Anterior to S3
The rectosigmoid junction
At what anatomical point does the rectum become the anal canal
Anterior to the tip of the coccyx just prior to passing through the elevator anti muscle
What is the anus?
The distal end of the anal canal
The orifice through which faeces pass
What out of rectum, anal canal and anus are located in the perineum and what are located in the pelvis?
Rectum = pelvis
Anal canal and anus = perineum
What is the rectal ampulla?
What do the walls of this do to accommodate faecal matter?
The dilated part of the rectum where faeces are stored until they are eliminated via the anal canal (lies immediately superior to the elevator ani muscle)
Walls can relax to accommodate faecal matter
What covers the superior rectum?
Peritoneum
What pouch lies anterior to the superior rectum? - in males and females
Rectouterine pouch (in females) Rectovesical pouch (in males)
In males, what lies anterior to the inferior rectum?
The prostate gland
In females, what lies anterior to the inferior/ middle rectum?
Vagina and cervix
What is the pouch between the uterus and bladder in females?
Vesicouterine pouch
What forms the pelvic diaphragm (aka pelvic floor)? - also most of the roof of the perineum
Mostly the elevator ani muscle along with the fascial coverings
What are the 3 smaller muscles that makes up the elevator ani muscle?
Iliococcygeus muscle (ileum to coccyx)
Pubococcygeus (pubic bone to coccyx)
Puborectalis (pubic bone to rectum)
Under voluntary control - skeletal muscle
What is the purpose of the elevator ani muscle? (3)
Provides continual support for the pelvic organs (tonically contracted most of the time)
Reflexively contracts further during increase in intra-abdominal pressure e.g. coughing, sneezing
Muscle must relax to allow defecation (and urination) to occur
What is the elevator ani muscle supplied by?
“Nerve to levator ani”
A branch of the sacral plexus and pudendal (S2, 3, 4)
What is the part of the elevator ani muscle that is particularly important for maintaining faecal continence?
Skeletal/ smooth muscle?
The puborectalis
Skeletal
What does contraction of the puborectalis do?
Decreases the anorectal angle (acting like a sphincter)
What does the puborectalis do when the rectal ampulla is relaxed and filled with faeces?
voluntarily contracts and helps to maintain continence
What is the junction at which the anal canal begins?
The anorectal junction
How many anal sphincters are there and what type of muscle supplies each?
2
Internal (smooth muscle)
External (skeletal muscle)
Can control external but not internal
What parts of the anal canal is the external and internal anal sphincters found in?
Internal = superior two thirds External = inferior two thirds (superior part of the external sphincter is containers with the puborectalis muscle)
What stimulates/ inhibits contraction of the internal anal sphincter?
Stimulated by sympathetic nerve i.e. sphincter is close
Inhibited by parasympathetic nerve
What stimulates the external anal sphincters?
Pudendal nerve
Describe the state of the internal anal sphincter in terms of contraction?
Contracted all the rime, relaxes in response to distension of the rectal ampulla
Describe the state of the external anal sphincter in terms of contraction?
Voluntarily contracted (along with puborectalis muscle) in response to rectal ampulla distension and internal sphincter relaxation
When deciding which nerve fibre types are carrying out which function, what does it mean if the structure is in the pelvis?
It is in the body cavity and therefore supplied by sympathetic, parasympathetic and visceral afferents
When deciding which nerve fibre types are carrying out which function, what does it mean if the structure is in the perineum?
Body wall and therefore somatic motor and somatic sensory
In terms of the nerve supply to the rectum/ anal canal, what happens with the sympathetic fibres - where do they travel?
What do they do? (2)
Sympathetic fibres from T12-L2 travel to the inferior mesenteric ganglia, synapse, then travel via the periarterial plexuses around branches of the IMA causing contraction of the internal anal sphincter and inhibit peristalsis
In terms of the nerve supply to the rectum/ anal canal, what happens with the parasympathetic fibres - where do they travel?
What do they do? (2)
Parasympathetic fibres from S2 - S4 pass via the pelvic splanchnic nerves, synapse in walls of the rectum and inhibit internal anal sphincter, stimulate peristalsis
In terms of the nerve supply to the rectum/ anal canal, where do the visceral afferents run back to?
What do they run with?
What do they sense?
S2-4
Run with parasympathetics
Sense stretch, ischaemia, etc.
What provides somatic motor supply?
What does this cause?
Pudendal nerve (S2-S4) and nerve to levator ani (S3, S4) Contraction of the external anal sphincter and puborectalis
Where does the pudendal nerve come from?
what anterior rami form it?
Branch of the sacral plexus
S2, S3, S4 (S2, 3 and 4 keeps the pelvis off the floor)
What does the pudendal nerve exit the pelvis via?
Where does it enter the perineum?
The greater sciatic foramen (branches to supply structures of the perineum)
Through the lesser sciatic foramen
What can happen to the pudendal nerve during labour?
Can be stretched
How can labour cause faecal incontinence?
Fibres within the puborectalis or external anal sphincter muscle could be torn resulting in weakened muscle
What is the line which marks the junction between the part of the embryo which formed the GI tract (endoderm) and the part that formed the skin (ectoderm)?
Pectinate line - can see division (ridges and change in mucosa) in individuals
Comparing above and below the pectinate line: Nerve supply? Arterial supply? Venous drainage? Lymphatic drainage?
Above: Autonomic, From inferior mesenteric artery, to portal venous system (IMV), inferior mesenteric nodes (internal iliac nodes)
Below: Somatic/ pudendal, from internal iliac artery, to systemic venous system (internal iliac), superficial inguinal nodes
What structures do lymph vessels tend to lie alongside?
The arteries
What are the main groups of lymph nodes draining the pelvic organs and what do each drain?
Internal iliac (drains 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 raining through the common iliac nodes then drains to the lumbar nodes
Where does the hindgut extend to?
The proximal had of the anal canal (the pectinate line)
What is the blood supply to the:
Proximal half of the anal canal?
Distal half?
Proximal = inferior mesenteric artery
Distal half = internal iliac artery
(degree of anastomoses between these)
Venous drainage of anal canal:
Proximal half?
Distal half?
Proximal = inferior mesenteric vein
Distal half = internal iliac vein
What is the venous plexus?
A soft plexus of veins that sit around the anus
When it is prolapses it forms haemorrhoids (these are completely different to rectal varies which are related to portal hypertension)
What causes rectal varrices
Dilation of collateral veins between the portal and systemic venous systems due to portal hypertension
What causes haemorrhoids?
Prolapses of rectal venous plexuses (not related to portal hypertension - caused by raised pressure e.g. chronic constipation)
What are the name of the fossae which lie on each side of the anal canal?
What are these filled with
Ischioanal fossae
Fat and loose connective tissue (communicate with each other posteriorly)
What is an infection within the ischioanal fossae called?
An ischionala abcess
