Flashcards in Anatomy 4 (lecture 6) Deck (53)
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?
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?
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?
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?
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?
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?