Feacal continence of the GI tract Flashcards
What does the control of excretion of feaces require?
A “holding area” (the rectum) to store faeces until appropriate to defecate
Normal visceral afferent nerve fibres to sense “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 feacal continence be affected by?
neurological pathology
Affected by medications
Affected by the natural age-related degeneration of nerve innervation of muscle
Affected by consistency of stool
What is the Levator ani muscle?
pelvic floor
Describe the pelvic cavity?
Lies within the bony pelvis
Continuous with abdominal cavity above
Lies between pelvic inlet and pelvic floor
Contains pelvic organs and supporting tissues
What do openings in the pelvic floor allow?
alimentary, renal and reproductive tracts to pass from the pelvic cavity into the perineum
What happens at S3?
“Recto-sigmoid junction”
Sigmoid colon becomes rectum
Where does the rectum become anal canal?
the tip of the coccyx
Are the anal canal and anus in the pelvis or perineum?
perineum
What is the purpose of the 3 lateral folds of the rectum?
staggering effect and allows expansion (walls can relax to accommodate faecal material)
What are the 3 parts of the pelvic diphragm?
Pubococcygeus
Puborectalis
Iliococcygeus
What is the role 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, e.g. coughing, sneezing
The muscle must relax to allow defecation (and urination) to occur
What innervates the Levator ani muscle?
“nerve to levator ani”: (a branch of the sacral plexus) pudendal (S2, 3, 4) - keep the guts off the floor
What is the Puborectalis?
Part of the levator ani muscle
Particularly important for maintaining faecal continence
Contraction of it decreases the anorectal angle, acting like a sphincter
This is a skeletal muscle: contraction is under voluntary control
Describe the internal anal spinchter?
smooth muscle
involuntary - contraction is inhibited by parasympathetic nerves
thickening of muscle - an enlargement
Superior two thirds of anal canal
Describe the external anal spinchter?
skeletal muscle
voluntary - contraction is stimulated by the pudendal nerve
Inferior two thirds of anal canal
What is below the anorectal junction?
anal canal
What applies to a structure if it is above the levator ani muscle?
In pelvis
Body cavity
Sympathetic, parasympathetic and visceral afferent
What applies to a structure if it is below the levator ani muscle?
In perineum
Body wall
somatic motor and somatic sensory
What is the role of the sympathetic fibres? Where do they leave from?
T12-L2: travel to inferior mesenteric ganglia – synapse - then travel via periarterial plexuses around branches of IMA.
Contraction of internal anal sphincter
Inhibit peristalsis
Where do visceral afferents run to? What do they do?
S2-S4
Run with parasympathetics
Sense stretch, ischaemia etc.
What is the role of the parasympathetic fibres? Where do they leave from?
S2-S4: via pelvic splanchnic nerves, synapse in walls of rectum
Inhibit internal anal sphincter
Stimulate peristalsis
What is the pudendal nerve a branch of?
sacral plexus
S2, S3, S4 anterior rami
What could happen to the pudendal nerve during labour?
be stretched or damaged which leads to incontinence
What is the importance of the pectinate line?
Marks the junction between the part of the embryo which formed the GI tract (endoderm) and the part that formed the skin (ectoderm).
-check lecture
What are organs above the pectinate line derived from?
endoderm
visceral
What are organs below the pectinate line derived from?
ectoderm
parietal
What is the trend of the lymphatics in the GI system?
follow arteries
What supplies the hindgut?
inferior mesenteric artery
What supplies the anus and anal canal?
internal iliac artery
What vein drains below the pectinate line?
internal iliac vein
What are rectal varices?
Dilation of collateral veins between portal and systemic venous systems
What are haemorrhoids? What causes them?
Prolapses of the rectal venous plexuses
Raised pressure e.g. chronic constipation, straining, pregnancy
What is an Ischioanal fossae? What is an infection within it called?
bottom fat
infection within the ischioanal fossa is called an ischioanal abscess
