anatomy of the rectum, anus and associated glands Flashcards
what is the rectum
the most distal part of the large bowel (stores feces)
what is the anus
distensible short section terminating in a valved opening
is there any anatomical difference between the rectum and large colon
no, arbitrarily delineated. just the terminal end of large bowel
- begins at the pelvic inlet and ends at anal canal
- straight rectangle
what is the difference between adventitia and serosa and where will you find these along the rectum
- visceral peritoneum = serosa, covers most of cranial rectum
- adventitia = connective tissues. surrouns caudal rectum - = retroperitoneal
what are peritoneal pouches
where the peritoneum turns around within the pelvic canal
what is mesorectum
- an extension of the mesocolon
- mesenteric support
- wider cranially
- tapers away
discuss rectal histology
- same as large intestine
- no villi
- solitary lymphoid aggregates
- columnar epithelium
- more goblet cells
discuss vascular supply of the rectum
- cranial rectal artery = branch off aorta, caudal mesenteric artery branches into left colic and cranial rectal artery
- middle and caudal arteries branch off internal pudendal artery
discuss venous drainage of the rectum
- cranial rectal artery drains into caudal mesenteric then hepatic portal vein
- middle and caudal rectal drain into internal pudendal artery then internal iliac to enter systemic circ
explain why rectal suppositories are effective
- middle and caudal rectum drains into systemic circulation
- bypasses heptic portal vein
- doesnt get metabolised by liver
what is the pelvic diaphragm
- tent of muscles plus internal and external sphincter
- supports rectum
- made of coccygeus and levator ani muscles
- sacrotuberous ligament supports muscles and makes “tent”
discuss coccygeus muscle
- originates at ischiatic spine
- insters on transverse process of caudal vertebrae 2-4
- innervated by branches of sacral plexus and pudendal nerve
- function is to compress rectum during defecation and pressing tail against anus
discuss levator ani muscle
- originates from medial ilium and pelvic symphysis
- inserts on tendons caudal to vertebrae 3-7
- innervated by branches of sacral plexus and pudendal nerve
- function to compress rectum during defecation and press tail against anus
what types of muscle are the anal sphincter muscles
- internal = smooth muscle
- external = skeletal muscle (striated)
the external anal sphincter muscle functions to do what
- cover anal sacs and compresses them during defecation
- conscious control
list the zones of the anus
compare the zones of the anus
what are anal sacs and where are they located
- paired diverticula present in carnivores
- located within the lamina propria/submucosa
- lined by apocrine paranal sinus gland
- paired ducts open into anal canal
- vets call them anal glands but they are sacs
discuss anal sacs histologically
- cornified stratified epithelium
- coiled apocrine tubules contained within wall of sacs
- secrete foul secretion
discuss innervation of the internal anal sphincter
- sympathetic = excitatory = constricts
- parasympathetic - inhibitory = relaxes
- in resting state, there is high internal sphincter tone
discuss the defecation reflex
The process of defaecation is normally a combination of both voluntary and involuntary processes
As faecal material enters the rectum, it distends – if the wall is sufficiently distended the anorectal reflex produces concurrent contraction of the rectal wall, relaxation of the internal sphincter and (mostly) relaxation of the external anal sphincter.
Untrained animals, or those without behavioural constraints, will defaecate at this point.
