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
what muscles make up the internal anal sphincter
fibres of rectal circular muscles are organised caudally to form the smooth muscle of internal sphincter
list the zones of the anus
compare the zones of the anus
list glands and sacs around the anus
- anal glands
- circumanal glands
- anal sacs
what are anal glands and where are they located
- cranial to the anocutaneous line
- fatty secretion
- contained scattered apocrine sweat glands around the anus in the cutaneous zone
what are circumanal glands
- present in dogs
- all around anus in cutaneous zone
- subcutaneous
- sebaceous secretion
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
how do the anal sacs get empied
- embedded between internal and external anal sphincter muscles
- normally compressed during defecation to coat feces in scent
discuss anal sacs histologically
- cornified stratified epithelium
- coiled apocrine tubules contained within wall of sacs
- secrete foul secretion
what is tenesmus
straining = forced expiration against a closed glottis which raises intra-abdominal and intra thorcic pressure
whatis dyschezia
painful straining
discuss innervation of the internal anal sphincter
- sympathetic = excitatory = constricts
- parasympathetic - inhibitory = relaxes
- in resting state, there is high internal sphincter tone
discuss innervation of the external anal sphincter
- innervated by branches of pudendal nerve
- allows for conscious contraction
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.
discuss the reflex for defecatio after eating
- There is often an urge to defaecate after eating (especially a large meal)
Notable in young carnivores - This is related to distension of the stomach which initiates the gastrocolic reflex (gastrin release) causing onward passage (emptying) of faecal material from the colon into the rectum thereby initiating the anorectal reflex
list common clinical conditions of the bum
- anal sac impaction/abscess
- anal furunculosis
- hepatoid adenomas
- adenocarcinomas
- rectal prolapse
- ## perineal hernia
what is an anal sac impaction
- inflammation of anal sac duct
- impaction of anal sac secretion
- secondary infection
- abscess ruptures to skin surface
what is anal furunculosis
- immune mediated fistula
- can be seen in combination with anal sac abscess
what is a hepatoid adenoma
- most common anal tumor in the dog (mostly in intact older males)
- testosterone dependant benign masses
- found in external region of outer cutaneous zone
- single or multiple
- malignant form of tumor rare
- rare in cats
what is an anal adenocarcinoma
circumanal gland adenocarcinoma
- malignant lesion of perianal sebaceous glands - rare
- occur in same areas as adenomas
- can diffusely infiltrate anal areas
- often adherent to deeper tissues
- rapidly grow
- do not respond to castration
or anal sac (apocrine) adenocarcinoma
- predominently affects older bitches
- small discrete nodules in wall of either sac
- pananeoplastic syndrome often accompanies
- secretes PTH like susbstance
- hypercalcemia causes pu/pd, depression, weakness, weight loss
- aggressive, 50% metastisied at presentation
what is rectal prolapse
- associated with endopatasites/enteritis in young animals and tumours or perineal hernias in middle aged/older animals
- incomplete prolapse =mucosa only
- complete = all layers of rectal wall
- few mm to many cm
- everted tissue is oedematous, excoriated and can be bleeding
