Rectum, hernias, atresias etc Flashcards Preview

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Flashcards in Rectum, hernias, atresias etc Deck (64):

What is the rectum?

Most distal component of the large bowel
In the pelvic cavity


What is the anus?

A distensible short section terminating in a valved opening


What is the function of the rectum?

Faecal storage


What is the function of the anus?

Faecal continence


What is the function of the lower bowel?

- Absorbs and stores
- Absorbs water, Na, Cl and VFAs
- Produces faecalith which moves to rectum


What are the landmarks of the rectum?

- Cranially the pelvic inlet
- Caudally the anal canal


Describe the gross anatomy of the rectum compared to the descending colon

There is no significant difference between the two


Describe the histology of the rectum

- Largely similar to rest of GI
- Mucosa, submucosa, Muscularis and serosa
- No villous processes as no absorption is taking place
- Solitary lymph nodules
- Small cratered nodules present


Describe the mucosa of the rectum

- No villi
- Columnar epithelium
- Longer, taller intestinal galnds
- More goblet cells


Describe the submucosa of the rectum

- Lymph nodules
- Nerve plexuses
- Vascular supply


Describe the muscularis of the rectum

- Thicker outer layer (stratum longitudinale)
- Fibres organised dorsocaudally to form rectococcygeus muscle
- Thinner inner layer (stratum circulare)
- Fibres organised caudally to form internal anal sphincter muscle


Describe the serosa of the rectum

- Visceral peritoneum covers most of crnail rectum
- Airtight, watertight seal, prevents bacterial infection
- Caudal rectum (and anal canal) therefore retroperitoneal
- Cranial peritoneum extends from colon, caudal gradully lost and hence retroperitoneal


Descrieb the mesenteric support of the rectum

- Mesorectum
- Extension of mesocolon
- Wider cranially
- Tapers away at coccygeal vertebrae 2 with serosal layer


Describe the structure of the anus

- Fianl section of lower bowel
- Specialised junction between mucosa and integument (mucocutaneous junction)
- Surrounded by smooth and striated muscle sphincters
- Internal and external anal sphincter (muscle rings) present
- Anal sac sits between these sphincters
- Different histological areas


What are the histological regions of the anus?

- Proximal columnar zone (first)
- Short intermediate zone (middle)
- Terminal cutaneous zone (last)


Describe the proximal columnar zone of the anus

- Series of longitudinal ridges (columns)
- Folds which create anal sinuses (pockets)
- Proximal section is anorecta junction


Describe the intermediate zone of the anus

- Narrow mid-section
- 1mm wide
- Ano-cutaneous margin


Describe the cutaneous zone of the anus

- Exernal and internal components
- Anal sac ducts open in this region


Describe the internal anal sphincter

- Smooth muscle
- Autonomic
- Parasympathetic (post-ganglionic) fibres via pelvic and hypogastric plexuses
- Sympathetic is hypogastric via caudal mesenteric ganglion


Descriebt the external anal sphincter

- Striated muscle
- Wider
- Main constrictor muscle of anus
- Laterla: intimate fascial attachment to levator ani mmuscle
- Dorsal attaches to fascia of tail
- In female, ventral part blends with contrictor vulvae muscle
- In male ventral blends with bulbospongiosus muscle


Describe the vascular supply to the rectum

- Extensive
- Caudal, middle and cranial rectal arteries
- Cranial from caudal mesenteric, supplies cranial aspect of rectum
- Caudal from branches of internal pudendal artery
- Anastomoses between middle and caudal rectal


Describe the venous drainage of the rectum

- Cranial rectal artery into caudal mesenteric then portal vein
- Mid and caudal rectal arteries into internal pudendal and then internal iliac vein


Describe the innervation of the rectum

- Sympathetic and parasympathetic
- Sympathetic from many ganglia
- Parasympathetic via pelvic nerves


Describe the blood supply to the anus

- Via anastomoses from the rectum
- Anal extensions of rectal arteries
- Most from caudal rectal, some from middle and less from cranial rectal arteries


Descrbe the inneration of the anus

- Internal sphincter autonomic
- External innervated by anal branch of pudendal nerve


What are the reflexes involved in the control of defaecation?

- Series of other reflexes
- Rectal filling (accomodation)
- Anorectal reflex
- Rectosphincteric reflex


Describe the anorectal reflex

- Rectal fioling
- Rectal stimulation during accomodation increases anal closing pressure
- More stimulation, increase in closure pressure of IAS
- IAS stimulated by SNS innervation via hypogastric nerves, tonically contracted most of the time
- EAS contributes some additional tone
- Increased distension leads to increased stimulation and therefore increased contraction of anal ring
- Movement of faeces from rectum through anus limited to defaecatory episodes i.e. faecal continence


Describe the rectosphincteric reflex

- Distension sufficiently large, leads to afferent stimulation to sacral cord and CNS
- Distension of bowe = conscious perception of needing to defecate
- Parasympathetic system take unconscious control and causes IAS to relax, allowing defecation


What are the events in defaecation?

- Neural initiation
- IAS relaxes
- Rectal peristalsis occurs
- Increased abdominal pressure
- Contraction of pelvic diaphragm muscles
- Once faecolith passed, returns to resting state


What muscles make up the pelvic diaphragm?

Coccygeus, levator ani and anal sphincter muscles


What is the function of the pelvic diaphragm?

- Supports rectum laterally
- Used in defaecation


What is the rectal function during defaecation dependent on?

The capacity of the pelvic diaphragm muscles to compress the pelvic contents


Describe the levator ani (origin, insertion, innervation)

- Origin: medial ilium, pelvic symphysis
- Insertion: tendon to 7th coccygeal vertebrae
- Innervation: ventral branches of S3 and Co1 nerve


What is the function of the levator ani?

- Medial compression bilaterally of rectum during defaecation
- Presses tail against anorectal region = increases pressure on rectum, expel faeces


Describe the coccygeus muscle (origin, insertion, innervation)

- Origin: tendon on ischiatic spine, cranial to internal obturator muscle
- 2nd-5th CO vertebrae
- Innervation: ventral branches of S3


What is the function of the coccygeus muscle?

Compresses during defaecation, presses tail ventral


Describe the relationship between the anal sphincter, levator ani and coccygeus muscle in the pelvic diaphragm

- Fibrous unrion betweel EAS, levator ani, coccygeus
- No gap
- Pelvic diaphragm is intact structure


Describe the retrococcygeus muscle

- Pararectal muscle
- Origin; dorsolateral surface of rectum
- Insertion: fused below 5th-6th Co vertebrae
- Runs up to tail base
- Stabilises anal canal during defaecation


What are the perianal structures?

- Anal sacs
- Circumanal glands
- Anal glands


Describe the anal sacs

- Not glands, glands within walls of sacs
- Paired, pea sized
- Either side of anal opening
- 20-to-4 position
- Embedded between IAS and EAS muscles
- Short duts open to anal area
- Coiled, apocrine tubules
- Cornified, stratified epithelium
- Secrete foul smelling fluid


Describe the circumanal glands

- Around anus in subcut layer
- Sebaceous
- Not in cats
- Often referred to as hepatoid glands


Describe the anal glands

- Cranial to circumanal glands
- Secrete fatty substance


Where do the lymphatics of the anus drain to?

Drain to sacral hypogastric and internal iliac nodes


List some of he clinical conditions commonly affecting the rectum and anus

- Perineal hernias
- Anal sac impaction/abscess
- Anal furunculosis
- Tumours


Describe perineal herniation

- degeneration of pelvic diaphragm
- Separation of anal sphincter and levator muscle
- Less commonly coccygeus and levator
- Rectal enlargement seen
- Faecal accumulation beyond pelvic brim, sacculation, deviation of rectum into hernial sac, unable to defecate as pelvic diaphragm not in tact


What is unilateral perineal swelling in a perineal hernia caused by?



What is bilateral perineal swelling in a perineal hernia caused by?



Describe some of the pathophysiology of perineal herniation

- Failure of pelvic diaphragm allows movement of abdominal contents into perineal region
- Fat, bladder, prostate gland
- Bladder can retroflex caudally due to straining to defecate pushing bladder caudally
- Prevents urination due to kink in urethra


Describe anal sac impaction/abscessation

- Inflammatin of anal sac ducts
- Impaction of anal sac secretion due to failure to empty, fluid thickens
- Secondary infection
- Abscess ruptures to skin surface


Describe anal furunculoses

- Immune mediated fistula
- Breakdown at mucocutaneous junction
- Immune suppressive therapy needed


Desribe anal tumours

- Benign tumours (adenomas) common in older male entire dogs
- growth hormonally mediated
- Castrate, remove hormonal drive, tumour regresses


What is an anal atresia?

Where the anal opening has failed to develop properly


What are the types of anal atresia?

- 4 types
- I, II, III, IV


Describe a type I anal atresia

Congenital stenosis of anus


Describe a type II anal atresia

Persistent anal membrane with blin ending rectal pouch just cranial to anus


Describe a type III anal atresia

Closed anus with rectum ending in pelvic canal


Describe a type IV anal atresia

Anus and distal rectum normal, proximal rectum ends as pouch in pelvic canal


What are the clinical signs of an anal atresia

- Tenesmus and constipation
- Thin
- Pot bellied


What is tenesmus?

Continual or recurrent inclination to evacuate the bowels, caused by disorder of rectum or other illness


What is a faecalith?

- Akafaecaloma, coprolith
- Stone made of faeces
- Hardening of faeces into lumps of varying size inside the colon which may appear whenever chronic obstruction of transit occurs e.g. megacolon and chronic constipation


How could you repair an anal atresia?

- Depending on type can treat surgically
- Can treat type I and type II
- Make hole in membrane, will not damage the anal sphincters


Describe umbilical hernias

- Intestines protruding through intestinal wall
- Can be classified as indirect or direct
- Can occur in most species
- Large ernias require surgery to repair deficit


Describe scrotal/inguinal hernias

- Intestines in inguinal canal
- Everything may continue to function normally so animal may not show signs of discomfort
- More common in males than females


Describe a bilateral perineal hernia

- Pelvic diaphragm degenerated
- Bladder may be retroflexed by straining to defecate
- Large swelling around anus, stranguria occurs