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GI > Rectum, hernias, atresias etc > Flashcards

Rectum, hernias, atresias etc Flashcards

1
Q

What is the rectum?

A

Most distal component of the large bowel

In the pelvic cavity

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2
Q

What is the anus?

A

A distensible short section terminating in a valved opening

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3
Q

What is the function of the rectum?

A

Faecal storage

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4
Q

What is the function of the anus?

A

Faecal continence

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5
Q

What is the function of the lower bowel?

A
  • Absorbs and stores
  • Absorbs water, Na, Cl and VFAs
  • Produces faecalith which moves to rectum
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6
Q

What are the landmarks of the rectum?

A
  • Cranially the pelvic inlet

- Caudally the anal canal

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7
Q

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

A

There is no significant difference between the two

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8
Q

Describe the histology of the rectum

A
  • 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
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9
Q

Describe the mucosa of the rectum

A
  • No villi
  • Columnar epithelium
  • Longer, taller intestinal galnds
  • More goblet cells
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10
Q

Describe the submucosa of the rectum

A
  • Lymph nodules
  • Nerve plexuses
  • Vascular supply
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11
Q

Describe the muscularis of the rectum

A
  • 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
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12
Q

Describe the serosa of the rectum

A
  • 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
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13
Q

Descrieb the mesenteric support of the rectum

A
  • Mesorectum
  • Extension of mesocolon
  • Wider cranially
  • Tapers away at coccygeal vertebrae 2 with serosal layer
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14
Q

Describe the structure of the anus

A
  • 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
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15
Q

What are the histological regions of the anus?

A
  • Proximal columnar zone (first)
  • Short intermediate zone (middle)
  • Terminal cutaneous zone (last)
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16
Q

Describe the proximal columnar zone of the anus

A
  • Series of longitudinal ridges (columns)
  • Folds which create anal sinuses (pockets)
  • Proximal section is anorecta junction
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17
Q

Describe the intermediate zone of the anus

A
  • Narrow mid-section
  • 1mm wide
  • Ano-cutaneous margin
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18
Q

Describe the cutaneous zone of the anus

A
  • Exernal and internal components

- Anal sac ducts open in this region

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19
Q

Describe the internal anal sphincter

A
  • Smooth muscle
  • Autonomic
  • Parasympathetic (post-ganglionic) fibres via pelvic and hypogastric plexuses
  • Sympathetic is hypogastric via caudal mesenteric ganglion
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20
Q

Descriebt the external anal sphincter

A
  • 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
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21
Q

Describe the vascular supply to the rectum

A
  • 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
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22
Q

Describe the venous drainage of the rectum

A
  • Cranial rectal artery into caudal mesenteric then portal vein
  • Mid and caudal rectal arteries into internal pudendal and then internal iliac vein
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23
Q

Describe the innervation of the rectum

A
  • Sympathetic and parasympathetic
  • Sympathetic from many ganglia
  • Parasympathetic via pelvic nerves
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24
Q

Describe the blood supply to the anus

A
  • Via anastomoses from the rectum
  • Anal extensions of rectal arteries
  • Most from caudal rectal, some from middle and less from cranial rectal arteries
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25
Q

Descrbe the inneration of the anus

A
  • Internal sphincter autonomic

- External innervated by anal branch of pudendal nerve

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26
Q

What are the reflexes involved in the control of defaecation?

A
  • Series of other reflexes
  • Rectal filling (accomodation)
  • Anorectal reflex
  • Rectosphincteric reflex
27
Q

Describe the anorectal reflex

A
  • 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
28
Q

Describe the rectosphincteric reflex

A
  • 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
29
Q

What are the events in defaecation?

A
  • Neural initiation
  • IAS relaxes
  • Rectal peristalsis occurs
  • Increased abdominal pressure
  • Contraction of pelvic diaphragm muscles
  • Once faecolith passed, returns to resting state
30
Q

What muscles make up the pelvic diaphragm?

A

Coccygeus, levator ani and anal sphincter muscles

31
Q

What is the function of the pelvic diaphragm?

A
  • Supports rectum laterally

- Used in defaecation

32
Q

What is the rectal function during defaecation dependent on?

A

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

33
Q

Describe the levator ani (origin, insertion, innervation)

A
  • Origin: medial ilium, pelvic symphysis
  • Insertion: tendon to 7th coccygeal vertebrae
  • Innervation: ventral branches of S3 and Co1 nerve
34
Q

What is the function of the levator ani?

A
  • Medial compression bilaterally of rectum during defaecation
  • Presses tail against anorectal region = increases pressure on rectum, expel faeces
35
Q

Describe the coccygeus muscle (origin, insertion, innervation)

A
  • Origin: tendon on ischiatic spine, cranial to internal obturator muscle
  • 2nd-5th CO vertebrae
  • Innervation: ventral branches of S3
36
Q

What is the function of the coccygeus muscle?

A

Compresses during defaecation, presses tail ventral

37
Q

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

A
  • Fibrous unrion betweel EAS, levator ani, coccygeus
  • No gap
  • Pelvic diaphragm is intact structure
38
Q

Describe the retrococcygeus muscle

A
  • Pararectal muscle
  • Origin; dorsolateral surface of rectum
  • Insertion: fused below 5th-6th Co vertebrae
  • Runs up to tail base
  • Stabilises anal canal during defaecation
39
Q

What are the perianal structures?

A
  • Anal sacs
  • Circumanal glands
  • Anal glands
40
Q

Describe the anal sacs

A
  • 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
41
Q

Describe the circumanal glands

A
  • Around anus in subcut layer
  • Sebaceous
  • Not in cats
  • Often referred to as hepatoid glands
42
Q

Describe the anal glands

A
  • Cranial to circumanal glands

- Secrete fatty substance

43
Q

Where do the lymphatics of the anus drain to?

A

Drain to sacral hypogastric and internal iliac nodes

44
Q

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

A
  • Perineal hernias
  • Anal sac impaction/abscess
  • Anal furunculosis
  • Tumours
45
Q

Describe perineal herniation

A
  • 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
46
Q

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

A

Sacculation

47
Q

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

A

Dilatation

48
Q

Describe some of the pathophysiology of perineal herniation

A
  • 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
49
Q

Describe anal sac impaction/abscessation

A
  • Inflammatin of anal sac ducts
  • Impaction of anal sac secretion due to failure to empty, fluid thickens
  • Secondary infection
  • Abscess ruptures to skin surface
50
Q

Describe anal furunculoses

A
  • Immune mediated fistula
  • Breakdown at mucocutaneous junction
  • Immune suppressive therapy needed
51
Q

Desribe anal tumours

A
  • Benign tumours (adenomas) common in older male entire dogs
  • growth hormonally mediated
  • Castrate, remove hormonal drive, tumour regresses
52
Q

What is an anal atresia?

A

Where the anal opening has failed to develop properly

53
Q

What are the types of anal atresia?

A
  • 4 types

- I, II, III, IV

54
Q

Describe a type I anal atresia

A

Congenital stenosis of anus

55
Q

Describe a type II anal atresia

A

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

56
Q

Describe a type III anal atresia

A

Closed anus with rectum ending in pelvic canal

57
Q

Describe a type IV anal atresia

A

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

58
Q

What are the clinical signs of an anal atresia

A
  • Tenesmus and constipation
  • Thin
  • Pot bellied
59
Q

What is tenesmus?

A

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

60
Q

What is a faecalith?

A
  • 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
61
Q

How could you repair an anal atresia?

A
  • Depending on type can treat surgically
  • Can treat type I and type II
  • Make hole in membrane, will not damage the anal sphincters
62
Q

Describe umbilical hernias

A
  • Intestines protruding through intestinal wall
  • Can be classified as indirect or direct
  • Can occur in most species
  • Large ernias require surgery to repair deficit
63
Q

Describe scrotal/inguinal hernias

A
  • Intestines in inguinal canal
  • Everything may continue to function normally so animal may not show signs of discomfort
  • More common in males than females
64
Q

Describe a bilateral perineal hernia

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

GI (31 decks)

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