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Flashcards in Pelvic part of the GI tract Deck (17):

What are anal coulmns?

Longitudinal ridges of mucosa that encircle the anal canal. They are connected at their inferior ends by anal valves


Describe the structure of the rectum (7 points)

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Made up of three transverse folds (valves of Houston)

Dilated portion called ampulla

Meets sigmoid colon at S3

No taenia coli

Follows curvature of the sacrum

Pierces pelvic floor to join anal canal


Lined with simple columnar epithelium


Structure of the anal canal

3-4cm long muscular tube that connects the rectum to the anus.

Internal anal sphincter formed by a continuation of the inner circular layer of muscularis externa from the rectum. Innervated by autonomic nerves (involuntary)

External anal sphincters formed from skeletal muscle. Controlled by somatic nerves (voluntary)


Describe the histological features of the anal canal

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What is the anorectal angle?

The anorectal angle is a change in the direction at the anorectal junction from anterior to posterior, forming a 90 degree angle.

It is formed by the action of the puborectalis element of the levator ani muscle mulling anteriorly. This forms a pinch valve mechanism which aids in the maintenaance of faecal contidence. 


Describe the changes that take place at the pectinate line (5 points)

The pectinite line marks the point where the embryonic hindgut meets the embryonic ectoderm. There is a change in:

Epithelium: from simple columnar to keratinised stratified squamous

Arterial suppy: superior rectal artery above and middle and inferior rectal arteries below the pectinate line

Venuous drainage: superior rectal vein (portal system) above, middle and inferior rectal veins (systemic system)

Nerve supply: Above the pectinate line autonomic and visercal afferents are from the inferior hypogastric plexus (visceral part, stretch). Below the pectinate line is innervated by the inferior rectal nerve which is a branch of the pudendal nerve (somatic part, pain)

Lymphatic drainage: going to Inferior mesenteric nodes if above the pectinate line and superficial inguinal nodes if below. 


Sigmoid volvulus

A volvulus is a condition where a portion of bowel twists on its mesentery

Sigmoid colon is the most common site of volvulus due to its long mesentery which is attached to a narrow part of the bowel. 

This twisting can result in obstruction of the bowel lumen and may lead to occlusion of the blood supply


Rectal prolapse

Condition in which part of the rectum descends towards the pelvic floor during straining and often emerges out of the anus. 



How are haemorrhoids caused?

Haemorrhoids are caused by disrupted and dilated anal cushions and are usually asymptomatic. 

Classified as internal or external. Relationship to the pectinate like determines the response to painful stmuli because of the differences in innervation

Symptoms of rectal bleeding, pain or itch may be due to enlargement, inflammarion, prolapse or thrombosis



List three common anorectal malformations

Imperforate anus: results from a failure of the anal membrane to rupture. Associated with further developmental anomalies

Rectovesical fistula: abnormal connection between the rectum and urinary bladder due to incomplete separation of the urogenital hiatus and the hindgut by the urorectal septum




Describe the stages of the defaecation reflex (5)

Activation of pressure/stretch receptors in rectum by faecal material excites afferent fibres which travel to the sacral spinal cord

This leads to increased activity in parasympathetic pelvic splanchnic nerves resulting in increased peristalsis & relaxation of the internal anal sphincter. An initial reflex contraction of the external anal sphincter prevents defaecation occurring

Sensory signals travel to the cortex so that the desire to defaecate is consciously perceived and a decision taken as to whether to proceed.

If yes,  Relaxation of the external sphincter & pelvic floor (increasing anorectalangle) and faeces are expelled. he Valsalva manouvere may be used to increase intraabdominalpressure to aid defaecation

If no, There is conscious further contraction of the external anal sphincter and faecal material is moved back into the rectum. The rectum accommodates this material and sensory afferent signals decrease. The urge to defaecate passes


What is the effect of increased activity in parasympathetic pelvic splanchnic nerves?

Increased peristalsis and relaxation of the internal anal sphincter



Define faecal incontinence

Inability to control the process of defaecation


Give 5 causes of faecal incontinence

Normal structure and function disrupted: e.g. cholera, gastroenteritis

Pelvic floor injury: damage to puborectalis muscle leading to a descending perineum and increased anorectal angle

Pudendal nerve injury: loss of conscious control of external anal sphincter

Visceral nerve injury: results in loss of sensation and poor coordination of reflexes e.g. diabetes, MS

Anal sphincter injury: unable to generate sufficient anal tone to maintain continence e.g. following a tear during parturition

Anatomical anomalies: Congenital or aquired abnormalities that bypass normal continence mechanisms

Higher cortical dysfuntion


Name 5 features of the sigmoid colon

Meets the descending colon at the pelvic brim

Has simple columnar epithelium

Has haustrations, taenia coli and appendices epiploicae

Intraperitoneal, has a mesentery (sigmoid mesocolon)

Is mobile, and can have variable positions


What are anal cushions?

Dilates subepithelial vascular tissue at the anal columns which protrude into the lumen and help maintain faecal continence. 


What is defaecation?

The process which elimates faecal material from the body via the rectum and anal canal. 

Reflex process initiated by the presence of faeces in the rectum but can be consciously controlled.