1. Dr. mohammed Abdzaid agool Fibms, mrcs, facs
The rectum
Dr. mohammed Abdzaid agool
Fibms, mrcs, facs

2. Surgical anatomy
The rectum begins where the taenia coli of the sigmoid colon join to form a continuous outer longitudinal muscle layer at the level of the sacral promontory.
The rectum follows the curve of the sacrum, to end at the anorectal junction.
The puborectalis muscle encircles the posterior and lateral aspects of the junction, creating the anorectal angle (normally 120°).

3. The rectum has three lateral curvatures: the upper and lower are convex to the right, and the middle is convex to the left. On the luminal aspect, these three curves are marked by semicircular folds (Houston’s valves).
That part of the rectum that lies below the middle valve has a much wider diameter than the upper third and is known as the ampulla of the rectum.

4. The adult rectum is approximately 12–18 cm in length and is conveniently divided into three equal parts:
the upper third, which is mobile and has a peritoneal coat.
the middle third where the peritoneum covers only the anterior and part of the lateral surfaces.
the lowest third, which lies deep in the pelvis surrounded by fatty mesorectum and has important relations to fascial layers.
The lower third of the rectum is separated by a fascial condensation– Denonvilliers’ fascia – from the prostate/vagina in front, and behind by another fascial layer – Waldeyer’s fascia – from the coccyx and lower two sacral vertebrae.

6. Blood supply
The superior rectal artery is the direct continuation of the inferior mesenteric artery and is the main arterial supply of the rectum.
The arteries and their accompanying lymphatics lie within the loose fatty tissue of the mesorectum, surrounded by a sheath of connective tissue (the mesorectal fascia).
The middle rectal artery arises on each side from the internal iliac artery and passes to the rectum in the lateral ligaments. It is usually small and breaks up into several terminal branches.
The inferior rectal artery arises on each side from the internal pudendal artery as it enters Alcock’s canal. It hugs the inferior surface of the levator ani muscle as it crosses the roof of the ischiorectal fossa to enter the anal muscles

7. Venous drainage
The superior haemorrhoidal veins draining the upper half of the anal canal above the dentate line pass upwards to become the rectal veins: these unite to form the superior rectal vein, which later becomes the inferior mesenteric vein. This forms part of the portal venous system and ultimately drains into the splenic vein.
Middle rectal veins exist but are small, unimportant channels unless the normal paths are blocked.

8. Lymphatic drainage
The lymphatics of the mucosal lining of the rectum communicate freely with those of the muscular layers. The usual drainage flow is upwards, and only to a limited extent laterally and downwards.
For this reason, surgical ablation of malignant disease concentrates mainly on achieving wide clearance of proximal lymph nodes. However, if the usual upwards routes are blocked, flow can reverse, and it is then possible to find metastatic lymph nodes on the side walls of the pelvis (along the middle rectal vessels) or even in the inguinal region (along the inferior rectal artery).

9. Anorectal Nerve Supply.
Both sympathetic and parasympathetic nerves innervate the anorectum. Sympathetic nerve fibers are derived from L1-L3 and join the preaortic plexus.
The preaortic nerve fibers then extend below the aorta to form the hypogastric plexus, which subsequently joins the parasympathetic fibers to form the pelvic plexus. Parasympathetic nerve fibers are known as the nervi erigentes and originate from S2-S4.
These fibers join the sympathetic fibers to form the pelvic plexus. Sympathetic and parasympathetic fibers then supply the anorectum and adjacent urogenital organs.

10. The internal anal sphincter is innervated by sympathetic and parasympathetic nerve fibers; both types of fibers inhibit sphincter contraction. The external anal sphincter and puborectalis muscles are innervated by the inferior rectal branch of the internal pudendal nerve.
The levator ani receives innervation from both the internal pudendal nerve and direct branches of S3 to S5. Sensory innervation to the anal canal is provided by the inferior rectal branch of the pudendal nerve. While the rectum is relatively insensate, the anal canal below the dentate line is sensate.

11. physiology Defecation.
Defecation is a complex, coordinated mechanism involving colonic mass movement, increased intra-abdominal and rectal pressure, and relaxation of the pelvic floor. Distention of the rectum causes a reflex relaxation of the internal anal sphincter (the rectoanal inhibitory reflex) that allows the contents to make contact with the anal canal.
This “sampling reflex” allows the sensory epithelium to distinguish solid stool from liquid stool and gas.
If defecation does not occur, the rectum relaxes and the urge to defecate passes (accommodation response).
Defecation proceeds by coordination of increasing intra-abdominal pressure via the Valsalva maneuver, increased rectal contraction, relaxation of the puborectalis muscle, and opening of the anal canal.

12. Continence.
The maintenance of fecal continence is at least as complex as the mechanism of defecation. Continence requires adequate rectal wall compliance to accommodate the fecal bolus, appropriate neurogenic control of the pelvic floor and sphincter mechanism, and functional internal and external sphincter muscles.
At rest, the puborectalis muscle creates a “sling” around the distal rectum, forming a relatively acute angle that distributes intra- abdominal forces onto the pelvic floor.
With defecation, this angle straightens, allowing downward force to be applied along the axis of the rectum and anal canal.
The internal and external sphincters are tonically active at rest. The internal sphincter is responsible for most of the resting, involuntary sphincter tone (resting pressure). The external sphincter is responsible for most of the voluntary sphincter tone(squeeze pressure).

13. CLINICAL FEATURES OF RECTAL DISEASE
Symptoms
Rectal diseases are common and serious and can occur at any age. The symptoms of many of them overlap. In general, the inflammations affect younger age groups, while the tumours occur in the middleaged and elderly. But no age is exempt from any of the diseases, however young: ulcerative colitis has been reported in the newborn and rectal cancer can occur in young people.
Bleeding
This is often bright red in colour but may be darker, and should be carefully investigated at any age.
Altered bowel habit
Early-morning stool frequency (‘spurious diarrhoea’) is a symptom of rectal carcinoma, while blood-stained frequent loose stools characterise the inflammatory diseases.
Discharge
Mucus and pus are associated with rectal pathology

14. Tenesmus
Often described by the patient as ‘I feel I want to go but nothing happens’, this is normally an ominous symptom of rectal cancer but can occur with any rectal pathology.
Prolapse
This usually indicates either mucosal or full-thickness rectal wall descent.
Loss of weight
This usually indicates serious or advanced disease, e.g. hepatic metastases.

15. Signs
Because the rectum is accessible via the anus, these can be elicited by systematic examination. The patient is either positioned in the left lateral (Sims’) position or examined in the knee–elbow position.
Inspection
Visual examination of the anus precedes rectal examination to exclude the presence of anal disease, e.g. fissure or fistula.
Digital examination
The index finger used with gentleness and precision remains avaluable test for rectal disease .
Tumours in the lower and middle thirds of the rectum can be felt and assessed; by asking the patient to strain, even some tumours in the upper third can be ‘tipped’ with the finger. After it is removed, the finger should be examined for tell-tale traces of mucus, pus or blood.

16. Proctoscopy
This procedure can be used to inspect the anus, anorectal junction and lower rectum (up to 10 cm) . Biopsy can be performed of any suspicious areas.
Sigmoidoscopy
The sigmoidoscope was in the past a rigid stainless steel instrument of variable diameter and normally 25 cm in length, The rectum must be empty for proper inspection with a sigmoidoscope. Gentleness and skill are required for its use, and perforations can occur if care is not exercised.
Flexible sigmoidoscope
The ‘flexiscope’ can be used to supplement or replace rigid sigmoidoscopy. It requires special skill and experience, and the lower bowel should be cleaned out with preliminary enemas. In addition to the rectum, the whole sigmoid colon is within visual reach of this instrument.