The rectum

The rectum is 5 in (12 cm) in length. It commences anterior to the third segment of the sacrum and ends at the level of the apex of the prostate or at the lower quarter of the vagina, where it leads into the anal canal.

The rectum is straight in lower mammals (hence its name) but is curved in man to fit into the sacral hollow. Moreover, it presents a series of three lateral inflexions, capped by the valves of Houston, projecting left, right and left from above downwards.

Relations (Figs 62, 63)

The main relations of the rectum are important. They must be visualized in carrying out a rectal examination, they provide the key to the local spread of rectal growths and they are important in operative removal of the rectum.

Posteriorly lie sacrum and coccyx and the middle sacral artery, which are separated from it by extraperitoneal connective tissue containing the rectal vessels and lymphatics. The lower sacral nerves, emerging from the anterior sacral foramina, may be involved by growth spreading posteriorly from the rectum, resulting in severe sciatic pain.

Anteriorly, the upper two-thirds of the rectum are covered by peritoneum and relate to coils of small intestine which lie in the cul-de-sac of the pouch of Douglas between the rectum and the bladder or the uterus. In front of the lower one-third lie the prostate, bladder base and seminal

Sacral promontory

Symphysis pubis

Prostate

Sacral promontory

Symphysis pubis

Prostate

Prostate Rectum Fascia

Seminal vesicle Rectum Fascia of Denonvilliers

Anal sphincter

Fig. 62 Sagittal section of the rectum and its related viscera in the male.

Seminal vesicle Rectum Fascia of Denonvilliers

Anal sphincter

Fig. 62 Sagittal section of the rectum and its related viscera in the male.

Vagina Saggital Section

Fig. 63 Sagittal section of the rectum and its related viscera in the female.

vesicles in the male, or the vagina in the female. A layer of fascia (Denonvilliers) separates the rectum from the anterior structures and forms the plane of dissection which must be sought after in excision of the rectum. Laterally, the rectum is supported by the levator ani.

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