Despite the inclusion of the term "rectal" into the name, the venous plexus is positionally, functionally, and clinically primarily related to the anal canal.[6]
Anatomy
The rectal venous plexus consists of an external rectal plexus[4]: 598 [5]: 294 that is situated outside to the muscular wall,[3][4]: 598 [5]: 294 and an internal rectal plexus[4]: 598 [5]: 294 that is situated in the submucosa[5]: 294 /deep to the mucosa[3][4]: 598 of the rectum and proximal anal canal[3] at the anorectal junction.[4]: 598
Internal rectal plexus
The internal plexus presents a series of dilated pouches which are arranged in a circle around the tube, immediately above the anal orifice, and are connected by transverse branches.[citation needed]
The internal plexus (sources differ) forms[4]: 641 /is continuous distally/inferiorly with[5]: 294 the hemorrhoids (the vascular cushions of the anal canal).[5]: 294 [4]: 641
The veins of the hemorrhoidal plexus are contained in very loose connective tissue, so that they get less support from surrounding structures than most other veins, and are less capable of resisting increased blood-pressure.[citation needed]
The internal rectal plexus may prolapse into the anal canal to form pathological internal haemerrhoids; these are often strangulated by the contraction of the anal sphincter, causing ulceration and bleeding.[4]: 645
The external rectal plexus may be affected by blood clots (thrombi), resulting in external haemerrhoids.[4]: 645
^ abcdefghijkMoore, Keith L.; Dalley, Arthur F.; Agur, Anne M. R. (2018). Clinically Oriented Anatomy (8th ed.). Wolters Kluwer. ISBN978-1-4963-4721-3.
^Moore, Keith L.; Dalley, Arthur F.; Agur, Anne M. R. (2017). Essential Clinical Anatomy (6th ed.). Lippincott Williams & Wilkins. p. 598. ISBN978-1496347213.