The rectal venous plexus (or hemorrhoidal plexus) surrounds the

rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the Gastrointestinal tract, gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the s ...

, and communicates in front with the

vesical venous plexus The vesical plexus envelops the lower part of the bladder and the base of the prostate and communicates with the pudendal and prostatic plexuses. It is drained, by means of several vesical veins The vesical veins are veins in the pelvis that d ...

in the male, and the

vaginal venous plexus The vaginal venous plexus is a group of veins draining blood from the vagina. It lies around the sides of the vagina. Its blood is eventually into the internal iliac veins. Structure The vaginal venous plexus lies around the sides of the vagi ...

in the female. A free communication between the portal and systemic venous systems is established through the rectal venous plexus. This allows administration of some medications normally given by mouth to be given rectally, while still bypassing

first pass metabolism The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism whereby the concentration of a drug, specifically when administered orally, is greatly reduced before it reaches the system ...

. Examples include rectal

Diazepam Diazepam, first marketed as Valium, is a medicine of the benzodiazepine family that acts as an anxiolytic. It is commonly used to treat a range of conditions, including anxiety, seizures, alcohol withdrawal syndrome, muscle spasms, insomnia, a ...

and orally dissolving medications.

Parts

It consists of two parts, an internal in the submucosa, and an external outside the muscular coat.

Internal 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. This internal plexus is also known in some medical communities as the Irving plexus.

External plexus

* The upper part of the external plexus is drained by the

superior rectal vein The inferior mesenteric vein begins in the rectum as the superior rectal vein (superior hemorrhoidal vein), which has its origin in the hemorrhoidal plexus, and through this plexus communicates with the middle and inferior hemorrhoidal veins. The ...

which forms the commencement of the

inferior mesenteric vein In human anatomy, the inferior mesenteric vein (IMV) is a blood vessel that drains blood from the large intestine. It usually terminates when reaching the splenic vein, which goes on to form the portal vein with the superior mesenteric vein (SMV) ...

, a tributary of the

portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approxima ...

. * The middle part of the external plexus is drained by the

middle rectal vein The middle rectal veins (or middle hemorrhoidal vein) take origin in the hemorrhoidal plexus and receive tributaries from the bladder, prostate, and seminal vesicle. They run lateralward on the pelvic surface of the levator ani to end in the inte ...

which joins the internal iliac vein. * The lower part of the external plexus is drained by the

inferior rectal veins The lower part of the external hemorrhoidal plexus is drained by the inferior rectal veins (or inferior hemorrhoidal veins) into the internal pudendal vein The internal pudendal veins (internal pudic veins) are a set of veins in the pelvis. They ...

into the

internal pudendal vein The internal pudendal veins (internal pudic veins) are a set of veins in the pelvis. They are the venae comitantes of the internal pudendal artery. Internal pudendal veins are enclosed by pudendal canal, with internal pudendal artery and pudendal ...

Support

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 Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

References

Veins of the torso Rectum {{circulatory-stub