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 gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...

, 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 The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is f ...

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 vag ...

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. 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, ...

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. Th ...

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 (SM ...

, 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. Approx ...

. * 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 The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine ...

which joins the internal iliac vein. * The lower part of the external plexus is drained by the inferior rectal veins into the internal pudendal vein

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.

References

Veins of the torso Rectum {{circulatory-stub