The rectal venous plexus (or hemorrhoidal plexus
) is the
venous plexus surrounding the
rectum
The rectum (: rectums or recta) is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. Before expulsion through the anus or cloaca, the rectum stores the feces temporarily. The adult ...
.
It consists of an internal and an external rectal plexus.
It is drained by the superior, middle, and inferior rectal veins. It forms a
portosystemic (portocaval) anastomosis.
This allows rectally administered medications to bypass
first pass metabolism.
Despite the inclusion of the term "rectal" into the name, the venous plexus is positionally, functionally, and clinically primarily related to the
anal canal
The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional s ...
.
Anatomy
The rectal venous plexus consists of an external rectal plexus
that is situated outside to the muscular wall,
and an internal rectal plexus
that is situated in the
submucosa
The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal, respiratory, and genitourinary tracts. It is the layer of dense irregular connective tissue that supports the mucosa (mucous membrane) an ...
/deep to the mucosa
of the rectum and proximal
anal canal
The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional s ...
at the
anorectal junction.
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.
The internal plexus (sources differ) forms
/is continuous distally/inferiorly with
the
hemorrhoids
Hemorrhoids (or haemorrhoids), also known as piles, are vascular structures in the anal canal. In their normal state, they are cushions that help with stool control. They become a disease when swollen or inflamed; the unqualified term ''he ...
(the vascular cushions of the
anal canal
The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional s ...
).
Venous drainage
According to the 42nd edition of ''
Gray's Anatomy
''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter and first published in London in 1858. It has had multiple revised editions, and the current edition, the 42nd (October 2020 ...
'' (2020), the internal rectal plexus is drained mostly by the
superior rectal vein (→
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) ...
→
splenic vein
In human anatomy, the splenic vein (formerly the lienal vein) is a blood vessel that drains blood from the spleen, the stomach fundus and part of the pancreas. It is part of the hepatic portal system.
Structure
The splenic vein is formed from ...
→
hepatic 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. Appro ...
).
According to the 8th edition of ''Clinically Oriented Anatomy'' (2017), the internal rectal plexus is drains mostly into the
superior rectal vein superior/proximal to the
pectinate line
The pectinate line (dentate line) is a line which divides the upper two-thirds and lower third of the anal canal. Developmentally, this line represents the hindgut- proctodeum junction.
It is an important anatomical landmark in humans, and fo ...
, and into the
inferior rectal veins (→
internal pudendal vein→
internal iliac vein
The internal iliac vein (hypogastric vein) begins near the upper part of the greater sciatic foramen, passes upward behind and slightly medial to the internal iliac artery and, at the brim of the pelvis, joins with the external iliac vein to for ...
→
common iliac vein
In human anatomy, the common iliac veins are formed by the external iliac veins and internal iliac veins. The left and right common iliac veins come together in the abdomen at the level of the lumbar vertebrae, fifth lumbar vertebra, forming the ...
→
inferior vena cava
The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...
) around the margin of the
external anal sphincter
The external anal sphincter (or sphincter ani externus) is an oval tube of skeletal muscle fibers. Distally, it is adherent to the skin surrounding the margin of the anus. It exhibits a resting state of tonical contraction and also contracts duri ...
inferior/distal to the pectinate line.
External rectal plexus
Venous drainage
* The proximal/superior part mostly drains into the
superior rectal vein (→
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) ...
→
splenic vein
In human anatomy, the splenic vein (formerly the lienal vein) is a blood vessel that drains blood from the spleen, the stomach fundus and part of the pancreas. It is part of the hepatic portal system.
Structure
The splenic vein is formed from ...
→
hepatic 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. Appro ...
)
* The middle part drains into
middle rectal vein(s) (→
internal iliac vein
The internal iliac vein (hypogastric vein) begins near the upper part of the greater sciatic foramen, passes upward behind and slightly medial to the internal iliac artery and, at the brim of the pelvis, joins with the external iliac vein to for ...
→
common iliac vein
In human anatomy, the common iliac veins are formed by the external iliac veins and internal iliac veins. The left and right common iliac veins come together in the abdomen at the level of the lumbar vertebrae, fifth lumbar vertebra, forming the ...
→
inferior vena cava
The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...
)
* The distal/inferior part drains into
inferior rectal veins (→
internal pudendal vein→
internal iliac vein
The internal iliac vein (hypogastric vein) begins near the upper part of the greater sciatic foramen, passes upward behind and slightly medial to the internal iliac artery and, at the brim of the pelvis, joins with the external iliac vein to for ...
→
common iliac vein
In human anatomy, the common iliac veins are formed by the external iliac veins and internal iliac veins. The left and right common iliac veins come together in the abdomen at the level of the lumbar vertebrae, fifth lumbar vertebra, forming the ...
→
inferior vena cava
The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...
)
Structure
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.
Anastomoses
The rectal venous plexus represents a
portosystemic (portocaval) anastomosis.
The transition from drainage into the portal system to drainage into the inferior caval system occurs in the region of the
anal columns.
It communicates anteriorly with the
uterine
The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic and fetal development of one or more fertilized eggs until bir ...
and
vaginal venous plexus in the female, and with the
vesical venous plexus
The vesical venous plexus is a venous plexus situated at the fundus of the urinary bladder. It collects venous blood from the urinary bladder in both sexes, from the accessory sex glands in males, and from the corpora cavernosa of clitoris in fem ...
in the male.
Clinical significance
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.
The external rectal plexus may be affected by
blood clots (thrombi), resulting in external haemerrhoids.
References
Veins of the torso
Rectum
{{circulatory-stub