The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation. The colon is the longest portion of the large intestine, and the terms are often used interchangeably but most sources define the large intestine as the combination of the cecum, colon, rectum, and anal canal. Some other sources exclude the anal canal.
Hemorrhoids, 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 hemorrhoid is often used to refer to the disease. The signs and symptoms of hemorrhoids depend on the type present. Internal hemorrhoids often result in painless, bright red rectal bleeding when defecating. External hemorrhoids often result in pain and swelling in the area of the anus. If bleeding occurs, it is usually darker. Symptoms frequently get better after a few days. A skin tag may remain after the healing of an external hemorrhoid.
In human anatomy, the inferior mesenteric artery (IMA) is the third main branch of the abdominal aorta and arises at the level of L3, supplying the large intestine from the distal transverse colon to the upper part of the anal canal. The regions supplied by the IMA are the descending colon, the sigmoid colon, and part of the rectum.
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).
In human anatomy, the hepatic veins are the veins that drain venous blood from the liver into the inferior vena cava. There are usually three large upper hepatic veins draining from the left, middle, and right parts of the liver, as well as a number (6-20) of lower hepatic veins. All hepatic veins are valveless.
The middle rectal artery is an artery in the pelvis that supplies blood to the rectum.
The inferior rectal artery is an artery that supplies blood to the lower third of the anal canal below the pectinate line.
In human anatomy, the hepatic portal system or portal venous system is the system of veins comprising the portal vein and its tributaries. The other portal venous systems in the body are the renal portal system, and the hypophyseal portal system.
The rectal venous plexus is the venous plexus surrounding the rectum. 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.
The superior rectal artery is an artery that descends into the pelvis to supply blood to the rectum.
The inferior rectal nerves usually branch from the pudendal nerve but occasionally arises directly from the sacral plexus; they cross the ischiorectal fossa along with the inferior rectal artery and veins, toward the anal canal and the lower end of the rectum, and is distributed to the sphincter ani externus and to the integument (skin) around the anus.
The inferior mesenteric vein begins in the rectum as the superior rectal vein, which has its origin in the hemorrhoidal plexus, and through this plexus communicates with the middle and inferior hemorrhoidal veins.
The lower part of the external hemorrhoidal plexus is drained by the inferior rectal veins into the internal pudendal vein.
The inferior mesenteric lymph nodes consist of:
The superior rectal plexus supplies the rectum and joins in the pelvis with branches from the pelvic plexuses.
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 12 centimetres (4.7 in) long, and begins at the rectosigmoid junction at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. Its diameter is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring or the dentate line, again depending upon which definition is used. In humans, the rectum is followed by the anal canal, which is about 4 centimetres (1.6 in) long, before the gastrointestinal tract terminates at the anal verge. The word rectum comes from the Latin rectumintestinum, meaning straight intestine.
Rectal administration uses the rectum as a route of administration for medication and other fluids, which are absorbed by the rectum's blood vessels, and flow into the body's circulatory system, which distributes the drug to the body's organs and bodily systems.
Transanal hemorrhoidal dearterialization (THD) is a minimally invasive surgical procedure for the treatment of internal hemorrhoids.
Anorectal varices are the dilation of collateral submucosal vessels due to backflow in the veins of the rectum. Typically this occurs due to portal hypertension which shunts venous blood from the portal system through the portosystemic anastomosis present at this site into the systemic venous system. This can also occur in the esophagus, causing esophageal varices, and at the level of the umbilicus, causing caput medusae. Between 44% and 78% of patients with portal hypertension get anorectal varices.
A liver segment is one of eight segments of the liver as described in the widely used Couinaud classification in the anatomy of the liver. This system divides the lobes of the liver into eight segments based on a transverse plane through the bifurcation of the main portal vein, arranged in a clockwise manner starting from the caudate lobe.
