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Introduction to Rectum

The digestive system of humans consists of the gastrointestinal tract and some other organs that are required for digestion. Along with the GI tract, the digestive system consists of the small intestine, large intestine, and anus. The large intestine is called the large bowel. According to many sources, the large intestine is a combination of the cecum, colon, rectum, and anal canal. Generally, the long straight final portion of the large intestine in the human digestive system and also in some other mammals is the rectum. The word rectum is derived from the Latin word, intestinum rectum which means straight. The rectum length in adults is about twelve centimetres. Let us learn the rectum length, facts about the rectum, and more.

Rectum - Structure

The Rectum Consists of Two Flexures:

  1. Sacral Flexure: It is known as dorsal bend, which is extended from the concave form of the sacrum.

  2. Perineal Flexure: It is known as the ventral bend, it occurs as a result of the levator ani muscle encircles the rectum. 

It consists of three constant transverse folds called Houston’s valves, where the middle rectal fold known as Kohlrausch’s valve is the strongest one and it is located about 7cm from the location of the anus. During the process of defecation, the rectal ampulla acts as a reservoir and it is quite stretchable. The rectum consists of three arteries that include, superior rectal artery, middle rectal artery, and inferior rectal artery. 

The venous drainage present in the rectum is carried out by veins such as the superior, middle, and inferior rectal veins. The upper part of the rectum is drained into the portal venous system with the help of superior rectal veins whereas the lower part of the rectum is drained into the internal iliac vein with the help of the middle and inferior rectal vein.

The internal structure of the rectum is made up of mucosa, submucosa, muscularis, and serosa. 

  • The mucosa consists of the typical intestinal epithelium that is made up of simple columnar erythrocytes and a number of goblet cells. But this epithelium gets flattened to become the stratified squamous epithelium, at the transitional zone of the anal. This squamous epithelium is non-keratinized.

  • The connective tissue layer is present after the epithelial layer, this connective tissue layer is made of blood, muscular layer, and lymph vessels.

  • The next one is the submucosa layer, which consists of loose connective tissue that has lymph follicles, blood vessels, and the Meissner’s plexus. This layer consists of a network of veins and is found thickened at the transverse folds.

  • The last one is the muscularis layer, which consists of Auerbach’s plexus that lies in between the inner circular and outer longitudinal musculature. In the sphincter system,  inner circular or ring musculature continues to form sphincter ani externus muscle and the outer longitudinal musculature continues to form corrugator cutis ani muscle present in the skin around the anus.

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In the anal canal before the elimination of the feces, the rectum is the last stage that is found in the canal. Similar to that of the colon, in the rectum electrolytes are absorbed and the food that is indigestible is decomposed by the anaerobic bacteria. The entire length of the colon in the human body is about five feet, among that the rectum size is about 10 to 15cm. Due to the absorption of water, the stools are thickened and it gets mixed with the mucus. 

The rectum is said to be the part of the continence organ, where it plays its major role in the mechanism of the defecation. The rectal ampulla consists of stretch receptors, when stools enter the rectal ampulla the signals are sent to the central nervous system, when these signals are received by the brain then the person feels the urge to defecate. Now the person can relax or tense the sphincter ani externus muscle and the levator ani muscle to initiate or delay the process of defecation. But the increase in the pressure of holding the stools can increase the effort, along with this abdominal pressure is increased due to the voluntary tension of abdominal muscles and the diaphragm. Due to the contraction of the rectum, it supports in the defecation.

Clinical Significance of Human Rectum

To provide diagnosis the examination is necessary that include fecal impaction, prostatic cancer, and fecal incontinence. The medical imaging forms that are used to examine the rectum are CT scan and the MRI scan. To view the nearby structures as prostate an ultrasound probe might be inserted into the rectum. The forms of endoscopy used to view the rectum directly are colonoscopy and sigmoidoscopy. For diagnosis of certain diseases such as cancer, biopsies are done. 

To check the temperature of the rectum a medical thermometer has to be inserted inside the rectum through the anus. The length of the thermometer should not increase by more than one inch. The normal rectal temperature is known to be present in between 36 to 38 degrees Celsius. 

  1. One of the major disorders found is constipation, which is found commonly in people who have different forms of lifestyles and poor diet balance. This includes the inadequate supply of water or hydration, the poor fibre content in the diet, immobility, and many other causes. These causes may include diseases that may affect the nerves which control the bowel movement, local diseases, or the slow bowel transit time. The use of medications such as opioids, due to severe illness, or diabetes mellitus can cause constipation. Low thyroid activity or high calcium levels can also increase the causes of constipation. 

  2. Rectal cancer can also be caused by the linings of the rectum. The usual causes for rectal cancer are still unknown, but according to some experts, there are some risk factors such as a person with age more than 50years, high fat diet, smoking, family history, or inflammatory bowel disease. 

  3. After the birth of the child, due to the weakened pelvic floor, rectal prolapse can occur. This is nothing but the prolapse of the rectum into the external area or anus. 

Facts about Rectums

  • Spending most of the time in the toilet can result in haemorrhoids, where the veins are swollen in the part of the anus and rectum. 

  • The consumption of fibre content plays a major role in maintaining colon health, it helps to prevent diseases such as haemorrhoids and diverticulitis. The fibre can be found abundantly in fruits, whole grains, vegetables, nuts, seeds, beans, and legumes. 

  • Melanoma, a kind of skin cancer can be caused in the areas where the skin does not receive sunlight. 

  • If you find blood in the stools and pain in the anal region then one must consult a doctor.

  • When a person has reached the age of 50, then he or she must get done with the colonoscopy in order to have knowledge about the health of the colon.

Rectal Problem

  1. Rectal Itching: 

It is not a sign of severe disorder, at first the skin might appear red, where the itching can cause the skin to become thick and white. Some of the reasons for itching may be:

  • Poor cleaning of the area after the defecation.

  • Antibiotics that can cause diarrhoea and constipation.

  • Cleansing the anus with hot water and strong soaps. 

  • Usage of scented ointments, toilet papers, or soaps.

  • Haemorrhoids.

  • Infection is caused due to some bacteria or viruses. Pinworm is the most common cause of itching that is found in children.

  • Certain foods such as tomatoes, spicy food, coffee, tea, and food that is high in vitamin C4.

  • Even travelling for longer periods of time can cause itching in some people.

  1. Rectal Pain: 

It is caused due to some of the causes such as:

  • Enlarged or swollen veins in the rectal region.

  • Some of the structural problems such as anal fissures or rectal prolapse.

  • Infection is due to sexually transmitted diseases.

  • Cancer in the rectum.

  • Rectal spasms.

  1. Rectal Bleeding:

Many people find small amounts of rectal bleeding. Haemorrhoids and anal fissures can cause bleeding due to constipation. This type of bleeding can cause pain in the bowel movement. The bleeding can be found in any part of the digestive tract. The bleeding in the stomach looks black and tarry. The blood that moves fast from the digestive tract can appear as red near the rectum. Sometimes the food we consume can also change the colour of the stool, that foods include beetroots, diarrhoea, and iron tablets can cause the stools to appear red, whereas consumption of blue food colouring can turn the stools black.


The chamber begins at the ending stage of the large intestine, it is followed to end at the anus with the help of the sigmoid colon is known to be the rectum. Initially, the rectum will be empty until the stools are passed from the colon when the descending colon is full. As soon as the stools are passed into the rectum, it causes an urge for defecation. 

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FAQs on Rectum

1. How Big the Human Rectum is and What are the Functions of the Rectum?

Ans: The lower part of the large intestine is known as the rectum, the rectum length is about 15cm long which helps to connect to the sigmoid colon. The job of the rectum is to collect the stools from the colon as soon as the stools move to the rectum it causes an urge to defecate by the signals that are passed to the central nervous system.

2. Is the Rectum Considered an Organ?

Ans: It is not only considered as the conduit for the passage of stools but also to store the stools if the amount passed from the colon is small. When there are circumstances where the defecation cannot be done, then in such cases also the stools are stored in the rectum.