ArticlesAnatomyAbdomenLarge intestineSigmoid colon

ArticlesAnatomyAbdomenLarge intestineSigmoid colon

Sigmoid colon

Author: Christina Loukopoulou, MSc • Reviewer: Danijel Tosovic, PhD
Last reviewed: August 27, 2023
Reading time: 16 minutes

The sigmoid colon is a critical component of the large intestine, situated just before the rectum. It is a curved, S-shaped segment that plays a vital role in the digestive process by facilitating the movement of fecal matter, absorbing water, and storing waste before it is excreted from the body.

Understanding the anatomy, functions, and potential health conditions associated with the sigmoid colon is crucial for medical professionals and those interested in digestive health.

This article will cover key aspects of the sigmoid colon, including its anatomy, blood supply, innervation, functions, as well as common clinical disorders like diverticulitis, sigmoid volvulus, inflammatory bowel diseases (IBD), and the surgical procedure sigmoid colectomy.

Key facts about the sigmoid colon
Sigmoid colon	The S-shaped section of the large intestine, located between the descending colon and rectum, responsible for transporting and storing fecal matter.
Sigmoid mesocolon	The peritoneal attachment that supports the sigmoid colon, allowing some mobility within the abdominal cavity.
Mesocolic tenia	One of the longitudinal muscle bands of the sigmoid colon, located along the mesenteric border, responsible for creating haustra and assisting in motility.
Omental tenia	A longitudinal muscle band on the anterior surface of the sigmoid colon, aiding in motility and helping form haustra.
Free tenia	The longitudinal muscle band along the free border of the sigmoid colon, playing a role in peristalsis and fecal movement.
Haustra	Sacculations formed by the contraction of the teniae coli, allowing segmentation and efficient water absorption in the sigmoid colon.
Vascular supply	Supplied by the sigmoidal branches of the inferior mesenteric artery, providing oxygenated blood to the sigmoid colon.
Venous drainage	Drained by the inferior mesenteric vein, which joins the splenic vein before entering the portal vein.
Lymphatic drainage	Follows the route of the arterial supply, with lymph draining to mesenteric and lumbar lymph nodes.
Parasympathetic nerve supply	Innervated by the pelvic splanchnic nerves (S2-S4), promoting peristalsis and relaxation of the internal anal sphincter.

Contents

Anatomy
1. Teniae coli
2. Haustra
Blood supply
Innervation
Function
Clinical notes
Sources

+ Show all

Anatomy

The sigmoid colon is a distinct, S-shaped section of the large intestine located between the descending colon and the rectum. It plays a vital role in moving and storing fecal matter before it is excreted. Positioned in the pelvic cavity, the sigmoid colon is intraperitoneal, meaning it is encased in peritoneum and connected to the posterior abdominal wall by the sigmoid mesocolon, which allows for mobility and flexibility.

The sigmoid mesocolon is a peritoneal fold that supports the sigmoid colon, facilitating its attachment to the posterior abdominal wall while still allowing it to move slightly. This mesentery varies in length, with the central portion being relatively long, providing flexibility, and the lower part being shorter, stabilizing the rectum and descending colon. Additionally, the mesocolon serves as a conduit for blood vessels, allowing the passage of the sigmoid colon’s blood supply.

The exact positioning of the sigmoid colon can vary depending on an individual’s body structure. In some cases, due to its mobility, the sigmoid colon can extend into the abdomen, although it generally remains within the pelvic region. Its location is critical for understanding the risk of conditions like sigmoid volvulus or diverticulitis, which can occur when the sigmoid colon is displaced or inflamed.

Teniae coli

The sigmoid colon has three prominent longitudinal smooth muscle bands known as the teniae coli. These are formed by the thickening of the muscular layer of the colon and are responsible for the characteristic segmental appearance of the colon. These muscle bands contract to create the haustra (sacculations) seen throughout the colon and assist in the peristaltic movements that propel fecal matter.

Mesocolic tenia: This tenia coli runs along the mesenteric border of the sigmoid colon, where the mesocolon attaches. It is the most prominent of the three and contributes to the formation of haustra, which aid in the movement and segmentation of contents within the colon.
Omental tenia: This tenia is located along the anterior surface of the sigmoid colon. It is connected to the greater omentum, a large fold of peritoneum that drapes over the intestines. The omental tenia plays a role in the motility of the colon and assists with segmentation by creating the haustra.
Free tenia: The free tenia runs along the free border of the sigmoid colon, without any peritoneal attachment. It contributes to the contractile forces needed for peristalsis, helping move waste material toward the rectum.

Haustra

The haustra are small pouches or sacculations formed by the contraction of the teniae coli. These pouches are essential for the segmentation of the colon, which allows for more efficient absorption of water and electrolytes. Haustra also serve as an indicator of the peristaltic activity within the colon, which moves the fecal matter along its length. The presence of haustra is particularly notable in the sigmoid colon, where they create the distinct, segmented appearance that is crucial for its function in waste storage.

Blood supply

The blood supply to the sigmoid colon is derived from the inferior mesenteric artery, which arises from the abdominal aorta at the vertebral level of L3. Several sigmoidal branches of the inferior mesenteric artery provide blood flow to the sigmoid colon, ensuring the delivery of oxygen and nutrients necessary for its functions.

Arterial supply: The inferior mesenteric artery is the main artery that supplies blood to the sigmoid colon. The branches of this artery nourish the colon, facilitating proper function.
Venous drainage: Venous blood from the sigmoid colon drains into the inferior mesenteric vein, which ultimately connects to the portal vein, facilitating the return of deoxygenated blood to the liver.
Lymphatic drainage: The lymphatic system of the sigmoid colon mirrors its arterial supply. Lymph nodes along the path of the inferior mesenteric artery filter lymphatic fluid, playing a role in immune defense and the removal of waste products from the colon.

Innervation

The nerve supply to the sigmoid colon is controlled by both the autonomic nervous system and the enteric nervous system (ENS):

Parasympathetic innervation: The pelvic splanchnic nerves (S2-S4) provide parasympathetic stimulation, promoting peristalsis, the wave-like motion that propels fecal matter along the colon. This parasympathetic input is critical for normal colon motility and the relaxation of the internal anal sphincter during defecation.

Sympathetic innervation: The lumbar splanchnic nerves (L1-L2) provide sympathetic innervation, which serves to slow peristalsis and contract the internal anal sphincter, which helps regulate fecal retention until defecation is appropriate.
Enteric nervous system (ENS): The myenteric plexus (of Auerbach) and submucosal plexus (of Meissner) of the enteric system ensure the coordination of smooth muscle contractions for effective digestion and waste movement.

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Function

Water absorption and nutrient conservation

The sigmoid colon plays a crucial role in absorbing water, electrolytes, and some nutrients from the remaining food matter before it is expelled from the body. As the digestive residue passes through the sigmoid colon, the colon walls actively absorb water, making the stool more solid and preventing dehydration. This process is vital for maintaining the body's hydration balance and conserving essential nutrients.

Storage and transport of feces

The sigmoid colon temporarily stores fecal matter before it is moved to the rectum for eventual elimination. This storage function is critical for coordinating the timing of defecation. The sigmoid colon's ability to hold and move waste ensures that the body expels feces at the right time, while the muscles of the colon maintain tight control over the process.

Role in peristalsis

The sigmoid colon, like other parts of the large intestine, relies on peristalsis to move its contents. Peristalsis refers to a series of coordinated muscle contractions that push the waste material toward the rectum. The proper functioning of this mechanism is vital for maintaining healthy digestion and ensuring that feces are not retained too long, which can lead to constipation.

Test your knowledge on the large intestine with this quiz.

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Clinical notes

Several disorders affect the sigmoid colon, leading to discomfort and potential complications. The following are some of the most common conditions:

Diverticulitis

Diverticulitis occurs when small, bulging pouches called diverticula form in the walls of the sigmoid colon. These pouches can become inflamed or infected, leading to symptoms like left lower abdominal pain, bloating, nausea, and blood in the stool. The condition is commonly linked to chronic constipation, low-fiber diets, and aging.
Treatment for diverticulitis typically involves antibiotics, rest, and a high-fiber diet to promote healing. In severe cases, surgery may be required to remove the affected portion of the colon.

Sigmoid volvulus

Sigmoid volvulus is a medical emergency in which the sigmoid colon twists on itself, causing a bowel obstruction. The condition is most likely to occur in people with a long sigmoid colon and excessive mobility of the sigmoid mesocolon. Symptoms include severe abdominal pain, nausea, vomiting, and constipation.
Diagnosis of sigmoid volvulus often involves imaging studies, such as an abdominal x-ray, where the classic coffee bean sign may be seen. Treatment typically includes endoscopic decompression or, if the condition persists, surgical intervention to correct the twist and prevent complications like intestinal ischemia or necrosis.

Inflammatory Bowel Disease (IBD)

The sigmoid colon is commonly involved in inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis:

Crohn’s disease is a chronic condition that can affect any part of the gastrointestinal tract, including the sigmoid colon. It causes symptoms like abdominal cramps, bloody diarrhea, and weight loss. Extra-intestinal symptoms such as arthritis and skin rashes are also common.
Ulcerative colitis mainly affects the rectum and extends proximally to involve the sigmoid colon. It causes bloody diarrhea, weight loss, and a higher risk of developing colon cancer over time.

Management of IBD typically involves anti-inflammatory medications, immunosuppressants, and biologic therapies. In severe cases, surgical resection of the affected bowel may be necessary.

Sigmoid colectomy

A sigmoid colectomy is a surgical procedure used to remove the sigmoid colon. This surgery may be necessary for conditions like severe diverticulitis, colon cancer, or complicated Crohn’s disease. The procedure involves removing the affected segment of the colon and reconnecting the remaining bowel to the rectum. This helps restore normal bowel function and prevent further complications.

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders.
Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.
Jones J, MD and Knipe H, MD: Sigmoid colon. Radiopaedia.org (accessed 26/02/2016).

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