What Is the Sigmoid Colon Definition Structure Function and Diagram
The sigmoid colon is a part of the large intestine, the last section of the bowel, closest to the rectum and anus. It is a loop that resembles a Latin letter S or Greek letter sigma (ς). The length of sigmoid colon is around 40 centimetres, i.e., roughly a foot and a half long.
This part usually lies within the pelvis but can displace into the abdominal cavity due to freedom of movement. It comprises a set of muscle tissue arranged in two ways. Some bundles of muscle tissues, running up and down the length of the sigmoid colon, while some are arranged in annular bands around the tube. The annular bands pinch the tube shaping small sacs called haustra, making the sigmoid colon appear like a line of plethoric beads.
Sigmoid colon function is to hold faeces until you have the urge to use the bathroom.
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Layers of Colon
There are four layers of colon, namely, mucosa, submucosa, muscularis, and serosa.
The mucosa membrane is the innermost layer of the colon and is made of mere columnar epithelial tissue. Its primary functions are to prevent the body from absorbing the bacteria present in the faecal matter and help the faeces waft through the tube.
The second layer of the colon is a sheet of connective tissue, nerves, and blood vessels called the submucosa. It supports other layers of the large intestine and absorbs the remaining nutrients present in the digested food.
The submucosa is surrounded by the muscular, the third layer of the colon, which contains multiple layers of visceral muscle cells that helps along the sigmoid tube in a process known as peristalsis.
The outermost layer of the colon, known as the serosa, is a smooth thin sheet of epithelial tissue. Its primary function is to secrete a watery fluid to keep the organ protected from frictional movement.
Sigmoid Colon Function
The primary sigmoid colon function is to act as a chamber that holds the faecal matter until it is expelled out of the body.
The slurry known as chyme passes through the ileocecal valve, and the cecum reaching the colon mixes with beneficial bacteria present there. It then flows through the four sections of the colon (haustra) over hours due to peristalsis. In some cases, this process can increase its speed by stronger waves of peristalsis that ensue a heavy meal.
If you think the only function of the sigmoid colon is to act as a chamber that holds faeces, you are highly mistaken. Though, maximum nutrients are already being absorbed in the small intestine and stomach before reaching the sigmoid colon. Sigmoid still plays a crucial role in absorbing vitamins from the faeces while it's waiting to be discharged.
These vitamins are necessary for good health and are produced by good bacteria present in the colon through fermentation and include:
Vitamin K
Biotin (vitamin B7)
Sigmoid Colon Problems
How is one supposed to know that one is having sigmoid colon problems? Well, you would probably feel sigmoid colon pain which is usually categorized as abdominal pain. Besides, one might also witness other symptoms such as nausea, loss of appetite, blood in stool, and might also experience constipation or diarrhoea. Besides these symptoms, some people suffering from sigmoid colon problems might also feel fatigued, lose weight and become anaemic. Now with an acquired knowledge about sigmoid colon pain and its general symptoms let's get into the depth and know what sigmoid colon problems can arise.
Polyps
Polyps are masses of tissue occurring in the colon; although most are non-cancerous, late detection can turn them cancerous as they get bigger over time. Its occurrence isn't restricted to age but is most likely formed as you get older. Habitual smoking and overweighting can ignite its occurrence.
Colorectal Cancer
Reports assert that colorectal cancer is the third most common cancer in the United States.
Sigmoid colon cancer transpires when abnormal cells grow inside the colon tube, usually in polyps. If these cells are left untreated, they grow over time and develop from the inner layers of the colon into the walls of the organ and eventually into the blood vessels and lymph system.
Since early detection boosts the odds of recovery, it is advised to get regular colon screenings, especially if you are experiencing sigmoid colon cancer symptoms.
Some of the Most Common Sigmoid Colon Cancer Symptoms Are:
A resolute difference in your bowel practices, including constipation or diarrhoea or a change in the texture of the stool.
Persistent abdominal uneasiness (sigmoid colon pain), such as cramps or gas.
An uneasiness of not having a clean bowel.
Rectal bleeding or witnessing blood in the stool.
Weakness or fatigue.
Besides Polyps and sigmoid colon cancer, several other sigmoid colon problems can arise, including ulcerative colitis, fistulae, volvulus, and more. Since each of them has a distinct impact, they require to be treated by a different specialist. Depending on the character of your colon problem, you could consult a gastroenterologist, a radiologist, an oncologist, or a colorectal surgeon.
Did You Know?
The four layers of the colon carry out different functions, and each has unique importance.
The average length of the sigmoid colon is 25 to 40 cm, about one-fifteenth as tall as a Giraffe.
An estimate of 149500 Americans witnessed sigmoid colon cancer symptoms this year.
The sigmoid colon is also termed pelvic colon.
Despite lying within the pelvis, the sigmoid colon can displace into the abdominal cavity due to freedom of movement.
FAQs on Sigmoid Colon Anatomy and Role in the Large Intestine
1. What is the sigmoid colon?
The sigmoid colon is the S-shaped final segment of the large intestine that connects the descending colon to the rectum. It is located in the lower left abdomen and plays a key role in storing fecal matter before elimination. In human anatomy, it is named “sigmoid” because of its curved, S-like shape. It forms part of the distal colon and is essential in the final stages of digestion.
2. Where is the sigmoid colon located in the body?
The sigmoid colon is located in the lower left quadrant of the abdomen, between the descending colon and the rectum. Specifically, it:
- Begins at the end of the descending colon
- Forms an S-shaped loop in the pelvic cavity
- Ends at the rectum
3. What is the function of the sigmoid colon?
The main function of the sigmoid colon is to store and regulate the passage of feces before defecation. Its functions include:
- Temporary storage of solid waste
- Absorption of remaining water and electrolytes
- Controlled propulsion of feces into the rectum through peristalsis
4. Why is the sigmoid colon S-shaped?
The sigmoid colon is S-shaped to allow flexibility, expansion, and efficient storage of feces. Its curved structure:
- Provides extra space for temporary fecal storage
- Allows movement within the pelvic cavity
- Helps regulate pressure before defecation
5. How does the sigmoid colon move waste toward the rectum?
The sigmoid colon moves waste toward the rectum through rhythmic muscular contractions called peristalsis. The process involves:
- Contraction of circular and longitudinal smooth muscles
- Formation of wave-like movements
- Gradual propulsion of fecal matter into the rectum
6. What is the difference between the sigmoid colon and the rectum?
The sigmoid colon is a curved section of the large intestine that stores feces, while the rectum is the straight terminal part that expels feces from the body. Key differences include:
- Shape: Sigmoid colon is S-shaped; rectum is straight
- Function: Sigmoid stores and regulates; rectum initiates defecation reflex
- Location: Sigmoid lies before the rectum in the lower left abdomen
7. What type of tissue makes up the sigmoid colon?
The sigmoid colon is made of four main tissue layers typical of the gastrointestinal tract. These layers include:
- Mucosa – inner lining for absorption and mucus secretion
- Submucosa – connective tissue with blood vessels and nerves
- Muscularis externa – smooth muscle layers for peristalsis
- Serosa – outer protective covering
8. What are common diseases of the sigmoid colon?
Common diseases of the sigmoid colon include diverticulitis, sigmoid volvulus, and colorectal cancer. These conditions involve:
- Diverticulitis – inflammation of small pouches (diverticula)
- Sigmoid volvulus – twisting of the sigmoid colon causing obstruction
- Colorectal cancer – abnormal cell growth in the colon lining
9. How long is the sigmoid colon?
The sigmoid colon is typically about 35–45 cm (14–18 inches) long in adults. Its length can vary depending on age, body structure, and individual anatomy. Because it is relatively mobile and curved, its exact position and length may differ slightly among individuals.
10. Why is the sigmoid colon important in digestion?
The sigmoid colon is important in digestion because it regulates the final storage and controlled elimination of solid waste. Its importance includes:
- Maintaining proper bowel movement timing
- Preventing premature defecation
- Supporting water balance by absorbing residual fluids
