Haustra are pouch-like structures found along the large intestine, also known as the colon. They give the colon its characteristic segmented appearance. Haustra also aid in digestion and absorption, preparing waste material for elimination.
Anatomy and Location
The colon’s distinct segmented appearance is due to haustra. These pouches form from the unique arrangement of muscular layers within the large intestine wall. The outer longitudinal muscle layer of the colon is concentrated into three distinct bands called taeniae coli, which run along most of its length.
Because the taeniae coli are shorter than the overall length of the colon, their tonic contraction causes the colon wall to gather and form these sacculations. This muscular arrangement creates the visible bulges and folds that define the haustra. They are present throughout the colon, from the cecum through the sigmoid colon, but are not found in the rectum. Their wider spacing, compared to the circular folds of the small intestine, can assist in distinguishing the large intestine from the small intestine during medical imaging.
Role in Digestion
Haustra play a role in processing chyme, the semi-liquid food mixture entering the large intestine from the small intestine. Haustral contractions are the primary movement, involving slow, segmenting, and often uncoordinated movements. These occur roughly every 25 to 30 minutes.
When a haustrum fills with chyme, it distends, stimulating its smooth muscles to contract. This contraction mixes contents and slowly propels chyme into the next haustrum. This mixing brings chyme into close contact with the intestinal wall, maximizing absorption of water and electrolytes like sodium and chloride. The colon absorbs a significant amount of water daily, aiding in the formation of solid stool. While haustral contractions contribute to forward movement, their primary function is mixing and facilitating absorption, not rapid propulsion, which stronger mass movements handle.
Clinical Significance
Haustra are observable through medical imaging techniques like colonoscopy, barium enema, and computed tomography (CT) scans. Changes in haustral appearance provide diagnostic clues for various gastrointestinal conditions.
For instance, a widespread loss of haustral markings can be a sign of chronic inflammatory conditions like ulcerative colitis. In such cases, the colon may appear smooth-walled and cylindrical, sometimes described as having a “lead pipe” appearance, due to changes in the muscular layer. Haustra are also relevant in diverticular disease, where small pouches called diverticula can form in the colon wall, often in areas of weakness. While the presence of diverticula (diverticulosis) is often asymptomatic, their inflammation (diverticulitis) can lead to symptoms and complications.