ändtarmskanalen

The ändtarmskanalen, also known as the anal canal, is the terminal part of the large intestine, extending from the rectum to the anus. It is a short passage, typically measuring around 3 to 4 centimeters in length in adults. The primary function of the anal canal is to control the expulsion of feces from the body.

The lining of the anal canal consists of several structures. At its upper end, it is lined with mucous membrane containing longitudinal folds called anal columns. These columns contain arteries and veins, and their inflammation can lead to conditions like hemorrhoids. Between the anal columns are small pouches called anal crypts, which secrete mucus to aid in lubrication.

The lower part of the anal canal is lined with stratified squamous epithelium, which is more resistant to friction. Surrounding the anal canal are two sphincter muscles: the internal anal sphincter, which is involuntary, and the external anal sphincter, which is voluntary. These muscles work together to maintain continence, preventing involuntary defecation.

The external anal sphincter is a crucial component for voluntary bowel control. When the rectum is distended with feces, sensory receptors trigger a reflex that relaxes the internal anal sphincter. At an appropriate time and place, conscious relaxation of the external anal sphincter allows for defecation. The anal canal is rich in nerve endings, contributing to the sensation of needing to defecate and the control of bowel movements.