Sfinktern

Sfinktern, the Swedish term for sphincter, denotes a circular muscle that constricts a tubular passage or orifice in the body. Sphincters regulate the opening and closing of passages, contribute to pressure maintenance, and coordinate with organ function. They can be composed of smooth muscle (involuntary) or skeletal muscle (voluntary) depending on location.

Key examples include the lower esophageal sphincter (LES) at the gastroesophageal junction, the pyloric sphincter between stomach and duodenum, and the ileocecal sphincter between ileum and colon. The internal anal sphincter is a smooth-muscle sphincter that maintains continence at rest, while the external anal sphincter is a skeletal-muscle sphincter under voluntary control. Other sphincters include the urethral sphincters (internal and external) and the pupillary sphincter in the eye (sphincter pupillae) that constricts the pupil. Additional sphincters exist around the lips (orbicularis oris) and other orifices.

Physiology and control: Sphincters respond to neural input from the autonomic nervous system and, for skeletal muscles, somatic motor pathways. They maintain baseline tone and relax at appropriate times to permit passage, aided by peristalsis or secretions.

Clinical relevance: Sphincter dysfunction can lead to incontinence (fecal or urinary), obstruction, or reflux. Treatments include pelvic floor rehabilitation, surgical reconstruction (sphincteroplasty), artificial bowel or urinary sphincters, and devices like sacral nerve stimulation. Understanding sphincter function is essential in gastroenterology, urology, and neurology.