Food moves through the alimentary canal via peristalsis and segmentation and moves from one organ to another through sphincters.
Peristalsis and segmentation are mechanisms for moving food in the digestive system. Peristalsis is waves of smooth muscle contraction in the walls of the alimentary canal. When the circular muscles contract, the diameter of the lumen decreases and when the longitudinal muscles contract the diameter of the lumen increases. The coordinated efforts of these muscles unidirectionally move digestive substances from one location to another. These movements are strong enough to work against gravity.
Segmentation is the coordinated contraction of circular muscles that moves the partially digested food in a back-and-forth motion. In segmentation, waves of muscle contractions shift directions to mix the contents in a particular location for a longer period of time while digestive processes are occurring. This serves to expose more of the food mixture of partially broken down food, stomach acids, and enzymes called chyme to the absorptive cells in the lumen. Segmentation is common in the small and large intestines. Peristalsis, churning, and segmentation are all generated by contractions of smooth muscles of the muscularis externa layer of the alimentary canal organs.
Peristaltic Movement of Food through the Esophagus
A sphincter is a thick band of circular muscle tissue in the muscularis externa used to regulate food moving from one organ to another. Sphincters are composed of smooth muscle tissue with the exception of the external anal sphincter, which contains skeletal muscle tissue. When the muscle contracts, the tubular opening closes and when it relaxes the sphincter opens the lumen to allow digestive contents to pass through. When waves of peristaltic contractions reach a sphincter, this triggers the sphincter to relax and allow contents through. There are seven sphincters found within the digestive system.
- The upper esophageal sphincter regulates the movement of food from the pharynx to the esophagus.
- The lower esophageal (gastroesophageal) sphincter regulates the movement of food from the esophagus to the stomach.
- The pyloric sphincter separates the stomach from the start of the small intestine.
- The hepatopancreatic sphincter is between the duodenum and the ducts from the gallbladder and pancreas.
- The ileocecal sphincter is between the small and large intestines.
- Internal and external anal sphincters are at the end of the alimentary canal and control defecation.