The submucosa is the layer of tissue directly underneath the lining, or mucosa, of the gut. It contains glands, smooth muscle, nerves, blood and lymphatic vessels. An important network of nerve fibers, known as Meissner’s plexus, is situated within the submucosa. Below the submucosa is a layer known as the muscularis, containing smooth muscle which contracts to propel food along the intestine.
Submucosa is a type of connective tissue, where cells are contained inside a network of fibers and a gel-like background substance. As well as containing arteries and veins, the submucosa holds a number of glands. Within the esophagus, these are goblet cells, which are tiny mucus-secreting glands.
In the duodenum, the part of the intestine leading from the stomach, the glands are known as duodenal or Brunner’s glands. They produce mucus that is alkaline in nature, helping protect the lining of the duodenum against the effects of stomach acid. Their alkaline secretions also mean the gut contents are at a more suitable pH for enzymes from the pancreas to function.
The submucous plexus, a nerve fiber network in the submucosa, is sometimes known as Meissner’s plexus. Together with the myenteric plexus, which is situated in the muscularis, it forms part of what is called the enteric nervous system. The enteric nervous system is extremely important in regulating the function of the gastrointestinal tract.
While it is connected to the central nervous system, or CNS, the enteric nervous system can also act independently, although connections between the two systems are needed for the gut to act normally. Information from the gut can be relayed to the CNS which then sends signals back to modify intestinal function. In turn, stimulation from outside, such as the sight of tasty food, can be transmitted to the gut from the CNS, triggering secretion of intestinal juices.
The myenteric plexus controls the muscle contractions of the gut wall, while the submucous plexus regulates glands and blood vessels. This means that the submucous plexus affects blood circulation in the intestine and the secretion of substances into the gut. It is also involved in the production of hormones by nerve cells and glands, which can then enter the general circulation.
In the autoimmune disease known as scleroderma, there is overgrowth of connective tissue. Fibrous tissue may be deposited in the submucosa, impairing the gut’s ability to move normally. Pain, abdominal bloating, and diarrhea or constipation can result. There is no cure, so treatment is aimed at resolving symptoms. As long as no serious complications occur, patients can lead full and active lives.