How is the duodenum protected from stomach acids?
The duodenum, being the first part of the small intestine, is directly connected to the stomach and is exposed to the acidic gastric juices that aid in digestion. To protect itself from the harmful effects of these acidic conditions, the duodenum has several defence mechanisms:
1. Epithelial Barrier:
- The innermost layer of the duodenal wall consists of a specialised epithelial cell lining. These cells form tight junctions, creating a physical barrier that prevents the backflow of acidic gastric contents into the duodenum.
2. Mucous Layer:
- Goblet cells in the duodenal epithelium secrete a thick, alkaline mucus that lines the intestinal lumen. This mucus layer acts as a protective barrier, neutralising stomach acids and preventing direct contact with the duodenal cells.
3. Bicarbonate Secretion:
- The pancreas, a vital digestive organ closely associated with the duodenum, plays a crucial role in protecting it from acidity. The pancreas secretes a fluid rich in bicarbonate ions (HCO3-) into the duodenum. Bicarbonate acts as an alkali, neutralising the acidic chyme (partially digested food mixed with gastric juices) as it enters the small intestine.
4. Secretin Hormone:
- The presence of acidic chyme in the duodenum stimulates the release of the hormone secretin from specialised cells in the duodenal wall. Secretin promotes the pancreas to increase its bicarbonate secretion, further enhancing the neutralisation of stomach acids.
5. Enteric Nervous System:
- The duodenum's enteric nervous system (part of the autonomic nervous system) plays a role in coordinating protective reflexes. When exposed to acidic conditions, the duodenum can initiate local muscle contractions that slow down the movement of chyme, allowing more time for neutralisation.
6. Prostaglandins:
- The duodenal mucosa produces prostaglandins, hormone-like substances that have various protective functions. They help maintain blood flow to the duodenal lining and stimulate the production of mucus and bicarbonate.
These mechanisms work together to create a protective environment in the duodenum, allowing it to withstand the acidic chyme from the stomach and continue its crucial role in the digestion and absorption of nutrients.