The gastric juice is a semi-transparent and hypotonic liquid compared to the plasma, strongly acid and odorless.
The gastric juice consists of a heterogeneous set of substances, such as water, hydrochloric acid, bicarbonates, mucus, sodium, potassium, intrinsic factor and digestive enzymes such as pepsin, gastric lipase, gelatinase and rennin.
- Hydrochloric acid: it is present in gastric juice in very high concentrations, such as to make the environment particularly acidic (pH 1.5 / 3). Its presence facilitates the action of pepsin, while it hinders the salivary amylase (ptyalin) up to inhibit it. Hydrochloric acid also has a precious antimicrobial effect.
- Mucus and bicarbonate ions: they protect the stomach mucosa from the strong acidity of gastric juices.
- Pepsin: secreted as an inactive precursor, pepsinogen, intervenes in the digestion of proteins. The activation of pepsinogen (or rather of pepsinogens) is entrusted to the hydrogenions (H +) of hydrochloric acid and to the newly formed pepsin.
- Gastric lipase: an enzyme intended for the digestion of food lipids, but which presents a low activity due to the environmental conditions in which it is forced to operate.
- Gelatinase: it is a proteolytic enzyme with action mainly directed to the hydrolysis of gelatin.
- Rennina: typical of infants, it coagulates milk proteins, facilitating the action of pepsin.
- Intrinsic factor: fundamental glycoprotein for the correct absorption of vitamin B12, which occurs in the final part of the small intestine (called the ileum).
The chemical work of gastric juice is facilitated by the contractile activity of the muscular stomach of the stomach, which causes a continuous mixing of the ingested food, promoting the action of enzymes.
The various components of gastric juice are not secreted all together, but their synthesis is entrusted to specialized cells:
- the main or peptic cells are deputed to the secretion of pepsinogen and gastric lipase;
- the parietal cells (ossintiche) secrete hydrochloric acid and intrinsic factor;
- the mucous cells of the collar secrete mucin (the most important mucus protein) and bicarbonate.
When the concentration of hydrochloric acid in gastric juices is low or even absent (hypochloridria / achlorhydria), the body is subject to an increased risk of infections of the gastro-intestinal tract; often there is also a lack of vitamin B12, due to a lack of intrinsic factor secretion, and the onset of dyspepsia (difficult digestion), with symptoms similar to those caused by reflux disease.
When, on the other hand, gastric juices are excessively acidic, as occurs in Zollinger-Ellison syndrome, the defenses of the gastric mucosa can be overwhelmed, with the appearance of gastric ulcers. The same result can also be obtained in perfectly healthy patients, with normal acidity of the gastric juice, but who make extensive use of some non-steroidal anti-inflammatory drugs (such as aspirin, ketoprofen, indomethacin and piroxicam). These medicines, in fact, decrease the natural defenses of the stomach against gastric juices, increasing the susceptibility to gastrolesive phenomena.
