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The secretions of the different exocrine gastric gland cells produce a watery, acidic fluid into the stomach lumen called gastric juice. [5] [6] Gastric juice contains water, hydrochloric acid, intrinsic factor, pepsinogen, and salts. Adults produce around two to three litres of gastric juice per day. [5]
Every day, seven liters of fluid are secreted by the digestive system. This fluid is composed of four primary components: ions, digestive enzymes, mucus, and bile. About half of these fluids are secreted by the salivary glands, pancreas, and liver, which compose the accessory organs and glands of the digestive system.
The secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, a level maintained by the proton pump H + /K + ATPase. [1]
The pH of the secreted fluid can fall by 0.8. Gastrin primarily induces acid-secretion indirectly, increasing histamine synthesis in ECL cells, which in turn signal parietal cells via histamine release and H 2 stimulation. [6] Gastrin itself has no effect on the maximum histamine-stimulated gastric acid secretion. [7]
The churning motion of the stomach was described among other findings. [53] In the 19th century, it was accepted that chemical processes were involved in the process of digestion. Physiological research into secretion and the gastrointestinal tract was pursued with experiments undertaken by Claude Bernard, Rudolph Heidenhain and Ivan Pavlov.
A fourth phase of acid secretion is known as the basal state which occurs in the times between meals (interdigestive phase). The level of acid secretion during these times is regulated by body weight, individual, number of parietal cells, and time of day. Acid secretion is lowest in the morning before awakening and highest at night. [2]
The enzymes that are secreted in the stomach are gastric enzymes. The stomach plays a major role in digestion, both in a mechanical sense by mixing and crushing the food, and also in an enzymatic sense, by digesting it. The following are enzymes produced by the stomach and their respective function: Pepsin is the main gastric enzyme.
Secretion of the hormone glucose-dependent insulinotropic peptide, which stimulates the release of insulin M cells: Intestinal glands of duodenum and jejunum: Secretion of the hormone motilin, which accelerates gastric emptying, stimulates intestinal peristalsis, and stimulates the production of pepsin S cells: Intestinal glands