Magensekretion

Magensekretion, or gastric secretion, is the process by which the stomach lining releases gastric juice into the lumen. The juice is a digestive fluid that normally contains water, electrolytes, mucus, hydrochloric acid, the enzyme precursor pepsinogen, and, in many individuals, intrinsic factor required for vitamin B12 absorption.

The secretion is produced by several gastric mucosal cell types. Parietal cells secrete hydrochloric acid and intrinsic factor; chief cells release pepsinogen; surface mucous cells produce protective mucus enriched with bicarbonate; G cells secrete gastrin; ECL cells release histamine; D cells secrete somatostatin to regulate the process. The combination of acid and enzymes in the juice enables protein digestion and helps create an antimicrobial environment in the stomach.

Control and phases: Secretion is orchestrated through three interacting phases: cephalic, gastric, and intestinal. The cephalic phase is triggered by the sight, smell, or thought of food and is mainly mediated by vagal stimulation. The gastric phase is stimulated by stomach distension and amino acids, promoting gastrin release which increases acid and pepsinogen secretion. The intestinal phase provides feedback from the duodenum, with hormones and neural signals that can dampen further secretion. Overall, neural (mainly parasympathetic) and hormonal signals, including gastrin and histamine, promote secretion, while somatostatin and prostaglandins help limit it.

Physiology and clinical relevance: In a healthy adult, gastric juice is produced continuously at low levels and increases after meals; the total daily volume varies but typically reaches up to a couple of liters. The gastric juice is highly acidic, with a pH roughly between 1.5 and 3.5, maintained by the mucosal barrier and regulated acid production. Disorders can include hypo- or hyperchlorhydria, gastritis, peptic ulcers, and vitamin B12 deficiency if intrinsic factor production declines. Tests of gastric secretion assess basal and stimulated acid output for diagnosis.