Acidic Secretion
A corrosive biological fluid that digests proteins and protects against pathogens.
Gastric acid, also known as stomach acid, is the acidic component – hydrochloric acid – of gastric juice. It is produced by parietal cells in the gastric glands of the stomach lining. In humans, the pH is between one and three, much lower than most other animals, but is very similar to that of carrion-eating carnivores that need protection from ingesting pathogens. With this higher acidity, gastric acid plays a key protective role against pathogens. It is also key in the digestion of proteins by activating digestive enzymes, which together break down the long chains of amino acids.
- Nature
- Corrosive Enzymatic Fluid
- Function
- Breaching Barriers & Combat Dissolution
Lore & Background
Gastric acid 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 level is maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide. The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH of between 1 and 3. There is a small continuous basal secretion of gastric acid between meals of usually less than 10 mEq/hour. A typical adult human stomach will secrete about 1.5 liters of gastric juice daily.
In Their Own Story
The secretion of gastric acid is produced in several steps. Chloride and hydrogen ions are secreted separately from the cytoplasm of parietal cells and mixed in the canaliculi. This creates a negative potential of between −40 and −70 mV across the parietal cell membrane that causes potassium ions and a small number of sodium ions to diffuse from the cytoplasm into the parietal cell canaliculi. The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water to form carbonic acid. This acid immediately dissociates into hydrogen and bicarbonate ions. The hydrogen ions leave the cell through H+/K+ ATPase antiporter pumps. At the same time, sodium ions are actively reabsorbed. This means that the majority of secreted K+ and Na+ ions return to the cytoplasm. In the canaliculus, secreted hydrogen and chloride ions mix and are secreted into the lumen of the oxyntic gland.
Reader's Guide
Gastric acid production is regulated by both the autonomic nervous system and several hormones. The parasympathetic nervous system, via the vagus nerve, and the hormone gastrin stimulate the parietal cell to produce gastric acid, both directly acting on parietal cells and indirectly, through the stimulation of the secretion of the hormone histamine from enterochromaffin-like cells (ECLs). Vasoactive intestinal peptide, cholecystokinin, and secretin all inhibit production. Four types of cells are involved in this process: parietal cells, G cells, D cells and enterochromaffin-like cells. The release of histamine is the most important positive regulation mechanism of the secretion of gastric acid in the stomach. Its release is stimulated by gastrin and acetylcholine and inhibited by somatostatin. In the duodenum, gastric acid is neutralized by bicarbonate. The secretion of bicarbonate from the pancreas is stimulated by secretin. This polypeptide hormone gets activated and secreted from so-called S cells in the mucosa of the duodenum and jejunum when the pH in the duodenum falls below 4.5 to 5.0.
Did You Know?
- The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi, about 3 million times that of arterial blood.
- The lowest pH of the secreted acid is 0.8, but it is diluted in the stomach lumen to a pH of between 1 and 3.
- A typical adult human stomach will secrete about 1.5 liters of gastric juice daily.
- The role of gastric acid in digestion was established in the 1820s and 1830s by William Beaumont on Alexis St. Martin, who had a fistula in his stomach.
- The release of histamine is the most important positive regulation mechanism of the secretion of gastric acid in the stomach.
Frequently Asked Questions
What exactly is Acidic Secretion?
This corrosive biological fluid is produced by Parasites to digest organic matter and breach physical barriers.
Which characters utilize this ability?
All members of the alien species possess this trait, but Migi frequently employs it during combat scenarios for defense.
How does it affect human tissue upon contact?
The enzymatic fluid rapidly dissolves proteins and flesh, causing severe burns that can be fatal without immediate medical intervention.
Is this substance similar to human stomach acid?
While both are acidic, the Parasite's secretion is far more potent and acts instantly outside of a digestive system environment.
What role does it play in their survival strategy?
It serves as a primary tool for consuming hosts and escaping confinement by melting through solid objects like concrete or steel.
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