what is the function of the hydrochloric acid produced by the gastic
Answers
Hydrochloric acid (HCl), another component of the gastric juice, plays a crucial role in creating the pH required for pepsin activity. Parietal cells produce HCl by secreting hydrogen and chloride ions. When pepsinogen and hydrochloric acid exist together in the gastric juice, pepsin takes its active form.
Answer:
Stomach Acid
Gastric acid is a colourless, watery, acidic, digestive fluid produced in the stomach. It is one of the main solutions secreted, together with several enzymes and intrinsic factors. In chemical terms, it is an acid solution with a pH of 1 to 2 in the stomach lumen, consisting mainly of hydrochloric acid (HCl) (around 0.5%, or 5000 parts per million), and large quantities of potassium chloride (KCl) and sodium chloride (NaCl).
Physiology
Gastric acid is produced by parietal cells (also called oxyntic cells) in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the gastric acid is secreted into the lumen of the stomach. These cells are part of epithelial fundic glands in the gastric mucosa. The pH of gastric acid is 1 to 2 in the human stomach lumen, the acidity being maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the blood stream in the process, which causes a temporary rise of pH in the blood, known as alkaline tide.
The resulting highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein’s peptide bonds. The chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and renin).Gastric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment, which is helpful to prevent infection.
Secretion
Gastric acid secretion happens in several steps. Chloride and hydrogen ions are secreted separately from the cytoplasm of parietal cells and mixed in the canaliculi. Gastric acid is then secreted into the lumen of the oxyntic gland and gradually reaches the main stomach lumen.
Chloride and sodium ions are secreted actively from the cytoplasm of the parietal cell into the lumen of the canaliculus. This creates a negative potential of -40 mV to -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. Carbonic anhydrase is a zinc dependent enzyme.
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.
There are three phases in the secretion of gastric acid:
1. The cephalic phase: Thirty percent of the total gastric acid to be produced is stimulated by anticipation of eating and the smell or taste of food.
2. The gastric phase: Sixty percent of the acid secreted is stimulated by the distention of the stomach with food. Plus, digestion produces proteins, which causes even more gastrin production.
3. The intestinal phase: The remaining 10% of acid is secreted when chyme enters the small intestine, and is stimulated by small intestine distention.