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| Name | Stomach (आमाशय) | Gastric Glands | Biology | Small Intestine and Dudenum | ग्रहणी और छोटी आंत |
| Video Uploader | Video From Random stuff study |
| Upload Date | This Video Uploaded At 25-02-2021 16:14:09 |
| Video Discription | Stomach (आमाशय) | Gastric Glands | Biology | Small Intestine and Dudenum | ग्रहणी और छोटी आंत #Digestion #ChemicalAndMechanicalDigestionInStomach #ExplainDigestionInStomach Digestion in the Stomach The stomach, which is located just below the diaphragm, stores food and begins digestion of proteins. With accordion like folds and a very elastic wall, this organ can stretch to accommodate about 2 L of food and fluid. The stomach secretes a digestive fluid called gastric juice and mixes it with the food through a churning action. This mixture of ingested food and gastric juice is called chyme. Chemical Digestion in the Stomach Two components of gastric juice carry out chemical digestion. One is hydrochloric acid (HCl), which disrupts the extracellular matrix that binds cells together in meat and plant material. The concentration of HCl is so high that the pH of gastric juice is about 2, acidic enough to dissolve iron nails (and to kill most bacteria). This low pH denatures (unfolds) proteins in food, increasing exposure of their peptide bonds. The exposed bonds are attacked by the second component of gastric juice—a protease, or protein-digesting enzyme, called pepsin. Unlike most enzymes, pepsin works best in a very acidic environment. By breaking peptide bonds, it cleaves proteins into smaller polypeptides. Further digestion to individual amino acids occurs in the small intestine. Why doesn’t gastric juice destroy the stomach cells that make it? The answer is that the ingredients of gastric juice are kept inactive until they are released into the lumen (cavity) of the stomach. The components of gastric juice are produced by two types of cells in the gastric glands of the stomach. Parietal cells use an ATP-driven pump to expel hydrogen ions into the lumen. At the same time, chloride ions diffuse into the lumen through specific membrane channels of the parietal cells. It is therefore only within the lumen that hydrogen and chloride ions combine to form HCl. Meanwhile, chief cells release pepsin into the lumen in an inactive form called pepsinogen. HCl converts pepsinogen to active pepsin by clipping off a small portion of the molecule and exposing its active site. Through these processes, both HCl and pepsin form in the lumen of the stomach, not within the cells of the gastric glands. After hydrochloric acid converts a small amount of pepsinogen to pepsin, pepsin itself helps activate the remaining pepsinogen. Pepsin, like HCl, can clip pepsinogen to expose the enzyme’s active site. This generates more pepsin, which activates more pepsinogen. This series of events is an example of positive feedback (see Concept 40.2). Why don’t HCl and pepsin eat through the lining of the stomach? For one thing, mucus secreted by cells in gastric glands protects against self-digestion (see Figure 41.11). In addition, cell division adds a new epithelial layer every three days, replacing cells before they are fully eroded by digestive juices. Under certain circumstances, however, damaged areas of the stomach lining called gastric ulcers can appear. It had been thought that they were caused by psychological stress and resulting excess acid secretion. However, Australian researchers Barry Marshall and Robin Warren discovered that infection by the acid-tolerant bacterium Helicobacter pylori causes ulcers. They also demonstrated that an antibiotic could cure most gastric ulcers. For these findings, they were awarded the Nobel Prize in 2005. Stomach Dynamics Chemical digestion by gastric juice is facilitated by the churning action of the stomach. This coordinated series of muscle contractions and relaxations mixes the stomach contents about every 20 seconds. As a result of mixing and enzyme action, what begins as a recently swallowed meal becomes the acidic, nutrient-rich broth known as chyme. Stomach (आमाशय), Gastric Glands, Enzymes, jatar Biology in hindi, pachan tantra in Hindi, digestive system Related Question Answer, science classes, ntpc science, small intestine, intestine in hindi, Stomach (आमाशय), Gastric Glands, Enzymes, jatar granti, aamasahay, Biology in hindi, pachan tantra in Hindi, digestive system Related Question Answer, study 91 science classes, ntpc science, biology classes |
| Category | Education |
| Tags | Stomach (आमाशय) | Gastric Glands | Enzymes | Biology in hindi | pachan tantra in Hindi | digestive system Related Question Answer | ncrt science classes | small intestine in hindi | jatar granti | aamasahay |
