34.1E: Digestive System: Mouth and Stomach

Animal digestion begins in the mouth, then moves through the throat, into the esophagus, and then into the abdomen and little intestine. The extensive chemical action of digestion begins in the mouthpiece. As food is chewed, saliva, produced by the salivary glands, mixes with the food. Saliva is a watery substance produced in the mouths of many animals. There are three major glands that secrete saliva : the parotid, the submandibular, and the sublingual. Saliva contains mucus that moistens food and buffers the ph of the food. Saliva besides contains immunoglobulins and lysozymes, which have antibacterial action to reduce tooth decay by inhibiting growth of some bacteria. In accession, saliva contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme, lipase, is produced by the cells in the spit. It is a extremity of a class of enzymes that can break down triglycerides. linguistic lipase begins the dislocation of fat components in the food. The chew and wetting action provided by the teeth and saliva shape the food into a mass called the bolus for swallowing. The tongue aids in swallowing by moving the bolus from the mouth into the throat. The throat opens to two passageways : the trachea, which leads to the lungs, and the esophagus, which leads to the stomach. The tracheal open, the glottis, is covered by a cartilaginous flap, the epiglottis. When swallow, the epiglottis closes the glottis, allowing food to pass into the esophagus, not into the trachea, preventing food from reaching the lungs. The oral cavity, or mouthpiece, is the item of entrance of food into the digestive organization. The food is broken into smaller particles by chew, the chewing natural process of the teeth. All mammals have teeth and can chew their food. The esophagus is a tubular electric organ connecting the mouth to the stomach. The chew and softened food passes through the esophagus after being swallowed. The politic muscles of the esophagus undergo a series of curl like movements called peristalsis that push the food toward the abdomen. The peristalsis wave is unidirectional : it moves food from the mouthpiece to the digest ; reverse motion is not possible. The peristaltic campaign of the esophagus is an involuntary reflex, taking place in answer to the act of swallowing.

Stomach

A large partially of digestion occurs in the stomach. The stomach, a bursiform organ, secretes gastric digestive juices. The ph in the stomach is between 1.5 and 2.5. This highly- acidic environment is required for the chemical breakdown of food and the extraction of nutrients. When empty, the stomach is a preferably small organ ; however, it can expand to up to 20 times its resting size when filled with food. This characteristic is particularly utilitarian for animals that need to eat when food is available .
imageFigure \(\PageIndex{1}\): Stomach digestion: The human stomach has an extremely acidic environment where most of the protein gets digested.
The stomach is besides the major site for protein digestion in animals early than ruminants. Protein digestion is mediated in the abdomen chamber by an enzyme called pepsin, which is secreted by the head cells in the stomach in an inactive class called pepsinogen. Another cellular telephone type, parietal cells, secrete hydrogen and chloride ions, which combine in the lumen to form hydrochloric acid, the chief acidic part of the abdomen juices. Hydrochloric acerb helps to convert the inactive pepsinogen to pepsin. The highly-acidic environment besides kills many microorganisms in the food and, combined with the natural process of the enzyme pepsin, results in the hydrolysis of protein in the food. Chemical digestion is facilitated by the churning action of the stomach. compression and liberalization of smooth muscles mixes the stomach contents about every 20 minutes. The partially-digested food and gastric juice assortment is called chyme. Chyme passes from the stomach to the small intestine. Further protein digestion takes plaza in the belittled intestine. Gastric emptying occurs within two to six hours after a meal. lone a modest sum of chyme is released into the humble intestine at a time. The drift of chyme from the digest into the little intestine is regulated by the pyloric sphincter .

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