|
The stomach is often considered the most intrinsic, and distensible, portion of the entire gastrointestinal tract. Found in the upper left quarter of the abdominal region, the stomach is positioned immediately under the diaphragm. When the stomach is empty, it resembles the letter J, and it connects with the esophagus and empties directly into the duodenal region of the small intestine. The stomach more or less holds food, continuously churning it and mixing it with digestive enzymes. This ultimately creates a chime, which is pasty and one step closer to the molecular form that food must present before the body can ultimately utilize it. It is the chime that enters the small intestine.
The stomach can be divided into four basic segments. Just under the esophagus, where the stomach meets the exit of the gullet, one can identify the cardia. It is narrow, and is the intake portion for the bolus.
The second segment is in the shape of dome and makes direct contact with the diaphragm, just off to its left. This is known as the fundus. The body is the larger section, discernable by its size and its central position.
The terminal end of the stomach is known as the pylorus. It is discerned by its funnel shape. Modified circular muscle tissue helps to create the pyloric sphincter, the obvious connection between the stomach and the small intestine. Pylorus is actually a Greek term meaning, “Gatekeeper,” which a perfect description for this end of the stomach. The sphincter not only permits the chime to enter the small intestine, but it is also designed to deter regurgitation back into the stomach.
The stomach is designed of two surfaces and ultimately two borders. The anterior and the posterior surfaces are broad and rounded. The border with the slighter curvature is known as the medial concave border while the border with the more distinctive curvature is known as the lateral convex border. Between the lesser curvature and the liver is the lesser omentum, while the greater curvature has the greater omentum attached directly to it.
Just like elsewhere in the gastrointestinal tract, the wall of the stomach is comprised of the basic four tunics. There are however, two very basic modifications in the stomach. In the tunic layer the muscularis, there is an additional oblique layer of muscle tissue. The mucosa layer is in the midst of numerous lengthwise folds. This is so that the folds (known as gastric folds or alternatively gastric rugae) can allow the stomach to distend. The mucosa additionally is covered with microscopic gastric pits and microscopic gastric glands. The gastric glands contain several different cells, each responsible for the secretion of various substances.
Mucous, for the task of protection, is secreted by the goblet cells. Hydrochloric acid is secreted by the parietal cells. Pepsinogen is secreted by the principle, or chief cells. Pepsinogen is very similar to the substance known as pepsin however, pepsin is an active enzyme digestive substance while pepsinogen is now. Autocrine regulators, serotonin, and histamine are all secreted by the argentaffin cells. Gastrin, a hormone that is released into the bloodstream, is secreted by endocrine cells. While it is unclear but potentially determined that the parietal cells likely secrete another substance known as polypeptide. This is an intrinsic factor required by the small intestine to help with the absorption of Vitamin B-12.
When the stomach is empty, there is a direct sensation sent to the body known as hunger pangs, which results from continuous gastric activity without substances to dissolve and churn. Gastric regulation is autonomic, and when the stomach is once again satiated, the hunger pangs are replaced with the sensation of fullness.
The vagus nerves supply the parasympathetic neurons to the stomach while the sympathetic neurons are supplied by the celiac plexus. The myeneteric plexus and the submucosal plexus (located in the muscular layers and the submucosa, respectively) are the sites of synapse for the parasympathetic neurons.
When the stomach requires quick, efficient emptying, the body will vomit. Vomiting is a reflexive action that empties the stomach contents through the esophagus, up through the pharynx, and then out into the oral cavity. This is the body’s natural defense against poisonous or dangerous toxins, or a reaction to an infection or viral illness. The medulla oblongata controls the process of vomiting. Stimulation within the gastrointestinal tract and most often the duodenum, as well as visual, psychological, odiferous stimulation, as well as motion stimulation can all trigger the process of vomiting. There are also synthetic stimulations available to intentionally stimulating the vomiting reflex, such as emetics.
Vomiting follows a very intensive mechanically oriented routine. Contractions begin in the upper segment of the small intestine. These contractions are long, strong, and sustained. The pyloric sphincter then contracts, followed by a relaxation of the lower esophageal sphincter. The pyloric section of the stomach also contracts. The stomach is literally compressed against the liver by the abdominal muscle, causing the glottis to close. As the stomach is compressed with the alternate muscle contracting, a forceful ejection of the stomach contents is likely to erupt. The sensation of nausea triggered by various elements does not guarantee vomiting, but can be a precursor to it.
|