Of course, this is not true. An important function of the stomach is to serve as a temporary holding chamber. You can ingest a meal far more quickly than it can be digested and absorbed by the small intestine. Thus, the stomach holds food and parses only small amounts into the small intestine at a time. Foods are not processed in the order they are eaten; rather, they are mixed together with digestive juices in the stomach until they are converted into chyme, which is released into the small intestine.
As you will see in the sections that follow, the stomach plays several important roles in chemical digestion, including the continued digestion of carbohydrates and the initial digestion of proteins and triglycerides.
Little if any nutrient absorption occurs in the stomach, with the exception of the negligible amount of nutrients in alcohol. There are four main regions in the stomach : the cardia, fundus, body, and pylorus. The cardia or cardiac region is the point where the esophagus connects to the stomach and through which food passes into the stomach. Located inferior to the diaphragm, above and to the left of the cardia, is the dome-shaped fundus.
Below the fundus is the body , the main part of the stomach. The funnel-shaped pylorus connects the stomach to the duodenum. The wider end of the funnel, the pyloric antrum , connects to the body of the stomach. The narrower end is called the pyloric canal , which connects to the duodenum.
The smooth muscle pyloric sphincter is located at this latter point of connection and controls stomach emptying. In the absence of food, the stomach deflates inward, and its mucosa and submucosa fall into a large fold called a ruga. Figure 1. The stomach has four major regions: the cardia, fundus, body, and pylorus.
The addition of an inner oblique smooth muscle layer gives the muscularis the ability to vigorously churn and mix food. The convex lateral surface of the stomach is called the greater curvature; the concave medial border is the lesser curvature.
The stomach is held in place by the lesser omentum, which extends from the liver to the lesser curvature, and the greater omentum, which runs from the greater curvature to the posterior abdominal wall. The wall of the stomach is made of the same four layers as most of the rest of the alimentary canal, but with adaptations to the mucosa and muscularis for the unique functions of this organ.
In addition to the typical circular and longitudinal smooth muscle layers, the muscularis has an inner oblique smooth muscle layer.
As a result, in addition to moving food through the canal, the stomach can vigorously churn food, mechanically breaking it down into smaller particles. Figure 2. The stomach wall is adapted for the functions of the stomach. In the epithelium, gastric pits lead to gastric glands that secrete gastric juice.
The gastric glands one gland is shown enlarged on the right contain different types of cells that secrete a variety of enzymes, including hydrochloride acid, which activates the protein-digesting enzyme pepsin.
A vast number of gastric pits dot the surface of the epithelium, giving it the appearance of a well-used pincushion, and mark the entry to each gastric gland , which secretes a complex digestive fluid referred to as gastric juice.
Although the walls of the gastric pits are made up primarily of mucus cells, the gastric glands are made up of different types of cells. The glands of the cardia and pylorus are composed primarily of mucus-secreting cells. Cells that make up the pyloric antrum secrete mucus and a number of hormones, including the majority of the stimulatory hormone, gastrin.
The much larger glands of the fundus and body of the stomach, the site of most chemical digestion, produce most of the gastric secretions. These glands are made up of a variety of secretory cells. These include parietal cells, chief cells, mucous neck cells, and enteroendocrine cells. The secretion of gastric juice is controlled by both nerves and hormones. Stimuli in the brain, stomach, and small intestine activate or inhibit gastric juice production.
This is why the three phases of gastric secretion are called the cephalic, gastric, and intestinal phases. However, once gastric secretion begins, all three phases can occur simultaneously. Figure 3. Gastric secretion occurs in three phases: cephalic, gastric, and intestinal.
During each phase, the secretion of gastric juice can be stimulated or inhibited. The cephalic phase reflex phase of gastric secretion, which is relatively brief, takes place before food enters the stomach. The smell, taste, sight, or thought of food triggers this phase. For example, when you bring a piece of sushi to your lips, impulses from receptors in your taste buds or the nose are relayed to your brain, which returns signals that increase gastric secretion to prepare your stomach for digestion.
The rugae enlarge because of an overgrowth of mucous cells in the stomach wall. In a normal stomach, mucous cells in the rugae release protein-containing mucus. The mucous cells in enlarged rugae release too much mucus, causing proteins to leak from the blood into the stomach.
This shortage of protein in the blood is known as hypoproteinemia. Growth factors are proteins in the body that tell cells what to do, such as grow larger, change shape, or divide to make more cells. In these cases, treatment for H. CMV is one of the herpes viruses. This group of viruses includes the herpes simplex viruses, which cause chickenpox, shingles, and infectious mononucleosis, also known as mono. Most healthy children and adults infected with CMV have no symptoms and may not even know they have an infection.
However, in people with a weakened immune system, CMV can cause serious disease, such as retinitis, which can lead to blindness. Researchers are not sure how H. The disease is more common in men than in women. The average age at diagnosis is The abdomen is the area between the chest and hips.
A health care provider also may order blood tests to check for infection with H. Medical and family history. He or she will ask the patient to provide a medical and family history. Physical exam. During a physical exam, a health care provider usually. CT scan. CT scans use a combination of x rays and computer technology to create images. There are differences in the distribution of these cell types among regions of the stomach - for example, parietal cells are abundant in the glands of the body, but virtually absent in pyloric glands.
The micrograph to the right shows a gastric pit invaginating into the mucosa fundic region of a raccoon stomach. Notice that all the surface cells and the cells in the neck of the pit are foamy in appearance - these are the mucous cells. The other cell types are farther down in the pit and, in this image, difficult to distinguish.
Here's an interesting piece of trivia about the stomach: the platypus does not have one. In this strange mammal, the distal esophagus is dilated, but the platypus does not have a glandular stomach. Stomach: Introduction and Index.
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