Description of the digestive system
We welcome suggested improvements to any of our articles. The pharynx is responsible for the passing of masses of chewed food from the mouth to the esophagus. But some animals — including seahorses, lungfishes and platypuses — have no stomach. The intestinal phase is not fully understood, because of a complex stimulatory and inhibitor process. I wanted to give you basic information so that you might make choices without having to spend hours digging through information. When you do eat, the saliva breaks down the chemicals in the food a bit, which helps make the food mushy and easy to swallow. Little digestion of food actually takes place in the mouth.
The secretion of gastric acid is an important inhibitor of gastrin release. If the pH of the antral contents falls below 2. Some of the hormones that are released from the small intestine by products of digestion especially fat , in particular glucagon and secretin, also suppress acid secretion.
Although the stomach absorbs few of the products of digestion, it can absorb many other substances, including glucose and other simple sugars, amino acids, and some fat-soluble substances. The pH of the gastric contents determines whether some substances are absorbed.
At a low pH, for example, the environment is acidic and aspirin is absorbed from the stomach almost as rapidly as water, but, as the pH of the stomach rises and the environment becomes more basic, aspirin is absorbed more slowly. Water moves freely from the gastric contents across the gastric mucosa into the blood. The net absorption of water from the stomach is small, however, because water moves just as easily from the blood across the gastric mucosa to the lumen of the stomach.
The absorption of water and alcohol can be slowed if the stomach contains foodstuffs and especially fats, probably because gastric emptying is delayed by fats, and most water in any situation is absorbed from the small intestine.
The rate of emptying of the stomach depends upon the physical and chemical composition of the meal. Fluids empty more rapidly than solids, carbohydrates more rapidly than proteins, and proteins more rapidly than fats.
When food particles are sufficiently reduced in size and are nearly soluble and when receptors in the duodenal bulb the area of attachment between the duodenum and the stomach have a fluidity and a hydrogen ion concentration of a certain level, the duodenal bulb and the second part of the duodenum relax, allowing emptying of the stomach to start.
During a duodenal contraction, the pressure in the duodenal bulb rises higher than that in the antrum. The pylorus prevents reflux into the stomach by shutting. The vagus nerve has an important role in the control of emptying, but there is some indication that the sympathetic division of the autonomic nervous system is also involved. Several of the peptide hormones of the digestive tract also have an effect on intragastric pressure and gastric movements, but their role in physiological circumstances is unclear.
The small intestine is the principal organ of the digestive tract. The primary functions of the small intestine are mixing and transporting of intraluminal contents, production of enzymes and other constituents essential for digestion, and absorption of nutrients.
Most of the processes that solubilize carbohydrates, proteins, and fats and reduce them to relatively simple organic compounds occur in the small intestine. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Your contribution may be further edited by our staff, and its publication is subject to our final approval. Unfortunately, our editorial approach may not be able to accommodate all contributions.
Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. Gastric secretion The gastric mucosa secretes 1. Absorption and emptying Although the stomach absorbs few of the products of digestion, it can absorb many other substances, including glucose and other simple sugars, amino acids, and some fat-soluble substances.
Small intestine The small intestine is the principal organ of the digestive tract. Previous page Gastric mucosa. Page 8 of Learn More in these related Britannica articles: A number of alterations, often causing more or less distress, occur in the physical condition and functions of the gastrointestinal tract during pregnancy.
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Everyone has intestinal gas, which can lead to uncomfortable bloating and even pain.