The stomach releases hydrochloric acid and dash juices which act on food

Gastric secretion The gastric The process of gastric secretion can be divided into three phases (cephalic, gastric, and intestinal) that depend upon the primary The cephalic phase of gastric secretion occurs in response to stimuli received by the senses—that is, The gastric phase is mediated by the vagus nerve and by the release of The intestinal phase is not fully understood, because of a complex stimulatory and inhibitor process. Amino acids and small peptides that promote gastric acid secretion are infused into the circulation, however, at the same time chyme Absorption and emptying Although the stomach absorbs few of the products of digestion, it can absorb many other substances, including The rate of emptying of the stomach depends upon the

When you eat food, the body’s digestive system breaks down dietary protein into individual amino acids, which are absorbed and used by cells to build other proteins and a few other macromolecules, such as DNA. Let’s follow the path that proteins take down the gastrointestinal tract and into the circulatory system. Eggs are a good dietary source of protein and will be used as our example as we discuss the processes of digestion and absorption of protein. One egg, whether raw, hard-boiled, scrambled, or fried, supplies about six grams of protein. In the image below, follow the numbers to see what happens to the protein in our egg at each site of digestion. Fig. 6.17. Protein digestion in the human GI tract. Unless you are eating it raw, the first step in digesting an egg (or any other solid food) is chewing. The teeth begin the mechanical breakdown of large egg pieces into smaller pieces that can be swallowed. The salivary glands secrete saliva to aid swallowing and the passage of the partially mashed egg through the esophagus. The mashed egg pieces enter the stomach from the esophagus. As illustrated in the image below, both mechanical and chemical digestion take place in the stomach. The stomach releases gastric juices containing hydrochloric acid and the enzyme, pepsin, which initiate the chemical digestion of protein. Muscular contractions, called peristalsis, also aid in digestion. The powerful stomach contractions churn the partially digested protein into a more unifor...

• Explain the processes of digestion and absorption • Compare and contrast different types of digestive systems • Explain the specialized functions of the organs involved in processing food in the body • Describe the ways in which organs work together to digest food and absorb nutrients Animals obtain their nutrition from the consumption of other organisms. Depending on their diet, animals can be classified into the following categories: plant eaters (herbivores), meat eaters (carnivores), and those that eat both plants and animals (omnivores). The nutrients and macromolecules present in food are not immediately accessible to the cells. There are a number of processes that modify food within the animal body in order to make the nutrients and organic molecules accessible for cellular function. As animals evolved in complexity of form and function, their digestive systems have also evolved to accommodate their various dietary needs. Herbivores, Omnivores, and Carnivores Herbivores are animals whose primary food source is plant-based. Examples of herbivores, as shown in Figure 15.2 include vertebrates like deer, koalas, and some bird species, as well as invertebrates such as crickets and caterpillars. These animals have evolved digestive systems capable of handling large amounts of plant material. Herbivores can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters). Figure 15.2. Herbivores, lik...