![]() ![]() Saliva contains mucus that moistens food and buffers the pH of the food. The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands ( Figure 16.5). All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles. The food is broken into smaller particles by mastication, the chewing action of the teeth. Oral Cavityīoth physical and chemical digestion begin in the mouth or oral cavity, which is the point of entry of food into the digestive system. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces it is stored until it is excreted through the anus.įigure 16.4 The components of the human digestive system are shown. The smaller molecules are absorbed into the blood stream through the epithelial cells lining the walls of the small intestine. Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion. This acidity kills microorganisms, breaks down food tissues, and activates digestive enzymes. The stomach contents are extremely acidic, with a pH between 1.5 and 2.5. Using peristalsis, or wave-like smooth-muscle contractions, the muscles of the esophagus push the food toward the stomach. The food is then swallowed and enters the esophagus-a long tube that connects the mouth to the stomach. The enzymes present in saliva also begin to chemically break down food. The teeth play an important role in masticating (chewing) or physically breaking food into smaller particles. The process of digestion begins in the mouth with the intake of food ( Figure 16.4). The rise in obesity and the resulting diseases like type 2 diabetes makes understanding the role of diet and nutrition in maintaining good health all the more important. Taking in more food energy than is used in activity leads to storage of the excess in the form of fat deposits. One of the challenges in human nutrition is maintaining a balance between food intake, storage, and energy expenditure. This happens by both physical means, such as chewing, and by chemical means. During digestion, food particles are broken down to smaller components, which are later absorbed by the body. The conversion of the food consumed to the nutrients required is a multistep process involving digestion and absorption. Animals must convert these macromolecules into the simple molecules required for maintaining cellular function. However, the food consumed consists of protein, fat, and complex carbohydrates. At the cellular level, the biological molecules necessary for animal function are amino acids, lipid molecules, nucleotides, and simple sugars. While plants can obtain nutrients from their roots and the energy molecules required for cellular function through the process of photosynthesis, animals obtain their nutrients by the consumption of other organisms. Describe how excess carbohydrates and energy are stored in the bodyĪll living organisms need nutrients to survive.Describe the essential nutrients required for cellular function that cannot be synthesized by the animal body.Describe the ways in which organs work together to digest food and absorb nutrients. ![]() Explain the specialized functions of the organs involved in processing food in the body.Explain the processes of digestion and absorption.Learning Objectives By the end of this section, you will be able to: ![]()
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