Chapter 3 The Digestive System 91 food into smaller molecules, allowing nutrients to be absorbed into the small intestine and transported throughout the body by the blood. The activities of chemical digestion and nutrient absorption both occur in the small intestine. The duodenum is the first segment of the small intestine, the jejunum is the middle part, and the ileum is the last—and the longest— segment of the small intestine. The large intestine or colon, is the last section of the digestive system. It absorbs water and electrolytes and eliminates waste. The large intestine is so named because its diameter is wider than that of the small intestine. In comparison, the small intes- tine is much longer than the large intestine but smaller in diameter. The rectum receives waste products (feces) from the sigmoid colon, an S-shaped section of the large intestine, and stores it prior to elimination from the anus. The study of the digestive system is called gastroenterology (GĂS-trō-ĕn-tĕr- ŎL-ō-jē). Even though the medical term gastroenterology literally means “the study of the stomach and intestines,” the term is used to refer to the study of the entire digestive system. A gastroenterologist (GĂS-trō-ĕn-tĕr-ŎL-ō-jĭst) is a physician who specializes in the study and treatment of the digestive system. Anatomy and Physiology Vocabulary Now that you have been introduced to the basic structure and functions of the digestive system, let’s explore in more detail the key terms presented in the introduction. Key Term Defi nition digestive tract (also called alimentary canal or gastrointestinal tract) long, hollow tube that starts at the pharynx and ends at the anus duodenum fi rst part of the small intestine esophagus tubular structure that carries food from the pharynx (throat) to the stomach gastroenterologist physician who specializes in the study and treatment of the digestive system gastroenterology the study of the digestive system ileum fi nal and longest part of the small intestine jejunum middle part of the small intestine large intestine last section of the digestive system, which absorbs water and electrolytes and eliminates waste the colon pharynx the throat rectum last part of the large intestine leading to the anus sigmoid S-shaped section of the large intestine small intestine long, narrow, folded tube that extends from the stomach to the large intestine the site where chemical digestion and absorption of food occur stomach an expandable organ that stores and breaks down food located between the esophagus and small intestine