The gastrointestinal tract is susceptible to various disorders. If the lower esophageal sphincter is damaged, stomach acid can flow back into the esophagus, causing irritation and inflammation of the lining. This condition is called gastroesophageal reflux disease (known as heartburn) and may cause chest pain and difficulty swallowing. In the stomach, prolonged use of nonsteroidal anti-inflammatory drugs like aspirin, chronic alcohol consumption, bacterial infections such as Helicobacter...

Carbohydrate digestion and metabolism break down simple and complex carbohydrates from food into saccharides (i.e., sugars) for the body to use as energy. Carbohydrate digestion starts in the mouth during mastication, or chewing. The masticated carbohydrates remain intact in the stomach. Digestion resumes in the duodenum of the small intestine, where pancreatic alpha-amylase and brush border enzymes of the microvilli convert complex carbohydrates to monosaccharides. Finally, the monosaccharides...

The human body contains a monogastric digestive system. In a monogastric digestive system, the stomach only contains one chamber in which it digests food. Several other animal species also have monogastric digestive systems, including pigs, horses, dogs, and birds. This chapter, however, focuses on the human digestive system.

Intrinsically disordered proteins are a group of proteins that do not fold into specific three-dimensional structures. Their structural flexibility allows them to complement ordered proteins to perform functions that are inaccessible to rigid structures. They are more common in eukaryotes than prokaryotes and may either be exclusively intrinsically disordered or hybrid proteins, consisting of a mix of ordered and disordered regions. The absence of a rigid structure in these proteins can be...

Lipids are large molecules that are generally not water-soluble. Since most of the digestive enzymes in the human body are water-based, there are specific steps the body must take to break down lipids and make them available for use.

Protein digestion begins in the stomach, where the highly acidic environment can easily disrupt protein structure by exposing the peptide bonds of polypeptide chains. After polypeptide chains are broken into individual amino acids by a series of digestive enzymes, the amino acids are transported to the liver via the bloodstream to produce energy.