Gut Structures, Functions and Control of Digestion
The gastrointestinal (GI) tract extends from the mouth to the anus over 7-10 m. It includes the mouth and salivary glands, the oesophagus, the stomach, the small intestine, the pancreas, the liver and the gall bladder, and the colon, rectum and anus (Figure 9.1). Each anatomical site performs a specic set of tasks enabling digestion and/or absorption of food components and nutrients. The wall of the GI tract comprises (inward to outward) the mucosa, either squamous or columnar, the submucosa (connective tissues), the muscularis, smooth muscle bres responsible for waves of contractions, peristalsis and motility along the GI tract, and the serosa, another layer of connective tissues. Glands, blood vessels and nerves are present in the GI tract wall, enabling lubrication, digestion, sensing, control and transport of nutrients.