1. The functions of the digestive system are to digest food and absorb all digested end products (including vitamins and minerals). The physiological processes of the digestive system are ingestion, propulsion, mechanical breakdown, digestion, absorption and defecation. Mechanical digestion involves using force to break down food, such as by chewing or contracting muscles. Chemical digestion occurs when food is broken down chemically into smaller particles, similar to the use of saliva in the mouth.2. The four tissue layers are the mucosa, submucosa, muscularis externa, and serosa. The mucosa is the innermost layer which is also its own layer; the epithelium, lamina propia and muscular mucosa. The mucous membrane secretes hormones, digestive enzymes but also mucus. The submucosa is composed of areolar connective tissue, which contains a rich blood supply, nerve fibers, and lymphatic vessels and follicles. The muscularis externa is the layer responsible for the function of segmentation and peristalsis. It contains an inner circular layer as well as an outer longitudinal layer composed of smooth muscle cells. The serosa is the outermost layer. It is also called visceral peritoneum and is areolar connective tissue covered by mesothelium.3. The enteric nervous system is composed of intrinsic nerve plexuses, submucosal nerve plexuses, and myenteric nerve plexuses. The submucosal nerve plexuses are located in the submucosa. The myenteric nerve plexuses are located between the circular muscle layer and the longitudinal muscle layer. They provide an important nerve supply to the wall of the GI tract and also control the motility of the GI tract.4. Neutral mechanism...... middle of paper ......s in absorption. The lining of the small intestine also has a submucosa, which forms the circular folds, and increases the surface area of ​​the intestines.14. The migratory motor complex (MMC) is described as strong, rhythmic contractions in the small intestine and stomach during the fasting state. Segmentation is described as the rhythmic contraction in the small intestine that allows chyme to mix.15. (NOT APPLICABLE)16. The lining of the colon is composed of a simple columnar epithelium and unlike the lining of the small intestine, it contains neither villi nor plicae circularis. However, it contains crypts.17. Haustral contractions occur at 30 minute intervals, they mix the contents of the intestine back and forth. Mass movements occur 3 to 4 times per day and bring the contents of the large intestine to the rectum for storage..