As food passes through the digestive tract, digestion occurs in the order of ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation. In terms of the process that operates the steps of digestion, the human body performs four vital functions known as motility, digestion, absorption and secretion. As the mouth digests food, it chews and mixes with a chemical of carbohydrates. After that the food moves to the pharynx, and makes it into lipids. The pharynx takes food from the oral cavity and moves it to the esophagus. The stomach mixes and churns food with gastric acids from the chyme, and it begins to break down the proteins. The stomach also absorbs fat-soluble substances like alcohol and aspirin. In the small intestine it pushes food slow enough where it can digest and absorb. Carbohydrates, proteins, lipids, and nucleic acids, along with vitamins are being absorbed by the small intestine. The large intestine further breaks down the food and their residues. The access water, electrolytes, adn vitamins are also benign taken out by the large intestine. It pushes the rest of the food towards the rectum and eliminates the feces. The mucosa layer, is the innermost layer, and functions in absorption and secretion.it is composed of epithelium cells and a thin connective tissue.