1. How does the food change in consistency and form?
Food is first masticated into smaller particles in the mouth by the teeth and turns into bolus, which is a semi-solid food mass, with the help of saliva. The stomach then mixes it with saliva and gastric juice to form the semifluid chyme. The small intestine further breaks the chyme down using brush border enzymes and pancreatic juice. At this point, about 90% of the water and nutrient has been absorbed. The remnants will be dried out by the large intestine by absorbing water, after which the residue along with bacteria and other wastes are ejected out as the generally solid feces.
2. How could the body absorb the nutrients from the foods we eat?
For the body to absorb nutrients from the food, the food has to be broken down which starts from the mouth. It goes through chemical and mechanical breakdown. In mechanical breakdown, food is grinded and cut by our teeth and is then further churned by the stomach and small intestine. The digestive enzymes help with the chemical breakdown and carbohydrates, proteins and other substances from the food is catabolized into simpler molecules. Most of the digested products are then absorbed by the bloodstream which occurs along the small intestine through active transport. Some are absorbed passively through diffusion like fats or lipids. The microvilli and villi, by increasing the surface area, facilitate the absorption process.
Ref: Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy & physiology. Fifteenth edition; Wiley Loose-Leaf Print Companion. Hoboken, New Jersey, John Wiley & Sons, Inc.