1. How does the food change in consistency and form?
Food changes from solid small pieces, to liquid with thick consistencies, returning to another solid state in excretion. In the oral cavity, the mechanical breakdown (mastication) of food allows it to be in smaller pieces and hydrolysis, which is the chemical breakdown of food take place. The food is called "bolus", a rounded mass, until the end of the esophagus. In the stomach, the food is churned by the circular and longitudinal muscles and chemically broken down by enzymes, resulting into a more liquid substance called "chyme", which is then absorbed in the small intestine. Its indigestible portion is excreted by the large intestine as "feces".
2. How could the body absorb the nutrients from the food we eat?
The absorption of nutrients begins in the latter part of the stomach, specifically at the pyloric sphincter, and is mainly occurring in the small intestine, at the jejunum and ileum. The small intestine has various structures (villi, microvilli, plicae circulares) which make it specialized for absorption. Some of these structures are connected to a mesh of capillaries that pass the nutrients into the bloodstream. On the other hand, the absorption of water, ions, and Vitamin K (part of the microflora) occurs in the large intestine.