Food undergoes changes in consistency and form during digestion, which involves both mechanical and chemical processes. Mechanical digestion refers to the physical breakdown of food into smaller pieces through actions such as chewing, churning, and segmentation. This process is crucial as it prepares the food for chemical digestion, where enzymes and pH changes further decompose the smaller particles into absorbable nutrients. These nutrients are primarily absorbed in the small intestine through specialized structures called villi, which increase the surface area for absorption. Once absorbed, they enter the bloodstream. Nutrient absorption occurs via two main pathways: the paracellular pathway, which allows molecules to passively move between intestinal cells, and the trans cellular pathway, an active process that requires energy. Most nutrients are absorbed through the trans cellular pathway before being distributed throughout the body via the bloodstream.
Reference:
Basile et al. (2023)
Physiology, Nutrient Absorption. StatPearls Publishing.
https://www.ncbi.nlm.nih.gov/books/n/statpearls/article-145837/