1. How does the food change in consistency and form?
The solid food ingested is chewed and lubricated in the mouth by saliva. It is then called bolus, and it will travel to the stomach, whose gastric juices will further melt or liquify it into chyme. Next, the chyme travels to the small intestine where the food’s nutrients will be absorbed, and then to the large intestine where its water, ions, and vitamins are absorbed. This means that as it passes through the large intestine, the chyme becomes less and less liquid and more and more solid. It turns into feces, which may be defecated at one’s desired time (ideally).
2. How could the body absorb the nutrients from the foods we eat?
First, absorption refers to the passage of digested nutrients, such as monosaccharides, amino acids, and fatty acids, from the GI tract into the blood or lymph. It occurs via diffusion, facilitated diffusion, osmosis, and active transport.
Thus, in order for the body to absorb the nutrients, the body converts the food into forms (monosaccharides, amino acids, fatty acids, etc.) that it can absorb. Specifically, this means converting food into forms that can pass through the absorptive epithelial cells lining the mucosa and into the underlying blood and lymphatic vessels. This absorption mostly (~90%) happens in the small intestine and the large intestine (10%). Unabsorbed materials pass on to the large intestine, and unabsorbed materials in the large intestine form the feces that can be eliminated by defecation.