Nutrients enter the bloodstream through the microvilli that line the walls of the small intestine. A single microvillus consists of a blood capillary that serves as the entry point into the bloodstream for absorbed nutrients.
Digestion is the process of breaking down food into nutritive components that can be absorbed by the bloodstream and delivered to the cells. It begins with the mechanical breakdown of food in the mouth, where smaller food particles then enter the stomach through the esophagus. Chemical digestion through enzymatic action and acidic secretions further hydrolyzes the food in the stomach, which then enters the small intestine after 2 hours.
The final breakdown of food occurs in the small intestine. The pancreas and gall bladder discharge digestive juices to hydrolyze carbohydrates, fats and proteins. When the digested food is down to absorptive levels, the nutrients travel down the intestinal walls through the action of peristalsis. This process pertains to the muscular movement that occurs in the digestive tract, where alternating contractions and relaxations generate wave-like motions that push the nutrients forward.
The intestinal lining is permeated with tiny, finger-like projections known as microvilli. These microscopic structures greatly increase the surface area of the intestinal walls to take in more nutrients. The blood vessels found in each microvillus absorb the nutrients into the bloodstream to be circulated throughout the body and provide the cells with the energy to perform essential life processes.