How does the food change in consistency and form?
During the digestion process, food goes through changes in consistency and form due to mechanical and chemical actions. Mechanical digestion is initiated in the mouth, where mastication breaks down food into bits and combines it with saliva, forming a mass known as the bolus. After swallowing, the bolus moves down through the esophagus through contractions called peristalsis. In the stomach, the bolus undergoes churning, where it is mixed with gastric juices such as hydrochloric acid and pepsin. This chemical digestion, combined with mechanical churning, turns the bolus into a fluid substance known as chyme. Once chyme reaches the intestine, the bile from the liver and enzymes from the pancreas are added to it, allowing the breaking down of carbohydrates, proteins, and fats into their simplest form.
How could the body absorb the nutrients from the foods we eat?
The majority of nutrient absorption happens in the small intestine. The inner lining of the small intestine has tiny finger-like projections called villi and even smaller projections called microvilli, which help increase the surface area for absorption and allow enzymes to further break down nutrients. Carbohydrates broken down into monosaccharides, proteins broken down into amino acids, and lipids broken down into fatty acids, are absorbed through the villi. Monosaccharides and amino acids go directly into the bloodstream via active transport or facilitated diffusion, while fatty acids are absorbed into intestinal cells. Water-soluble vitamins and minerals are absorbed into the bloodstream, while fat-soluble vitamins are absorbed along with lipids. The rest of the water and electrolytes are absorbed by the large intestine to complete the absorption process.