1. The process begins in the mouth, where chewing and the mixing of food with saliva break the food into smaller and more manageable pieces. This forms a soft, moist substance called a bolus, which is then swallowed and moves into the stomach. In the stomach, muscular contractions and gastric juices further break it down and transform it into a semi-liquid mixture known as chyme. The chyme then enters the small intestine, where it is mixed with enzymes and bile, breaking it down further into its simplest forms, such as amino acids, fatty acids, and glucose. By the time the remaining material reaches the large intestine, most nutrients have been absorbed, and what remains is primarily water, fiber, and waste. The large intestine absorbs water and compacts the waste into feces for elimination.
2. The body absorbs nutrients from food through the walls of the small intestine. Tiny finger-like projections called villi, covered with even smaller structures called microvilli, increase the surface area for absorption. These structures allow nutrients to pass through into the bloodstream or lymphatic system, where they are transported to cells throughout the body for energy, growth, and repair. The large intestine absorbs water and some minerals, completing the nutrient absorption process. This whole process ensures that the body can extract and use the essential nutrients from the food we eat.
The body absorbs nutrients in the intestine through:
- Passive diffusion - allows nutrients like small lipids to move naturally from high to low concentration.
- Facilitated diffusion - uses carrier proteins to help nutrients cross the intestinal wall without energy.
- Active transport - requires energy (ATP) to move nutrients like glucose and amino acids against their concentration gradient.
- Endocytosis - enables the absorption of larger molecules by engulfing them into the cell.