1. How does the food change in consistency and form?
- Digestion of food begins from the mouth, or the oral cavity, with mastication (chewing). During mastication, food is broken down mechanically into tinier pieces. With the help of saliva, the food is moistened, creating bolus. Along with this, salivary enzymes, like amylase, start to break down carbohydrates. After that, the bolus moves down through the esophagus. During its travel, the bolus remains unchanged but continues to soften. Peristalsis then pushes the bolus towards the stomach. Chemical digestion mainly occurs in the stomach where the bolus is mixed with gastric juices, such as hydrochloric acid (HCl) and pepsin. This acidic environment turns the bolus into chyme, a semi-liquid mixture. As the chyme continues down to the small intestine, it becomes thinner as it mixes with bile. Nutrients are then broken down into absorbable units and these molecules are taken by the bloodstream and/or the lymphatic system. The remaining material then becomes thicker in the large intestine as water is absorbed; the undigested food, fiber, and waste become a compact solid form, called feces, which will be eliminated from the body through the rectum and anus through defecation.
- In summary, the food we ingest transforms from solid to semi-liquid to liquid and back to its solid state again.
2. How could the body absorb the nutrients from the food we eat?
- In relation to the first answer, the food we eat goes through various phases where it is transformed to smaller units through mechanical digestion and chemical digestion. These smaller units allow for easier absorption of nutrients, specifically in the small intestine. The small intestine has finger-like projections, called villi and microvilli which help increase the surface area for absorption. In the small intestine, enzymes from the pancreas break macronutrients into forms that can be easily absorbed by the bloodstream and the lymphatic system. Carbohydrates become simple sugars through amylase; proteins become amino acids via trypsin and peptidases; and fats become fatty acids and glycerol through lipase. Simple sugars and amino acids are absorbed by the blood stream through facilitated diffusion, while fatty acids and glycerol are absorbed by the lymphatic vessels.
- After the absorption, the liver processes the nutrients, stores them, and distributes them throughout the body to fuel cells.