1. How does the food change in consistency and form?
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During digestion, food undergoes mechanical and chemical processes that change its consistency and form. It begins in the mouth, where chewing or mastication breaks food into smaller pieces, and saliva, containing enzymes like amylase, starts breaking down starch into sugars. The tongue then pushes the food towards the back of the throat, where it travels down the esophagus as a bolus, which transports it to the stomach. In the stomach, churning mixes food with gastric juices, breaking down proteins and transforming it into a semi-liquid mixture called chyme. The chyme moves to the small intestine, where bile emulsifies fats and digestive enzymes from the pancreas and interstitial lining further breaking down nutrients into absorbable forms like sugars, amino acids, and fatty acids. In the large intestine, water and electrolytes are absorbed, solidifying undigested material into feces, which is stored in the rectum until expelled during defecation.
2. How could the body absorb the nutrients from the foods we eat?
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The small intestine in our body is the primary site for nutrient absorption, and it utilizes its specialized structure to maximize efficiency. The inner wall of the small intestine is lined with millions of villi and microvilli, which significantly increase the surface area, allowing efficient nutrient absorption into the blood. All of the chemical and mechanical phases of digestion from the mouth through the small intestine transform food into absorbable forms: monosaccharides from carbohydrates, amino acids, and peptides from proteins, and fatty acids and glycerol from fats. Nutrients are absorbed through various mechanisms, including diffusion, facilitated diffusion, osmosis, and active transport. Sugars and amino acids enter blood capillaries, while fatty acids and glycerol are absorbed into lymphatic vessels called lacteals. Around 90% of nutrient absorption occurs in the small intestine, with the remainder in the stomach and large intestine, where some nutrients of the undigested material are absorbed before waste is eliminated. The absorbed nutrients are transported via blood or lymph for energy, growth, and repair.