7. Human Nutrition (Part 2) (Cambridge IGCSE Biology 0610 for exams in 2023, 2024 and 2025)

Chemical Digestion Processes
📌 Chemical digestion breaks down large insoluble molecules into small soluble molecules necessary for absorption.
💧 Amylase breaks down starch into maltose (in the mouth/duodenum), which is further broken down into glucose by maltase on the small intestine lining.
🥩 Protease enzymes (like pepsin in the acidic stomach and trypsin in the alkaline duodenum) break down protein into amino acids.
🥑 Lipase digests fats and oils into fatty acids and glycerol within the duodenum.

Enzyme Secretion and Location
🔍 Amylase is secreted by salivary glands and the pancreas, acting in the mouth and duodenum, respectively.
🌬️ Pepsin is produced and acts in the acidic stomach environment.
🧪 Trypsin and lipase are both secreted by the pancreas and act in the duodenum.

Role of Hydrochloric Acid and Bile
🦠 Hydrochloric acid in gastric juice kills harmful microorganisms present in food.
🧪 Hydrochloric acid provides the acidic pH required for pepsin to achieve its optimum activity rate.
🟡 Bile, an alkaline mixture, neutralizes the acidic food mixture entering the duodenum, providing a suitable alkaline pH for intestinal enzymes.

Absorption in the Small Intestine
🔬 The ileum of the small intestine is highly adapted for absorption due to millions of villi and microvilli, which greatly increase the surface area for efficiency.
🩸 Capillaries within the villi absorb digested molecules like glucose and amino acids, transporting them away via the blood.
🥛 Lacteals absorb fatty acids and glycerol, transporting them away from the small intestine through the lymph.

Key Points & Insights
➡️ The primary goal of chemical digestion is producing small, soluble molecules capable of being absorbed into the bloodstream.
➡️ Pepsin requires an acidic pH (provided by HCl) for optimal function, while intestinal enzymes require an alkaline pH (provided by bile).
➡️ Absorption efficiency in the ileum is maximized by structural adaptations like villi and microvilli, increasing the absorptive surface area.

📸 Video summarized with SummaryTube.com on Nov 30, 2025, 14:26 UTC