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Chapter 9 — Chapter 9 — Human Digestive System
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📘Easy summary
Digestive system breaks food into small absorbable molecules (digestion) and absorbs them; eliminates waste. Mouth: teeth chew (mechanical digestion); tongue mixes food with saliva, forms bolus, tastes, pushes bolus to pharynx. Saliva (1–1.5 L/day; pH ~6.8) from three pairs of glands: water moistens, mucus lubricates, salivary amylase (ptyalin) begins chemical digestion of starch → maltose, lysozyme kills bacteria, bicarbonate buffers. Swallowing: soft palate/uvula closes nasopharynx; larynx rises and epiglottis covers glottis preventing food entry into trachea; oesophagus moves bolus by peristalsis (waves of circular and longitudinal muscle contraction); lower oesophageal (cardiac) sphincter.
⭐Key points
- Carbohydrate digestion begins in mouth.
🔬Diagram
🌿Real-life example
Bread tastes sweet on chewing.
💡Exam tip
- Epiglottis role.
✅Quick check
1. Starch digestion starts:
2. Prevents food entering trachea:
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