The Amazing Journey: How Your Body Digests Food

Think about the last meal you ate. You chewed it, swallowed it — and then what? It seems to simply disappear. But inside your body, that food is about to take a remarkable 9-metre journey through a series of specialised organs, each with a specific job to do. By the time the journey ends, your body will have extracted every useful molecule it needs to keep you alive and growing.

Digestion is the process of breaking food down into molecules small enough to pass into your bloodstream and be used by your cells. There are two types of digestion happening at the same time. Mechanical digestion means physically breaking food into smaller pieces — like tearing paper. Chemical digestion means using special proteins called enzymes to split large food molecules into smaller ones — like cutting rope with scissors at a molecular level. **1. Mouth** Digestion begins here. Your teeth perform mechanical digestion by grinding food. At the same time, salivary glands release saliva containing an enzyme called amylase, which begins breaking down starch (a carbohydrate) into simpler sugars. Your tongue shapes the chewed food into a ball called a bolus, ready to swallow. **2. Oesophagus** The bolus travels down this muscular tube connecting your mouth to your stomach. The oesophagus uses waves of muscle contraction called peristalsis to push food along. Peristalsis works even if you are upside down — it does not rely on gravity. **3. Stomach** The stomach is a muscular bag that churns food — more mechanical digestion. Its walls release gastric juice, which contains hydrochloric acid (making the stomach very acidic, around pH 2) and an enzyme called pepsin that begins breaking down proteins. The semi-liquid mixture that leaves the stomach is called chyme. **4. Small Intestine** This is the key site of chemical digestion and absorption. Despite being called 'small', it is roughly 6–7 metres long. The pancreas releases enzymes into the small intestine to break down carbohydrates, proteins, and fats. The liver produces bile, stored in the gall bladder, which emulsifies fats — meaning it breaks large fat droplets into tiny ones so enzymes can work on them more easily. The inner wall of the small intestine is covered in tiny finger-like projections called villi. Villi massively increase the surface area, allowing digested nutrients to be absorbed efficiently into the bloodstream. **5. Large Intestine** Undigested material (mainly fibre and water) passes into the large intestine. Its main job is to absorb water back into the body. The remaining solid waste, called faeces, is stored in the rectum and leaves the body through the anus. **Key model — the tube within a body:** Think of the digestive system as a long, specialised tube running through you. Food travelling inside the tube is technically still outside your body until nutrients cross the gut wall into your blood.