1 Holes, tubes and valves

The food tube running through the body (Figure 1) is extremely coiled. When opened out, it is about 7.5 to 8 metres long (the length varies with body size and nutritional status). It also has valves (muscular ones called sphincters) allowing the food to move one way only – under normal circumstances. Generally, these sphincters work automatically, although we have control over the one at the far end!