At approximately 9 meters (30ft) in length the digestive system is the converter of food to fuel. It is hugely complex, yet after food has been swallowed the entire process is involuntary. From the mouth to the anus the journey is complex and yet simply occurs without conscious thought from the individual. The process begins of course with a meal being consumed, the meal is then broken down and the process of generating life sustaining fuel begins.
Food is broken down by complex processes splitting the food into fats, vitamins, minerals, proteins and carbohydrates which serve to nourish the body, replace cells, and supply energy to muscles, aid the immune system and so much more.
Your teeth grind up each mouthful of food. The tongue, which is actually a group of muscles rather than a single muscle, works the food into a bolus, or ball shape for swallowing.
Chemical digestion begins in the mouth with saliva containing enzymes, which break large molecules of food into smaller molecules that the body is able to absorb. Enzymes play an important part in the digestion process at other stages too.
Food slides down the throat to the oesophagus, the first of several hollow organs, by muscular contractions called peristalsis. The peristaltic flow can be imagined as being similar to the movement of a caterpillar moving along a leaf, gentle and steady.
The oesophagus empties into the stomach, a large muscular chamber, located on the left side of the upper abdomen, which mixes the food with more enzymes including pepsin which targets proteins and lipase which works on fats. Amazingly hydrochloric acid helps to dissolve the contents of the stomach and kills harmful bacteria. The stomach muscles contract periodically churning the food to aid digestion. This process eventually creates a semi fluid paste called chime which is sealed in the stomach. The pyloric sphincter, a muscular valve opens to allow food to pass from the stomach to the small intestine of three sections called duodenum, jejunum, and ileum.
The duodenum produces large quantities of mucus to protect the lining of the intestine from the acid in the chime. At approximately 6 meters (20 feet) in length this is where most of the digestion and absorption of nutrients take place. The nutrients are taken into the bloodstream and transported to the liver. Millions of villi, which are finger like projections, move the nutrients into the blood stream.
Whatever remains passes into the large intestine, where it is consumed by billions of bacteria and mixed with dead cells to form solid faeces. Water is reabsorbed into the body, while the faeces are moved into the rectum to await evacuation.
Other organs take part in the digestive process, the liver, gallbladder and pancreas.