69 The longest intestine is that of the blue whale. It reaches about 220 metres. Food is stored in our stomach for about 3 to 5 hours, while it can stay in our large intestine for about 6 to 20 hours. THE DIGESTIVE AND URINARY SYSTEMS The digestive system The function of the digestive system is to convert the food we eat into its simplest forms, like glucose (sugars), amino acids (that make up proteins), or fatty acids (that make up fats). The broken-down food is then absorbed into the blood from the small intestine and the nutrients are carried to each cell in the body. The system includes two types of organs: the alimentary canal, or digestive tract, which is a one-way tube of about 7.62 meters from the mouth to the anus, and which includes: the pharynx, a canal linked to the oesophagus where chewed food mixed with saliva, called bolus, is pushed into by the tongue (muscular organ that moves food around the mouth); the oesophagus, a muscular tube about 25 cm long that carries food into the stomach; the stomach, an expanded organ in the abdominal cavity which digests food thanks to enzymes and acids. The result, a semi-liquid mixture of gastric juice and food, goes to the URINARY SYSTEM small intestine; Adrenal the small intestine, the longest part Descending gland of the alimentary canal which aorta Inferior absorbs most of the nutrients from vena cava digested food. Digestive juices from the liver and the pancreas Left kidney enter it through a small opening Right Ureter in the duodenum (hollow tube kidney connecting the stomach to the small intestine) to end the process Bladder and pass on the remains to the Urethra large intestine; the large intestine, the final section bladder: vescica of the digestive tract which stores to chew: masticare kidney: rene and eliminates undigested waste and large intestine: intestino reabsorbs water. At intervals, the crasso involuntary muscles within its walls liver: fegato propel solid waste material, called small intestine: intestino faeces, towards the rectum, in a tenue sore: piaga process called defecation; 138 SCIENCE AND PHYSICS Salivary glands Anus the accessory organs, i.e. the liver and the pancreas: the former produces bile, a chemical that turns fats into energy, the latter releases insulin, which lowers blood sugar, and glucagon, which increases blood sugar. The urinary system The function of the urinary system is to remove waste from blood in the form of urine. It consists of: two kidneys (bean-shaped organs), which extract waste from the blood, balance body fluids, and form urine; two ureters, which are the tubes that conduct urine from the kidneys to the urinary bladder; the bladder, which is a hollow organ that receives and stores urine; the urethra, which is a tube that takes urine outside for elimination.