The Human Digestive System

• The food you take in is made up of large, insoluble molecules, which your body can't absorb. They need to be broken down to form smaller, soluble molecules that can be absorbed and used by your cells
• In the digestive system, the mouth chews up food and breaks down starch into smaller pieces with the help of the enzyme amylase
• The mouth contains salivary glands which produce amylase
• The oesophagus is also known as the gullet, which carries food from the mouth to the stomach
• The stomach contains hydrochloric acid which kills bacteria. The stomach churns up food with its muscular walls
• The stomach produces the protease enzyme pepsin
• Bile is produced in the liver. It neutralises stomach acid and emulsifies fat which is then absorbed into the small intestine
• The gall bladder stores bile
• The pancreas is a gland that produces protease, amylase, and lipase enzymes which are then released into the small intestine.
• The small intestine absorbs nutrients from the digested food into the blood
• The large intestine absorbs water from undigested food and forms faeces
• The rectum stores faeces before being passed out the anus
• Faeces contains indigestible material such as cellulose fibres and bacteria.
• The oesophagus transports food to the stomach by peristalsis (muscular contractions).
• The mouth has teeth to break down food mechanically and salivary glands produce saliva containing amylase enzyme to begin digestion chemically.
• Adaptations of small intestine:

  1. The walls are covered in villi - finger-like projections that increase the surface area
  2. Good blood supply
• Villi and a good blood supply increase the rate of diffusion and active transport of nutrients into the blood