Biol 1 - Digestive System

Digestion : The breaking down of large molecules into small molecules
                             OR
                   Polymers --> Monomers

Polymers are insoluble
So need to be hydrolysed into smaller molecules to be absorbed 

• Uses waves of contractions to move food along called 'peristalsis'
• Mucus is secreted from tissues in the walls for lubrication

• Small sac with folds allowing expansion
• Entrance and exit controlled by sphincters
• Stomach walls secrete Gastric Juice; made of - HCL, Mucus and the precursor for pepsin
  -Pepsin (enzyme) hydrolyses breakdown of proteins and only works in acidic conditions (hence the HCL!)
• Peristalsis of stomach churns food into 'Acid Chyme' 

• Acid chyme moved along by peristalsis
• In Duodenum chyme is neutralized by bile and panreatic juice
  -which breaks it into smaller moleucules
• In the Ileum small molecules are absorbed by villi in intestinal epithelium (gut wall) 

• Absorbs water, salts and minerals
• Folded wall provides large surface area for absorption

• Faeces stored and passed through sphincter muslces

• Produce Saliva made of; salivary amylase, mucus and mineral salts
• Salivary amylase (enzyme) breaks starch into maltose
• Saliva also lubricates food

• Secretes pancreatic juice into Duodenum via pancreatic duct
• Juice contains amylase and other digestive enzymes
• Also contains sodium hydroxide which neutralises acidity of HCL from stomach acid