digestive

• Digestive system


  Permits food to be digested, absorbed and excreted
• Digestive system


  • 3 main functions: Digestion, Absorption of nutrients, Elimination of solid food waste
• Digestion


  1. Breaking down food so the body is able to absorb it

  2. Mechanical and chemical digestion
• Absorption of nutrients


  Process where substances pass from the digestive tract into the blood stream where they can circulate around the body
• Elimination of solid food waste

  All remaining food that could not be digested and absorbed pass into the large intestine as waste, then eliminated from the body via the anus
• Mouth and salivary glands


  • Food enters the mouth and begins mechanical digestion by chewing
  • Saliva contains enzymes that begin chemical digestion
  • Saliva helps soften the food
  • Tongue helps mix food with saliva, creating a mixture called bolus
• Oesophagus


  • A long narrow tube that connects the mouth to the stomach
  • Contains a muscle called a sphincter which controls the entrance to the stomach
  • Sphincter opens and closes preventing food from passing back into the oesophagus
• Reflux


  When the sphincter function fails
• Stomach


  • Food is mixed by churning
  • Protein digestion begins
  • Very acidic environment
  • Contains pepsin which chemically digests proteins
  • The paste produced is called chyme which passes to the small intestine through another sphincter
• Small intestine


  • Long tube with high surface area where nutrients are absorbed
  • Consists of the duodenum, jejunum and the ileum
• Duodenum


  • First and shortest part
  • Most chemical digestion takes place here
  • Enzymes that act in the duodenum include:
• Jejunum


  • Second part of the small intestine and is where most nutrients are absorbed into the blood
  • Contains villi and micro villi which work to increase the surface area to increase absorption
• Ileum


  • Final section of the small intestine
  • Main function is to absorb vitamin B12, Bile salts and whatever products of digestion that were not absorbed by the jejunum
• Large intestine


  • The final section of the alimentary canal
  • Water and dissolved minerals are absorbed
  • Connects the small intestine with the anus
  • Consists of the ascending/ transverse/ descending/ sigmoidal colon as well as the rectum
• Accessory organs


  • Liver
  • Gallbladder
  • Pancreas
• Accessory organs


  They are called accessory organs because food does not pass through them, instead they secrete or store substances needed for digestion
• Pancreas


  • Produces enzymes that are released into the small intestine via the duodenum
  • Enzymes released include: amylase (responsible for breaking down carbohydrates), trypsin (responsible for breaking down proteins), lipase (responsible for breaking down lipids)
  • Other functions include: Secrete hormones insulin and glucagon which regulate blood sugar level, Release alkaline compounds (e.g. bicarbonate ions) which neutralise the acids produced in the stomach as they enter the small intestine
• Liver


  • Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
  • Main roles include: Detoxification, Storage, Metabolism, Bile production, Haemoglobin breakdown
• Bile


  • A liquid produced by the liver and secreted into the duodenum
  • Bile is produced in the liver and stored in the gallbladder
  • Bile breaks down Lipids during a process called emulsification
  • Bile acidity of food coming from the stomach into the duodenum, this is important because the duodenum works in a neutral environment
• Gallbladder


  • Stores and concentrates bile from the liver and then secretes it into the small intestine via the bile duct