digestive system

• nutrition is a process in which an organism gets food
• autotrophs - make their own food e.g. plants

  heterotrophs - take in their food from the environment e.g. humans
• parasites - take in food from a live source, e.g. fleas

  saprophytes - take in their food from a dead source, e.g. fungi and bacteria of decay.
• the digestive system allows us to break down food and transport nutrients to body organs
• digestion - is the physical or chemical breakdown of food

  ingestion - is the taking in of food into the digestive system through the mouth
• physical digestion is the mechanical breakdown of food e.g. stomach-churning

  chemical digestion is the breakdown of food using enzymes e.g. amylase breaking down starch in mouth.
• Main events of digestive system

  1. Injestion
  2. digestion
  3. absorption
  4. assimilation
  5. egestion
• adsorption - when digested food passes from the digestive system and enters the blood
• assimilation - absorption of food particles from the blood into the cells
• egestion - removal of unabsorbed waste from the digestive system
• incisors - chisel shaped - cut and slice food
• canines - pointed and fang-like - grip & tear food
• premolars - large flat surfaces - crush & grind food
• molars - large surfaces - crush and grind food
• $2(I 2/2, C 1/1, P 2/2, M 3/3)$ - DENTAL FORMULA
• Saliva contains - salts, water, mucus, amylase, lysozyme
• a ball of food is called - bolus
• bolus is pushed backwards into your pharynx and down the oesophagus, the epiglottis closes over the trachea to prevent food entering trachea
• peristalsis - is a wave of involuntary muscular action in the walls of the alimentary canal that pushes food along. It:

  • Pushes food along the gut
  • helps break down food mechanically
  • prevents constipation
• Role of Fibre

  • Fibre also known as roughage cannot be broken down by humans. Fibre absorbs water, causing the waste to expand. The physical increase in waste stimulates muscular movement meaning fibre stimulates peristalsis.
• the stomach is a muscular bag, with the lining having heavy folding forming, gastric glands. These produce gastric juice which has pepsinogen, mucus & hydrochloric acid
• Self digestion

  • mucus - coats stomach, stops protein-digesting enzymes from digesting stomach muscle
  • pepsin in inactive form - pepsinogen is produced in an inactive form and does not digest the stomach lining that produces it. It is converted into active pepsin by hydrochloric acid in the stomach
• pepsin - converts protein into smaller peptides
• hydrochloric acid functions

  • activates pepsinogen
  • kills bacteria
  • destroys salivary amylase
• mixture that leaves the stomach is called chyme
• pancreas

  • secretes the hormone insulin into the blood and digestive materials into the duodenum
  • consists of sodium bicarbonate which neutralises chyme from the stomach
  • enters duodenum from pancreatic duct
• • lipids with the enzyme of lipase make fatty acids and glycerol
  • starch with the enzyme of amylase make maltose
• liver

  • Makes bile
  • breaks down red blood cells
  • breaks down toxic materials e.g. alcohol
  • stores trace materials e.g. zinc, iron
  • produces body heat
  • deamination of excess amino acids to form urea
• bile

  • formed by red blood cells
  • yellow/green
  • water, salts, bile pigments
  • made in liver,stored in gall bladder
  • enters duodenum through bile duct
• Functions of Bile

  • emulsifies lipids - into tiny droplets to increase surface area for enzyme digestions
  • neuralises chyme - bile is alkaline due to sodium carbonate from pancreas
  • excretes pigment - biliverdin, bilirubin - from damaged red blood cells
• duodenum - digestion

  ileum - absorption
• duodenum

  • duodenum cell lining produces digestive enzymes, these enzymes enter from liver and pancreas also
  • inner lining has many villi which have microvilli (increases surface area)
  • increased surface area slows down food
  • intestinal glands between the villi produce a range of enzymes called intestinal juice
• ileum

  • absorbs nutrients

  Carbohydrates - digested to - monosaccharides

  proteins - digested to - amino acids

  lipids - digested to - fatty acids and glycerol
• Villi adaptations for diffusion

  • one cell thick
  • large number to increase surface area
  • rich blood supply
• Lacteal

  Inside each villus, is a lacteal containing liquid, lymph. Fatty acids and glycerol are absorbed into the cells of the villus lining. They reform into fat droplets and are now coated in protein and pass along the lymph which transports them into the bloodstream in the lymph vessels. The protein coat is now dissolved in the blood and fats are absorbed into cells.
• caecum and appendix known as vestigial organs - lost former use
• colon - reabsorbs water
• mutualistic - both organisms benefit and it is a two way relationship.

  bacteria in the colon feed on the waste from human but produce vitamin b and K, which are good bacteria.

  This bacteria prevents pathogenic bacteria and fungi
• Beneficial effects of a high fibre diet:

  • normalises bowel movement (prevents constipation)
  • prevents colon cancer
  • aids in weight management (foods high in fibre are more filling so you eat less)