Digestive system

• digestive system:

  • function: extracts nutrients from food and absorbs for use by the cell
• Alimentary canal:

  • continuouse tube from mouth to anus that food goes through
• Digestion: the proccess in which carbs, proteins and lipids are broken down into smaller units
• mechanical digestion:

  • physical breakdown of food into smaller pieces to increase SA for more efficient chemical breakdown
• chemical digestion:

  • chemical breakdown of large compex molecules into simpler molecules which can then be absorbed in to the body
• purpouse of mechanical digestion is to increase SA for more efficienct chemical breakdown
• The purpouse of chemical digestion is to breakdown things into smaller molecules that can be absorbed into the body.
• what are 6 basic activities of the digestive system:

  • ingestion
  • mechanical digestion
  • chemical digestion
  • movement
  • absorbtion
  • elimination
• Mouth:

  • ingestion
  • teeth cut and tear
  • salavary amylayse breaksdown complex carbs into simple carbs
• Teeth:

  • 2 incisors - biting/cutting (I2)
  • 1 canine - tearing at meat (C1)
  • 2 premolars - transition between tearing and crushing (P2)
  • 3 molars - crushing/grinding (M3)
• Oesophogus:

  • tounge helps form food into bolus and pushes it towords pharynx which has a double layer of muscle (circular and longitudinal muscles)
• circular muscles:

  • muscle fibres arranged in a circle
  • contraction of these muscles causes peristalsis in oesophagus
• longitudinal muscles:

  • muscle fibres arranged along the length of the tube
• Stomach pt.1:

  • mechanical digestion occurs, waves of musclular contractions, churning
  • contains oblique, circular and longitudinal muscle layers
  • muscles enable stomach to churn efficiently, mix the bolus into a liquid called chyme.
  • also contains gastric juices
• Chyme:

  _____________
• Stomach pt.2:

  • nutrients not absorbed due to thick musus lining
  • the pyloric sphincter is at the bottom and leads into small intestine
• Small intestine:

  • mechanical digestion
  • segmentation - contractions of a circular muscle narrow intestines which helps break up bolus and mix up juices and bile
  • about 6m long
  • recives material passed through pylonic sphincter of stomach
  • split into 3 parts: duodenum, illium, jejunum
• Dudenum:

  • first part of the small intestine
  • most chemical digestion and some selective absorbtion happens here
  • 25cm in length
• Ileum:

  • final part of the small intestine
  • vitamin B12, bile salts and any remaining products of digestion are absorbed
• Digestion in duodenum:

  • chemical digestion
  • pancreatic juice from pancreas
  • intestinal juice by glands in the lining
  • bile by liver (stored in galbladder)
• Pancreatic juice:

  • enters duodenum from pancreas through bile duct
  • neutralises the acid coming from the stomach
  • also helps in digestion of food using enzymes
• Pancreatic Amylayse:

  • breaksdown complex carbs (e.g starches) into simple carbs (e.g dissaccurides)
• Pancreatic Protease (trypsin):

  • breakdown of protein into peptides
• Nucleases:

  • ribonucleases and deoxyribonuclease
  • digests nuclic acids (DNA and RNA) into sugars and nitrogen bases
• Pancreatic Lipases:

  • breaksown lipids into fatty acids and gycerol
• Bile:

  • bile salts emulsifies fats , breaking it down into tiny droplets
  • form of mechanical digestion, increases SA for lipases to act on
  • dosen't contain any enzymes but contains bile salts
  • made in liver -> stored in gallbladder + moved into duodenum
• Amylase:

  • Breaks down simple carbs (e.g. disaccharides) into simple sugars (e.g. glucose)
• Lipases:

  • Breakdown lipids into Fatty acids and glycerol
• Absorption:

  • Nutrients, vitamins, minerals and water absorbed through the internal surface of the small intestine
  • not in duodenum
• How is a large SA the small intestine achieved:

  • Mucose (inner lining) highly folded
  • Villi further folds inner surface
  • microvilli located of outside of villi
  • small intestine is 6 – 7m long
• Structure of villi:

  ·       _______
• What is absorbed in the blood capillaries in a villi:

  • Amino acids – active transport
  • Glucose – active transport
  • Water and water soluble vitamins – diffusion
• What is absorbed into the lacteal in the villi:

  • Fatty acids and glycerol – diffusion
• villius absorbtion:

  • simple sugars/ amino acids, water and water soluable vitimins which enter the blood capillery travel to liver by hepactic vein
  • some removed of processed befor going into other cells
  • fatty acids and glycerol recombine to form fats in the lacteal
  • transported into lymph system which eventually empties out into blood through upper part of chest
• large intestines:

  • 1.5 m long
  • no villi or digestive juices
  • made up of caecum, colon, rectum and anus
  • large amount of water absorbtion, waste becomes more solid
  • bacteria works to breakdown remaining organic compounds
• elimination:

  • faeces contain water, undigested food matierial, bacteria, bile pigments and dead cells.
  • faeces pushed along rectum by peristalsis
  • excretion is the removal of metabolic wastes (most faeces not metabolic wastes)