Digestive System

• Human Digestive System

  Parts of the body that takes in nutrition and then breaks it down so that our body cells can use it
• The human digestive system consists primarily of the digestive tract
• Human Nutrition

  Process by which substances in food are transformed into body tissues and provide energy for the full range of physical and mental activities that make up the human life
• Five Stages of Human Nutrition

  • Ingestion
  • Digestion
  • Absorption
  • Assimilation
  • Egestion
• Ingestion


  In order to accomplish its function the digestive system begins with the mouth where food enters
• The food is put into the mouth with the help of hands
• Digestion


  Breakdown of complex food into their simple soluble absorbable sub-units
• Absorption


  The small intestine is the main region for absorption of digested food
• Villi


  • Finger-like projections on the inner surface of the small intestine that increase the surface area for rapid absorption of digested food
• Through absorption the products of digestion enter into the blood or lymph
• Assimilation


  The blood carries digested food and dissolved food to all parts of the body where it becomes assimilated as part of the cells and utilised for obtaining energy, building up new tissues and the repair of old tissues
• The process of assimilation converts the absorbed nutrients into complex molecules for growth, repair and defence
• Egestion


  The unabsorbed food is sent into the large intestine where more villi absorb water from this material, and the waste products which remain behind must be excluded from the body
• Mouth


  It is where the food first enters our body
• Mouth's Digestive Functions


  • Mechanical Digestion
  • Chemical Digestion
• Mouth's Mechanical Digestion


  The mouth is where food is mechanically digested. Here, teeth physically break down the food. The food is broken down so that it can be easier to swallow and has a greater surface for enzymes to act on
• The initial stages of eating and swallowing are under voluntary control, governed by the brain
• Mouth's Chemical Digestion


  The mouth contains the enzyme amylase (also called ptyalin) in the saliva, which is secreted by 3 pairs of salivary glands. Saliva also contains lysozyme which helps destroy micro-organisms. Amylase digests starch into maltose
• Oesophagus


  It connects the mouth with the stomach. Food moves through oesophagus by involuntary wavelike muscular contraction called peristalsis
• Parts of the Digestive System

  • Mouth
  • Oesophagus
  • Stomach
  • Pyloric sphincter
  • Duodenum
  • Small Intestine
  • Duodenum
  • Jejunum/Ileum
  • Pancreas
  • Liver
  • Large Intestine
  • Caecum
  • Appendix
  • Colon
• Stomach


  A muscular sac that stores and digests food. There is a sphincter muscle at the end of the oesophagus that opens and closes to allow food into the stomach and to prevent food from going back up into the oesophagus
• Stomach Lining


  • Mucosa
  • Gastric glands
  • Mucous
  • Pepsinogen
  • Hydrochloric Acid (HCl)
• Stomach Digestion


  As the stomach wall contracts the food is churned and thus digested mechanically. The food becomes a thick milky mixture called chyme, which will leave the stomach and go into the small intestine through the pyloric sphincter
• Small Intestine


  The food is absorbed into the blood to be taken to the body cells. The small intestine is about 6 meters long and is made up of 3 parts: the duodenum, jejunum, and ileum
• Villi and Microvilli


  • The lining of the small intestine consists of many folds called villi, each of which has about 600 microvilli. Intestinal glands located between the villi produce numerous enzymes, which are collectively called intestinal juices
• Duodenum


  The main function of duodenum is to finish the digestive process. The cells lining in the duodenum produce digestive enzymes. Also, products from the pancreas and liver enter the duodenum to do their work
• Jejunum/Ileum


  By the time the food enters this part of the small intestine it is fully digested. The job of jejunum and ileum is to absorb the food. The lining of these sections of the small intestine contain many villi
• Pancreas


  Secretes pancreatic juice for the digestive system, consisting of sodium hydrogen carbonate which neutralizes chyme in the stomach, and the digestive enzymes amylase and lipase
• Liver Functions


  • Production of bile
  • Detoxifying the body
  • Breaking down excess amino acids to urea
  • Converting glucose to glycogen for storage
  • Converting excess carbohydrates to fats
  • Storing vitamins
  • Storing minerals
  • Making plasma proteins such as fibrinogen
  • Making cholesterol used to form many hormones
  • Producing heat for the blood and body
• Large Intestine


  The last part of the alimentary canal where the final phase of the nutrition process occurs. It has a diameter of about 6 cm and a length of about 1.5 meters, where food stays for varying lengths of time from 10 hours to as long as a few days
• Parts of the Large Intestine

  • Caecum
  • Appendix
  • Colon
• The function of the caecum and appendix in humans is not known, but in herbivores they serve as the area where bacteria exist and aid in digestion of cellulose
• The colon absorbs water from the remaining food that has passed through the alimentary canal
• Enzymes


  Special proteins that can break large molecules into small molecules. They are biological catalysts needed to make the breaking of food happen quickly enough to be useful
• Digestive Enzymes


  • Amylase - Digests starch (starch into sugar)
  • Protease - Digests protein (protein into amino acids)
  • Lipase - Digests lipid or fats (lipids to glycerol and fatty acids)
• Minerals, vitamins, and water are already small enough to be absorbed by the body without being broken down by digestive enzymes
• Digestive enzymes cannot break down dietary fibre, which is why the body cannot absorb it