DIGESTIVE SYSTEM FUNCTIONS

• Macromolecules


  Large molecules made up of smaller units
• Ingestion


  Process of taking in food and water
• Mechanical Digestion


  Physical breakdown of food particles
• Chemical Digestion


  Breakdown of large molecules into smaller ones by chemicals
• Simple Sugars


  Basic sugar molecules like glucose
• Amino Acids


  Building blocks of proteins
• Fatty Acids


  Building blocks of fats
• Digestion


  Process of breaking down food for absorption
• Enzymes


  Biological catalysts that speed up chemical reactions
• Monosaccharides


  Simple sugars like glucose, fructose, and galactose
• Peptides


  Short chains of amino acids
• Nucleotides


  Basic building blocks of nucleic acids
• Bile


  Fluid that aids in the digestion and absorption of fats
• Stomach


  Site of mechanical and chemical digestion by churning action and pepsin.
• Rennin


  In infants, coagulates milk protein for digestion.
• Gall bladder

  Stores and releases bile to emulsify lipids in the small intestine.
• Digestion


  Breaking down of carbohydrate, protein and fat molecules into products small enough to be absorbed into the blood and into the cells
• Mechanical digestion


  The physical breakdown of food particles into smaller pieces to increase the surface area
• Mechanical digestion


  1. Teeth cut, tear and grind the food

  2. Churning action in the stomach breaks the food down further

  3. Gall bladder releases bile into the small intestine, bile salts act as emulsifying agents, breaking fat down into smaller droplets
• Chemical digestion


  Uses enzymes to break down large, complex molecules into smaller, simpler molecules that are small enough to be absorbed into the bloodstream
• Chemical digestion


  1. Carbohydrates split into monosaccharides

  2. Proteins split into peptides and amino acids

  3. Lipids split into fatty acids and glycerol

  4. Nucleic acids split into nucleotides
• Alimentary canal


  Continuous tube that runs from the mouth to the anus, together with associated organs like the pancreas and gall bladder, makes up the digestive system
• Lining of the alimentary canal


  Surface through which nutrients are absorbed
• Mouth


  1. Intake of food (ingestion)

  2. Food is chewed (mastication)

  3. Food is mixed with saliva, which contains mucus and salivary amylase to begin chemical digestion

  4. Jaws and teeth begin mechanical digestion

  5. Tongue shapes food into a bolus and pushes it into the pharynx
• Oesophagus


  1. Circular muscle contracts in waves (peristalsis) to push food towards the stomach

  2. Mucus lubricates the inner lining
• Stomach


  Food undergoes mechanical and chemical digestion, but nutrients are not absorbed into the bloodstream due to a thick layer of mucus
• Small intestine


  1. Receives material from the stomach

  2. Duodenum - most chemical digestion occurs

  3. Jejunum - effective absorption of carbohydrates and proteins

  4. Ileum - absorption of B12, bile salts, and remaining digestion products

  5. Digestion continues under influence of pancreatic juice, bile, and intestinal juice

  6. Mechanical digestion continues through segmentation
• Absorption of nutrients


  • Products of digestion, along with vitamins, minerals and water, are absorbed through the wall of the small intestine into the blood
  • Lining of small intestine has folds, villi and microvilli to maximise absorption
• Large intestine


  • No digestive juices secreted, but lining secretes mucus
  • Movement of material is slow, allowing water absorption
  • Bacteria break down remaining organic compounds and produce vitamins
• Healthy diet is important for a healthy digestive system
• Constipation


  Reduced movement of large intestine, leading to drier and harder faeces, difficult and painful defecation, often caused by lack of roughage (insoluble fibre) in diet
• Diarrhoea


  Frequent defecation of watery faeces, caused by irritation of small or large intestine increasing peristalsis before adequate water absorption
• Bowel cancer


  Uncontrolled growth of cells in the wall of the large intestine, linked to diet, alcohol consumption and smoking
• Coeliac disease


  Inability to tolerate gluten, leading to damage or destruction of villi in small intestine and malnutrition