The Digestive System

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  • THE DIGESTIVE SYSTEM
    • Digestion breaks down large molecules into smaller molecules.
      • Many of the molecules in our food are polymers.
        • Large complex molecules composed of long chains of monomers (small basic molecular units).
          • In proteins the monomers are called amino acids, they contain hydrogen, oxygen and nitrogen.
          • In carbohydrates the monomers are called monosaccharides, they contain carbon, hydrogen and oxygen.
        • Insoluble - they cannot be directly absorbed into our bloodstream and assimilated in to new products.
        • Polymers have to be hydrolysed into smaller, more soluble molecules by adding water.
          • This process happens during digestion.
          • Hydrolysis is catalysed by digestive enzymes.
    • Functions
      • (2) The Stomach
        • A small sac with lots of folds that allow it to expand = can hold up to 4 litres of food and liquid.
        • The entrance and exit are controlled by sphincter muscles.
        • The walls of the stomach produce gastric juice to help break down the food.
          • Gastric juice = HCl, pepsin (an enzyme) and mucus.
            • Pepsin hydrolyses proteins into smaller polypeptide chains - only works in acidic conditions provided by HCl.
        • Peristalsis of the stomach turns food into an acidic fluid called chyme.
      • (1) Oesophagus
        • The tube that takes food from the mouth to the stomach using waves of muscle contractions = peristalsis.
        • Mucus is secreted from tissues in the walls to lubricate the foods passage downwards.
      • (3) The Small Intestine
        • Two main parts: the duodenum and ileum.
          • Chyme is moved along the small intestine by peristalsis in the duodenum.
          • In the ileum, the small, soluble molecules are absorbed through structures called villi that line the gut wall.
            • Molecules are absorbed by diffusion, facilitated diffusion and active transport.
      • (4) Large Intestine
        • Absorbs water,salts and minerals.
        • Has a folded wall = large surface area for absorption.
        • Bacteria that decompose some of the undigested nutrients are found in the large intestine.
      • (5) Rectum
        • Faeces are stored in the rectum and then pass through the sphincter muscles at the anus during defecation.
    • Glands
      • The Salivary Glands
        • There are three main pairs of salivary glands in the mouth.
          • They secrete saliva that consists of mucus, mineral salts and salivary amylase.
            • Salivary Amylase breaks down starch into maltose, a disaccharide.
            • It helps to lubricate food, making it easier to swallow.
      • The Pancreas
        • Releases pancreatic juice into the duodenum through the pancreatic duct.
          • Pancreatic juice contains amylase, trypsin, chymotrypsin and lipase.
            • Also contains sodium hydrogencarbonate, which neutralises the acidity of the hydrochloric acid from the stomach.
    • Enzymes
      • Location:
        • Salivary glands
          • Enzyme:
            • Pancreas: Amylase Trypsin Chymotryspin Carboxypepti-dase              Lipase
            • Stomach: Pepsin
            • Salivary glands: Amylase
              • Class
                • Pancreas: Amylase Trypsin Chymotryspin Carboxypepti-dase              Lipase
                • Stomach: Pepsin
                • Ileum:  Maltase = Carbohydrase Sucrase = Carbohydrase Lactase = Carbohydrase Peptidase = Protease
                • Stomach: Pepsin = Protease
                • Salivary glands: Amylase = Carbohydras-e
                • Pancreas: Amylase = Starch Trypsin = Protein Chymotryspin = Protein Carboxypepti-dase = Peptides Lipase = Lipids
                  • Hydrolyses
                    • Salivary glands: Amylase = Carbohydras-e
                    • Stomach: Pepsin = Protease
                    • Ileum:  Maltase = Carbohydrase Sucrase = Carbohydrase Lactase = Carbohydrase Peptidase = Protease
                    • Stomach: Pepsin = Protein
                    • Salivary glands: Amylase = Starch
                    • Ileum:  Maltase = Maltose Sucrase = Sucrose Lactase = Lactose Peptidase = Peptides
        • Stomach
          • Enzyme:
            • Salivary glands: Amylase
              • Class
                • Pancreas: Amylase = Starch Trypsin = Protein Chymotryspin = Protein Carboxypepti-dase = Peptides Lipase = Lipids
                  • Hydrolyses
                    • Stomach: Pepsin = Protein
                    • Salivary glands: Amylase = Starch
                    • Ileum:  Maltase = Maltose Sucrase = Sucrose Lactase = Lactose Peptidase = Peptides
        • Pancreas
          • Iluem
      • Digestion breaks down large molecules into smaller molecules.
        • Many of the molecules in our food are polymers.
          • Large complex molecules composed of long chains of monomers (small basic molecular units).
            • In proteins the monomers are called amino acids, they contain hydrogen, oxygen and nitrogen.
            • In carbohydrates the monomers are called monosaccharides, they contain carbon, hydrogen and oxygen.
          • Insoluble - they cannot be directly absorbed into our bloodstream and assimilated in to new products.
          • Polymers have to be hydrolysed into smaller, more soluble molecules by adding water.
            • This process happens during digestion.
            • Hydrolysis is catalysed by digestive enzymes.
      • Mucus is secreted from tissues in the walls to lubricate the foods passage downwards.
      • Into
        • Pancreas:  Amylase = Maltose Tryspin = Peptides Chymotryspin = Peptides Carboxypepti -dase = Amino acids     Lipase = Fatty acids and glycerol
        • Salivary glands: Amylase = Maltose
        • Stomach: Pepsin = Peptides
        • Ileum:  Maltase = Glucose Sucrase = Glucose and Fructose Lactase = Glucose and Galactose Peptidase = Amino acids
      • Pancreas: Amylase = Starch Trypsin = Protein Chymotryspin = Protein Carboxypepti-dase = Peptides Lipase = Lipids
        • Into
          • Pancreas:  Amylase = Maltose Tryspin = Peptides Chymotryspin = Peptides Carboxypepti -dase = Amino acids     Lipase = Fatty acids and glycerol
          • Salivary glands: Amylase = Maltose
          • Stomach: Pepsin = Peptides
          • Ileum:  Maltase = Glucose Sucrase = Glucose and Fructose Lactase = Glucose and Galactose Peptidase = Amino acids

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