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Parts of the digestive system

Teeth, mouth, peristalsis, liver

Duodenum, stomach, pancreas, ileum

Detailed stomach and duodenum

Enzymes and digestion

Lipase experiment

Liver, gall bladder and bile

Review and test
                                      1
Main parts of the digestive system


                       mouth
      details salivary glands


                                     oesophagus


                       liver
                                     stomach
               gall bladder

  small intestine (duodenum)
                                     pancreas


                                     small intestine (ileum) details

                                     large intestine


                  appendix
                                     rectum

                                     anus
                                                                       2
 Main functions of the digestive system
     teeth - mechanical digestion                                           Saliva contains the enzyme salivary
    Break food down into smaller                                            amylase (pH optimum 7), which breaks
   parts. Small chunks are easier                                           down starch to maltose.
                                          mouth
    to swallow and have a greater                                           Saliva also contains mucus which binds
                                          salivary glands
        surface area for digestion                                          chewed food together and also lubricates
               enzymes to act on                                            swallowing                   MORE DETAIL

                                                            oesophagus



                                           liver



                                      gall bladder                       stomach


                                     small intestine
                                     (duodenum)                      pancreas




                                                                         small intestine
                                                                         (ileum)

                                                                         large intestine
The liver produces bile which
emulsifies fats and neutralises
        stomach acids
                                     appendix
                                                                         rectum

                 MORE DETAIL
                                                                          anus

                                                                                                                   3
   Main functions of the digestive system

The duodenum is the first part of                                                           The stomach secretes
the small intestine and its walls                                                           hydrochloric acid and the enzyme
secrete a range of enzymes, some           mouth                                            pepsin to break down proteins into
similar to those prodced by the            salivary glands
                                                                                            peptides. Its muscular walls churn
pancreas:                                                                                   the food and acid, mixing them well
Amylase – converts starch to                                                                to help digestion
maltose
                                                             oesophagus
Lipase converts lipids to fatty
acids and glycerol
Protease converts proteins into             liver

amino acids
                                       gall bladder                       stomach

                                                                                             The pancreas produces 3
The ileum is also part of the small   small intestine                                        important enzymes –
intestine. It is designed for the     (duodenum)                      pancreas
absorption of food digestion by the                                                          Amylase – converts starch to
duodenum and stomach.                                                                        maltose
                                                                                             Lipase converts lipids to fatty
                                                                          small intestine
                                                                          (ileum)
                                                                                             acids and glycerol

                                                                          large intestine    Protease converts proteins into
                                                                                             amino acids
                                                                                             These pass down the pancreatic
                                      appendix                                               duct into the alkaline duodenum
                                                                          rectum             where they digest food.

                    MORE DETAIL                                            anus

                                                                                                                                  4
 The stomach
                   FOOD FROM
                  OESOPHAGUS
                                     The stomach produces
                                     hydrochloric acid.
                                     HCl provides the acid pH
                                     required by the enzyme
                                     pepsin to work efficiently
                                     HCl also kills most of
                                     the bacteria taken in
                               HCl   with the food

                                     The stomach produces
                                     the enzyme PEPSIN.
                     PEPSIN          Pepsin catalyses the
                                     conversion of proteins
                                     into amino acids.
                                     Pepsin requires an acid
                                     pH (3) to work effectively.
SMALL INTESTINE
  (DUODENUM)                                                   5
The ileum
The ileum is lined with villi, designed for the efficient absorption of food


  DIGESTED FOOD IN GUT LUMEN
       DIFFUSION




                                          Their finger-like                  Thin wall for
                                         shape and large                     quick
                                       numbers increase                      absorption of
                                     the surface area for                    digested food
                                         food absorption
                                        and so speed the
                                         rate of uptake of                   Capillaries
                                            digested food                    absorb
                                                                             digested food
                                                                             and transport
                                                                             it to the liver
                                                                             Lymph vessel
                                                                             to carry away
                                                                             digested fats
                                                              Diagram of a
Villi lining the wall of the ileum                               villus
                                                                                        6
The role of enzymes in digestion
Enzymes are biological catalysts. They speed up most of the
reactions in the body which would otherwise be far too slow.
Enzymes are made of protein, a sensitive substance whose structure
is altered easily by temperature or pH
Digestive enzymes all break down large molecules into ones small
enough to pass through the intestine wall

                                               Coiled protein strands made
                                               of 100s of amino acids



                                                Enzymes are globular in
                                                shape and each type of
                                                enzyme has a very
                                                distinctive shape.
                                                e.g. amylase and pepsin
                                                can be distinguished by
     amylase                     pepsin         their shapes                 7
The role of enzymes in digestion
Enzymes are biological catalysts. They speed up most of the
reactions in the body which would otherwise be far too slow.
Enzymes are made of protein, a sensitive substance whose structure
is altered easily by temperature or pH
Digestive enzymes all break down large molecules into ones small
enough to pass through the intestine wall

                                                The shape of enzymes
                                                is vital to their role as
                                                catalysts and
                                                determines which
                                                reaction they catalyse

                                                The shape of enzymes is
                                                easily changed by heat or
                                                pH. The enzymes stop
                                                working and are said to be
                                                denatured.
     amylase                     pepsin
                                                                             8
 The role of enzymes in digestion



           ENZYME-CATALYSED REACTION
                                             Optimum     HUMAN ENZYME
                                           temperature


 Rate of
                                                                    ENZYMES CATALYSE
reaction                                                         EFFECTIVELY ONLY IF THEIR
                                                                    SHAPE IS CORRECT




                         Reaction rate           Enzyme shape
                        increases due              changing -
                       to kinetic effect          denaturation

                                            36.7 deg C
                           temperature

                                                                                       9
 The role of enzymes in digestion



           ENZYME-CATALYSED REACTION



                                                                    Two forms of
                                                                    trypsin.

 Rate of
reaction                                                            Where do
                                                                    they come
                                                                    from?

                                                       Pancreas /
                        Stomach                        small
                                                       intestine

                1   2   3   4     5   6    7   8   9     10    11
                                      pH
                                                                                10
The role of enzymes in digestion


                                    AMYLASE
                 part of a starch
                 molecule


                                    Amylase is produced by:
                                    The salivary glands (pH 7 -
                                    neutral)
                                    The pancreas
              AMYLASE
                                    The small intestine (pH 8)




                 sugar molecules
                       (maltose)

                                                                  11
  The role of enzymes in digestion


                                         LIPASE
                        A lipid
                        molecule
                                         Lipase is produced by:
                                         The pancreas
                                         The small intestine
                  LIPASE                 It works best at a slightly
                                         alkaline pH (8 or 9) - the
                                         pH of the duodenum

                    3 fatty acids

glycerol

                          Glycerol and
                          fatty acids

                                                                       12
The role of enzymes in digestion


   Small part of a protein
                                          PROTEASE
  molecule (9 amino acids)

                             Protein
                                               Protease is produced by:
                                               The stomach (pH 3)
                                               The pancreas
                  PROTEASE                     The small intestine (pH 8)
                                               There are different kinds of
                                               protease, one working best
                                               at pH 3 in the stomach,
                                               another at pH 8 or 9 in the
                                               duodenum
                             amino acids (9)


                                                                              13
  Lipase activity and denaturation
  This experiment is designed to discover if high temperatures denature the
  enzyme lipase
  INSTRUCTIONS
     1      2     3    4
                                1                                2
                                                               Cool to
                                                                room
                                                                temp


                                        RT   40OC 60OC 80OC


1 ml of lipase in each                  5 minutes water bath             2 ml milk
     boiling tube                            treatment
                                                                         1 ml sodium carbonate
                                                                         2 drops of phenolphthalein
 3       Time how long it takes for the mixture in                         MIX THOROUGHLY
         each of the 4 tubes to turn from pink to white

 4       Does amylase work in your experiments at 60 and 80 degrees?                             14
Lipase activity and temperature
THEORY

                                                      The mixture of lipase, milk and
                                                      sodium carbonate starts off alkaline
                                                      because of the sodium carbonate

                                                      As the lipase works on the milk it
                                                      converts fats to fatty acids.

                                                      The mixture turns acid

                    TIME                              The phenolphthalein turns
                                                      colourless as the fatty acids build
                                                      up

                                                      Does temperature denature lipase
    ALKALI                        ACID                in your experiment?
phenolphthalein is pink in alkali and white in acid

                                                                                            15
The liver and bile

The liver produces bile which emulsifies fats and neutralises stomach acids.




 Bile is stored in the gall
     bladder and passes
 down the bile duct into
  the duodenum during
                 digestion




                                             duodenum
                                                                               16
 The liver and bile
 Bile contains bile salts which act as a natural detergent. When mixed with
 fat bile breaks down the fat into much smaller droplets (emulsification)
                       CLICK TO ADD
                           BILE




                                          BILE
           LARGE FAT
            DROPLET




                                                        Thousands of smaller droplets –
                                                         much greater surface area –
PREVIOUS                                                 more surface for the enzyme
                                                           lipase to ‘attack’ the fat.
 BACK


  Bile also contains sodium bicarbonate (NaHCO3) which neutralises
  stomach acid (HCl) which has passed into the duodenum. Duodenum
  enzymes need neutral or alkaline pH to work effectively
              NaHCO3    + HCl         =     NaCl   +   CO2    +    H2O                17
                                                             WHAT YOU SHOULD
                                                             KNOW AT THE END
                                                               OF THIS UNIT
Digestion breaks down large insoluble substances into ones small enough for absorption
through the wall of the small intestine
Where mucus is produced and the role of mucus and peristalsis in digestion

Enzymes are catalysts made of protein and are sensitive to heat and pH. Digestive
enzymes speed up the digestive process
The function of the following enzymes, including where they are found in the intestine:
Amylase, protease, lipase

The structure and function of the mouth, oesophagus, stomach, small intestine and large
intestine
How the liver produces and stores bile

How and why bile emulsifies fats and how produces an alkaline pH in the small
intestine to help digestion

                                                          TEST QUESTIONS                  18
19

				
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posted:8/15/2011
language:English
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