Digestive System Parts and Function

					Digestive System


  Parts and Function
Digestion
 All organisms are composed of four complex
 biological molecules: lipids (or fats), proteins,
 carbohydrates, and nucleic acids.
 For consumers such as humans, these molecules
 must be broken down into their component parts.
   Lipids to fatty acids, proteins to individual amino acids,
   and carbohydrates into simple sugars
 The chemical breakdown of complex biological
 molecules into their component parts is the
 process of digestion.
The digestive system
 In most animals the digestive system is made up
 of a tube (alimentary canal) that runs more or less
 the length of the body.
 Generally the food moves in one direction and
 different parts are responsible for doing different
 jobs in the digestive process.
 There are also accessory organs that are important
 in digestion that connect to the alimentary canal
 via ducts.
Principle Parts of Alimentary
Canal
  Mouth- mechanical breakdown of food; tasting; secretion of
  salivary glands (salivary amylase)
  Esophagus- muscular tube that connects the mouth with the
  stomach
  Stomach- large muscular storage organ; functions in
  storage, mixing, some secretions (acid and pepsinogen)
  Small intestine (3 parts)
      Duodenum, jejunum, ileum
      Receives bile, pancreatic amylase, other secretions;
      absorption of nutrients (most sugars absorbed here)
  Large intestine- reabsorption of water; bacteria in colon
  produce Vit. K
  Anus- external opening surrounded by sphincter muscle
Accessory Organs Connected to
Digestive System
 Liver- has many functions including
 regulation of amino acids in blood,
 production of glycogen (a storage molecule)
 and bile, converting ammonia to urea
 Pancreas- secretion of amylase and insulin
 (lack on insulin may cause diabetes)
 Gall Bladder- storage of bile
A. Salivary Glands
B. Esophagus
C. Stomach
D. Pancreas
E. Large Intestine
F. Appendix
G. Small intestine
H. Gall Bladder
I. Liver
Connections to the Circulatory
System
 Mesenteric Veins- veins connected to capillary
 bed closely tied with the intestine
 Hepatic Portal System- major blood vessel that
 takes blood from the intestine to the capillary bed
 in the liver
 Circulatory system- major system that transports
 nutrients to the rest of the body
   Absorption of nutrients from the small intestine occurs
   with the aid of villi and microvilli in the small intestine
   which increase surface area for diffusion
The Villi of the small intestine
Enzymes
 They are biological catalysts which greatly
 increase the rate of a chemical reaction but are not
 themselves changed during the process
 Enzymes are central in the digestion of many
 substances including carbohydrates, fats and
 proteins.
 In most animals, the digestive enzymes are
 secreted into a special extracellular (outside of the
 cells) cavity called a gut where digestion actually
 takes place
   These smaller molecules can then be absorbed by the
   circulatory system and distributed to cells throughout
   the body.
Importance of Proteins
 Proteins are important as a structural
 element in bones, cartilage, hair, feathers,
 nails, and cell membranes.
   They are also important as enzymes, hormones,
   antibodies, and in oxygen transport in red blood
   cells.
 Proteins are formed by the linkage of amino
 acids into polypeptides.
Digestion of Proteins
 Any enzyme that digests proteins is called a
 protease
 Chemical digestion of proteins begins in the
 stomach
   The stomach is very acidic (has a low pH,   1.5 - 7)
 Pepsin is the primary digestive enzyme in the
 stomach
 The small intestine carries out further digestion
 with trypsin, which is secreted by the pancreas
 As proteins are digested, the polypeptide chains
 unravel and break up into small chains of amino
 acids called peptides
Importance of Lipids
 They are fats and oils which are a fundamental
 component of cell membranes and may be used
 for energy storage or insulation
 A characteristic feature is that they do not dissolve
 in water
Digestion of Lipids
 It begins in the small intestine by making the molecules more
 compatible with water so that the digestive enzymes can
 access them.
    This is accomplished by breaking up the lipid into small droplets
    which can be distributed in the water of the small intestine
      • This process is referred to as emulsification
    Bile which is produced by the liver, stored in the gall bladder and
    pumped into the small intestine when lipids are present is responsible
    for emulsification
 Once emulsified, they may be digested into their subunits
 (glycerol and fatty acids) by digestive enzymes called lipases.
    They are produced in the pancreas and secreted into the small
    intestine
Importance of Carbohydrates
 These include simple sugars such as glucose and sucrose
 and polysaccharides such as starch and cellulose
 They are important as structural compounds and as a
 source of energy that can be used as ATP
 Starch is a complex polysaccharide made in plants cells for
 the storage of energy
    Foods such as potatoes and pumpkins are rich in starch
    and can be good sources of energy
 Cellulose is one of the most common carbohydrates and
 can be found in the cell walls of plants
    Human digestive system is unable to break down
    cellulose and is the largest component of dietary fiber
Digestion of carbohydrates
 The digestion begins by converting
 polysaccharides (long chains of simple sugars) and
 disaccharides (two sugars linked together) into
 monosaccharides (simple sugar units) that can be
 absorbed by body cells
   It begins in the mouth and is completed in the small
   intestine (they are not digested in the stomach)
 Amylase is the enzyme responsible for digesting
 starch
   It can be found in the mouth in one’s saliva as well as
   in the small intestine secreted by the pancreas

				
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posted:4/7/2008
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