Digestive System

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Digestive System

• Oral Cavity

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Oral Cavity

• Formed by
• - cheeks
• - lips (labia)
• - hard palate
• - soft palate
• - tongue

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Oral Cavity (cont.)

• vestibule - space bounded externally by cheeks
  and lips, and internally by gums and teeth
• oral cavity proper - space that extends from gums
  and teeth to fauces
• fauces - (opening) between oral cavity and the
  pharynx

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Cheeks

• form lateral walls
• muscular structures covered by skin on the
  outside
• lined on inside by nonkertanized stratified
  squamous epithelium

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Lips (labia)

• fleshy folds of skin surrounding the orifice
  (opening) of the mouth
• vermilion border - transitional zone of lips
  where external skin meets internal mucous
  membrane
• inner surface of lips are connected to gingiva
  (gum tissue) by mucous membrane called the frenum

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Hard Palate

• anterior portion of roof of mouth
• formed by maxillary and palatine bones
• covered by mucous membrane
• forms partition between oral and nasal cavities

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Soft Palate

• forms posterior portion of roof of mouth
• lacks bony quality of hard palate
• arch-shaped muscular partition
• between oropharynx and nasopharynx
• lined with mucous membrane
• uvula - muscular process that hangs from free
  border of soft palate
• posterior border opens into oropharynx through
  fauces

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Palatopharyngeal Arch

• anterior muscular fold on either side of base of
  uvula
• runs down lateral side of soft palate
• extends to side and base of tongue
• Palatoglossal Arch
• posterior muscular fold on either side of base of
  uvula
• extends to side of pharynx

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Tonsils

• masses of lymphatic tissue
• Three types
• - palatine
• - lingual
• - pharyngeal (adenoids)

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Tongue

• forms floor of oral cavity
• composed of skeletal muscle fibers running in
  several directions
• covered with mucous membrane
• connected in midline to floor of oral cavity by
  lingual frenum
• papillae are located on the tongue which aid in
  the manipulation of food

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Muscular Fibers of Tongue

• extrinsic muscles
• - originate outside tongue
• - insert into tongue
• - maneuver and move food
• intrinsic muscles
• - originate and insert within tongue
• - alter shape and size of tongue

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Tongue Papillae

• filiform
• - thickly distributed over anterior two-thirds
  of dorsum of tongue
• fungiform
• - scattered irregularly on dorsum of tongue
• circumvallate
• - 8-12 papillae
• - form V-shape in posterior of tongue

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Taste Buds

• located in and around papillae on tongue
• Four Primary Tastes
• - sweet - lateral border in anterior
• - sour - anterior 1/2 to midline
• - salty - lateral borders in anterior
• - bitter - bitter

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Salivary Glands

• parotid
• - located anterior and inferior to ears
• - largest
• submandibular
• - located beneath the base of tongue
• sublingual
• - located in the floor of mouth
• - smallest

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Salivary Secretions

• Two types of cells
• - serous cells produce a watery fluid that
  contains a digestive enzyme called amylase
• - mucous cells secrete thick mucus that binds
  particles together and lubricates during
  swallowing
• pH of saliva is 6.35 to 6.85

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Teeth

• aid in mastication
• mechanically break food into smaller pieces
• helps to mix food with saliva
• Two sets of teeth
• - deciduous (begin erupting by 6 months old
  begin exfoliating by 6 years old)
• - permanent (begin erupting by 6 years old)

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Types of Teeth

• Primary Permanent
• incisors 8 8
• cuspids 4
  4
• premolars 8
• molars 8
  12
• 20
  32

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Incisors

• two pairs in each jaw
• one central, one lateral
• chisel-shaped
• one root
• cuts food

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Cuspids

• also known as canines
• one pair in each jaw
• one cusp or pointed surface
• used to tear or shred food

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Premolars

• also known as bicuspids
• two pairs in each jaw
• first and second premolar
• two cusps and one root (maxillary first premolars
  have two roots)
• used to crush and grind food

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Molars

• three pairs in each jaw
• first, second, and third molars
• flattened crowns
• prominent ridges
• three roots
• used to crush and grind food

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Anatomy of a Tooth

• crown
• - exposed portion above level of gingiva
• - contains the pulp cavity
• neck
• - narrow junction between crown and roots
• root
• - embedded in alveolar bone
• - contains root canals - nerves, blood and
  lymphatic vessels

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Composition of a Tooth

• dentin
• enamel
• pulp
• cementum
• periodontal ligament

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Dentin

• dense, hard, light yellow substance
• makes up bulk of tooth
• calcified connective tissue
• harder than bone, but softer than enamel
• gives the tooth its basic shape and rigidity
• encloses pulp cavity

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Enamel

• hardest tissue in the human body
• consists of primarily calcium phosphate and
  calcium
• hard tissue that covers the entire crown of the
  tooth
• protects the dentin

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Pulp

• connective tissue containing blood and lymphatic
  vessels, and nerves
• fills pulp cavity and root canals

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Cementum

• bone-like
• covers roots of teeth in a thin layer
• joins enamel near cervix of tooth

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Periodontal Ligament

• group of connective fibers
• suspends the tooth in the socket
• absorbs shock of mastication
• supports gingiva