The Digestive
System
Chapter 23
Anatomy of the Digestive
System – Part 1
Overview
• Organs:
– Mouth, pharynx,
esophagus,
stomach, small
intestine, and
large intestine
Overview
• Accessory Organs
– Teeth, tongue,
gallbladder,, salivary
glands, liver,
pancreas
– Contribute to the
breakdown of food
Imagine
yourself
taking a bite
of food….
The Mouth
• AKA: oral cavity or buccal
cavity
• Opening  oral orifice
• Boundaries:
–
–
–
–
–
Lips anteriorly
Cheeks laterally
Palate superiorly
Tongue inferiorly
Continuous with oropharynx
posteriorly
The Lips (Labia) and Cheeks
• Lips – orbicularis oris
– Very large! Extend from
bottom of nose to bottom
of chin
– Red margin – lipstick or
kisses
• Cheeks – buccinators
• Both help to keep food
between the teeth when
we chew
• Also play a role in speech
• Labial frenulum – median
fold that joins the internal
aspect of lips to the gum
The Palate
• Roof of the mouth
– Hard palate
• Palatine and maxillae
bones
• Rigid surface against
which the tongue
forces food during
chewing
– Soft palate
• Posterior – arch
shaped
• Mobile fold formed
mostly of skeletal
muscle
Palate
– Soft Palate
• Uvula – projects down
from the free edge of the
soft palate
• During swallowing both
are drawn upwards
closing off the
nasopharynx and
preventing foods/liquids
from entering the nasal
cavity
• Try and breathe and
swallow at the same time
Teeth
• Teeth break and rip apart food
– Increases surface area
• Smaller pieces increases the surface area  enzymes in
the saliva can get at the food easier  chemical
breakdown of food takes place quicker
Teeth
• 2 sets of teeth
– Primary  baby teeth (20)
• First teeth appear ~6 mo
• Fall out b/t 6-12 years
– Permanent  adult (32)
• Absorb roots of baby teeth
causing them to fall out
• Usually all have erupted
(except 3rd molars) by end
of adolescence
• Wisdom teeth (3rd molars)
 erupt b/t 17-25 years
Teeth - Types
• Incisors
– Chisel-shaped
– Cutting or nipping off
pieces of food
• Canines
(cuspids/eyeteeth)
– Conical or fanglike
– Tear and pierce
• Premolars (bicuspids)
– Broad crowns and rounded
cusps
– Grinding or crushing
• Molars
– Broad crowns and rounded
cusps
– Grinding or crushing
Teeth - Regions
• Crown
– Exposed part of the
tooth
– Covered in enamel  a
cellular, brittle material
that bears the force of
chewing. Hardest
substance in the body.
Can’t repair itself!
• Root
– Portion embedded in the
jaw
Teeth - Cavities
• Result from a gradual
demineralization of
enamel and underlying
dentin by bacteria
• Dental plaque (film of
sugar, bacteria, etc.)
adheres to teeth 
bacteria dissolve
trapped sugars  those
produce acids, which
dissolve the enamel.
Salivary Glands
• We see food or think of food  Mouth starts
to water  saliva is released from the salivary
glands
Salivary Glands
• Secrete saliva
– Cleanses mouth
– Dissolves food chemicals
for tasting
– Moistens food and aids in
bolus formation
– Contains enzymes that
begin chemical breakdown
of starchy foods
• Three glands  parotid,
submandibular, sublingual
– Lie outside oral cavity and
empty saliva into it
Composition of Saliva
• Water  97 – 99.5%
• Slightly acidic  pH 6.757.0
• Digestive enzyme 
salivary amylase
• Proteins 
– Mucin – dissolved in water
forms a thick mucus that
lubricates the oral cavity
– Lysozyme – inhibits bacterial
growth in the mouth
– IgA – antibodies, protection
against microorganisms
• Metabolic wastes  urea
and uric acid
Tongue
• Occupies most of the
floor of the mouth and
fills most of the oral
cavity when mouth is
closed
• Composed of interlacing
bundles of skeletal
muscle fibers  during
chewing grips and
repositions food between
the teeth
Tongue
• Mixes food with saliva
 forms bolus (“lump”)
• Initiates swallowing 
pushes bolus
posteriorly
• Helps to form
consonants when we
speak
• Helps to keep food
between the teeth by
pushing the food
against the hard palate
Tongue
• Lingual frenulum –
secures tongue to floor
of mouth, limits
posterior movements
• Ankyloglossia (“fused
tongue”) aka tonguetied  when lingual
frenulum is too short 
limits movements of
tongue so speech is
distorted.
Tongue
• Filiform papillae
– Smallest and most
numerous
– Roughness that aids
in licking foods and
provides friction for
manipulating foods
in mouth
– Aligned in parallel
rows
– Whitish appearance
Tongue
• Fungiform papillae
– Mushroom-shaped
– Scattered widely over
the tongue surface
– Have a reddish hue
– House taste buds
• Circumvallate (vallate)
papillae
– 10-12, large, located in
a V-shaped row at that
back of the tongue
– House taste buds
Tongue
• Foliate papillae
– Pleatlike, located on
the lateral aspects of
the posterior tongue
– House taste buds
(only in infancy and
early childhood)
• Sulcus terminalis
– Posterior to
circumvallate
papillae
– Groove that
distinguishes
anterior and
posterior tongue
Taste
• For a chemical to be tasted it must dissolve in
saliva, diffuse into the taste pore, and contact
the gustatory hair. This causes a reaction
from the nervous system that allows us to
“taste” our food
Taste
• Taste buds – sensory receptors for taste
• Located mostly in the oral cavity ~10,000
• Most are on tongue. Few on soft palate, inner
surface of cheeks, pharynx, and epiglottis
• Most are found in papillae
– Tops of fungiform papillae, sides of foliate papillae
and circumvallate papillae
Taste
• Taste qualities: sweet, sour, salty, bitter, and
umami (“delicious”)
• Most taste buds respond to 2 or more taste
qualities and many substances produce a
mixture of the basic taste sensations
Taste
• Taste maps, although common, are inaccurate
(sweet tip, salty and sour  sides, bitter 
back, umami  pharynx
• In reality, there are only slight differences in
the localization of specific taste receptors in
different regions of the tongue, all types of
taste can be elicited from all areas that
contain taste buds
Taste
• Taste likes and dislikes have a
homeostatic value
• Umami guides intakes of proteins
• A liking for sugar and salt helps
satisfy the body’s need for
carbohydrates and minerals.
• Many sour, naturally acidic foods
(lemons, tomatoes, oranges) are
rich sources of vitamin C.
• Many natural poisons and spoiled
foods are bitter, our dislike for
bitterness is protective.
Taste
• Taste is 80% smell. When olfactory receptors
are blocked, food is bland.
• Mouth also contains thermoreceptors
(temperature), mechanoreceptors (touch), and
nociceptors (pain). The temperature and
texture of foods can enhance or detract from
their taste. Spicy or “hot” foods bring about
their effects by activating the pain receptors in
our mouth