660
UNIT FIVE
PRACTICE
10
How do primary teeth dif
er From secondary teeth?
11
How are types oF teeth adapted to provide specialized Functions?
12
Describe the structure oF a tooth.
13
Explain how a tooth is attached to the bone oF the jaw.
17.4
SALIVARY GLANDS
The
salivary
(sal
ı˘-ver-e)
glands
secrete saliva. This fl
uid
moistens food particles, helps bind them, and begins the
chemical digestion of carbohydrates. Saliva is also a sol-
vent, dissolving foods so that they can be tasted, and it helps
cleanse the mouth and teeth. Bicarbonate ions (HCO
3
) in
saliva help buffer the acid concentration so that the pH of
saliva usually remains near neutral, between 6.5 and 7.5.
This is a favorable range for the action of the salivary enzyme
and protects the teeth from exposure to acids in foods.
Many minor salivary glands are scattered throughout the
mucosa of the tongue, palate, and cheeks. They continuously
secrete fluid, keeping the lining of the mouth moist. The
three pairs of major salivary glands are the parotid glands,
the submandibular glands, and the sublingual glands.
Salivary Secretions
The different salivary glands have varying proportions of
two types of secretory cells,
serous cells
and
mucous cells.
Serous cells produce a watery fl uid that contains a digestive
enzyme called
salivary amylase
(am
ı˘-la
¯s). This enzyme
splits starch and glycogen molecules into disaccharides—the
F
rst step in the chemical digestion of carbohydrates. Mucous
cells secrete a thick liquid called
mucus,
which binds food
particles and acts as a lubricant during swallowing.
Like other digestive structures, the salivary glands are
innervated by branches of both sympathetic and parasym-
pathetic nerves. Impulses arriving on sympathetic fibers
stimulate the gland cells to secrete a small volume of vis-
cous saliva. Parasympathetic impulses, on the other hand,
elicit the secretion of a large volume of watery saliva. Such
parasympathetic impulses are activated refl exly when a per-
son sees, smells, tastes, or even thinks about pleasant foods.
Conversely, if food looks, smells, or tastes unpleasant, para-
sympathetic activity is inhibited, so less saliva is produced,
and swallowing may become difF
cult.
A thin layer of bonelike material called
cementum,
sur-
rounded by a
periodontal ligament
(periodontal membrane),
encloses the root. This ligament, composed of collagen,
passes between the cementum and the bone of the alveolar
process, F
rmly attaching the tooth to the jaw. The ligament
also contains blood vessels and nerves near the surface of
the cementum-covered root
(f
g. 17.10)
. Clinical Application
17.1 describes the effect of bacteria on teeth.
Table 17.3
sum-
marizes the mouth parts and their functions.
Extracted primary and wisdom teeth may one day provide stem cells
that can be used to regenerate tooth roots and supporting periodon-
tal ligaments. The stem cells are in the pulp and a region called the
apical papilla. Dental researchers hope that these stem cells may
be cultured to yield replacement teeth For people who do not have
enough jawbone to support dental implants.
TABLE
17.3
|
Mouth Parts and Their Functions in Digestion
Part
Location
Function
Part
Location
Function
Cheeks
±orm lateral walls
oF mouth
Hold Food in mouth; muscles chew Food
Tongue
±loor oF mouth
Mixes Food with saliva; moves Food toward
pharynx; contains taste receptors
Lips
Surround mouth
opening
Contain sensory receptors used to
judge characteristics oF Foods
Palate
±orms rooF oF mouth
Holds Food in mouth; directs Food to
pharynx
Teeth
In sockets oF mandibular
and maxillary bones
Break Food particles into smaller pieces;
help mix Food with saliva during chewing
Crown
Gingiva
Alveolar
process
Root canal
Periodontal
ligament
Cementum
Root
Pulp
cavity
Dentin
Enamel
FIGURE 17.10
A section oF a tooth.
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