Page 930 - Fundamentals of anatomy physiology
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Chapter 24 The Digestive System 917
Figure 24–7 The Salivary Glands. ATLAS: Plates 3c,d; 18a,b
Parotid duct Mucous Serous
cells
Openings of Duct cells
sublingual
ducts Salivary Glands
Parotid salivary
Lingual gland
frenulum Sublingual
salivary gland
Opening of left Submandibular
submandibular salivary gland
duct Submandibular salivary gland LM × 300
Submandibular b The submandibular gland secretes a mixture of
duct mucins, produced by mucous cells, and enzymes,
produced by serous cells.
a A lateral view, showing the relative positions of the salivary
glands and ducts on the left side of the head. For clarity,
the left ramus and body of the mandible have been
removed. For the positions of the parotid and submandibu-
lar ducts in the oral cavity, see Figure 24–6.
secretions of each parotid gland are drained by a parotid by bacteria. In addition, saliva contains antibodies (IgA) and
duct, which empties into the vestibule at the second upper lysozyme. Both help control populations of oral bacteria. A
molar. reduction in or elimination of salivary secretions—caused by
radiation, emotional distress, certain drugs, sleep, or other
2. The sublingual (sub-LING-gwal) salivary glands are cov- factors—triggers a bacterial population explosion. This pro-
ered by the mucous membrane of the floor of the mouth. liferation rapidly leads to recurring infections and progressive
These glands produce a mucous secretion that acts as a buf- erosion of the teeth and gums.
fer and lubricant. Numerous sublingual ducts open along
either side of the lingual frenulum. The saliva produced when you eat has a variety of func-
tions, including the following:
3. The submandibular salivary glands lie along the inner
surfaces of the mandible within a depression called the Lubricating the mouth.
mandibular groove. Cells of the submandibular glands
(Figure 24–7b) secrete a mixture of buffers, glycoproteins Moistening and lubricating food in the mouth.
called mucins, and salivary amylase. The submandibular
ducts open into the mouth on either side of the lingual Dissolving chemicals that can stimulate the taste buds and
frenulum immediately posterior to the teeth (Figure 24–6b).
provide sensory information about the food. 24
Saliva
Beginning the digestion of complex carbohydrates before
The salivary glands produce 1.0–1.5 liters of saliva each day.
Saliva is 99.4 percent water. The remaining 0.6 percent includes the food is swallowed. The enzyme involved is salivary
electrolytes (principally Na+, Cl−, and HCO3−), buffers, glyco-
proteins, antibodies, enzymes, and waste products. The glyco- amylase, also known as ptyalin or alpha-amylase. Saliva also
proteins, called mucins, give saliva its lubricating action. About
70 percent of saliva comes from the submandibular salivary contains a small amount of lingual lipase secreted by the
glands. Another 25 percent comes from the parotid glands, and
5 percent from the sublingual salivary glands. glands of the tongue. The digestive process begins in the
Saliva continuously flushes the oral surfaces, helping to oral cavity, but it is not completed there. No absorption
keep them clean. Buffers in the saliva keep the pH of your
mouth near 7.0. They prevent the buildup of acids produced of nutrients takes place across the lining of the oral cavity.
Control of Salivary Secretions
The autonomic nervous system normally controls salivary
secretions. Each salivary gland has parasympathetic and sym-
pathetic innervation. The parasympathetic outflow originates
in the salivatory nuclei of the medulla oblongata and syn-
apses in the submandibular and otic ganglia. pp. 523, 525
