Transcript 24.4

Chapter 24
4 – Oral Digestion
Oral Digestion
• The first portion of the GI tract (alimentary
canal) that receives food and saliva is called
the mouth.
Oral Digestion
• The mouth (oral cavity) is formed by the
cheeks, hard and soft palates, and tongue.
Oral Digestion
• The major portion of saliva in the mouth is
secreted by the salivary glands, which lie
outside the mouth and pour their contents
into ducts that empty into the oral cavity.
Oral Digestion
• Salivary glands are glands that release a
secretion called saliva into the oral cavity.
Oral Digestion
• Saliva is a secretion that lubricates and
dissolves food and starts the chemical
digestion of carbohydrates.
Oral Digestion
– Saliva also functions to keep the mucous
membranes of the mouth and throat moist.
Oral Digestion
• Three are three pairs of major salivary glands:
1. The parotid glands
2. The submandibular glands
3. The sublingual glands
Oral Digestion
1. The parotid glands are located inferior and
anterior to the ears, between the skin and
cheek muscle.
Oral Digestion
2. The submandibular glands are found in the
floor of the mouth medial and inferior to the
mandible.
Oral Digestion
3. The sublingual glands are located beneath
the tongue and superior to the
submandibular glands.
Oral Digestion
• The tongue is an accessory digestive organ
composed of skeletal muscle covered by a
mucous membrane.
Oral Digestion
– The apical and lateral surfaces of the tongue are
covered with papillae; some papillae contain taste
buds, others contain touch receptors that make it
easier for the tongue to move food in the oral
cavity.
Oral Digestion
• Papillae are projections of the lamina propria
covered with keratinized epithelium.
Oral Digestion
• The teeth (dentes) are accessory digestive
organs located in the sockets of the mandible
and maxillae.
Oral Digestion
• A typical tooth has three major external
regions:
1. The tooth crown
2. The tooth root
3. The tooth neck
Oral Digestion
1. The tooth crown is the visible portion of the
tooth above the level of the gums.
Oral Digestion
2. The tooth root is the part of the tooth
embedded into the jawbone sockets.
Oral Digestion
3. The tooth neck is the constricted junction of
the crown and root near the gum line.
Oral Digestion
• **Teeth are composed primarily of dentin;
dentin is harder than bone because of its
higher content of calcium salts (70%).
Oral Digestion
• Dentin is a calcified connective tissue that
gives teeth its basic shape and rigidity.
Oral Digestion
• Enamel is the hard white substance covering
the crown of a tooth; it is the hardest
substance in the body with a content of
calcium salts (95%).
Oral Digestion
• Humans have two dentitions, or sets of teeth:
1. Deciduous teeth (primary)
2. Permanent teeth (secondary)
Oral Digestion
1. Deciduous teeth are twenty teeth that erupt
in pairs beginning at 6 months of age; all
deciduous teeth are generally lost between
ages 6 and 12.
Oral Digestion
2. Permanent teeth are thirty-two teeth that
erupt between age 6 and adult hood; four
types result: incisors, canines, premolars and
molars.
Oral Digestion
1. Incisors are used for biting
2. Canines are used for tearing
3. Premolars are used for crushing and grinding
4. Molars are used for crushing and grinding
Oral Digestion
• **Digestion in the mouth is both mechanical
and chemical and results from chewing or
salivary enzyme activity.
Oral Digestion
• Two enzymes contribute to chemical
digestion in the mouth:
1. Salivary amylase
2. Lingual lipase
Oral Digestion
1. Salivary amylase is an enzyme secreted by
the salivary glands that initiates the
breakdown of starch.
Oral Digestion
2. Lingual lipase is an enzyme secreted by
glands in the tongue that begins the
breakdown triglycerides; it isn’t activated
until it reaches the acidic environment of the
stomach.
Homework
• Finish handout:
– “Oral Digestion”
• Study for mini-quiz