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