DIGESTIVE SYSTEM

DIGESTION IN THE MOUTH 3

Physical breakdown Teeth, palate & tongue Chemical digestion Saliva & amylases 4

Teeth, tongue and palate mechanically break down large food particles into small food particles. Saliva moisturizes and lubricates the food. Salivary amylases begin the chemical digestion of large starch and glycogen chains into smaller chains carbohydrate chains.

Amylases begin the breakdown of starch & glycogen into maltose & glucose. 7

Cellulose from plant cell walls cannot be digested Cellulose from plant cell walls cannot be digested. Forms fiber / roughage.

Mouth structures: salivary glands Epithelial tissue that secretes saliva & amylases.

Mouth structures: Masseter & Temporalis muscles Main mastication skeletal muscles. Superficial and very, very strong. 10

Mouth structures: Tongue A muscular hydrostat (a muscle with no skeletal bone support). Essentially, muscle and water! Used to manipulate food. Packed with sensory receptors.

Mouth structures: Uvula Used for voice articulation.

Ever had uvulitis?

Mouth structures: Teeth! Used for the mechanical breakdown of food!

The dentin is similar to enamel but not as hard. Adds support. Enamel is crystalline calcium phosphate, the hardest substance in the body. Only visible layer. Created by ameloblast cells. The dentin is similar to enamel but not as hard. Adds support. The pulp is connective tissue with blood vessels and nerves. Odontoblasts produce dentin. Cementum is a “glue” layer produced by cementoblasts. 15

Human teeth include the incisors, the canines, the premolars & the molars.

Human Teeth Incisors (8): front flat teeth, very sharp. Adapted for cutting and shearing. Canines (4): also called cuspids or fangs are long, pointed teeth that evolved for holding food in place. 4 in total. Premolars (8): also called bicuspids are transitional teeth between canines and molars. Used for mastication (chewing). Molars (12): have four cusps. Used for grinding and crushing food. Last molar is the wisdom tooth.

Human teeth anchor in the bone via the root Human teeth anchor in the bone via the root. Nerves and blood vessels keep them supplied and controlled.

Original 20 teeth begin to be replaced at around age 7.

Adult humans have 32 teeth. Notice how the wisdom teeth no longer lock in place

Wisdom teeth are vestigial structures left over from when our ancestors had a more herbivores diet. The jaw doesn’t have enough space for wisdom teeth, and so as they grow they may become impacted and may have to be surgically removed.

Teeth arrangement and size indicates the diet of the organism.

Ominovorous diet Omnivores: Incisors to tear, molars & premolars to crush, canines to hold.

Omnivores: Bears.

Carnivores: Small incisors to tear & hold, massive canines to rip and shred, premolars and molars chiseled and razor- edged to slice.

Cetaceans: In toothed whales and dolphins the mammalian dentition is heavily modified. 29

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Herbivores: Large incisors for cutting and nipping, canines much reduced and chisel-shaped to help incisors, large premolars and molars.

Teeth Afflictions

1. Dental Plaque A build-up of bacterial film around teeth. If not removed, may lead to dental tartar (hardened plaque).

2. Dental Cavities (caries) Acid produced by bacteria in plaque destroys the enamel and the dentin, creating a cavity. Tooth fillings may be necessary.

3. Root canals Damaged or infected pulp resulting from cavities is removed and root is replaced with a filler.

4. PERIODONTITIS Around-tooth damage caused by excess plaque build up. May lead to gingivitis, or the inflammation of jaw gum. The gums retreat and expose the roots of teeth.

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