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Module 1: Módulo 3: Introdução ao sistema digestivo humano

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When an individual needs foods, he experiences a sensation known as hunger.

The hypothalamus area of the brain controls the degree of hunger or satiation (feeling of being well fed).

To do this, the hypothalamus receives various types of information from throughout the body.

Page 2 Food Selection
When food is presented, an individual goes through a process of food selection.

He or she has a greater appetite for some foods than others.

This process is related both to previous learning and to current, internal chemical requirements.

Page 3 Biting
Together, the upper and lower incisors (anterior teeth) create two cutting surfaces like a pair of scissors.

As food items are placed in the opening of the oral cavity, bite-size chunks of food are cut off.

These chunks are usually just the right size for the mouth to handle.

Page 4 Two Key Facts about Digestion
In general terms, there are two key facts to understand about digestion:

a. First, digestion is a chemical process. Through a process called hydrolysis,
food is broken down into its constituent parts.
b. Second, this chemical process takes place only at wet surfaces of the food.

Page 5 Mastication
During the process known as mastication (chewing), the food particles are
gradually broken down into smaller and smaller pieces. At the same time, the total
surface area of the food increases greatly.
a. This grinding and crushing of the food particles are accomplished by the
posterior teeth, the premolar and molar teeth. For this purpose, these teeth have broad,
opposing surfaces.
b. Together, the tongue and cheeks act to keep the food particles between the
surfaces of the grinding teeth. This is accomplished as the lower jaw moves up and
down.

Page 6 Saliva
a. Secreting fluids into the oral cavity are such glandular structures as the
salivary glands and the buccal glands. (The buccal glands are serous and mucous
glands on the inner surfaces of the cheeks.) These fluids are collectively known as the
saliva.
b. Saliva serves to wet the surface areas of the food particles produced by
mastication. In addition, saliva also dissolves some of the molecules of the food items.
c. Taste buds sample these dissolved molecules and test the quality of the food
being eaten. Taste buds are located on the tongue and the back of the oral cavity.
d. Another component of the saliva is mucus. The mucus tends to hold the food
particles together as a bolus. Since the mucus also makes this bolus somewhat
slippery, the bolus can slide readily through the initial portion of the digestive tract.