1. Chapter 15 Section 2: Digestive process begins
Key Concepts: What functions are carried out in the digestive system? What roles do the mouth, esophagus, and stomach play in digestion?
Key terms: Digestion, absorption, saliva, enzyme, epiglottis, esophagus, mucus, peristalis, stomach

2. Functions of the digestive system
The digestive system has three main functions:
Breaks down the food into molecules the body can use
Molecules are absorbed into the blood
Wastes are eliminated from the body

3. Functions
Digestion – the process by which your body breaks down food into small nutrient molecules
Two kinds: mechanical and chemical
Mechanical – foods are physically broken down into smaller pieces
Chemical – chemicals produced by the body break foods into smaller chemical building blocks

4. Absorption and elimination
Absorption is the process by which nutrient molecules pass through the wall of your digestive system into your blood
Materials that are not absorbed, such as fiber, are eliminated from the body as wastes

5. The mouth Both mechanical and chemical digestion begin in the mouth
Saliva – fluid released in your mouth – helps both kinds of digestion

6. Mechanical digestion in the mouth
Teeth carry out the first step
Incisors – cut the food, canines tear and slash the food, molars and premolars grind the food. Saliva moistens the food. This is all mechanical.
Chemical digestion – saliva has chemicals (enzymes – proteins that speed up reactions) that break food down. Enzyme shape enables it to take part in only one kind of chemical reaction.

7. Esophagus
A muscular tube that connects the mouth to the stomach. It is lined with mucus – a thick, slippery substance. Food remains in the esophagus for about 10 seconds. Smooth muscle contractions move the food down. The contractions are called peristalis (involuntary waves of muscle contraction)

8. Epiglottis
Stops food and other stuff from going into your windpipe (trachea) instead of your esophagus. It’s a little flap of tissue.

9. The Stomach Stomach – J shaped, muscular pouch
Most chemical and mechanical digestion happens here
Three strong layers of smooth muscle contract to churn the food
Chemical digestion occurs as food contains digestive juice which contains the enzyme pepsin. Pepsin breaks down proteins in food into amino acids. Digestive juice also contains HCl.

10. Why don’t you have holes in your stomach?
Mucus lines your stomach and the cells are replaced often.