1. Notes on
The Digestive System

2. Functions
1. Breaks down food into molecules the body can use (digestion).
2 types:
Mechanical (physical) – food broken down into smaller pieces
Chemical – enzymes break foods into their smaller chemical building blocks
2. Molecules are absorbed into the blood and carried throughout the body (absorption)
3. Wastes are eliminated from the body

3. The Mouth
Mechanical digestion – teeth break down food into smaller pieces, tongue mixes saliva with food, moistening them into a slippery mass
Chemical Digestion – Enzymes speed up chemical reactions in the body
Salivary gland produces amylase breaks down starch into sugar

4. Esophagus
Epiglottis closes over the trachea so food doesn’t go “down the wrong pipe”
Food travels down the esophagus, a muscular tube that connects the mouth to the stomach
Lined with mucus to help food move along
Peristalsis – waves of muscle contraction that move food through the digestive system

5. Stomach
Expands to store food until it can be liquefied and proteins can be broken down
Mechanical digestion – 3 layers of muscle contract to churn materials
Chemical digestion – 3 secretions of the stomach
Pepsin – digests proteins in your food
HCl – activates pepsin, also kills bacteria to keep you healthy
Mucus – coats and protects the lining of your stomach
Food squirted into small intestine a little at a time

6. Alexis St. Martin and William Beaumont

7. Small Intestine Food leaves the stomach as chyme, a thick liquid
Most chemical digestion takes place in the top 1/3 of the small intestine, called the duodenum
Small intestine produces enzymes that break down proteins, carbohydrates, and lipids
Also receives secretions from the accessory organs
Additionally, absorption of nutrients takes place here

8. Accessory Organs Food does not actually travel through these organs
Digestive juices are dumped into the top part of the small intestine
3 organs
Liver – produces bile to break up fat particles (not an enzyme)
Gallbladder – stores bile until it is needed, secretes it through the bile duct
Pancreas – produces enzymes that break down proteins, lipids, and carbohydrates

9. Which Surface is Larger?
1. Place your hand palm-side down on a table. Keep your thumb and fingers tightly together. Have your partner lay string along the outline of your hand from the wrist on one side to the wrist on the other side. Determine how long the outline of your hand is (in cm). Record the results in your lab notebook.

10. 2. Now, spread out your fingers as wide as possible
2. Now, spread out your fingers as wide as possible. Measure the length of the string now and record the result in your lab notebook.
3. Help your partner calculate the size of his or her hand.

11. Question #1: Which is larger – the outline when your hand is closed or when it is open?
Question #2: Which is more useful in absorption of nutrients – a flat surface or a folded surface? Why?

12. Absorption in the Small Intestine
Small nutrient molecules in the chyme are ready to be absorbed
Inner surface of the small intestine looks hairy – covered in tiny finger-shaped structures called villi
Villi have tiny capillaries inside where nutrients are absorbed
Villi increase the surface area of the small intestine so more nutrients get absorbed more quickly

13. The Large Intestine The last section of digestive system
Begins at the appendix, a vestigial organ
Water is absorbed into the bloodstream
Contain bacteria that feed on the material passing through (and give you vitamin K and outcompete bad bacteria)
Waste is compacted and ready for elimination
Last few inches of the large intestine is the rectum where waste is stored until it is eliminated
Waste leaves through the anus, a muscular opening at the end of the rectum