1. Mrs. Legro’s 6th grade Science Class
The Digestive System
Mrs. Legro’s 6th grade Science Class

2. Objective
Distinguish the differences between mechanical digestion and chemical digestion
Identify the organs of the digestive system and what takes place in each
Explain how homeostasis is maintained in digestion

3. Vocabulary Digestion Mechanical digestion Chemical digestion Enzyme
Peristalsis
Chyme
Villi

4. Functions of the Digestive System
Ingestion
Digestion
Absorption
Elimination
Food is processed in 4 stages

5. Ingestion
As soon as food enters your mouth, breakdown begins

6. Digestion
Digestion is the process that breaks down food into small molecules so they can be absorbed and moved into the blood.
Digestion is mechanical and chemical.
Mechanical digestion takes place when food is chewed, mixed and churned.
Chemical digestion occurs when chemical reactions occur that break down large molecules of food into smaller ones.
From the blood, food molecules are transported across the cell membrane to be used by the cell.
Unused molecules pass out of your body as wastes.

7. Chemical Digestion
Chemical digestion is possible only because of enzymes.
Enzymes are a type of protein that speeds up the rate of chemical reaction in your body.
Amylase: enzyme produced by glands near mouth. They help breakdown complex carbs into simpler carbs.
Pepsin: an enzyme in your stomach that break down complex proteins into less complex proteins.
One way enzymes speed up reactions is by reducing the amount of energy necessary for a chemical reaction to begin.
Small intestine, a number of other enzymes continue to speed up the breakdown of proteins into amino acids
Pancreas (organ on the back side of the stomach) releases several enzymes through a tube into the small intestine

8. Major Organs of the Digestive System
Tongue
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum
Anus
Accessory Organs: Very important to the mechanical and chemical digestion process.
tongue, teeth, salivary glands, liver, gallbladder and pancreas
All organs of the digestive system include: Food passes through all of these organs.
If stretched out, an adult’s digestive system is 6m – 9m long

9. The Mouth
Mechanical (MD) and chemical digestion (CD) begin in your mouth.
MD happens when you chew your food with your teeth and mix it with your tongue.
CD begins with saliva. As you chew, your tongue moves food around and mixes it with saliva.
Food mixed with saliva becomes a soft mass and is moved to the back of your mouth by your tongue. It is swallowed and passes into your esophagus.
Ingestion is now complete, but digestion continues.

10. The Esophagus It is a muscular tube about 25cm long.
It takes about 4 – 10 seconds for food to move down the esophagus to the stomach.
Mucous glands in the wall of the esophagus keep the food moist.
Smooth muscles in the wall move food downward with a squeezing action, called peristalsis, which moves food through the entire digestive track.

11. The Stomach MD and CD take place in the stomach.
Mechanically, food is mixed in the stomach by peristalsis.
Chemically, food is mixed with enzymes and strong digestive solutions, such as hydrochloric acid solution, to help break it down.
The acidic solution works with the enzyme pepsin to digest protein and it also destroys bacteria present in the food.
Stomach produces mucus, which makes food more slippery and protects the stomach from the strong digestive solutions.
Food moves through your stomach in 2-4 hours and is changed into a thin, watery liquid called chyme.
Little by little, chyme moves out of your stomach and into your small intestine.
The stomach is a muscular bag.

12. The Small Intestine
It is small in diameter by is 4 – 7meters in length.
As chyme leaves your stomach, it enters the duodenum, this is where most of the digestion takes place.
Bile, a greenish fluid from your liver, is added to break up the large fat particles (similar to the way detergent breaks up grease).
Absorption of food takes place in the small intestine.
Villi are fingerlike projections covering the wall of the small intestine. These increase the surface area of the small intestine so nutrients in the chyme have more places to be absorbed.
Nutrients move into blood vessels within the villi.
Then blood transports the nutrients to all cells in your body.
Peristalsis continues to force the remaining undigested and unabsorbed materials slowly into the large intestine.

13. The Large Intestine
The main job of the large intestine is to absorb water from the undigested mass.
Chyme may stay here for as long as three days.
After excess water is absorbed, the remaining undigested materials become more solid.
Muscles in the rectum, which is the last section of the large intestine, and the anus control the release of semisolid wastes from the body in the form of feces.

14. Bacteria Bacteria live in many organs of your digestive tract.
Bacteria in your large intestine feed on undigested material like cellulose.
Bacteria make vitamins you need, such as, vitamin K and two B vitamins.
Vitamin is needed for blood clotting
The two B vitamins are needed for your nervous system and other bodily functions.

15. Putting it all together…
Ingestion to Digestion from beginning to end