1. The Human Digestive System

2. Main Goal of the Digestive System
The human body, unlike plants, cannot produce its own food, and must instead consume and break down organic material in order to obtain the nutrients needed for each and every cell’s survival
These nutrients are delivered to every cell in the body by the Circulatory System
Leftover digestive material is eliminated from the body by the Excretory System

3. Our body needs six categories of substances to survive.
The Six Substances
Our body needs six categories of substances to survive.
Proteins
The building blocks of life
Needed for growth and repair
Composed of amino acids

4. The Six Substances Carbohydrates Sugars and starches
Main source of energy
Can be simple or complex
Complex carbohydrates must be broken down into simple sugars before they can be used

5. The Six Substances Fats and Oils (or Lipids)
Long-term high energy storage
Insulation
Can be solid or liquid

6. The Six Substances Vitamins Minerals Fiber
Chemicals your body needs to function that it cannot produce itself
Minerals
Chemical elements needed for proper body function
Fiber
Indigestible portions of plants that maintain digestive system and “move things along”

7. Hungry anyone? Protein Solid and Liquid Fats
Simple and Complex Carbohydrates

8. The Mouth
Digestion begins in the mouth. Your teeth grind and tear apart your food, allowing enzymes from your salivary glands to touch all surfaces of your food. Your saliva begins to break down carbohydrates in your food and also makes your food slippery enough to slide easily down your throat.
Chemical and physical digestion is taking place.

9. Chemical vs. Physical Digestion
Physical Digestion – breakdown of food into smaller pieces only. A chewed up steak is still a steak.
Chemical Digestion – breakdown of food pieces by enzymes into six essential substances. Amino acids don’t resemble and are no longer considered to be steak after digestion.

10. After the mouth…
The epiglottis is the crossing guard of the throat. It is a flap of tissue that prevents food from entering your windpipe and chocking you when you swallow.

11. The Esophagus (2 feet)
Your voluntary role in digestion is over. Your brain takes over from here. After moving past the epiglottis, the food (in a clump known as a bolus) now is moved by peristalsis through the tube connecting your stomach and your mouth. This tube is called the esophagus.

12. Peristalsis
The wavelike contraction of smooth muscle that moves food throughout the digestive system.

13. The Stomach
Food enters the stomach and is continually churned up. In the stomach, the following are secreted:
Gastric acid - dissolves nutrients and minerals
Pepsin – breaks down proteins into amino acids
Is physical or chemical digestion occurring?
BOTH!

14. After the stomach…
Proteins have begun breaking down, and carbohydrates continue to break down. Food is no longer a solid clump but rather a thick soupy liquid called chyme. The stomach allows the chyme to leave at a constant rate, much like a funnel. The chyme is extremely acidic.

15. The Small Intestine
The first foot of the small intestine (SI) is called the duodenum. Here, the extremely acidic chyme is neutralized by secretions from the pancreas. The pancreas then secretes additional enzymes to the chyme to break down the fats, remaining proteins, and remaining carbohydrates.

16. Fat (or lipid) Digestion
The liver produces bile and stores it in the gall bladder. As the chyme enters the duodenum, bile is released and begins to break the fat into smaller droplets. Does bile perform physical or chemical digestion?
Physical Digestion
The pancreas secretes enzymes into the duodenum which break fats into fatty acids and glycerol. Physical or chemical digestion?
Physical
Chemical Digestion

17. The Small Intestine (21 ft.)
The small intestine is divided into three sections:
The duodenum (1 ft.)
The jejunum (8 ft.)
The ileum (12 ft.)

18. The Small Intestine ~The Jejunum and Ileum~
As the chyme exits the duodenum, it continues to break down and nutrients are absorbed into the walls of the small intestine. These walls are covered with tiny fingerlike projections called villi, and these villi are covered with microvilli, which are even tinier finger like projections! What is the function of the villi?

19. Villi increase Surface Area
These villa and microvilli increase the surface area of the small intestine to over the size of a tennis court! Imagine chopping up the steak thin enough to stretch it over the surface of an entire tennis court.

20. After the small intestine…
Almost all the usable nutrients have been extracted from the chyme by the villi. It passes by the appendix and is pushed into the large intestine. If a portion of this waste enters the appendix, it can get stuck and cause an infection that can be fatal unless the appendix is removed.

21. The Large Intestine (5ft.)
As solid waste passes through the large intestine, water is absorbed by the intestinal walls. Also, helpful bacteria in the large intestine break down wastes into usable nutrients, such as vitamin K and B.
It is estimated that 40-60% of the weight of our feces is dead bacteria from the large intestine!

22. The Rectum (1 ft.) and Anus
After most water and any additional nutrients have been absorbed, the waste, known as feces, is pushed into the rectum. It will remain here until it is expelled through the opening at the end, the anus. Thankfully, this a voluntary decision.