1. Human Digestion

2. Aim: What are THE structures and functions of THE human digestive system?
I. THE Human Digestive system – gets THE nutrients from THE food you eat into your cells.
A. Tube-within-a-tube body plan – alimentary canal (digestive tract) that THE food stays in.
B. One Way digestive tract – THE food enters through THE mouth (ingestion), gets digested throughout the digestive tract, and undigested food is egested out through THE anus.

3. C. Digestion Organs
1. Mouth – performs both mechanical and chemical digestion.
a. THE teeth chew food (mechanical) THE to increase THE surface area for chemical digestion (incisors, canines, molars).
b. Saliva contains THE enzymes amylase which begins THE chemical digestion of starch into sugars.

5. 2. Pharynx – where THE respiratory and digestive system meet
2. Pharynx – where THE respiratory and digestive system meet. Food passes through to THE esophagus.
What is the meaning of the expression “the food went down the wrong tube?”
3. Epiglottis – flap of tissue that closes off the trachea during swallowing to prevent food from entering it.

6. Epiglottis in action

7. 4. Esophagus – pushes food towards THE stomach
4. Esophagus – pushes food towards THE stomach. No digestion occurs here. Peristalsis starts here.
a. Peristalsis – waves of muscular contractions that push food throughout the digestive tract. It starts in the esophagus and continues all the way through the large intestine.

8. 5. Stomach – both mechanical and chemical digestion occur here.

9. Why does the stomach have a mucus lining?
a. Three layers of muscles that churn (mix) the food (mechanical digestion).
b. Gastric glands release the enzyme pepsin and hydrochloric acid. Pepsin chemically digests proteins into peptides.
Why does the stomach have a mucus lining?
It protects the inner lining by neutralizing the hydrochloric acid.
c. Chyme – the liquid substance that leaves the stomach and enters the small intestine.

10. 6. Liver (accessory organ) – produces the substance bile which is stored in the gall bladder (accessory organ).
a. Bile emulsifies (mechanically breaks down) fats. It is released into the small intestine via the bile duct.

11. 7. THE Pancreas (Accessory organ) – produces pancreatic juice which is released into the small intestine via the pancreatic duct.
a. Pancreatic juice contains enzymes that break down fats (lipase), starch (amylase), and proteins (trypsin).

13. Q. Why does most chemical digestion occur in the small intestine?
A. Because it contains enzymes that break down each nutrient.
Q. The small intestine is 23 feet long. Why is it called THE small intestine?

14. 8. THE Small Intestine – chemical digestion and absorption occur here
8. THE Small Intestine – chemical digestion and absorption occur here. Last place that digestion occurs.
a. Intestinal juice contains enzymes that break the nutrients into their smallest subunits. Ex: carbohydrates into monosaccharides, proteins into amino acids, and lipids into fatty acids and glycerol.

16. b. Villi – finger-like projections that line the wall of the small intestine. Increase the surface area for both digestion and absorption. Nutrients enter the bloodstream through the villi.
9. THE Large Intestine – reabsorbs water into the body and eliminates feces.

17. 10. Rectum – feces (digestive wastes) is temporarily stored here before being eliminated through the anus.
List the organs of the digestive tract that food passes through, starting with the mouth and ending at the anus.