Download Digestive Systems

Unit 7: Human Anatomy
Content Outline: Digestive Systems (7.3)
I.
Digestion
A. The purpose of digestion is to break down food into forms that can be absorbed in to the bloodstream and
transported to the cells of the body. It is a series of processes.
B. There are two types of digestion that can occur in the system:
1. Mechanical Digestion- prepares food for the more complex process of chemical digestion.
2. Chemical Digestion- breaks the chemical bonds in nutrients so they can become small enough to be
absorbed into the bloodstream. This is accomplished by digestive enzymes.
II. The Human Digestive Tract
A. Mouth
1. Teeth- begins the process of mechanical digestion.
2. Saliva- cleanses the mouth and begins the process of chemical digestion with an enzyme called
Amylase, which breaks down simple carbohydrates.
3. Tongue- muscle that helps move food around the mouth and aids in swallowing by mashing food
against the roof of the mouth and creating bolus which is a moist ball of chewed food.
B. Esophagus
1. The journey from the mouth to the stomach takes approximately 6 seconds.
2. The esophagus coats food in mucus that assists in smooth movement of food through the
digestive tract.
C. Stomach- chemical and mechanical digestion happens here.
1. Stomach Acid and Enzymes- The stomach has glands which produce HCl (hydrochloric acid) and the
digestive enzyme pepsin, which breaks down proteins. The HCl activates the pepsin.
2. Mucus- excreted by the walls of the stomach and protects the stomach from the acidic contents.
3. Chyme- thick liquid produced by the digestive action of the stomach.
4. Food may remain in the stomach for up to 4 hours.
D. Small Intestine- 6 to 8 meters long
1. Digestion- a majority of digestion occurs here, completing the process.
2. Nutrient Absorption- occurs through the folds, villi, and microvilli of the small intestine through a
process called diffusion.
3. Nutrients are beginning to be absorbed within four to twelve hours.
E. Large Intestine1. Water and electrolyte absorption.
2. Within 18 hours water has been absorbed leaving solid waste.
F. Rectum- Solid waste accumulates here to be eliminated through the anus after a journey that typically takes
12 to 24 hours. Approximately 1/3 of this waste is dead bacteria.
G. Accessory Organs
1. Liver- makes bile, to help breakdown lipids, and sends it to the gall bladder.
2. Gall Bladder- holds the bile, until needed by the small intestine to aid in lipid digestion.
3. Pancreas- secretes pancreatic juices into the small intestine containing enzymes that help with
carbohydrate, protein, and fat digestion.
H. Sphincters- rings of thickened muscles controlling the passage of food between the different areas of the
digestive tract. There are 5. First is at the opening of the stomach. Second is at the end of
stomach. The third is between the small and large intestine. The last two are at the rectum.
III. Peristalsis- Is the rhythmic muscular contractions that keep the food moving in the right direction.