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Objectives 30.3
The Digestive
System
-Describe the organs of
the digestive system and
explain their functions.
-Explain what happens
during digestion.
-Describe how nutrients
are absorbed into the
bloodstream and wastes
are eliminated from the
body.
Vocabulary
Word
Definition
Mechanical digestion
Physical breakdown of large pieces of food into smaller
pieces
Chemical digestion
Process by which enzymes break down food into small
molecules that the body can use
Amylase
Enzyme in saliva that breaks the chemical bonds in
starches
Esophagus
Tube connecting the mouth to the stomach
Peristalsis
Contractions of smooth muscle that provide force that
moves food through the esophagus toward the stomach
Stomach
Large muscular sac that continues the mechanical and
chemical digestion of food
Pepsin
Enzyme that breaks down proteins into smaller
polypeptide fragments
Chyme
Mixture of enzymes and partially digested food
Small intestine
Digestive organ in which most chemical digestion and
absorption take place
Villi
Fingerlike projection in small intestine that aids in
absorption of nutrient molecules
Large intestine
Organ in the digestive system that removes water from
undigested material that passes through it, also called
colon
Lesson Overview
The Digestive System
The four steps of Digestion:
1.
2.
3.
4.
Ingestion
Digestion
Absorption
Elimination
Lesson Overview
The Digestive System
The Process of Digestion
During digestion, food travels through the mouth,
pharynx, esophagus, stomach, small intestine,
large intestine and anus.
Lesson Overview
The Digestive System
The Mouth
Chewing begins the process of mechanical digestion.
Chemical digestion begins as digestive enzymes, such as
amylase, in saliva, start the breakdown of carbohydrates.
Saliva also has lysozyme, an enzyme that fights infection by
digesting the cell walls of many bacteria that enter the mouth
with food.
Lesson Overview
The Digestive System
The Esophagus
The bolus of food passes through the pharynx into
a tube called the esophagus that leads to the
stomach.
Contractions of smooth muscles, known as
peristalsis, provide the force that moves food
through the esophagus toward the stomach.
Lesson Overview
The Digestive System
Chemical Digestion in the Stomach
The stomach is a large muscular sac that continues
chemical and mechanical digestion of food.
Pepsin is the enzyme in the stomach that breaks
down proteins into amino acids.
Lesson Overview
The Digestive System
Digestion in the Small Intestine
The small intestine secretes many enzymes, one of
which is lipase, to break down lipids.
Absorption of nutrients takes place in the small
intestine.
Lesson Overview
The Digestive System
Absorption From the Small Intestine
The folded surfaces of the small intestine are covered with fingerlike
projections called villi.
The surfaces of the cells of the villi are covered with thousands of tiny
projections known as microvilli, for absorption of nutrients.
This dramatically increases the surface area of the small intestine
allowing for maximum absorption.
Lesson Overview
The Digestive System
The Large Intestine
The large intestine’s function is to
reabsorb water before the remaining
food material is eliminated as feces
through the anus.
Lesson Overview
The Digestive System
Elimination
If not enough water is absorbed by the large
intestine, a condition known as diarrhea occurs.
If too much water is absorbed from the undigested
materials, a condition known as constipation occurs.
Lesson Overview
The Digestive System
True or False
1.
2.
3.
4.
5.
The gallbladder is a pouch-like organ responsible for
storing bile. _________________________
Peristalsis pushes food through the digestive tract.
_________________________
After chyme is produced in the large intestine, it moves
through the duodenum. _________________________
If too little water is absorbed from the large intestine,
constipation results. _________________________
While the pancreas processes cellulose and other
materials in some mammals, in humans it is only noticed
when it is inflamed or infected.
_________________________
Answers
1.
The gallbladder is a pouch-like organ responsible for storing
bile. True
2.
Peristalsis pushes food through the digestive tract. True
3.
After chyme is produced in the large intestine, it moves
through the duodenum False, Stomach
4.
If too little water is absorbed from the large intestine,
constipation results. False, Diarreah
5.
While the pancreas processes cellulose and other materials in
some mammals, in humans it is only noticed when it is inflamed
or infected. False, Appendix