Chapter 35 Notes,
The Digestive
System
The Digestive System
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The function of the digestive system is to ingest food,
break it down so that nutrients can be absorbed, and
eliminate the waste.
The first part of digestion is mechanical digestion.
Mechanical digestion is when food is chewed and
broken down into smaller pieces by the teeth and
tongue, and by smooth muscles of the stomach and
small intestine.
The second part, called chemical digestion is
accomplished by action of enzymes like amylase
found in the mouth.
The Digestive System
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After food is chewed in the mouth, it moves past the
pharynx, into the esophagus.
The esophagus is a long tube made of smooth muscle
that leads to the stomach.
Food moves through the esophagus by peristalsis,
the muscular contractions made by the smooth
muscles of the esophagus.
After food goes through the esophagus, it passes
through a circular muscle called the cardiac
sphincter into the stomach.
Peristalsis, The Esophagus and the
Cardiac Sphincter
The Digestive System
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When the cardiac sphincter muscles relax, stomach
acid can leak into the esophagus causing heartburn.
The acidic environment of the stomach is favorable to
an enzyme in the stomach called pepsin. Pepsin is
an enzyme in the stomach that breaks down proteins
into amino acids.
Cells in the stomach secrete a protective mucus that
prevent the acid and pepsin from digesting the walls
of the stomach.
The Digestive System
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After the food is broken down by chemical digestion in
the stomach, it is released by the pyloric sphincter
into the small intestine.
The small intestine is the longest part of the digestive
system. The human small intestine is about 7 meters
(over 20 ft.) long!
The small intestine is divided into three different
regions; the duodenum, jejunum, and ileum.
The smooth muscles of the small intestine move the
food by peristalsis.
Anatomy of the Stomach
Small Intestine
Digestive System
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Once food is in the small intestine, some other
organs assist chemical digestion of food.
The pancreas produces enzymes that digest
carbohydrates, proteins, and fats. It also secretes
hormones and helps regulate pH.
The liver produces bile, which breaks down fats, and
the bile is stored in the gall bladder.
The liver is the largest internal organ and it performs
a variety of functions including removing toxic
substances from the body.
Liver, Gall bladder, and Pancreas
Digestive System
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Chemical digestion is completed and absorption of
the nutrients into the bloodstream takes place in the
small intestine.
Small fingerlike structures called villi line the walls
of the small intestine to increase surface area. The
villi are filled with capillaries.
The villi increase the surface area of the small
intestine to give it about the same amount of surface
area as a tennis court!
Small Intestine
Digestive System
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Once digestion is complete, the food, now called
chyme, moves into the large intestine.
The large intestine includes the colon, the rectum,
and the appendix.
The function of the appendix is not fully understood,
although in animals that eat vegetation, a cecum is
used for digesting vegetable matter.
The function of the colon is to absorb water from the
chyme. After water is absorbed from the chyme,
feces is formed and removed through the rectum.
Anatomy of the Large Intestine
Comparative Anatomy of Digestive
Systems in Mammals
Complete Overview of the Digestive System