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Chapter 35 Notes,
The Digestive System
The Digestive System
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The three functions of the digestive system are
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 tract. 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, and it
secretes hormones and helps regulate the 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 appendix has no known function, although
in animals that eat vegetation, a caecum 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 eventually
removed through the rectum.
Anatomy of the Large Intestine
Complete Overview of the Digestive System