Digestive System Notes
The main function of the
digestive system is to:
1. breakdown foods into nutrients
that can be used by the body
2. absorb nutrients that are
necessary for energy, growth, and
maintenance
3. rid the body of solid waste
- Digestion – the process by which
your body breaks down food into
small nutrient molecules.
2 Kinds of Digestion
1. Mechanical – foods are physically
broken down into smaller pieces. Ex.
Chewing with your teeth.
2. Chemical – Chemicals produced by
the body break foods into their smaller
chemical building blocks.
- Absorption – the process by which
nutrient molecules pass through
the wall of your digestive system
into your blood.
- Saliva – the fluid released when
your mouth waters that plays an
important role in mechanical and
chemical digestion.
Digestion Process
1. Mouth - Begins to break down
food into smaller pieces through
mechanical digestion. Salivary
glands produce saliva; saliva in
the mouth starts the process
of chemical digestion. Saliva
contains a chemical substance
called ptyalin which is an
enzyme that breaks down
some starches into sugars.
- enzyme- a protein that speeds
up chemical reactions in the
body.
2. As you swallow, a small flap of
tissue called the epliglottis
automatically closes over windpipe
(so your food won’t go down the
wrong way).
3. Esophagus – The muscular
transport tube that carries chewed
food to the stomach. It is lined
with mucus.
-mucus- a thick, slippery substance
produced by the body. This makes
food easier to swallow. Food stays
in the esophagus about 10-12
seconds.
- peristalsis – waves of muscular
contractions that move food
through the digestive system.
4. Stomach – J-shaped, muscular
pouch located in the abdomen. It
continues the process of
mechanical digestion (Mostly
mechanical digestion is taking place
in the stomach). The stomach
churns and mixes food with
digestive juices continuing chemical
digestion that the mouth started.
An avg. adult’s stomach holds about
2 liters of food.
-pepsin- is an enzyme produced by
the stomach that digests proteins.
Pepsin, hydrochloric acid, and
mucus are secreted by cells in the
stomach. After 3 to 6 hours in
your stomach, muscle contractions
and enzymes have changed the
food into a soft, watery substance.
5. Small intestines - The organ
where most of the chemical
digestion of food takes place;
nutrients from food are also
absorbed through the small
intestines. The small intestine is
approx. 6 meters (21 feet) long and
is named for its small diameter (23 cm wide). The pancreas, small
intestine, and salivary glands are
organs that secrete digestive
enzymes.
-liver – organ that produces bile.
It is the largest and heaviest organ
inside the body.
- bile – a substance that breaks up
fat particles.
-gallbladder – the organ that
stores bile.
-pancreas – a triangular organ that
lies between the stomach and the
first part of the small intestine.
It produces pancreatic juice and
insulin. The enzymes produced by
the pancreas move into the small
intestine and help break down
proteins, starches, and fats.
The insulin produced is important
in controlling the body’s use of
sugar.
- Food does not pass through the
liver and pancreas – these are
digestive helpers. After a period
of 3 to 5 hours, most of the food
that is in the small intestine is
digested.
-villi – fingerlike structures that
line the small intestine through
which food is absorbed into the
bloodstream.
- By the time the food is ready to
leave the small intestine, it is
basically free of nutrients, except
for water.
6. Large intestines - The organ
where water is absorbed from the
food and taken into the
bloodstream; prepares the
remaining undigested food for
elimination from the body. The
large intestine is about 6.5 cm in
diameter but only 1.5 meters long.
Bacteria that are helpful to
digestion live in the large intestine.
-After spending 18 to 24 hours in
the large intestine, most of the
water that is contained in the
undigested food is absorbed.
Materials that are not absorbed in
the large intestine form a solid
waste.
7. Rectum and anus - The rectum
is a short tube that stores solid
waste until it is eliminated from
the body (end of the large
intestine).
-anus- opening at the end of the
rectum through which solid wastes
are eliminated.