Download The Human Body - Pearson SuccessNet

The Human Body
Everyone Needs
Healthy Systems
There are several systems that make up the human
body. Although their functions differ, they all work
together to keep your body “running” smoothly. Some
of these systems include the circulatory, respiratory,
digestive, and urinary systems.
Blood Vessels
The circulatory system of the human body consists
of the heart, the blood, and the tubes known as blood
vessels. This system constantly works to supply your
body with oxygen and nutrients. There are three kinds of
blood vessels that transport blood throughout your body.
They are arteries, capillaries, and veins.
Arteries are blood vessels that carry blood away from
the heart to other parts of the body. It’s their job to carry
blood that is rich in oxygen and deliver it to all parts of
your body. The walls of arteries are thick and muscular.
They can stretch out as the heart pushes blood through
them. The smallest arteries branch out into capillaries.
A capillary is the smallest kind of blood vessel. The
oxygen in your blood moves from the capillaries into
your cells. The wastes and carbon dioxide move out of
the cells and back into the capillaries. Unlike arteries,
capillary walls are very thin. In fact, they are only one
cell thick. Gases can pass through these thin walls.
Capillaries join together to make small veins. These
small veins join together to make larger veins. Veins
are blood vessels that transport blood toward the heart.
They help the return trip of blood to the heart. They have
valves that are like doors. These valves make sure the
blood only flows in one direction. They open to let blood
flow to the heart and close if blood begins to flow away
from the heart.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
The Human Heart
The heart is a vital muscle. In an adult human, it is
about the size of a fist. The heart beats twenty-four hours
a day—when you’re awake and when you’re asleep—in
order to pump blood to all parts of the body.
There are four chambers in the human heart. These
chambers are made of a special kind of muscle. They
work together in a rhythm that’s based on how active
you are being at the time. Two chambers make up each
side of the heart. The right atrium and right ventricle
make up one side, and the left atrium and left ventricle
make up the other side. The atrium is the upper part and
the ventricle is the lower part. The ventricle is stronger
than the atrium. The left and right sides of the heart
work separately to pump blood on different paths. The
heart contracts in order to pump blood.
The hearts of animals and humans are not the same.
Many reptiles have three chambers that make up their
heart. Fish only have two chambers.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
The Job of the
Respiratory System
The respiratory system moves oxygen and carbon
dioxide between the air and your blood.
Respiratory Parts
You inhale, or breathe air in, through your mouth and
nose. This is how respiration starts. Your sinuses work to
warm and moisten the air you breathe. Inside your nose
are small hairs and a layer of mucus. These work to trap
dirt and germs from getting into your lungs. From the
nose, the air moves to the back of the throat and into the
larynx. This is where the vocal cords are.
The trachea is a tube that carries the air from the
larynx toward the lungs. It branches into two tubes a
little below where your neck joins your body. These two
smaller tubes are the left and right bronchi. They deliver
air into your left and right lungs. Inside the lungs, the
bronchi branch out into smaller and smaller tubes. These
are called bronchioles.
The bronchioles finally end in tiny air sacs in the
lungs. The air sacs are where oxygen enters the blood
and carbon dioxide leaves it. At the bottom of your chest
is the diaphragm. This dome-shaped muscle expands
and contracts. When it expands, it forces air out of your
lungs and you exhale. When it contracts, you inhale, or
breathe air in.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
Systems Work Together
Living things require oxygen. Oxygen is important
because it helps cells release the energy that they need
from sugar. Insects have a respiratory system. They
breathe in oxygen through openings on their sides.
Worms have a circulatory system. This helps them get
oxygen. Their blood absorbs oxygen that is carried
through their body.
Humans are more complex living things. Their
respiratory and circulatory systems work together to get
oxygen to cells. It all begins when you take a breath.
Breathing—inhaling and exhaling—is the job of the
respiratory system. Oxygen comes in from the air that
you breathe. Oxygen fills the lungs. The lungs make
oxygen available to the circulatory system so that it can
be transported by your blood. Carbon dioxide is removed
from your blood and exhaled back out to the air outside
your body.
Two things are happening at the same time in the
air sacs. Oxygen leaves the lungs and enters the blood.
Carbon dioxide leaves the blood and enters the lungs.
If you hold your breath, carbon dioxide builds up in
your blood. The muscles in your diaphragm contract,
forcing you to breathe. This is one way your systems work
together to supply you with oxygen.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
The Digestive and
Urinary Systems
Digestive System
Turning the food you eat into fuel that your body can
use is the job of the digestive system. Digestion is the
process that changes food into forms that the body can
use. Many organs work together to break down food
into very small bits of materials. Once the food is broken
down it can be carried by the blood to your cells.
The Mouth and Esophagus
Where does the digestive system begin? With the
mouth, of course! In the mouth you chew pieces of food
so that they become small enough to swallow. The taste
buds on your tongue bring out the flavors of the food.
The tongue also helps move food to the back of your
mouth.
From there the food passes into a tube called the
esophagus. This organ is made up of rings of muscle.
The muscles move in a pattern to squeeze the food as it
travels down the tube to the stomach. Muscles behind the
food get tight as the food passes through each ring. This
entire process doesn’t take very long. Food reaches the
stomach in about two or three seconds.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
The Stomach and Intestines
Where is your stomach? It’s on the left side of your
body under your ribs. The walls of your stomach are
muscles. They can stretch enough to hold all the food
you eat in a meal. When you swallow, a muscle at the
bottom of your esophagus opens up. This allows food to
reach your stomach. The muscle then closes to keep food
there. The stomach muscles squeeze together at the same
time the stomach releases acids to break down food.
This soupy mixture is then ready for the next step in
digestion.
The partly digested food leaves the stomach and
enters the small intestine. This is a narrow, winding
tube. Over several hours, the small intestine breaks down
food even further. This is done with the help of the liver
and the pancreas. These organs send chemicals to aid in
digestion.
When the process of digestion is finished, the
digested food particles move into the blood vessels in
the small intestine. Some food, however, cannot be
digested in the small intestine. This undigested food
moves to the large intestine, often called the colon.
Here some water is recovered from the food. The waste
will be stored in another part of the colon, until it is
removed from the body.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
The Urinary System
Wastes from your body cells enter your blood. If they
stayed there for a long time, they would poison you.
Therefore, this waste must be removed. In humans, waste
is removed from the blood mostly by the urinary system.
Humans have a pair of organs called the kidneys.
Kidneys have the same dark red color and shape as
kidney beans. Located below the lowest ribs, there is one
kidney on either side of your backbone.
Kidneys filter wastes out of the blood. This mix of
water and wastes is called urine. There’s a tube from
each kidney that carries urine to the urinary bladder.
The bladder is a sac that collects and stores urine. At
the bottom of the bladder is a tight muscle. This holds the
urine in the bladder until the body removes it through
urination.
As the kidneys filter waste, other materials leave the
blood too. These materials include salt, calcium, and
other nutrients your body needs. The kidneys put the
right amount of these materials back into your blood.
They help to maintain a balance. Other organs besides
kidneys remove wastes. When you sweat, your glands
release a little bit of waste too.
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­
Glossary
air sacs
t he thin-walled sacs in the lungs where
oxygen enters the blood and carbon dioxide
leaves the blood
artery
blood vessel that carries blood away from
a
the heart to other parts of the body
bladder
t he sac that collects and stores urine formed
by the kidneys
bronchiole
small tube in the lungs that carries air to
a
air sacs
capillary
the smallest kind of blood vessels
digestion
t he process that changes food into a form
that the body can use
esophagus
t he tube that carries food from the mouth to
the stomach
large intestine
wider tube connected to the small intestine
a
that removes water from undigested food
and stores this waste until it is removed from
the body
small intestine
narrow, winding tube where food is
a
changed chemically and broken down into
small particles that can be absorbed into
the blood
trachea
t he tube that carries air from the larynx to
the lungs
vein
blood vessel that carries blood toward
a
the heart
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.­­