Science High School Reviewer | Grade 4 Science | Life Science | Systems of the Human Body | Lesson 14: The Respiratory and Circular Systems

The respiratory and circulatory systems work together to deliver
oxygen and nutrients to cells throughout the body.

The Respiratory System
Your body cells need a constant supply of oxygen to use the
nutrients in the food you eat. The cells get that oxygen from the
air you breathe. Air enters your body through your nose and
mouth. It passes through several organs on its way to your lungs.
Air moves from your nose and mouth to your pharynx, or
throat. Both air and food move through your pharynx, but only
air moves on to your trachea, or windpipe. The walls of the trachea
are made up of a stiff connective tissue called cartilage. The
trachea divides into two branches. Each branch, or bronchial tube,
connects to a lung. The bronchial tube inside each lung divides
into many tiny branches. Each tiny branch leads to an air sac.
Tiny blood vessels are wrapped around each air sac. Oxygen
from the air sacs passes into the blood through the walls of these
tiny blood vessels. Blood in the blood vessels carries the oxygen to
every cell in your body.
Take a Breath!
When your body cells use oxygen, they give off carbon dioxide.
The carbon dioxide leaves your body when you breathe out.
The respiratory system helps move these substances into and out
of your body.
The lungs are the main organs in the respiratory system.
But the lungs have no muscles, so how are they able to move?
A dome-shaped muscle called the diaphragm is just below the
lungs. As the diaphragm contracts and then relaxes, air is forced
in and out of your lungs. Muscles in your chest help too. You
breathe in and out.

Parts of the
Respiratory System (diagram)

Air moves from outside the
body through the nose and
mouth.
Each air sac has
tiny blood vessels
wrapped around it.
The lungs are the
main organs of the
respiratory system.
The diaphragm is the
main muscle involved
in breathing.

The trachea leads from the
pharynx toward the lungs.

The trachea splits into two bronchial
tubes. Inside the lungs these tubes
divide into tiny branches that lead to
the air sacs.

Each air sac has
tiny blood vessels
wrapped around it.

The lungs are the
main organs of the
respiratory system.

The diaphragm is the
main muscle involved
in breathing.

How Pumps and Passages Work Together
Your respiratory and circulatory systems work together to
bring oxygen to cells and carry carbon dioxide away from cells.
Each breath you take brings oxygen into your respiratory
system. Oxygen passes from the air sacs in your lungs into your
blood. Then blood vessels carry the blood with the oxygen to
your heart. Your heart pumps the blood to the rest of your body.
The blood brings oxygen to the body’s cells.
The circulatory system has the special job of moving blood
through your body. Your heart, blood vessels, and blood make
up your circulatory system. The blood carries nutrients to the
body’s cells and removes waste products from cells.
An Amazing Pump
The right and left sides of the heart each work as a pump. The
right side of the heart collects blood from the body. This blood is
full of carbon dioxide from the cells. The heart pumps the blood
to your lungs. The carbon dioxide will leave your body when
you breathe out. The left side of the heart collects the blood from
the lungs. This blood is full of oxygen. The heart pumps it to
the body. A wall of muscle separates the two pumps so that the
blood coming in does not mix with blood leaving the heart.
Each side of the heart has two chambers, an atrium and a
ventricle. Each atrium receives blood coming into the heart. The
right atrium receives the oxygen-poor blood returning from the
body. The left atrium receives the blood filled with oxygen from
the lungs. On each side of the heart, the blood passes from the
atrium through a one-way valve into the ventricle. The blood
that moves from the right atrium into the right ventricle is
pumped to the lungs. The blood that moves from the left atrium
into the left ventricle is pumped to the rest of the body.

The Heart (diagram Scott Foresman Gr4)