Your heart, blood, and the tubes that carry the blood make up your circulatory
system. The circulatory system takes
nutrients, oxygen, and water to all your body cells. The system picks
up wastes made by cells and carries the wastes to organs that get rid of
them. Your circulatory system also helps you keep you healthy.
is the watery part of your blood. Nutrients, wastes, and blood cells
float in plasma. Blood gets its color from red
blood cells protect you from diseases.
Some white blood cells surround germs and destroy them. Other
white blood cells make chemicals that kill germs. Platelets
are tiny parts of cells. When you get a cut, platelets help stop
the bleeding. When a blood vessel in your skin is cut, some blood
leaks out. But, platelets soon clump together at the place where
the blood vessel has been cut. The platelets give off a substance
that causes a tangle of sticky fibers to form. Platelets, fibers,
and trapped blood cells clump together to form a clot. The clot seals
the cut in the blood vessel. The bleeding stops.
After a while, the clot hardens and forms a scab. The scab helps
to keep germs out of the cut. If germs do get in the cut, white blood
cells attack them. If there are a lot of germs, some white blood
cells die in the attack. They form a thick yellowish liquid that
is called pus. Washing and bandaging a cut can help keep out germs
while the cut heals.
of Blood Vessels"
flows through a network of blood vessels. Your circulatory system
has three kinds of blood vessels. Each kind of blood vessel has and
performs a different job.
a blood vessel that carries blood away from the heart. If you put
the tips of your fingers on the inside of your wrist and press firmly,
you can feel a beat. The beat is called your pulse. Your pulse
tells you how many times your heart beats in 1 minute. When you take
your pulse, you are pressing on an artery. You feel the beat because
the walls of arteries stretch as the heart pumps blood through them.
Blood in the smallest arteries flows into tiny blood vessels that are called
Capillaries are so narrow that red blood cells go through them single file.
Capillaries have thin walls. Oxygen and nutrients carried by blood
pass through capillary walls into body cells. Wastes from the body
cells pass through capillary walls into the blood.
a blood vessel that carries blood from the capillaries back to the heart.
The blood in capillaries flows into tiny veins. These veins come
together to make bigger and bigger veins. Blood in veins flows more
slowly than blood in arteries. To keep blood from flowing backward,
many veins have valves that work like one-way doors.
Path of Blood Through the Heart"
heart is a hollow, muscular organ that pumps blood every single minute
of every single day. The inside of the heart is divided into 4 spaces.
blood from veins. Each ventricle
pumps blood out of the heart through arteries.
Find the 2 big veins from the body in the picture. These veins carry
blood that taken oxygen to body cells. The oxygen poor blood flows
into the right atrium and then into the right atrium and then into the
right ventricle. The right ventricle contracts, pumping blood into
a large artery. That artery divides into smaller arteries leading
to the lungs. Now find the veins that return oxygen rich blood to
the heart, from the lungs. The blood flows into the left atrium and
then flows into the left ventricle. The left ventricle contracts,
pumping blood into a big artery. That artery divides into smaller
arteries that lead to all parts of the body.
The 2 sides of the heart work together. For example, blood from the
lungs enters the left atrium at the same time that blood from the body
enters the right atrium. The left ventricle pumps blood to all parts
of the body at the same time that the right ventricle pumps blood to the
Body Home Page | Circulatory