4-1 The Circulatory System

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The circulatory system is made up of the blood, blood vessels, and the heart.  The circulatory system pumps and carries blood throughout the body.

Blood is made up of liquid and solid parts.  The solid part is made up of white blood cells, red blood cells, and platelets.  White blood cells help the body fight infection and disease.  Red blood cells are smaller than white blood cells.  They carry the oxygen.  There are more red blood cells than white blood cells in the blood.  Platelets are tiny bits of cells that are carried around in the blood.  They help stop bleeding.  Platelets clog the openings in blood vessels caused by cuts.  They start the healing process by forming a blood clot, which will then scab as the body begins to heal itself.

The liquid part of the blood is called plasma.  It is thin and clear.  Oxygen and nutrients from the digestive system are dissolved in the plasma and carried to where it is needed.  Plasma also dissolves wastes from the cells.


Directions: Answer the questions about blood.

Blood is made up of


liquid and solid parts

solid parts


The solid part of the blood is made up of red and white blood cells, and .

blood cells help the body fight infection and disease.

blood cells carry oxygen.

help stop bleeding.

blood cells are smaller than blood cells.

The liquid part of  blood is called .

Plasma is


thick and clear

thin and clear



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The Circulatory System