A scanning electron microscope image of normal...

A scanning electron microscope image of normal circulating human blood showing red blood cells, several types of white blood cells including lymphocytes, a monocyte, a neutrophil and many small disc-shaped platelets. (Photo credit: Wikipedia)

Blood is essential to life and if a person loses too much blood death will result. The average person has approximately five liters of  blood in their body that can weigh as much as eight percent of a person’s total weight. The body has veins and arteries through which blood circulates largely through the pumping action of the heart.

Carries oxygen to the tissues

Carries nutrients

Protects against infection

Carries hormones

Regulates body temperature

Removes waster products

Has components that assist blood clotting

Blood Composition

Approximately 55% of a human’s blood is plasmaPlasma is mostly water and proteins.  The remaining 45% of the blood is mostly red blood cells with a smaller percentage of white blood cells and platelets (parts of cells that are needed for blood clotting).

Red Blood Cells

Red blood cells:

Make up about 45% of blood
Contain hemoglobin (a red protein that transports oxygen through the body and gives the blood a red color)

Are produced in bone marrow (soft fatty substance in the bones)

Live for approximately 100 days

Primarily function as the means of carrying oxygen in the body

White Blood Cells

White blood cells:

Are called leukocytes (leuko=white, cyte=cell)

Normally only one percent of the blood
Protect against infections



Are called thrombocytes (thrombo=clotting of blood, cyte=cell)

Normally live under ten days

Responsible for blood clotting

Blood Plasma

Blood plasma:

Is about 92% water

Has eight percent dissolved proteins

Circulates nutrients throughout the body

Carries waste products to be disposed

Contains electrolytes