The major constituents of blood are blood plasma, erythrocytes, leukocytes, and thrombocytes.

You can read up on all these things on the web, I’m sure wikipedia has quite a bit of information on them.

Blood plasma, is mostly water, contains over 100 different dissolved solutes, including nutrients, gases, hormones, wastes and products of cell activity, ions, and proteins. In a healthy person – the composition of blood plasma is kept relatively constant by various homeostatic mechanisms.

Erythrocytes function as transport for oxygen and carbon dioxide.

Leukocytes are crucial to our defense against disease.

Thrombocytes make up to a very small amount of the blood. Important for bloods function to clot when bleeding.