The Characteristics and Components of Blood

Red bloodcells

White blood cells

Platelets

Blood is made up of solid particles and fluid. The solid particles are red blood cells, white blood cells, and platelets, and are commonly called the formed elements.

Red blood cells (RBC) = erythrocytes

White blood cells (WBC) = leukocytes

Platelets = thrombocytes

Remember!!!

These are theFORMED ELEMENTS

Red blood cells carry O2 & CO2

White blood cells help fight infection

Platelets help to clot the blood

Remember!!!

These are the functions of the

FORMED ELEMENTS

The average volume of blood for a man is

approximately 5 liters or 10 to12 pints.

The average volume of blood for a woman is

approximately 4.5 liters or 9 to 11 pints.

plasma

leukocytes & platelets

erythrocytes

The formed elements can be separated from the fluid portion (or plasma) by centrifugation. When blood is spun at high speeds, it separates into three layers.

These three layers, from the top, are the liquid portion or plasma, the “buffy coat” which contains white blood cells and platelets, and the packed red cells which is all the red blood cells packed together.

Buffy coat

Packed red cells

Liquid portion

(Formed elements)

(***note the percentages of total volume for each)

The percentage of the total volume that these packed red cells occupy is called the hematocrit.

The normal hematocrit percentage ranges from 42 to 48% within both genders with an average of 45%. Females can go as low as 39% and males as high as 50% and still be within the “norm”.

This is an important health indicator and is often ordered as a laboratory test to determine the effect of various diseases or drugs.

Packedred

cells45%

55%

45%

< 1%

Question: Why are the platelets and the white blood cells on “top” of the red cells?

The buffy coat occupies less than 1% of the total volume of the blood.

Plasma

Buffycoat

Packedred cells

lipids (fats), amino acids, dissolved gasses, hormones, vitamins, and metabolic waste products all dissolved in water.

The last portion of this centrifuged blood is the plasma layer. Plasma is

actually a very complex mixture of many components. It contains

dissolved salts (giving it a composition similar to diluted seawater), non-nutrient proteins, glucose,

the blood minus the RBC, WBC, and platelets. It is a straw-colored fluid which is

These solutes and colloids together make up about 8 to 10 % of the volume of plasma. A more detailed summary of the composition of plasma will follow.

Plasma

Buffycoat

Packedred cells