Blood and oxygen

Blood is made up of plasma and blood cells.

Plasma accounts for about 60% of the blood's volume, and is mainly water. Fluid overload occurs when there is too much water in the plasma. Dehydration occurs when there is not enough water in the plasma.

Blood cells make up the other 40% of blood. A single drop of blood contains at least 5 million blood cells, each so small it can only be seen through a microscope.

There are three kinds of blood cells, each of which plays an important role in your health:

  1. White blood cells fight infection.
  2. Platelets are involved in clotting the blood.
  3. Red blood cells carry oxygen around the body and thus help maintain energy levels.

Oxygen enters the lungs when we breathe in. It is then carried around the body in the blood. Nutrients from food can't provide energy until they combine with oxygen in the cells of the body. Too few red blood cells mean that cells in the body do not get enough energy. This leads to the symptoms of anemia:

  • tiredness
  • shortness of breath
  • pale skin
  • poor appetite
  • irritability
  • low sex drive
  • feeling cold

In each red blood cell there is a substance called hemoglobin (Hb) that carries the oxygen. The amount of hemoglobin in the blood is a guide to how many red blood cells there are. One of the routine blood tests for patients with kidney failure is a measurement of the Hb level.


Blood consists of plasma and blood cells. Each red blood cell has hemoglobin that carries oxygen around the body for energy. A routine blood test for kidney disease measures the Hb (hemoglobulin) level.

May 1, 2006