Stanley Goya.. age 14, of Gary, Ind.., for his question:
How does oxygen get into the blood?
Every time we breathe in, we take about a pint of gaseous air into the lungs. Here the gases fill countless tiny pockets in the spongy lung tissues: The walls of these pockets are very thin and tiny blood vessels come close to the surface. Waste carbon dioxide is returned t o the air through these cell walls and fresh oxygen is taken into the blood. The gaseous oxygen in the air must be dissolved in the liquid blood before it can be taken to the body cells where it is needed,
The job of carrying the carbon dioxide and the oxygen is done by the red blood cells. There are about 300 million of these little red saucers in every drop of healthy blood. Each is a sac filled with a substance called hemoglobin and this is the magic substance which dissolves the oxygen from the air pockets in the spongy lungs.
Hemoglobin is a very heavy and complex molecule containing globin, iron and a substance called heme. Four of its atoms are iron and these are the atoms which do the work of taking oxygen from the lungs and delivering it to the body cells.
The blood vessels which reach the walls of the lungs are so small that red blood cells travel through them in single file. This means that the red blood cells containing their hemoglobin are very close indeed to the air pockets in the lungs. As the blood stream carries them through these areas, a large number of the hemoglobin molecules are able to grab their quota of oxygen molecules.
An oxygen molecule consists of two atoms of oxygen. One of these molecules forms a loose attachment with each of the iron atoms in the hemoglobin molecule. This oxygen is then drawn through the wall of the fine blood vessel.
It is now dissolved in the blood stream as part of the red blood cells.
The hemoglobin plus this extra load of oxygen is called oxyhemoglobin and it takes on a bright red color.
The blood in the lungs is now returned to the heart from where it is pumped all over the body. This is arterial blood, much redder than the blood which is returned to the heart. As the red blood flows around the body, the molecules of oxygen are taken from the hemoglobin by the cells that need it. In return, they give up their waste carbon dioxide.
This waste gas is also gathered in by the hemoglobin in much the same way as it gathers the oxygen from the air in the lungs. Each iron atom in the hemoglobin atom forms a loose attachment with one molecule of carbon dioxide. This union gives a dark blue tinge to the vein or venous blood returning to the heart. When the red cells come in contact with the air pockets, the waste carbon dioxide is given out. Then the hemoglobin is ready to take on a fresh load of oxygen.