What change occurs in the lung capillaries?

Answer 1

When the blood is pumped through the pulmonary artery to the pulmonary capillaries The Oxygen diffuses across the alveolar-capillary membrane and is absorbed by the hemoglobin in the red blood cells.

That's the simple form. There are 4 Heme groups in each cell(heme is the iron containing substance that binds with oxygen). The first, second and third group saturate rather rapidly achieving a 75% saturation. The last group saturates at a slower rate simply because of the diffusion gradient and normally stops combining with oxygen at around 21% giving you a total of 96% saturation. This is why hemoglobin is so important. This saturation is effected by things like the patient's body temperature, the pH of the blood, the amount of hemoglobin available etc.

The oxygen content of the blood reaching the Pulmonary Veins is also effected by gravity. If the patient is upright most of the circulation goes to the bases of the lungs and the least amount of blood gets to the apices. The middle portion of the lungs gets just the "right" amount. This is important because the air ventilating the lungs goes preferentially to the apices and less to the bases. So you can see there is a mismatch in the bases and in the apices. But in the middle there is just the right matching. That is if the patient is upright. If they are lieing down the blood flow goes preferentially to to the lowest point. This whole thing is called the Ventilation/perfusion ratio. This is a very important concept when you are thinking about how a disease entity eg. pneumonia, effects the patient's Blood gases.

The other change that takes place is the exchange of CO2 that regulates the pH of the blood. CO2 is carried in the blood in combination with H2O. This forms carbonic acid. The carbonic acid is balanced by HCO3 and the result of the matching of the two results in the hydrogen ion concentration or simply, the pH. To explain the whole chemical process would be lengthy so I'll just leave it at that.

So the blood that has gone through the lungs has changed two basic ways. It has collected Oxygen to deliver to the tissues and it's had it's pH regulated so metabolic processes can go on normally.

I would explain how the pH is regulated in more detail at another time. Also, you should look up the Oxy-hemoglobin dissociation curve.There is a world of knowledge out there.

Answer 2

The blood becomes oxygenated