What variation ensue when blood reach the lungs?


Answers:    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 cell.
oxygen content of the blood reaching the Pulmonary Veins is also effected by gravity. If the patient is upright most of the circulation go to the bases of the lungs and the least amount of blood gets to the apices. The middle portion of the lungs get just the "right" amount. This is important because the air ventilate the lungs goes preferentially to the apices and less to the bases. So you can see here is a mismatch in the bases and in the apices. But surrounded by the middle there is just the right matching. That is if the long-suffering is upright. If they are lieing down the blood flow goes preferentially to to the lowest point. This whole point is called the Ventilation/perfusion ratio. This is a very important concept when you are thinking roughly 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 within the blood in combination with H2O. This forms carbonic acid. The carbonic acerbic 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 full chemical process would be lengthy so I'll just leave it at that.
So the blood that have gone through the lungs has changed two basic ways. It has collected Oxygen to deliver to the tissues and it's have 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-hemeglobin dissociation curve.There is a world of familiarity out there.

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