The cause of mutations in gene expressions are the changes of gene instructions that causes your protein to malfunction. The effect of mutations are the genes not being able to function properly and send the wrong codes/info to your cells.
The exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli. You can see more in wikipedia, or here: https://www.merckmanuals.com/home/lung-and-airway-disorders/biology-of-the-lungs-and-airways/exchanging-oxygen-and-carbon-dioxide
I'd say an <span>endocrinologist would be the best answer.</span>
The sickle cells have membranes stretched by their usual shape that becomes porous and leak nutrients that the parasite needs to survive and the faulty cells eventually get eliminated quite fast by the organisms destroying the parasite among the way