Describe and explain the adaptions of the human alveoli in making gas exchange efficient

Gas exchange can be made efficient in three main ways: shortening the diffusion distance, increasing the diffusion speed and increasing the surface area of the diffusion surface. The alveoli in the human lungs have special adaptions which use these means of efficiency to ensure that oxygen can get into the blood to travel to the cells and the waste-gas CO2 can leave the blood. Firstly, the alveoli are adapted to shorten the diffusion distance between the lungs and the alveoli. Both the alveoli and the capillary blood cell endothelium are just one cell thick. The endothelium also lie very close to the alveoli to shorten the distance the oxygen and CO2 has to travel even more. Secondly, the diffusion speed is very fast across the alveoli cell membranes. This is achieved by having a large diffusion gradient between the alveoli and the capillary. A rich blood supply of fast moving blood around the alevoli upkeeps the diffusion gradient of oxygen from the alveolus into the capillary. Thirdly, efficient diffusion is achieved by having a large surface area. Alveoli are very small and there are numerous amounts of them in the lung tissue, which increases the lungs' surface area hugely. Overall it is important that the lungs are well adapted to allow efficient gas exchange so that cells can be supplied with sufficient amounts of oxygen to allow respiration which drives many reactions in the cell. It is also necessary for CO2 to leave the cell and leave the body through expiration as it is a waste product of gas exchange and a build up of CO2 can be dangerous for the body, eg, by increasing the acidity of the blood.