EVALUATE THE CONDITIONS NECESSARY FOR EFFECTIVE GASEOUS EXCHANGE

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Gaseous exchange takes place in the lungs. The exact location is the alveoli situated in the lungs at the ends of the bronchioles.
Alveoli are tiny hollow sacs, which cluster together; hence they are often described as having a grape like appearance. Surrounding the alveoli is a network of capillaries commonly called capillary beds. Capillaries are the smallest blood vessels inside the body and they can carry both oxygenated blood and deoxygenated blood depending where they are in the body.

The alveoli walls are one cell thick, they are made of flattened epithelial cells. The capillaries too are also one cell thick. This allows for a short diffusion pathway, the gases only have to travel through 2 cell membranes to their destination, whichever direction they need to go i.e. oxygen from the lungs can readily diffuse into the capillaries into the red blood cells; carbon dioxide can readily diffuse out of the capillaries, into the lungs ready to be exhaled into the atmosphere If the diffusion pathway was longer than this, then for gaseous exchange to take place the process would take longer. Also, some of the gases maybe lost to other tissues which may cause problems to the body.

Lungs are moist, what keeps the lungs moist is mainly due to the presence of water.
Water is present in the alveoli. It needs to be present for effective gaseous exchange because it allows the gases to be transported in solution form making it easier to diffuse; oxygen and carbon dioxide are dissolved.
This water diffuses in and out of the alveoli and the epithelial cells, and some water is always present in exhalation. If the alveoli did not have this constant osmotic movement of water then alveoli could become dry. A dry environment is not at all effective for gaseous exchange; it makes it difficult for gases to exchange through cells, even if they are only one cell thick.

According to Abrahams (2002 pg 111) “Two other type of cells are found in the alveoli: macrophages (defence cells), which engulf any foreign particles that get down the respiratory tract; and cells which produce surfactant” Surfactant is a soapy solution that lowers the surface tension of the alveoli lining. This prevents the alveoli collapsing. Keeping the surface area of the alveoli large, therefore allowing optimum gaseous exchange. If the alveoli collapsed then the surface area will decrease hence less gaseous exchange will be able to take place.

A steep concentration gradient of the gases needs to be maintained. Gases will always move from a high concentration to a low concentration, in a constant strive for an equilibrium. The capillary beds contain RBC (red blood cells) which may contain little or no oxygen in them. When this is the case, they need more oxygen. The air in the lungs contains plenty of oxygen; to meet the body’s requirements. So gaseous exchange of oxygen will readily occur. This is true for the exchange of carbon dioxide. The RBCs contain high amounts of carbon dioxide; a waste product of cellular respiration. Carbon dioxide is poisonous to us; we need to eliminate it from our body system. The lungs have very small amounts of carbon dioxide, so carbon dioxide will readily diffuse out of our capillaries and into our lungs to be expelled by exhalation.