Essay On Marine Mammals

Marine mammals also breathe air, and must come up to the surface of the water to breathe. They have small lungs in relation to their body size compared to humans to reduce problems of nitrogen building up in the blood caused by diving. They have to make sure no water gets into the gas exchange system, and gas exchange must occur efficiently. Marine mammals have to be able to hold their breaths for long periods of time while they are diving. Air enters the lungs through the trachea, which splits into two bronchi and then smaller bronchioles. All of these tubes are held open by rings of cartilage. On the bronchioles are alveoli, where gas exchange takes place. These alveoli greatly increase the surface area:volume ratio, increasing the efficiency of gas exchange and more particles can diffuse at once. The alveoli are surrounded by capillaries so gases can diffuse between the air and blood. Mammals have a circulatory system, so their size isn't limited by their gas exchange system. Because mammals breathe air, unwanted particles sometime get into the gas exchange system. There is mucus in the trachea and bronchioles to keep them clean and moist. The alveoli must stay moist so oxygen can dissolve and then diffuse into the blood. The lungs are also kept moist
Not all of the air breathed in makes it to the gas exchange surface, so some air breathed out still has oxygen in it. Also, not all air makes it out of the body, so some air breathed in doesn't have oxygen in it any more. This isn't a very efficient way of ventilating the lungs, as not all of the oxygen coming into the body is absorbed by the blood.
Usually mammals can only live on land because they can only breathe air. This is another limitation of their gas exchange system. Some mammals have adapted to live in water, but they still have to come up to the surface to breathe air. They can only hold their breaths for a limited time, so must come up to the surface often to