The lungs major function is to offer uninterrupted exchange of gas
The lungs major function is to offer uninterrupted exchange of gas between the blood in circulation and inspired air, as well as taking out carbon dioxide through expiration and bringing in oxygen (Roberts, 2000). This process is known as respiration and is managed by the brain areas comprised of apneustic, pheumotaxic and medullary inspiratory Centre that “stimulate the contraction of the diaphragm and the intercostal muscles†(Roberts, 2000).
Circulation is “the movements of body fluids inside the animals from the place of formation to the place of its utilization†in a one-celled animal (unicellular), cells exchange materials directly with the environment; this implies that it has no circulatory system and the cells have to be close to the immediate medium of exchange (Universereview.ca, 2010). On the other hand, large multi-cellular animals have circulatory system to carry oxygen and nutrients to the body tissues and to carry away waste products; blood and lymph are the key body fluids used in circulation of materials (Universereview.ca, 2010).
The following section shows the similarities and differences amongst the worms, insects, fish, and human in anatomy and physiology of circulation and respiration.
