Indeed, the drawing and expulsion of air is driven by muscular action; in early tetrapods, air was driven into the lungs by the pharyngeal muscles, whereas in reptiles, birds and mammals a more complicated musculo-skeletal system is used. In the mammal, a large muscle, known as the diaphragm, manages to drive ventilation by periodically altering the intra-thoracic volume and pressure; by increasing volume and decreasing pressure, air is sucked into the airways, and by reducing volume and increasing pressure, the reverse occurs.
Absorption in the intestines occurs mainly in the small intestine. This is evidenced in the fact that the small intestine has a particular folded texture in order to increase the surface area available for diffusion of nutrients through the intestinal wall so...
These microscopic folds are called microvilli. In an adult human, the small intestine is, on average, about seven meters long - which is incredible given the size of a human body.
The large intestine, on the other hand, hosts several kinds of bacteria that deal with molecules the human body is not able to destroy itself. This is an example of symbiosis. These bacteria also account for the production of methane inside our intestine (which is released as flatulence when removed through the anus).
So, it is quite apparent that even though both the lungs and the intestines - especially the small intestine - feature and thrive on absorption, they are in different capacities and methods.
Bibliography
http://health.howstuffworks.com/lung.htm
