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Janice Shaub, age 12, of Lancaster, Pennsylvania, for her question:

How does the respiratory system work?

Janice plans a career in the health services and, naturally, now is a good time to grasp a general picture of the human body and its working operations. Breathing rates as one of its most vital, non stop operations. It is the major duty of the respiratory system that takes in air and distributes it to billions of living cells. It also totes waste carbon dioxide and sends it outside the body.

The respiratory system works by transporting gaseous molecules and for the reason some of its major parts must be mobile. The gases must be shunted between the lungs and multitudes of living cells throughout the entire body. These two ends of the system, lungs and cells, are fixed in place. The transporting work is done by the flowing, circulating bloodstream that never rests. Like all the body's major operations, the respiratory system depends on assistance from other organs and systems. The body's vital operations are related and all suffer when one fails to perform.

The spongy lungs in the chest are shielded by the pliable rib cage. Automatically, without your instructions, they expand and contract as they rhythmically breathe in and out. The rate is governed by complex chemicals released by the brain and endocrine glands. These orders are modified to adjust faster breathing when the body needs extra oxygen and slower breathing during restful sleep.

The lungs are riddled with porous pockets lined with super thin walls that separate them from spongy tissue intersected with fine, thin walled blood vessels. Tiny red blood cells send their used carbon dioxide through the thin walls and extract molecules of oxygen from the freshly inhaled air in the porous pockets.

Then the bloodstream transports the vital gas on its way. This part of the respiratory system depends on the beating heart to pump the circulating blood through¬out the body. Fresh from the lungs, the red arterial blood pulses through larger vessels that branch into finer and finer networks. Finally it reaches the tiny capillaries, just wide enough to let through one red cell at a time. Teeming cells in the tissues take its cargo of oxygen to use as fuel for their chemical activities. The depleted red cell then gathers molecules of their waste carbon dioxide.

When the red cells complete their duties they are ready to join the network of veins leading back to the heart. They stream into the right side of the heart    and it sends them pulsing up again to the lungs. There the red cells dispose of their carbon dioxide as before and load up with oxygen for a recent trip around the circuit.

The lungs are nourished by their own blood vessels and governed by their own network of nerves. The entire respiratory system invovles a series of highly complex bio¬chemical activities. The red cells, for example, have to perform their duties because they contain hemoglobin. This very active biochemical attracts oxygen molecules without trying.



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