Sistema Circulatori

The Circulatory System
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The Circulatory System is the main transportation and cooling system for the body. The Red Blood Cells act like billions of little UPS trucks carrying all sorts of packages that are needed by all the cells in the body. Instead of UPS, I'll call them RBC's. RBC's carry oxygen and nutrients to the cells. Every cell in thebody requires oxygen to remain alive. Besides RBC's, there are also White Blood Cells moving in the circulatory system traffic. White Blood Cells are the paramedics, police and street cleaners of the circulatory system. Anytime we have a cold, a cut, or an infection the WBC's go to work.

The highway system of the Circulatory System consists off a lot of one way streets. The superhighways ofthe circulatory system are the veins and arteries. Veins are used to carry blood *to* the heart. Arteries carry blood *away* from the heart. Most of the time, blood in the veins is blood where most of the oxygen and nutrients have already been delivered to the cells. This blood is called deoxygenated and is very *dark* red. Most of the time blood in the arteries is loaded with oxygen and nutrientsand the color is very *bright* red. There is one artery that carries deoxygenated blood and there are some veins that carry oxygenated blood. To get to the bottom of this little mystery we need to talk about the Heart and Lungs.

The Heart


This is a subject that is near and dear to my heart. The heart is a two sided, four chambered pump. It is made up mostly of muscle. Heart muscle is veryspecial. Unlike all the other muscles in the body, the heart muscle cannot afford to get tired. Imagine what would happen if every 15 minutes or so the pump got tired and decided to take a little nap! Not a pretty sight. So, heart muscle is always expanding and contracting, usually at between 60 and 100 beats per minute.

The right side of the heart is the low pressure side. Its main job is topush the RBC's, cargo bays mostly empty now, up to the lungs (loading docks and filling stations) so that they can get recharged with oxygen. Blood enters the right heart through a chamber called the Right Atrium. Atrium is another word for an 'entry room.' Since the right atrium is located *above* the Right Ventricle, a combination of gravity and an easy squeeze pushes the blood though theTricuspid Valve into the right ventricle. The tricuspid valve is a valve made up of three 'leaflets' that allows blood to go from top to bottom in the heart but closes to prevent the blood from backing up into the right atrium when the right ventricle squeezes.

After the blood is in the right ventricle, the right ventricle begins its contraction to push the blood out toward the lungs. Remember thatthis blood is deoxygenated. The blood leaves the right ventricle and enters the *pulmonary artery.* This artery and its two branches are the only arteries in the body to carry deoxygenated blood. Important: Arteries carry blood *away* from the heart. There is nothing in the definition that says blood has to be oxygenated.

When the blood leaves the pulmonary arteries it enters *capillaries* inthe lungs. Capillaries are very, very small blood vessels that act as the connectors between veins and arteries. The capillaries in the lungs are very special because they are located against the *alveoli* or air sacks. When blood in the capillaries goes past the air sacks, the RBC's pick up oxygen. The alveoli are like the loading docks where trucks pick up their load. Capillaries are so small,in some places, that only *one* RBC at a time can get through!

When the blood has picked up its oxygen, it enters some blood vessels known as the *cardiac veins.* This is fully oxygenated blood and it is now in veins. Remember: Veins take blood to the heart. The cardiac veins empty into the *left atrium.* The left side of the heart is the high pressure side, its job is to push the blood out...