The Circulatory System
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FAQ- Why do your blood vessels look blue? Is the color of blood inside the body really blue?  Does blood turn red when it hits oxygen outside the body?
Here is the statement of the American Society of Hemotology in Washington, DC, in the Jan 2003 The Science Teacher Journal : 
   " Contrary to popular belief, the color of blood inside the body, no matter how you look at it, is red.  Blood is bright red when oxygenated and dark red when it lacks oxygen.
   "When you look at blood throught your skin it may look blue, but that is the result of how color wavelengths travel through and are reflected by the skin.  To see a vein at all, light must pass through the skin and hit the blood in the vein.  The blood then absorbs certain colors of light and reflects others back through the skin.
   " In blood, longer, redder wavelengths can go more deeply into the skin than shorter, bluer wavelengths before being reflected.  Therefore, a blood vessel below the skin looks blue because the blue light is reflected.
   "In reality, blood is either dark or bright red, depending on the amount of oxygen.  Red blood cells contain hemoglobin, which carries oxygen.  When blood passes through your lungs, oxygen surrounds the hemoglobin, turning your blood bright red.  Also, when blood is exposed to the oxygen the air, like when you cut your finger, it turns bright red.  However, as blood moves through your body to nourish tissues, which reduces the amount of oxygen in the blood, it turns a darker shade of red."

  
I. Heart- consists of 4 chambers
    A. 2 Ventricles-- Pump the blood; the pressure in these chambers is very high.
                1. Ventricles have very thick walls to be able to endure such high pressures.
                      The wall of the left ventricle is much thicker than the wall of the right
                      ventricle.
                2. One-way valves are located between the atria and the ventricles. These
                       valves prevent the blood from flowing backwards when the ventricles
                       contract.
                3. One-way valves are located between the ventricles and the major receiving
                       artery (either the aorta or the pulmonary artery). These valves prevent
                       the blood from flowing into the arteries while the ventricle is filling up.
    B. 2 Atria- Receive the blood; the pressure in these chambers is very low.
    C. Pacemaker- located in the right atria; the function is to maintain the rhythmic
                       contractions of the heart.

II. Blood Vessels
    A. Arteries-
                1. Carry blood AWAY from the heart;
                2. Usually the blood  in arteries is oxygen-rich.   However, the one exception
                        is the pulmonary artery. The pulmonary artery carries blood from the
                        heart (right ventricle) to the lungs; the blood in this vessel is oxygen-poor.
                3. Walls of arteries are very thick.
                4. arterioles- small arteries
                5. Largest artery: Aorta, which carries blood from the left ventricle to
                        all parts of the body
                6. Structure/Function relationship: Arteries receive the blood as it comes
                        from the heart, consequently, the blood in the arteries is under very
                        high pressures.  The thick, elastic walls of the arteries enable the arteries
                        to cope with the pressure.
 
    B. Veins-
                1. Carry blood TOWARDS the heart;
                2. Usually the blood in veins is oxygen-poor.  However, the one exception
                        is the pulmonary vein.  The pulmonary vein carries blood from the
                        lungs to the heart (left atria); the blood in this vessel is oxygen-rich.
                 3. Walls of veins are thin.
                 4. Venioles- small veins
                 5. Largest vein: Vena cava, which carries blood from the body back to
                        the heart (the right atria). The Superior vena cava brings blood
                        back from the upper part of the body, and the Inferior vena cava
                        brings blood back from the lower part of the body.
                 6. Structure/Function Relationship: Veins carry blood back to the heart.  By
                        the time the blood gets into the veins it is usually under very low
                        pressure.  Veins contain one-way valves that help prevent the blood
                        from flowing backwards when there is very little pressure moving it
                        along.  Muscles contracting and squeezing veins help to push blood.

    C. Capillaries-
                1. Site of gas exchange and diffusion of substances
                2. Capillary walls are one-cell thick-- very, very thin.
                3. Capillaries must reach to each cell in the body.
                4. Structure/Function Relationship: Capillaries allow oxygen to diffuse
                        out of the blood into the cells, and allow carbon dioxide to diffuse
                        from cells into the blood.  Diffusion takes place through the
                        single-celled wall lining all capillaries.  Because it is only one cell
                        thick, diffusion and osmosis can take place rapidly.

III. Blood
    A. Parts of Blood
                1. Red Blood Cells-
                        a. Function: carry oxygenated blood
                        b. contain hemoglobin, which is the substance that makes
                                blood red and which actually is responsible for carrying
                                the oxygen molecules.
                2. White Blood Cells
                        a. Function: protection from foreign substances
                        b. WBC's work as part of the immune system
                3. Platelets
                        a. Function- important in blood clotting
                        b. appear to be small cell fragments
                4. Plasma
                        a. Function- contains dissolved substances like hormones, glucose, salts etc.
                        b. liquid part of the blood- is "straw-colored" (pale yellow)
 
 
 
 
 
 

Links:
William Harvey

Guided tour through the human heart, by the Franklin Institute

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