Cardiovascular System


                                                                          rculatory stem  vast network of organs and vessels that is responsible for the flow of blood, nutrients, oxygen and other gases, and hormones to and from cells. Without the circulatory system, the body would not be able to fight disease or maintain a stable internal environment — such as proper temperature and pH.

                                                                          • It is made up of three independent systems that work together: the heart (cardiovascular), lungs (pulmonary) and arteries, veins, coronary and portal vessels (systemic).

                                                                          • In the average human, about 2,000 gallons (7,572 liters) of blood travel daily through about 60,000 miles (96,560 kilometers) of blood vessels.

                                                                          • An average adult has 5 to 6 quarts (4.7 to 5.6 liters) of blood, which is made up of plasma, red blood cells, white blood cells and platelets.

                                                                                    • The heart, blood, and blood vessels make up the cardiovascular component of the circulatory system. It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated. It also incorporates the systemic circulation, which runs through the rest of the body to provide oxygenated blood.

                                                                          • Endocardium- Smooth layer that lines the inside of the heart.

                                                                          • Myocardium- Thick layer of muscle tissue that performs the pumping action.
                                                                          • Pericardium- Sac-like membrane that surrounds the heart.
                                                                          • Four chambers- Two for receiving blood (atria) and two for moving it out of the heart (ventricles). When blood is pumped out of the chambers, valves snap shut with a "thump-thump" (often referred to as "lub-dub"), which is the sound heard when listening to the heart. The valves prevent back flow of blood.

  • Though the brain can cause the heart to speed up or slow drain, it does not control the regular beating of the heart.
  • The muscle fibers of the heart are also self-excitatory. This means they can initiate contraction themselves without receiving signals from the brain.
  • The heart continues to beat with no further outside stimulus, sometimes for hours if bathed in the proper solution. In addition, cardiac muscle fibers also contract for a longer period of time than do skeletal muscles. This longer period of contraction gives the blood time to flow out of the heart chambers.

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