Additionally, there are two important but separate circuits: The pulmonary and systemic circuits. The pulmonary circuit is the route over which the blood is sent to the lungs to get oxygen. The systemic circuit is the route over which the blood is sent throughout the body to deliver oxygen (Cleveland Clinic, 2022).
Image 1: A Healthy Heart
Blood flow Once blood has entered an atrium, the only place it goes next (in healthy hearts) is down to the ipsilateral ventricle. The right and left sides are kept separate by a thick wall of tissue called the septum . Once the blood has entered the ventricle, it must be pumped out into the arteries destined for the lungs or the body. The blood should never go back up from the ventricle to the atrium. The right atrium (RA) receives deoxygenated blood from the body (through the systemic veins), and the right ventricle (RV) receives that blood from the atrium and pumps that deoxygenated blood to the lungs (through the pulmonary arteries). The left atrium (LA) receives oxygenated blood from the lungs (through the pulmonary veins), which then goes to the left ventricle (LV). The left ventricle then pumps that oxygenated blood to the body via the systemic arteries (Cleveland Clinic, 2022). See Image 2 for a simple diagram of the process. Image 2: Cardiovascular Process
Self-Assessment Quiz Question #3 What sequence best summarizes blood flow through the body? a. Right atrium – right ventricle – lungs – left atrium – left ventricle – body b. Left atrium – left ventricle – lungs – right atrium – right ventricle – body c. Lungs – body – right atrium – right ventricle – left atrium – left ventricle d. Body – lungs – left atrium – left ventricle – right atrium – right ventricle There is a common misconception about the flow of blood from the heart out through the arteries and back through the veins. It is well understood that the heart forcefully pumps blood out into the arteries. This pumping action does not, however, drive return flow through the veins. The blood is not pushed continuously through a loop. Rather, the arterial and venous flows are quite distinct and are driven by totally different mechanisms. Venous circulation is passive, relying on changes in position and pressure by breathing and squeezing from the contraction of the adjacent muscles. The “milking” action of nearby muscles creates the return flow of blood. For example, the soleus muscle aids the blood flow from the legs as it contracts with each step (Haff & Triplett, 2015). Each ventricle is separated by a valve that helps direct the flow of blood through the heart. Recall that in addition to transporting oxygen, the red blood cells also carry nutrients, hormones, and waste materials. Image 3 offers an interesting look at the circulatory scheme, including a view of some organs along the way such as the liver and stomach. Throughout this loop, called the hepatic portal circuit , the blood picks up nutrients from the digestive organs and delivers raw materials to the liver to be recycled into useful fuels and building materials.
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