Pulmonary and Systemic circulation
Systemic and Pulmonary Circulation
The left and right sides of the heart work independently. Blood from the left side of the heart contains more oxygen and is shown in red. This oxygen-rich blood is pumped from the left ventricle into the large artery (aorta), which delivers it throughout the body. The blood transports nutrients and oxygen to all cells — this is called systemic circulation.
Blood that has delivered oxygen becomes deoxygenated and turns dark blue or purple. This blood enters the right atrium through the veins and moves into the right ventricle, which pumps it to the lungs. In the lungs, carbon dioxide is removed and oxygen is absorbed — this is called pulmonary circulation. The now oxygenated blood returns to the left atrium and then the left ventricle, where the cycle starts again.
Common Mistake
Don’t confuse the colors in circulation diagrams: red usually shows oxygen-rich blood, and blue indicates deoxygenated blood. Both types of blood flow through arteries and veins depending on direction — not oxygen content alone.
Important Concept
The circulatory system is divided into two loops: systemic circulation, which delivers oxygen and nutrients to all body tissues, and pulmonary circulation, which carries blood to the lungs for gas exchange. The heart acts as a double pump, sending blood through both loops in a continuous cycle.
Questions
“All arteries carry oxygenated blood, and all veins carry deoxygenated blood.”
Show Answer
This statement is false. While most arteries carry oxygenated blood and most veins carry deoxygenated blood, there are exceptions. For example, the pulmonary artery carries deoxygenated blood from the heart to the lungs, and the pulmonary vein carries oxygenated blood back to the heart.
Show Answer
1. During atrial contraction, blood flows from the atria into the ventricles.
2. During ventricular contraction, blood is pushed from the ventricles into the large arteries (aorta and pulmonary artery).
3. During general rest (diastole), the heart relaxes and the cycle prepares to begin again.