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Blood returns from the lungs to the left side of the heart to be pumped to the rest of the body. There's substantial back pressure in the lungs, so if it went straight from there to the rest of the body without going back to the heart for a boost, it would be more of an ooze than a flow.
This problem could be overcome by starting with a higher blood pressure going to the lungs in the first place, but this introduces additional problems, namely that the barrier between the capillaries in the lungs and the airspace in the alveoli is fairly thin to maximize gas transfer, and increasing the pressure substantially here would mean either making the barrier thicker (and thus impeding gas transfer) or risking "blowouts".
If you're asking why the left side... it has to go somewhere, and the right side is already just about in the middle of the body where the great veins run, so it's just more efficient (not that that's necessarily a consideration in evolution) to have venous blood return to the right side, and oxygenated blood return to the left. There are people in which this gets mixed up (the condition is called "transposition of the great vessels", and there are various kinds, some of which are immediately life-threatening at birth... for example, there's a kind where venous blood returning to the heart is just pumped straight back out to the body, while the other side of the heart just pumps blood around and around through the lungs. Before birth, this isn't such a big deal, since the lungs aren't actually doing anything and the ductus arteriosus allows blood from both sides of the heart to mix anyway, but this normally closes shortly after birth).
What else can I help you with?
Where does the left side of the heart get its blood?
the left side of the heart gets its blood from the lungs through the pulmonary veins. this blood is deoxygenated. hope this helped...
What is the difference between the blood on the right side of the heart and the blood on the left side of the heart?
The right side of the heart pumps blood to the lungs, and the left side pumps blood to the rest of the body. The blood on the right side is deoxygenated and the blood on the left side is oxygenated.
How does the blood on the right side of the heart compare with that on the left side?
The right side is deoxygenated blood; the left side is oxygenated blood (returned from the lungs).
What does the right and left side of the heart pump?
Blood. The right side pumps deoxygenated blood and the left pumps the oxygenated blood.
What separates the right side of the heart?
The SEPTUM separates the right side of the heart from the left side. This is to prevent the mixing of oxygenated blood with deoxygenated blood.
Which number of the heart contains blood rich in oxygen?
The left side of the heart contains oxygen-rich blood. The right side of the heart contains deoxygenated blood.
What kind of fluid does your heart pump?
The right side pumps deoxygenated blood and the left side pumps oxygenated blood.
Why is half of the heart blue and half red?
Because the right side of your heart pumps deoxygenated blood and the left side pumps oxygenated blood.
True or False The left side of the heart contains oxegynated blood?
HorseIsle Answer: True JadeStephanie Gray Server!
Which side of your heart contains deoxgenated blood?
the right side of the heart contains deoxygenated blood.
What side of the heart sends blood to the lungs for oxygen?
The left side of the heart supplies blood to the body through the aorta, the largest artery in the body. The right side of the heart sends blood to the lungs for oxygenation.
Do oxygenated and deoxygenated blood mix in the heart?
No, the deoxygenated blood enters and leaves the heart through the right side and the oxygenated blood enters and leaves the heart through the left side. Both sides of the heart are separated by a wall called a septum. The wall between the left and right atria is the interatrial septum and the wall between the left and right ventricles is the interventricular septum.
