Veins primarily get oxygen as blood passes through the lungs, specifically via the pulmonary veins.
The Pulmonary Circuit: A Vein's Oxygen Source
The general rule is that veins carry deoxygenated blood back to the heart. However, there is a crucial exception related to the pulmonary circuit. According to provided information:
- Pulmonary Veins: "In your lungs, your blood refuels with oxygen and then returns to your heart through your pulmonary veins."
- The Role of the Heart: "Your heart then pumps out this oxygen-rich blood so it can begin a new lap on the systemic circuit."
This means that the pulmonary veins are the vessels responsible for carrying oxygenated blood from the lungs to the heart.
Systemic Circuit: Veins Returning Deoxygenated Blood
After the oxygenated blood is pumped from the heart, it travels through the arteries to deliver oxygen to the body's tissues and organs. Once the oxygen has been delivered, the now-deoxygenated blood enters the veins to be transported back to the heart to start the circuit again. Therefore, other than the pulmonary veins, most veins don't "get" oxygen; they carry deoxygenated blood.
In summary, veins (specifically the pulmonary veins) get oxygen when blood passes through the lungs, where oxygen diffuses from the air sacs (alveoli) into the blood.
