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This happens because the veins in the head do not have valves, responsible for pushing the blood upwards. Without this accessory, blood circulates more slowly in the region when we are upside down. But why then doesn’t the blood pool in the legs when you’re standing up? Because leg veins have valves, which help with circulation. “If the blood actually stopped in the head, we would certainly die”, says Ricardo José Gaspar, vascular and endovascular surgeon. “When we are upside down, there is an increase in pressure, but then the organism adapts, as it happens in sports and circus activities in which people are upside down.” So you don’t have to go all out to get your head upside down. Your body gives way.
round trip
How blood circulation works with the body standing up or facing down
STANDING
1. The heart pumps blood, pushing it into the arteries. They branch out until they reach the ends of the body (such as the feet), where there are microscopic capillaries.
2. On the way back, blood passes through venules, vessels that lead to veins. Inside the leg veins, there are hundreds of valves that close and prevent blood from returning to the feet.
3. When we walk, the calf muscles contract around the veins, also helping to pump blood back towards the heart.
4. Breathing also influences the process. When we fill the lung with air, we increase the pressure inside the abdomen and decrease the pressure inside the chest. When we release the air, the opposite occurs. This mechanism helps return blood from the legs to the heart.
UPSIDE DOWN
1. Blood also reaches the head via arteries and returns via veins, but they do not have valves, making the blood take a little longer to return to the heart. As the veins become fuller, the face becomes reddened.
2. The role of breathing also helps blood flow when we are upside down. As the skull is a smaller area, the pressure difference between the chest and abdomen is enough to cause blood to return to the heart.
• On long trips by bus or plane, take an hourly walk down the aisle