申し訳ありません、このコンテンツはただ今　English　のみです。

As humans we are under special stress by the ubiquitous gravitation on Earth. In hole evolutionary history we are the only animals with a bipedal gait and a completly erect spine.

This means, from head to toe there’s a constant pressure gradient not only on the skeleton but probably more importantly on the blood.

The other bipedal animals have or had (dinosaurs) a horizontal thoracic and lumbar spine which reduces the pressure gradients from the highest to the lowest point if the body. Penguins walkin on land are similar to humans woth this respect but stay in water unless the breed when they are laying on their eggs. So standing upright is more an exception for them. Staying in water counters gravitational force by buyoncy.

The blood is unique in being an uninterrupted column of fluid connecting all organs. Pressure onto such a fluid column spreads all along the column since fluids are incompressible. They cannout buffer pressure by increasing their density as gaseous matter can.

Organs being subjected to this pressure can but change the pressure of the blood column by modifying their vascular bed.