What prevents blood from pooling in the legs of humans and pigs?

In humans:

1. Muscle pump: The contraction and relaxation of leg muscles act as a pump that propels blood upwards against gravity. When we walk or move our legs, the muscles squeeze the veins, pushing the blood towards the heart.

2. Venous valves: Veins in the legs contain one-way valves that prevent backward flow of blood. These valves ensure that blood can only flow towards the heart and prevent it from pooling in the legs.

3. Elastic recoil of veins: The walls of veins are elastic and can stretch to store blood. When the leg muscles relax, the veins recoil, which helps in propelling blood upward.

In pigs:

Pigs have similar mechanisms to prevent blood pooling in their legs as humans do.

1. Muscle pump: Pigs use their leg muscles for locomotion, and the contraction of these muscles helps pump blood back towards the heart.

2. Venous valves: Pigs also have one-way valves in their leg veins to prevent backward flow of blood.

3. Respiratory pump: In addition to the muscle pump and venous valves, pigs also have a respiratory pump that aids in blood circulation. When pigs breathe, the changes in pressure in the chest cavity help move blood from the legs towards the heart.