Martha Olivo on the Hooves
Q: I have heard that the horse "has five hearts". What does that mean?
A: When blood is pumped from the heart, it flows into elastic-like arteries. With each pump of the heart, the arteries expand to accept the surge of blood, and then they shrink back down to their 'normal' size again. Blood travels in this manner, branching again and again until it is pushed into capillaries. These tiny little vessels are where the blood actually performs its duties: it provides nearby cells with oxygen and food, and removes waste and carbon dioxide.
As more blood surges behind it, the capillary blood is pushed into venules, which branch into larger veins. Veins are not elastic. Their adaptive quality is that they have little valves. These valves prevent the blood from sloshing backwards, as the pressure is no longer quite as intense as it was earlier in the circulatory journey.
The circulatory system functions much better if the veins have a little help in their task of getting blood back to the heart. This is one of the roles of muscles. Each time a muscle contracts, it squeezes blood through the vein toward the heart. The veins' valves trap the blood in its new location, and it waits there until the next surge of blood pushes it along or until the muscle contracts again. And so, with each squeeze of a muscle, the veins are provided with a little assistance in their daunting task of returning blood to the heart.
In the course of their evolution, horses have lost muscular structure in their lower legs. Through millions of years of evolution, these muscles have become tenuous straps. Therefore, the muscular function of aiding blood in its journey back to the heart has been minimized. And this is where the hoof comes into play.
When a hoof has proper mechanism, it both widens and flattens when bearing the horse's weight. This mechanism allows the blood into the corium that 'lines' the hoof wall and coffin bone. When the horse lifts his foot, the wall contracts, the sole becomes concave, and the coffin bone lifts slightly into the neck of the coronary band. Like the action of the heart, this action effectively pumps blood out of the foot.
The horse's hooves, or four 'auxiliary hearts', are paramount to his health. The function of each heart, including his real heart, depends upon proper hoof mechanism.
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