You already know that a penis has arteries to bring blood to its erectile tissues, and veins that take the blood away again when it returns to its normal flaccid state. You may not know that there's another set of vessels tucked under its skin. We just got our first good look at them.
As blood moves through capillaries, some of its plasma gets squeezed out of the tubes and into the body's tissues. The lymphatic system collects that fluid and returns it to the veins; if the vessels are blocked, or more plasma enters a tissue than the lymph vessels can carry out, the fluid can back up and swell that tissue up like a water balloon.
That's not at all pleasant when the tissue in question is a penis. I'll spare you the photos (though you can look here if you really want to know what it looks like). But no one knew much about how the lymphatic vessels were arranged underneath the skin, which limited treatments for swelling and increased the risk of complications during surgery.
So in a wince-inducing imaging experiment, Yan Liu and his colleagues at the Third Military Medical University in Chongqing, China built a map of the penile lymphatic system using MRI images captured from volunteers who agreed to have a medical contrast agent injected under their foreskins.
The results, published in the Anatomical Record this week, show that lymphatic vessels in the glans and foreskin form a network across the upper surface of the penis before merging to form larger vessels that send fluid into lymph nodes embedded in the groin. The network isn't connected to the erectile tissues in the centre of the penis, suggesting that those tissues have their own independent set of lymphatic vessels.
And that also tells us that there are three distinct routes to end up with a swollen penis, only one of which is any fun.
Picture: Long et al. 2015