You know the lyrics to “Head and Shoulders, Knees and Toes.” You also know you’ve got a heart, a liver, a stomach, and a brain. You might even know the names of most of your bones and muscles. But for most of us, the human body is just so complex that a few of the minor characters get forgotten. Here are five important body parts you probably didn’t know you have.
Thymus (aka Your Immunity Factory)
Your thymus is a small organ located beneath your breastbone, and while you may not have heard of it, it plays a pivotal role in keeping you healthy. It’s part of both the lymphatic system, which transports immune cells throughout your body, and the endocrine system, which deals with the chemical messengers known as hormones. The thymus is the source of T-cells (the T stands for thymus), which are a type of white blood cell that regulates your immunity and hunts down any illness-causing invaders.
Lacrimal Puncta (aka Your Teardrop Holes)
Ever wonder where your tears go? The lacrimal puncta (singular: punctum) are four tiny holes on the inside of your eyelids, one at the inner corner of each upper and lower eyelid, that help drain the tears that keep your eyes moist. You can even see these tiny holes if you want to — just gently push up on the lower corner of your eye to see the inner edge of the eyelid, and it’ll be there.
Mesentery (aka the Seatbelt for Your Guts)
Your skin, bones, and muscles hold your organs in — but what holds them up? Meet the mesentery, an organ we once thought was just a disparate collection of membranes but now know is one continuous structure. It’s responsible for attaching your intestines to the wall of your abdomen and keeping your guts from sloshing around when you ride a roller coaster or take the stairs.
Arrector Pilli (aka Your Goosebump Muscles)
You don’t need one tiny muscle attached to every single hair on your body to help it stand up straight when you’re cold or Adele starts singing, but evolution thought you might like to have ’em anyway. Your skin’s arrector pilli muscles and the involuntary reflex that makes them contract are leftoversfrom when your ancestors had long fur. Our fuzzier brethren benefitted from the ability to puff their fur out in chilly temperatures (to help them stay warm) and when facing an adversary (to make them look bigger).
Interstitium (aka Your Fluid Superhighway)
It wasn’t until this year that scientists realized that not only were there fluid-filled cavities surrounding everything inside your body — around your lungs, your blood vessels, your muscles, your bladder, you name it — but these cavities were all part of one huge organ. They called it the interstitium, after the interstitial fluid that fills it. That fluid drains into the lymphatic system and, like the thymus, plays a role in immunity. It may be new to us, but it’s been keeping you healthy all your life.