Funny things about humans

There are a number of funny things about our bodies that make me curious. So I have decided to devote an entry to a few miscellaneous things about the human anatomy that particularly intrigue me. For example, have you ever thought about why we have kneecaps? Or wondered why we have clumps of junk in the corners of our eyes when we wake up? Or how about earwax - what is that for?

First in my list of funny things about humans are kneecaps, also known as patella. The patella is a thick, triangular piece of bone that sits on top of your knee, covering and protecting it. It’s 1 of 4 bones in your knee, including the tibia (shin bone), the fibula (parallel to the tibia) and the femur (thigh bone). The kneecap is connected to the rest of your knee through tendons, ligaments and cartilage. The quadriceps tendon connects it to your thigh muscles, multiple ligaments connect it to the bones of the lower leg, and cartilage surrounds the whole thing. The patella is a sesamoid bone, which means it is a bone embedded within a tendon. (Do you remember my entry on the funny bone? The patellar tendon is the one that gets tapped in a knee jerk reflex test.) Sesamoid bones function to increase the mechanical effect of a particular tendon; that’s why they are mostly found in the hands, feet and knees. So the kneecap increases the leverage of the knee joint – actually, it increases the extension strength of your knee by about 30%.

Knees are complicated joints, and they have many things that can go wrong. There are several problems associated with kneecaps. Runner’s knee (or Chondrolmalacia) occurs when the cartilage directly underneath the kneecap becomes irritated. This is because the patella is directly rubbing against one side of the knee joint. Another problem is housemaid’s knee (or Prepatellar bursitis). There is a small lubricating sac between your skin and the surface of your kneecap called the bursa. People who spend a lot of time on their knees often have their patellar bursa become inflamed, causing swelling over the knee and limiting movement. Still another common problem is patellar dislocation. Your kneecap slides in a grove along your thigh bone as your knee extends. In some people, the patella moves out of that groove, and becomes dislocated. Kneecap dislocation is a fairly painful problem, underscoring how important it is for our knees for our kneecaps to be positioned properly. All in all, I’d say that kneecaps are really an underappreciated piece of our bodies.

Now on to another funny piece of our anatomies – eye gunk. Perhaps you call it crusts, sleepy eyes, or (here’s a truly unscientific name) eye goobers. Whatever it’s name, I’m talking about the clumps that accumulate in the corners of our eyes when we wake up in the morning. This junk is what’s left over from our tears once the water has gone away. Tears have 3 components – salt water, protein and fat. The salt water is produced by the tear gland, which sits behind the upper outer corner of the eyes. Protein is secreted by the conjunctiva, the clear film over the surface of the eye. And the fat comes from ducts in the eyelids. All 3 of these things serve very important functions. They clean the eye, help correct for imperfections in the cornea, and deliver nutrients to the eye. When you sleep, however, most of these things aren’t needed. We don’t get dirt in our eyes and we don’t need have the imperfections in the cornea corrected because we’re not looking at anything. So we don’t make tears. The liquid already on the surface of your eye seeps out as you sleep, and the water dries up. This leaves behind clumps of fat and protein. We don’t get this when we’re awake, because our eyes are always producing new liquid. So, tomorrow morning, if you find crusts in your eyes, you can tell yourself – look, it’s protein and fat!

Today’s final topic is earwax. Earwax is more properly known as cerumen (pronounced suh-ROO-mun). It is a yellow, waxy substance secreted by glands in the ear canal of many mammals, including humans. In humans, 2 types of glands in the outer ear canal produce the wax – the ceruminous glands (which are modified sweat glands) and sebaceous glands. It’s made up of over 40 different components, including wax and oils. The most abundant component is keratin, an extremely important protein found in all the outermost layers of our skin. Everyone’s earwax is unique, with a specific composition, color and consistency. Color can range from golden yellow to black – though no one knows what pigment is responsible for this coloration. Consistency can be either dry or wet – and that seems to be genetically determined, as dry earwax is common in Asians and Native Americans, while wet earwax is common in African-Americans and Caucasians.

Earwax is actually very important for your ears. It protects and moisturizes the inner ear canal. It helps prevent both bacterial and fungal infections within the ear canal. It keeps dirt, dust, and other unsavory things from accessing the inner portions of your ears. And it helps move dead skin cells out from the inside of the ear to be shed away. On your skin, dead cells are sloughed off through friction. Within the ear canal, the movement of your ears through talking, chewing and swallowing cause the earwax to rub against the cells, picking them up. Small hairs called cilia then move the earwax and dead cells towards the outside just like a conveyor belt. Without this, we would have no way of shedding dead cells from within our ear canals. All in all, while this is certainly something I’ve never really fully appreciated before, we should really be grateful for our earwax!

These are just a few of the intriguing questions I have about the human body. I have many others – but I’ll have to save those for another time. How about you? What about the human body makes you sit back and think, “Why on earth do we have that?”

The image of the kneecap was taken from:
http://orthopedics.about.com/cs/patelladisorders/a/kneecap.htm