in honor of the gill

Since it’s my best friend’s birthday this week, we’re going to talk about how fish gills work. (Her name is Ashley Gill. So it’s only fitting.)

The need to breathe is common to almost all organisms on earth. Breathing, in the broadest sense, is taking in an environmental element, extracting part of it for metabolic use (i.e. oxygen), and expelling the leftovers.

Critters live in all sorts of environments, so naturally there are varying methods of breathing. Air breathing animals, as a rule of thumb, use lungs. Animals that must take in water usually use gills. Sometimes animals do not have breathing structures at all and simply absorb what they need through their skin, via water or air. Well that sounds easier, doesn’t it? Why can’t we all just do that? Surface area, baby. That’s why.

Generally speaking, when an animal becomes big enough to exceed a specific volume: surface area ratio, they are no longer capable of meeting metabolic needs by absorbing oxygen through their skin alone. They simply need more tissue devoted to extracting oxygen from their environment to supply their bodies. Enter respiratory structures like gills and lungs.

Fish gills looking nice and feathery

When you think of gills, the first thing that should come to mind is surface area. Gills are made up of projections, with tiny projections on those projections, with tinier projections on those tiny projections (these tiny projections are called lamellae). As such, the result is the feathery looking thing we call a gill. These tissues are laden with blood vessels, which allow for oxygen exchange between the water and bloodstream.

A fish breathes by drawing in water into its oral cavity, then into the gill chamber, and out of the gills. This means there is a constant one-way flow of water over the tissues of the gills. A one way flow of water, huh? We have a two-way flow through our respiratory system (we breathe in, then out). Fish must know something we don’t. Let’s talk counter current exchange.

Now for some real-deal biology. In the lamellae, the part of the blood vessel coming in with deoxygenated blood is afferent, then it makes a U-turn and becomes efferent, carrying away oxygenated blood to the body. Somewhere between being afferent and efferent, the blood vessel follows alongside the current of water… in the opposite direction. This is the magic of countercurrent exchange. Blood flows in the opposite direction of water.

This way, the blood always has a lower concentration of oxygen than the water it encounters. Water will always give its oxygen to blood via passive diffusion when the oxygen is distributed this way. In a concurrent system, where water and blood flow in the same direction, the oxygen will balance out equally between blood and water, making maximum oxygen saturation of the blood 50%. Countercurrent exchange beats this by a lot, having 85% oxygen saturation the maximum. I could try to further explain this in words, but a visual is what’s really needed.

                            

                          

Neat, huh?! Simple and efficient. This is just another example of how newly evolved things are not necessarily better than more primitive things, like gills.

This week, we have two bonus questions. If you’re the first get one right, I will do one of two things. 1.) Write a blog on the subject of your choice 2.) Include you in an amusing way in an upcoming post. I can’t promise I won’t photoshop your head on a monkey or something if you select this option.

So c’mon! Play along. Please. I’ll pay you. No, I can’t afford to pay you. I’ll love you instead.

1.What do you think is the foremost reason fish are unable to extract oxygen when out of the water?

2. Are lungs the evolutionary descendents of gills? Explain your thoughts.

I would say there are no right or wrong answers here, but that’s not true. But not to worry, it’s the process of thinking about it that makes winners on this blog!

human color palette

My sister. (As interpreted by 11-year
old Claire)

When I was in the 6^th grade, I had an incident my family refers to as the “brown brown brown meltdown.” Alix, my older sister, was in high school and was the standard of beauty in my eyes (she still is). I thought she looked like Snow White. She had glossy onyx hair, olive skin, pink cheeks, long cow eyelashes (not to mention cool clothes and big boobs). I, however, was 11 and painfully skinny. I was in that stage that it is so difficult for little girls, what with gangly long limbs and a bad…really bad… haircut. My skin was dark and the same color as my rat-colored hair. My eyes were somewhere between poo and nutria colored. One day, I couldn’t take it anymore. Through tears, I bawled to my sister, “You’re just so pretty. And I… well, I’m just BROWN BROWN BROWN!”

Now, 12 years later, I’m still in my awkward stage. My haircut is better though, and I learned to put on makeup. And some people spend $19.99 a month to have my color skin (booyah!). To all the awkward little girls out there, know that you will become way less ugly. But it’s okay if you don’t turn into a Disney princess like they lead you to believe you will.

On a whole, all of us people are relatively drab animals. On the outside, we are pretty much varying shades of brown. We like to think we’re all super unique looking. But put together a collage of the entire human population and it will be unmistakably brown. However, we do show some other colors- for instance, our blood is red, and our veins look blue. There are the occasional green and blue eyes. Why are we colored the way we are?

hstroud.teachforus.org

Your skin and hair is filled with melanin. There are two types of melanin: Eumelanin and phaeomelanin. Phaeomelanin means “brown melanin” and eumelanin means “true melanin”. Eumelanin can be black or dark brown. African, Asian, and Indian folks have lots of eumelanin in their skin and hair. Phaeomelanin pigments account for the rest of the browns. Think about a kangaroo, or an Irish person. Or a squirrel. Phaeomelanin also includes what we describe as “red hair,” which actually isn’t red red. It’s a very warm brown. Blond/light haired people have both very light phaeomelanin and little of it. Which makes sense.

Eumelanin and melanin can both be present at the same time, and so can create a wide variety of brown colors. Us mammals are loaded with eumelanin and phaeomelanin. So even my Disney princess sister is “brown brown brown” in the end.

Why blood is red (dreamstime.com)

Blood is red, but not because of a red pigment. (Bonus points to anyone who can remember what pigments are red!?) Your blood is filled with hemoglobin, which is a little iron-laden protein that picks up oxygen for your tissues. What color do you associate with the element iron? Think about if a piece of iron is left outside in the elements for too long and it oxidizes. It rusts… and rust is red. So blood is actually rusty red. Ah hah!

But when you look down at your arms, you see blue veins. Maybe you’ve been told that if a hemoglobin loses its oxygen, it turns blue. False. Your blood is never blue. If you watch a surgery, you’ll see that veins are not blue in the body. They are a deeper red than the oxygenated blood in the arteries, but not blue. So, that means that blood only looks blue when viewed through the skin. Without getting into the hairy nitty gritty wavelength details, it can be said that skin filters the light in a way that make veins appear blue to our eyes, when they are actually red. It’s your skin’s fault, not the loss of oxygen.

This next one is going to be gross, but enlightening. When you have a pimple, you can see that the stuff in it is white. That stuff is literally a mass of your white blood cells that are trying to fight off the infection in your pore. They aren’t called white blood cells for nothing. They’re actually white.

Eyes, as mentioned, can be a variety of colors. If they’re brown, they are pigmented by melanin. But there are also blue and green pigments that can be produced. Pigments are lipids, meaning they are akin to fats. Next time you’re at a bar, I dare you to tell someone they have a nice fatty eye color. It’ll be really funny, I swear.