 we can quantify how much oxygen is on our hemoglobin bus. So look at what I've done here. I drew you a red blood cell. This whole thing is one red blood cell. Highly diagrammatic. Each one of my circles is representing one hemoglobin molecule. And each one of my little Ls is an oxygen seat on the bus. Does it work for you? Here's a hemoglobin molecule that can hold, that has seats for, for oxygen molecules. If oxygen, okay. I drew, I don't know, 10 hemoglobin molecules here. So I have a total of 10 hemoglobins, which means do you agree I actually have 40 seats for oxygen available? So I can calculate the saturation. How saturated is hemoglobin with oxygen in any given situation? Look at it right now. Is there any oxygen attached to any of my hemoglobins? This is scenario number one. The hemoglobin is 0% saturated with oxygen. Do you agree with that? Now watch and be amazed. Here come four oxygen molecules. And they're like, dude, let's sit in these seats. Now, what saturation am I in this exact scenario? Well, I've filled up four of my 40 seats. So at this exact moment, I am now 10% saturated. If I filled up half the seats, so I basically filled up all the seats in half of my hemoglobin molecules. And it definitely doesn't fill up like this. It's going to fill up evenly, you know. I mean, there's probably like whatever, it just fills up. I'm drawing them all sitting in the same hemoglobin molecule. I'm doing that just so that we can visualize. These guys are all full. These five are all empty, which means we are 50% saturated. Does that work for you? And then if I filled them all up, what am I going to be? I'm going to be 100% saturated. The percent saturation for hemoglobin is affected by the partial pressure of oxygen in the fluid surrounding it. And it's weird. Like, they're actually the stickiness of the bus seat changes depending on the partial pressure of the oxygen in the plasma surrounding the bus seat. Okay, so that concept is what we're going to talk about next. And so I will try not to say anything else until I get to that concept.