The Respiratory System

Go ahead! Go on outside and take a deep breath of this wonderful, spring air! I picked the theme for the webpages this week on the basis of the lovely spring weather we are having. Yippee!

Why are we doing the respiratory system before the digestive system? Because you are thinking about oxygen and blood right now. It is still fresh in your mind. So let's finish that material first. Then we'll go back and do digestion, and cover how we get nutrients in the blood as well.

Your book covers the respiratory system in the following order: Why We Breathe, Organs of the Respiratory System, Breathing Mechanism, Control of Breathing, Alveolar Gas Exchange, and Gas Transport. I'm going to follow those categories in these webpages, but change their order a bit. Also, I'm going to explain why we breathe right here on this page.

Why we breathe

We have gone over this a little bit in doing the blood unit. But I'm going to refresh your memory here, and maybe expand on it a little bit.

You know that we need to breathe all the time. If our breathing is interrupted for longer than 4 minutes, we start to have brain damage. You also know that we breathe to get oxygen into our bodies. I think that most of you realize that this oxygen is needed for us to make energy (ATP) in our cells, but, let me explain more.

The point that seems to get students stuck when they think about why we breathe, is that students think asking "why do we breathe?" is the same thing as asking "why do our lungs inflate?" In fact, these are not the same questions. If you are thinking about our lungs inflating, you are thinking about how we breathe, not why. The reason we breathe is to get oxygen in our bodies to make energy. How we do it is by inflating our lungs (this is explained in the "breathing mechanism" section).

So, when we breathe, we get oxygen into our bodies. This oxygen is needed by every single cell in our bodies. The oxygen just gets into the bodies through the lungs, but then, to get to every cell, it has to travel in our blood. You know that it travels in our blood by attaching to hemoglobin within the red blood cells. But once it is in blood, that is not its final destination. It must enter the body cells. You learned that oxygen diffuses out of the blood into the body tissues, and you will learn more about that in this unit. Once oxygen is in the body tissues, it will then diffuse into the cells of the body.

Once in a cell, oxygen diffuses into mitochondria (also look at this link and scroll down to the mitochondria section). Remember those organelles? They are the energy-making organelles in our cells. All eukaryotic cells have mitochondria (even plant cells, fungus cells, and protist cells). When our cells need to make energy, they start with glucose and begin to break it down. The products from breaking down glucose travel into the mitochondria, and so does oxygen. Within the mitochondria, these products and oxygen are used to manufacture ATP-- cellular energy. Without oxygen, we can only make a small quantity of ATP by breaking down glucose. When you learned about muscle, you learned that if oxygen can't get to the muscle fast enough, as glucose was broken down and only able to make a little bit of ATP, the broken down glucose was converted into lactic acid. The lactic acid, causing the muscle-burn-sensation, would later have to be re-converted back into glucose for ATP production in the presence of oxygen. Do you remember all of this?

Therefore, we breathe in order to get oxygen into our mitochondria for the production of energy. When we are unable to get oxygen to certain body tissues for any prolonged period (even just 4 minutes), a condition called ischemia, those body tissues are no longer able to make ATP. Without any energy, they begin to die.

Layout for the rest of the unit:

outline.jpg (18745 bytes)

I have also added a "Respiration Laws" page to have all the rules and laws about respiration in one place.