Biomedical Engineering 403
Gas Transport to the Periphery, Part 1

Reading for Today:

Chapter 6 in West .

Hi there!

This is what happened in class today (9-5-97). As usual, all of this is in outline format with hypertext, so if you want to review the specifics, or if you have any questions on a specific topic, click the hypertext for that topic.

Today’s topic:

How gases travel from the lungs to the tissues (and back again).

Consequently, we’ll discuss O2, CO2, how they get carried in the blood, and especially, the role of Hemoglobin.

Your lungs suck in oxygen gas (O2) and blow off carbon dioxide (CO2). They suck, and they blow. All day long. That’s what lungs do.

Your tissues need O2 to live. CO2 is a waste product of cell metabolism, and needs to be got rid of.

Take for example, your brain. The cells there need lots of O2, or they will die. If they die, that is bad. The cells there also generate buckets and buckets of CO2 as a waste product. You got to get rid of the waste product, or the cells will die. It is bad to let your brain cells die. Now your lungs have lots of O2, and are very good at getting rid of CO2. But, unless you’re a mutant, your brain is nowhere near your lungs. So how do these gases get transported?

This is why you have BLOOD!

O2 gets dissolved into blood. It can then be pumped from your lungs (where there is plenty of it) to your peripheral tissues (where it is needed).

CO2 is also dissolved in blood. It is then taken from the periphery (where it is generated) to the lungs (which blow it out of the body and make it go bye-bye).

How does this work? These gases are actually transported in significantly different ways.

O2: O2 is carried in the blood in TWO ways:
- 1. Directly dissolved in blood, in accordance with henry’s law .
  - For each mmHg of Po2, 0.003 mL of O2 can be dissolved in each 100 mL of blood. This means that with a normal PaO2 of 100 mmHg, only 0.3 mL of O2 can be dissolved in every 100 mL of blood. For those of you who are awake, you’ll probably notice that this is a very small amount. Insignificant. Piddly. Not a lot. It is not, in fact, enough to oxygenate your cells.
  - To be sure, this is why we have BLOOD running through our arteries, and not plain ordinary saline water. Red blood cells are packed with a molecule that binds oxygen like nobody’s business. This is the other way that O2 is carried in blood:
- 2. Hemoglobin!
CO2: CO2 is carried in the blood in THREE ways:
- 1. Directly dissolved in blood, in accordance with henry’s law .
  - Now, unlike O2, CO2 dissolves pretty nicely in blood plasma. In fact, it is 20 times more soluble in plasma than is O2. Still, only 10% of CO2 is carried in the blood as dissolved CO2.
- 2. Bicarbonate!
- 3. Carbamino Compounds!