Gas Exchange: Properties of Gases and Alveolar Gas Composition (Nursing)

00:01 So now let's talk a little bit about the gas exchange that occurs between the lungs and the blood as well as gas exchange between the blood and the tissues.

00:12 There are two types of respiration.

00:14 We have external respiration, which is going to be the diffusion of gases between the blood and the lungs.

00:22 And then we have internal respiration, which is going to be the diffusion of gases between the blood and the body's tissues.

00:30 Both of these processes are subject to the basic properties of gases as well as the composition of the alveolar gas.

00:41 So to understand the properties of gases in the blood and the atmosphere we use Dalton's law of partial pressures.

00:50 In Dalton's law the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted by each gas.

01:01 The pressures of each gas are referred to as partial pressures and the partial pressure is going to be directly proportional to its percentage in a mixture.

01:15 So let's break this down with an actual example.

01:18 So our total atmospheric pressure of the air that we breathe outside is 760 millimeters of mercury.

01:26 This actually is composed of 78.6% nitrogen.

01:32 Therefore there is actually 597 millimeters of mercury of nitrogen in our air that we breathe outside.

01:44 The other major component of the air we breathe is oxygen.

01:48 Oxygen makes up 20.9 percent of air.

01:52 So the partial pressure of oxygen in our air is a hundred and fifty nine millimeters of mercury.

02:00 Our air also contains some other gases including a little bit of carbon dioxide and a little bit of water vapor and a couple of other insignificant gases.

02:12 At high altitudes the partial pressures of these gases are actually going to decline a bit.

02:18 So when you go up in the mountains or for climbing Mount Everest, there's a lot less of these individual gases and that air compared to at sea level.

02:28 But when we go underwater the partial pressure is going to increase significantly of all of these gases.

02:37 So when we compare the gas partial pressures between the atmosphere and the alveoli we find that with nitrogen we have less in our alveoli then we do and our atmosphere.

02:51 The same can also be said for oxygen where there is less oxygen in the alveoli compared to the atmosphere.

03:00 This is a converse relationship when we get to carbon dioxide and water.

03:04 Where carbon dioxide is actually more prominent in the alveoli than in the atmosphere.

03:10 And as well water is more prominent in the alveoli than in the atmosphere and altogether these equal up to a hundred percent.

03:22 So to explain how these gases are taken up and release from liquids like the blood we use another law known as Henry's law.

03:31 And Henry's law for a gas mixture that is in contact with liquid each gas will dissolve in the liquid in proportion to its partial pressure.

03:44 So at equilibrium the partial pressures in the two phases will be equal to each other.

03:50 And the amount of each gas that will dissolve will depend on two factors the solubility in the blood where carbon dioxide is actually more soluble than oxygen and nitrogen actually does not really dissolve in our blood at all.

04:07 Although it can if you get enough pressure.

04:10 And also the temperature of the liquid so as the liquid temperature rises the solubility of these gases actually decreases, so think about it when you think of like the increase in the temperature of water causes the water molecules to evaporate.

04:29 A good example of Henry's law is hyperbaric chambers.

04:34 We use hyperbaric chambers in order to treat infections, and what we do is we place a person inside of a chamber that has a really high oxygen pressure.

04:45 So at because of this high oxygen pressure, it causes an increase in the uptake of oxygen into our body's tissues and that oxygen is used to fight certain bacteria, especially anaerobic bacteria.

05:02 So alveoli contain more carbon dioxide and water vapor than atmospheric air.

05:08 This is because gas exchanges in the lungs such as the oxygen that diffuses out of the lungs from the tissue and the carbon dioxide that diffuses into the lungs is going to cause a lot more carbon dioxide to be present inside of the alveoli.

05:26 Also, we have more water because of the humidification of air by are conducting passages.

05:34 Lastly, remember that we always have a little bit of air sitting in our alveoli.

05:40 So we're going to have a little bit more carbon dioxide there because we're going to have a mixing of the alveolar gas with each breath where we have some new inspired air mixed with the air that was already left between breaths.