Partial Pressure Gradient and Respiratory Membranes – External Respiration (Nursing)

00:01 So external respiration or pulmonary gas exchange is going to involve the exchange of oxygen and carbon dioxide across our respiratory membranes.

00:12 This exchange is going to be influenced by several things.

00:16 First, the partial pressure gradients of each of these gases as the gas solubilities.

00:23 Second, the thickness and the surface area of our respiratory membranes, and finally a phenomenon known as ventilation and perfusion coupling which is going to match alveolar ventilation with pulmonary blood perfusion.

00:39 So taking a closer look at these influences and starting with partial pressure, recall that there is a steep partial pressure gradient for oxygen that exists between the blood and the lungs.

00:52 Your venous blood are the blood returning from your tissues has a partial pressure of oxygen of 40 millimeters of mercury.

01:02 This is compared to the alveolar partial pressure of oxygen which is much higher at a hundred and four millimeters of mercury.

01:10 Because of this, oxygen is going to flow down its concentration gradient out of the alveoli and into the venous blood.

01:20 We reach an equilibrium between these two across the respiratory membrane at about .25 or a quarter of a second.

01:29 However, it takes our red blood cells about three-quarters of a second to travel from the start to the end of a pulmonary capillary.

01:39 Because of this delay and the travel of the red blood cells.

01:43 It allows for an adequate oxygenation of the blood cells because of this like slowing our bottleneck.

01:53 So the partial pressure gradient for carbon dioxide is a less steep than that of oxygen.

01:59 In the venous blood or the blood returning from the tissues.

02:03 The partial pressure of carbon dioxide is 45 millimeters of mercury.

02:08 And the alveoli, this is going to be a little bit lower at 40 millimeters of mercury.

02:15 Although this gradient is not as steep as that of oxygen.

02:19 The carbon dioxide is still going to diffuse out an equal amounts.

02:24 And the reason why is because carbon dioxide is much more soluble and plasma than oxygen and is therefore held on to a little bit more so it doesn't require a steep of a gradient in order for it to move out.

02:40 So another factor that is going to influence our external respiration is the thickness and the surface area of our respiratory membranes.

02:49 So recall that our respiratory membranes are extremely thin and there are only about a half to one millimeter thick.

02:57 This allows for efficient diffusion across this membrane into and out of the alveoli.

03:05 Also the alveoli have a huge surface area.

03:09 In fact, the surface area of all of our alveoli put together is more than 40 times the surface area of all of your skin.