 This video is intended to be a review for more of the respiratory kind of like critical care scenarios such as ARDS Acute Respiratory Stress Syndrome, Acute Respiratory Failure and so forth. And really what I'm trying to do with this video is have you become familiar with these terms so that then when you hear them for the more complicated topics that you know exactly what we're talking about. So now first let's review the basic physiology. So as we know we have our alveoli here in black and the blood flows into the lungs from the pulmonary artery and the blue here represents the deoxygenated blood. And so then CO2 is diffused into the alveoli and then O2 oxygen coming in through the lungs and the alveoli gets diffused into the pulmonary vein and then is transported to all the cells throughout the body. And this is by the simple principle of diffusion like so many things in our body so things move from an area of higher to a lower concentration. In this case the atmospheric pressure is higher than the intraciracic or intra-alveoli pressure therefore everything will diffuse. And then so another important topic we're talking about respiratory is oxygenation and the oxygen in the body can really be found in two different places or measured in two different places. So first of all it's dissolved in plasma which is expressed as millimeters of mercury in the partial pressure of oxygenation. And then the other part is bound to the hemoglobin in comparison to the amount the hemoglobin can carry. So the amount of total hemoglobin available and then how much of that is saturated with oxygen modules that can then be expressed in percentage which is also our oxygen saturation or pulse oximetry that we'll get to in a little bit here. The other important term here to know is ventilation. So ventilation is the actual process of air moving in and out of the lungs and that has two parts inspiration and exhalation. And the change again happens because of the ventilation happens because of the change in the intraciracic pressure and again the pressure in the atmosphere is higher than in the chest cavity and so oxygen will just diffuse in from a high to a low concentration. And the exhalation keep in mind is a passive process because of this elastic recoil of the lungs. So actually the inhalation is an agamora but an active process although we're not usually aware of the inhalation but then just by slowly recoiling the chest and all the accessory muscles and the costum muscles and the diaphragm being moving back in their original position is called the elastic recoil, the elastic recoil ability of the chest wall.