Hello, I am Juliet Barbarang and I'm in charge with the topics on diffusion and perfusion together with transport of uh oxygen and carbon dioxide in the blood. That will be the topics for respiration too. The objectives are one explain the factors involved in the diffusion of oxygen and carbon dioxide by recalling fixed law of diffusion differentiating external from internal respiration and discussing calibration rate of oxygen and carbon dioxide. Second compare and contrast the inspiratory and expiratory phases of respiration in terms of alvola surface area of the alvolo capillary barrier. the thickness of the alvolo capillary barrier and the gas content of the alvoli. And thirdly, describe how diffusion of oxygen and carbon dioxide is affected by the morphological changes in the alvolo capillary barrier. The respiratory tree is made up of two types of airways. The conducting airways which is made up of the trachea and the bronchulus. So this is up to the terminal bronchioles. The second airway is that of the ascenar airways or the respiratory airway wherein you have the respiratory bronchioles alvolar ducts and the alvular sacks. Okay. Since you have two types of airways, you have also two types of transport mechanisms. One is ball flow along the conduct conducting airways. We define ball flow as the movement of air containing gases like nitrogen, oxygen and carbon dioxide. We have learned in physics the that the atmosphere atmosphere is made up of several gases and that the atmospheric pressure is made up of the sum of the partial pressure of these gases nitrogen oxygen carbon dioxide and many more. Okay. So if we add the partial pressure of these uh gases that will up make 760 mm mercury and the partial pressure of oxygen being 21% the volume of contained in the air is 159 mm mercury. So that is B flow and reviewing what you have learned in physics. The second transport mechanism is diffusion and this is this occurs in the respiratory portion and we define diffusion as the movement of gases oxygen oxygen and carbon dioxide. We have learned or in the very first lecture in physiology given by Dr. Asinto okay gave this formula J which is the rate of diffusion is equal to D A * the quantity delta C over delta X in respiration we are not going to discuss concentration gradient but rather we are going We are interested in the partial pressure pressure gradient. So if we're going to expound or expand this formula, we give you fixed law of diffusion and the factors involved are for diffusion are pressure gradient and solubility coefficient. A is surface area over D is distance or the thickness of the barrier times the molecular square root of the molecular weight of the gas involved. The rate of gas diffusion is the volume of gas transferred across the alio capillary membrane per unit time. Okay. Again, okay. D the rate of gas diffusion having these factors. Okay. What will be the effect of these factors? Anything you find in the numerator will have a direct effect. Meaning that an increase in any of these factors will lead to a decrease also in the rate of diffusion. However, those found those factors found in the denominator will have an inverse effect. Meaning increase in these factors distance or thickness and the square root of molecular weight will have a decrease in the rate of diffusion. Okay. Look at the pressure gradient. Okay, we have discussed initially in the previous slide that the atmospheric pressure of oxygen is 159 mm mercury. But since the inhaled air would be unmixed with the previously exhaled air, then at the avoli we only have 104 mm mercury partial pressure of oxygen and the pulmonary artery partial pressure of oxygen is 40. Therefore, the pressure gradient, let's make this 100 minus 40 equals 60 as a pressure gradient. So what will be the uh movement of the oxygen from the aldoli to the pulmonary circulation and the pulmonary vein will now contain partial pressure of oxygen. than being 100 mm mercury. Diffusion plays a role in gas exchange and the sites for gas exchange are between the blood and the tissues which is the internal respiration and between the blood and the air is external respiration. So the mechanism involved of gas for gas exchange is simple diffusion following the down partial pressure gradient from high to low partial pressure what component of the cell membrane will diffusion takes place so recall the lecture of Dr. has to. So we said down the partial pressure gradient for oxygen we have a partial pressure of uh pressure gradient rather of uh 60 mm mercury. So in the alvoli we have two alvoli but in the tissue it will be two tissues. Okay because again of this uh pressure gradient of 60. Okay. For the carbon dioxide the pressure gradient is six this time from the tissues to the blood. Okay. from the pulmonary capillary to the alvoli. So what are the core concepts? Besides flow down gradient, we have also the structure function of this uh alvolo capillary barrier. Okay. So we have uh this thickness or the distance between the blood and the alvoli and the blood and the tissues. For simplicity, we'll just say the partial pressure of oxygen in the atmosphere is 160 and in the alvoli 100. So the pressure gradient is 60 between the alvoli and the blood. This steep gradient allows oxygen partial pressure to rapidly reach equilibrium in 25 of a second. And thus blood can move three times as quickly which is 75 seconds through the pulmonary capillary and still be adequately oxygenated. So this is the direction of the flow of blood from the arterolar end to the venol end of the pulmonary cap capillary. The transit time is 75 of a second. The time it takes for blood to traverse the pulmonary capillary 75. But equilibration time is 0.25. So what do you mean by equilibration time? The diffusion of uh or gas exchange of uh carbon dioxide and oxygen. Okay. takes only 25 second which is one/ird the transit time. So the equivalation time for oxygen and carbon dioxide is the same 25 of a second. So another factor that will affect diffusion is the distance or the thickness of the alvolo capillary barrier. So here we have the alvolo capillary barrier which is made up of the alvol alvular membrane. So we have epile basement membrane alvolar epithelium and the fluid of the surfactant layer. Plus you have anial space between the alvolus and the capillary and the capillary membrane is made up of the basement membrane capillary and bossilium and the RBC. So your oxygen and carbon dioxide has to traverse these layers of the basement bar alo capillary barrier. So another factor that will also affect the diffusion is the surface area. Okay as you can see that we have increased the surface area through the circulation of these uh avioli. So these are the factors affecting gas diffusion. So one partial pressure gradient of the gas across the alvular capillary membrane, 60 mm of mercury for oxygen and 6 mm for carbon dioxide. The surface area of the alvular capillary membrane about 70 square m and the thickness of the alvular capillary membrane about.5 micron. You have also diffusion coefficient of the gas which will be dependent on gas solubility. Carbon dioxide is 24 times soluble than oxygen and molecular weight of the gas with carbon dioxide molecular weight is 1.4 times greater than oxygen and the net effect will be carbon dioxide diffusion is 20 times faster than oxygen. Diffusion capacity is the volume of given gas transferred per millimeters mercury partial pressure difference between alvoli and blood. And the factors that will increase will be exercise because during exercise there will be opening of pulmonary capillaries leading to an increase in surface area. There will be recruitment of active capillary leading to a fall in the pulmonary vascular resistance and an increase in blood flow. There's an increase factor then the what condition will lead to a decrease in the diffusion capacity. We have an increase in alvolar capillary thickness like in lung fibrosis and pulmonary edema or a decrease in the effective area of for diffusion like in ataltosis emphyma and a vicio mismatch vio meaning ventilation per fusion ratio. So during inspiration and expiration there will be changes in the area and thickness of our capillary membrane as well as gas content. Okay. Let us look at this uh variation of the area of and thickness. So we have inspiration. During inspiration what happens to the surface area it will increase whereas the thickness of the barrier will become will be decreased. So at the end of uh inspiration [Music] stretch maximizes the area and minimizes the thickness. So at the end expiration. Okay. So we have now thicker wall. but less surface area. What about the variation of alvolar oxygen and carbon dioxide tension or the gas content? So dur during inspiration as more oxygen more gas must enters the aldoli then you have increased oxygen tension. So at the end of inspiration the influx of fresh air maximizes ovular oxygen tension and minimizes ox carbon dioxide tension. So here but at the end of but at during expiration rather okay so you exhaled so the alvoli you now contains uh alvoli contain less air so there will be less oxygen and more of carbon dioxide. This one variation of capillarity oxygen tension. We are going to elaborate on this in the next video. In the previous slides, we have talked about the external respiration. In this slide, we're going to discuss internal respiration which occurs at the tissue level. This is the exchange of gases between systemic capillary and tissues. So systemic capillary containing oxygen partial pressure of 95 to 100 and carbon dioxide tension of 40. So where will uh oxygen as well as carbon dioxide go? Okay. So carbon dioxide is actually produced by the cell activity of the cell metabolic activity of the cell. So in the interstitial space you have oxygen level of 40 and carbon dioxide of 45 to 46. So following the flow down gradient oxygen will diffuse into oxygen will diffuse into the tissues whereas carbon dioxide will move in to the capillary. [Music] This is a table differentiating internal respiration from that of external respiration. In internal respiration, we refer to the gas exchange across the respiratory membrane in the metabolizing tissues. Whereas external respiration refers to the gas exchange across the respiratory membrane of the lungs. Internal respiration the oxygen diffuses out of the blood into tissues whereas in external respiration oxygen diffuses from the alvular air into the blood. Internal respiration the partial pressure of oxygen in the blood is reduced from 100 mm mercury to 40 mm mercury. Whereas for external respiration the partial pressure of oxygen in the blood is increased from 40 mm mercury to 100 mm mercury. Internal respiration carbon dioxide diffuses into the blood from the tissues. Whereas for external respiration carbon dioxide diffuses out from the blood into the alvolar air. Internal respiration partial pressure of carbon dioxide in the blood is increased from 40 mm mercury to 45 in some books is 46 mm mercury. For external respiration, partial pressure carbon dioxide in the blood is reduced from 45 or 46 mm mercury to 40 mm mercury. Internal respiration only correlates with the internal environment. Whereas for external respiration it correlates with both internal and external environment. Oxygen delivery depends on the one amount of oxygen delivered in the lungs. Two adequacy of pulmonary gas exchange three blood flow to the tissues and four capacity of the blood to carry oxygen. Inadequate amount of oxygen delivered to the tissues is hypoxia. Whereas hypoxmia is the amount transported in the blood of oxygen. Hypoxmia is reduced arterial oxygen tension. It is a consequence of ventilation perusion mismatching and it is associated with a vaker ratio of less than one. There is impaired oxygen and carbon dioxide transfer. Oxygen diffusion is more seriously impaired than carbon dioxide diffusion. This is due to a greater diffusion coefficient of carbon dioxide and due to alolar arterial difference for oxygen a t. An increase in AAB is a hallmark of a normal oxygen exchange. Hypoxia is insufficient amount of oxygen in tissues to carry out normal metabolic functions. The types of hypoxia are hypoxic hypoxia which is reduced available oxygen from the atmosphere. Two, anemic hypoxia which is decreased oxygen carrying capacity. Three schemic or stagnant hypoxia which is slow blood flow and four istoxic hypoxia or tissues are not able to utilize oxygen. In this uh video we are just going to discuss hypoxic hypoxia. So these are the conditions that will lead to hypoxic hypoxia. Anatomic shunt, physiologic shunt, decrease in fraction of inspired oxygen, low vure ratio, diffusion of normality and hyperventilation. All of them will lead to a fall or a decreased art arterial oxygen tension. Okay. What's the difference between anatomical and physiologic sh? Okay. Show you by this diagram wherein you have a branch of the pulmonary capillary which will not have a corresponding associated alvoli or alvolus and will now go to the pulmonary vein. Okay. So there will be no oxygenation of this blood. Hence decrease in arterial O2. Okay. In physiologic shunt we have a corresponding alvolus. However this alvolus is unventilated. Okay. So therefore no no inspired air coming in therefore no gas exchange. So this will be an un oxygenated blood still un oxygenated blood hence decrease in Pa2. Okay. As to the difference in the alvolo arterial oxygen. Okay. The decreased function of inspired oxygen as well as hyperventilation will have normal AA oxygen difference but the rest will lead to an increase in AA oxygen oxygen difference. What about the response to uh infusing 100% oxygen? Okay. All of them will lead to an increased except for the shunt wherein in an anatomical shunt there is no significant change because there's no corresponding altos. But for special shant then it will now decrease and it has a decreased response. Okay you have learned that you need carbon dioxide for ventilation. This is ventilation blood flow coping. So if you have low oxygen in alvololis that will lead to baso constriction. If you have high oxygen in alvolus that will lead to baso dilation. If you have high carbon dioxide in alvolus that will dilate the bronchioles but a low carbon dioxide in the alvolus will lead to constriction of the bronchioles. So changes in the oxygen level in the aldulos will have an effect on the pulmonary vasculature whereas changes in the carbon dioxide in the aldolus will produce changes in the caliber of the bronchules. So in summary, so in this uh video we have discussed diffusion which is the movement of gas following pressure gradient. So we recall the different factors involved in fixed law of diffusion. So again diffusion is gas exchange of oxygen and carbon dioxide which is the balance between blood flow metabolic activity. Low P2 and high PCO2 will lead to vasilation of systemic arterios supplying the tissues but will have an hypoxic vasoc construction of formal vessels. So we have also discussed the external difference between external and internal respiration. External respiration is the gas exchange in the lungs and the pulmonary vessels. Whereas internal respiration is the gas exchange of the systemic blood with that of the tissues. Okay. So oxygen is unloaded and carbon dioxide is loaded. For references, we have Burning Navy chapters 23 and 24, Guidan and Hall chapter 39, chapter 3 for West Respiratory Physiology, Costans of BRS chapter 4, and videos in osmosis.