Armando Hassuran biology and medicine videos. Please make sure to subscribe, join the forum and group for the latest videos. Please visit Facebook Armandanda. In this video, we're going to look at gas exchange. So essentially, we're looking at how gases are transported around our body, the oxygen and carbon dioxide, and how our tissues receive this oxygen and how our lungs receive the carbon dioxide so we can exhale it. So let's just begin this journey with the lungs here and here I'm drawing the heart as well and also tissues. So here is our tissue, our heart and our lungs. After the tissue has um utilized or used oxygen, the blood return will then return to the heart. The blood returning to the heart is de oxygenated blood because it contains you can say low oxygen. The oxygen has been used by the tissue. Now the blood leaving the tissues in order will be venules veins and then as it enters the heart it can either enter through the inferior or superior vennearba. So it'll enter the heart and then from the heart the heart will pump this de oxygenated blood through the pulmonary artery. So why is it called de oxygenated blood? Well, it's because we have more concentration you can say of carbon dioxide compared to oxygen or it's properly said we have um higher partial pressure of carbon dioxide compared to oxygen. That is why they are deoxxygenated. As a de oxygenated blood enters the lungs, um it will the blood will offload the carbon dioxide and then the lungs will reoxygenate the blood essentially putting in more oxygen into the blood um forming oxygenated blood and this oxygenated blood supply will then go back to the heart through the pulmonary vein. So if we look at the partial pressure of oxygen and carbon dioxide again we can see that we have higher amounts of oxygen compared to carbon dioxide. Um so as this pulmonary vein brings this oxygenated blood back to the heart. The heart can then pump this oxygenated blood to tissues or around our body. first of all through the aorta, then the arteries, then the arterials where the arterials will then form capillaries and then in and then into tissues. And if we look at the partial pressure of gases in this oxygenated blood supply, we can see that we have higher amounts of oxygen compared to carbon dioxide. And so um within the tissues again we have oxygen being offloaded into the tissues so the tissue can use it as energy and then carbon dioxide released back into the blood as a byproduct. And within the tissues if we look at the partial pressure of the gases we have slightly higher amounts of carbon dioxide compared to oxygen. Carbon dioxide and oxygen are transported mostly within red blood cells. Now let's zoom into this area here and see how the red blood cells offloads the oxygen to the tissues and how the tissues will then offload the carbon dioxide back to the blood and how carbon dioxide is transported. So zooming into this area here we have the tissues uh the cells of the tissue and here I'm drawing the lining of the blood vessel. So in red here this means that this is here is the blood and here is the interstatial fluid. Let us firstly look at how oxygen enters the tissue. Some oxygen can be dissolved in plasma and can enter the interstatial fluid and then can enter the tissue where the tissue can utilize it as energy. However, most oxygen in our body is transported in red blood cells such as this one I am drawing here. Oxygen is transported bound to a um molecule known as hemoglobin HB. So here is hemoglobin oxygen bound to hemoglobin. The hemoglobin and oxygen can disassociate forming hemoglobin and oxygen gas. this oxygen can then enter the interstatial fluid and then oxygen can be used by the tissue. Okay, so that was the two ways oxygen um enters the tissue from the blood. Now let's look at carbon dioxide because the tissues um form carbon dioxide as a byproduct after using oxygen. Some of the carbon dioxide or little very little amount can actually just enter the blood and just be transported through plasma. Some of it can reenter the blood react with water and through a slow process form bicarbonate and hydrogen ions. And so carbon dioxide in this case is being transported um as bicarbonate. However, most of the carbon dioxide will actually enter the red blood cells and then here it will react with water. Within red blood cells, you have these membrane bound enzymes called carbonic and hydrates which will through a fast process convert carbon dioxide and water to form bicarbonate and hydrogen ion. Exactly the same as the process that occurred outside which was slow. And then bicarbonate can then be trans pumped out by the red blood cell into the actual plasma and so be transported as bicarbonate. The transporter will take bring in a chloride ion in exchange. The hydrogen ion here can react with the hemoglobin molecule within the red blood cell to form um the hydrogen hemoglobin. And then you have another mechanism where the carbon dioxide can enter the red blood cell and actually attach with hemoglobin to form carboaminohemoglobin. So now if we were look if we're going to look at the ways carbon dioxide is transported in the blood we can we know that there are at least three mechanisms. The first is that carbon dioxide can dissolve in plasma about 10% of it which is this one. Or carbon dioxide can react with a hemoglobin within red blood cells to form carbon carbo aminohemoglobin. And this is about 20% of the carbon dioxide being transported this way. And the last which is the majority which is the major mode of transportation for carbon dioxide is as bicarbonate in plasma. And this is about 70% of the carbon dioxide. But again forming bicarbonate um there are two ways. One is that it can be formed in red blood cells which is a fast process or it can be formed in the uh plasma itself which is much slower. Now it's also important to understand that carbon dioxide and pH is also very much related. If we have an increase in carbon dioxide, this will actually cause a decrease in pH, which means that it will make um the blood acidic. If we have a decrease in carbon dioxide, this will make the blood much more alkali. So, an increase in pH. Why is this? Well, first of all, let's just pretend that we have more carbon dioxide. If we have more carbon dioxide, this will shift the reaction to form more bicarbonate and hydrogen ions. If we have more hydrogen ions, this just means that it will be more acidic. So that was looking at how carbon dioxide uh gets transported. Now let's look at how carbon dioxide gets offloaded and then how oxygen is transported in a bit more detail. So let's by to look at this let's let's go back to the lungs here and zoom in. The lungs are made up of branches of bronchioles and the ends of them called alvoli or alvola sac. So the alvol this this cluster of alv alvol alvoli they have blood supply the essentially the pulmonary artery coming in and then the pulmonary vein leaving. So let us zoom into this area here where gas exchange takes place within the alvoli. So here I'm drawing the cell lining of one alvoli which is known as an alvolus. And then here I'm drawing the boundary of the um the blood vessel. And here we can find the red blood cell. So here is the alvololis. Here is the blood with the red blood cell. And here is just a fused membrane which is a thin gap. Before we continue, we have to understand that the alvolus is the lung. So it is what it is the structure that receives the carbon dioxide and that offloads oxygen into the blood. So let's first begin by looking at how carbon dioxide is transported from the blood back into the alvololis into the lungs so that we can exhale the carbon dioxide. So if you remember from the previous diagram some of the carbon dioxide is transported through plasma. So this carbon dioxide can just enter the alvololis. A majority of the carbon dioxide is actually transported if you remember in the blood as bicarbonate. And so this bicarbonate can react with hydrogen ions in the blood and through a slow process form as an end product carbon dioxide and water. The carbon dioxide can then just enter the alvololis. Of course, some of this actually a lot of it or how however much of this bicarbonate in plasma can actually enter the red blood cells through a transporter which will bring out chloride ion in exchange. Within the red blood cell, bicarbonate can react with hydrogen ion and through a fast process and with the help of the enzyme carbonic and hydrates, the bicarbonate and hydrogen reaction can form carbon dioxide and water. And it's fast compared to the outside because there's an enzyme present. And then this carbon dioxide can then just exit the red blood cell and enter the alvolus. Finally, you remember that some of the carbon dioxide is transported in the blood um bound to hemoglobin as carboaminohemoglobin and so this will disassociate and then the carbon dioxide after it's disassociated with hemoglobin can then enter the alvolus. Okay. So now we have a lot of the carbon dioxide in the alvolus. Our body will our lungs will exhale this carbon dioxide and then we'll inhale oxygen. So oxygen enters the alvololis and then oxygen can be transported via two ways. Small amount of oxygen will be transported in plasma just enters the plasma. However, most of the oxygen will actually enter the red blood cells and then bind to hemoglobin. Well, hydrogen bound hemoglobin and then this will form essentially your um oxyhemoglobin and so this hydrogen ion will is the hydrogen ion that supplies the bicarbonate uh reaction here. So again just to stress what I'm trying to say oxygen transport occurs through two ways. It can be dissolved in plasma which this is less than 2% of oxygen is transported this way. Most of the oxygen is bound to hemoglobin which is 98% plus. Um and this brings us to the last concept which is called oxygen saturation. Now oxygen saturation is a kind of an important term to know because it's essentially referring to the concentration of oxygen in the blood and normal blood oxygen levels normal blood oxygen saturation levels uh should be at least 95 to 100%. Thank you for watching. I hope you enjoy this video on gas exchange. The next video we will look at is control of respiration.