0:00 Hello, in this video we're going to talk about fetal circulation. 0:10 The fetus is you when you were inside your mother's womb, the uterus. 0:17 Now, the fetal circulation is actually very complicated and different to the 0:23 circulation 0:24 of a baby, which is essentially the circulation of an adult. 0:29 In this video, it is assumed that the viewer you will already have some 0:34 understanding of 0:35 normal adult human circulation. 0:38 So if you don't, please revise that. 0:41 Now let us focus on fetal circulation. 0:43 Here is a fetus and it's lungs and heart. 0:47 Let's zoom in and focus on the heart. 0:50 The heart has four chambers. 0:52 The right consists of the right atrium and right ventricle. 0:57 The right side of the heart is responsible to pump blood into the lungs. 1:03 Blood returns to the heart to the right side via veins here in blue, and will 1:10 enter the 1:11 right atrium and then the right ventricle before being pumped by the heart into 1:17 the lungs. 1:18 However, in the fetal circulation, there is actually an anatomical opening, a 1:24 hole called 1:25 the foramen ovale, which is the connection between the right atrium and the 1:31 left atrium. 1:32 And so when the blood flows from the right atrium to the right ventricle, blood 1:38 will 1:38 also flow from the right atrium to the left atrium. 1:44 The left side of the heart, it consists of the left atrium and left ventricle. 1:49 The left side of the heart is responsible for pumping blood to the rest of the 1:54 fetal body. 1:59 Aside for the anatomical hole, the patent foramen ovale, there is another 2:04 important connection 2:06 or sort of hole called the patent ductus arteriosus. 2:11 The patent ductus arteriosus is the connection between the pulmonary artery and 2:19 the aorta. 2:20 And so in the fetal circulation, blood traveling through the pulmonary artery 2:25 can bypass the 2:27 lungs and go straight to the aorta and be then transported to the rest of the 2:33 fetal tissue. 2:35 The blood can bypass the lungs because there is a lot of pressure in the fetal 2:41 lungs. 2:42 And so blood can actually easily go into the aorta. 2:49 The patent foramen ovale and patent ductus arteriosus allow a right to left sh 2:56 unt, which 2:57 means blood normally entering the right side of the heart can easily be shunted 3:02 to the left 3:03 side of the heart bypassing the lungs. 3:07 In fetal circulation, there is really no need for blood to go into the lungs 3:10 because 3:10 the fetus is not breathing air anyway. 3:13 Rather, the fetus relies on the oxygen delivered by the maternal circulation in 3:19 the placenta. 3:20 See, the placenta is this important connection between the mother and the fetus 3:26 . 3:26 The placenta delivers oxygen and nutrients to the growing fetus via the umbil 3:32 ical cord. 3:32 The umbilical cord attaches the fetus to the placenta. 3:37 The umbilical cord is not just a cord, it actually contains veins and arteries. 3:43 The umbilical vein here drawn in red travels from the placenta to the fetal 3:49 liver. 3:50 There is one umbilical vein and it is drawn here in red because it is oxygen 3:56 ated. 3:57 It contains oxygenated blood which was delivered from the mum. 4:02 It is called the umbilical vein because vein travels back to the heart. 4:07 Again, the one umbilical vein which is oxygenated travels to the fetal liver 4:13 and becomes the 4:13 ductus vanosis which then will join with the inferior vena cava here drawn in 4:20 blue. 4:21 The inferior vena cava in blue here is blue because it contains deoxygenated 4:26 blood from 4:27 the fetal circulation. 4:31 The inferior vena cava that is about to enter the right side of the fetal heart 4:35 now will 4:36 contain partly oxygenated blood and partly deoxygenated blood. 4:42 This blood will enter the right atrium and then either go into the right vent 4:47 ricle or 4:48 it will go through the patent foramen ovale into the left atrium bypassing the 4:54 lungs and 4:54 then it will enter the left ventricle which then will be the blood will be 4:59 pumped into 5:00 the aorta and into circulation. 5:05 The blood that is pumped from the right ventricle can also go through the 5:11 pulmonary artery and 5:12 enter the lungs or mainly it can bypass the lungs and just go straight into the 5:18 aorta 5:18 via the patent ductus arteriosus. 5:21 Okay, so now you have partly oxygenated blood in the aorta where it will now be 5:29 delivered 5:30 to the fetal tissue. 5:32 The fetus needs oxygenated blood. 5:36 Once the oxygenated blood is used by the tissue blood will then normally return 5:42 back 5:42 to the heart via the veins. 5:44 So here the veins are in blue which indicates deoxygenated blood. 5:49 But in fetal circulation there are actually umbilical arteries which carry some 5:56 of this 5:56 deoxygenated blood back towards the placenta and there are two umbilical 6:01 arteries that 6:02 do this and they again contain deoxygenated blood and their aim is to go to the 6:09 placenta 6:09 to reoxygenate the blood via the maternal blood. 6:17 So let's take a closer look at what happens here. 6:21 So here we are looking at where the fetal and maternal blood meet. 6:25 It is really important to understand that fetal and maternal blood do not 6:30 actually mix. 6:31 Okay, so here on the left you have the maternal circulation and on the right 6:36 you have the 6:36 fetal circulation. 6:38 These things here are red blood cells, the cells that actually carry your 6:43 oxygen. 6:44 What happens in the placenta is that the red blood cells from the maternal 6:50 circulation 6:50 will transfer its oxygen to the red blood cells in the fetal circulation. 6:55 And the fetal red blood cells will then offload their carbon dioxide into the 6:59 maternal circulation. 7:03 And so the umbilical artery is becoming essentially a reoxygenated by the 7:09 maternal circulation. 7:12 But how is this possible? 7:13 Why is the mum giving oxygen to the fetus? 7:17 Well it's because the maternal red blood cell and the fetal red blood cell are 7:21 actually 7:21 very different. 7:23 You see the maternal red blood cell, like the fetal red blood cell, contain hem 7:28 oglobin 7:29 molecules, the molecules that actually carry the oxygen. 7:35 But in the fetal red blood cells there are actually more hemoglobin molecules 7:41 and the 7:42 fetal hemoglobin has more affinity for oxygen. 7:47 And this has to do with the genes that are active early on in the fetus. 7:52 Anyway, this is the reason why oxygen is usually taken from the maternal red 7:57 blood cells and 7:58 into fetal red blood cells. 8:01 So the umbilical vein, which is now oxygenated thanks to the maternal 8:06 circulation, will travel 8:07 back to the fetus via the umbilical vein and it will go to the heart and then 8:12 it will 8:13 be pumped by the fetal heart to feed the fetal tissues. 8:18 So what happens in the fetal tissues? 8:20 Well, let's take a look. 8:23 So here is the fetal capillary. 8:25 Here is a fetal cell, let's just say it's the skin cell, and here is the red 8:30 blood cell 8:31 of the fetus, which contains hemoglobin, the molecule that carries the oxygen. 8:37 Now once in the fetal tissues, so let's just say the skin or whatnot, oxygen 8:44 will detach 8:45 from hemoglobin and will go into the fetal tissue, fetal cell and it will 8:51 undergo a 8:52 reaction together with glucose to produce energy for the cell and also produce 8:58 carbon 8:59 dioxide and water, H2O as well. 9:04 Carbon dioxide is a byproduct and actually needs to be excreted, otherwise it 9:07 can be 9:07 dangerous. 9:09 One way that carbon dioxide is excreted is that it can react with water in the 9:14 blood 9:15 vessel or in the red blood cell and here it will form bicarbonate ions. 9:22 The bicarbonate ions can travel in plasma. 9:26 This blood now is actually deoxygenated blood because it contains less oxygen. 9:33 Carbon dioxide is largely carried in blood in the form of bicarbonate ions and 9:39 so this 9:40 deoxygenated blood will now go back to the placenta via the two umbilical 9:45 arteries we 9:45 talked about. 9:47 In the placenta, this fetal circulation will again meet the maternal 9:53 circulation and so 9:55 the maternal red blood cell and fetal red blood cell will meet, sort of, and 10:00 the bicarbonate 10:01 ions will react with hydrogen again to form carbon dioxide and water. 10:07 Once this reaction takes place, carbon dioxide can then diffuse to the maternal 10:12 circulation. 10:13 Now in the placenta, the fetal red blood cell needs to receive oxygen like 10:18 before and the 10:19 whole process continues. 10:22 I hope this story actually made sense. 10:25 It's important to know that once the fetus grows and is delivered, so is born, 10:31 the circulation 10:32 changes into the adult circulation after several hours, two days. 10:38 So what happens is that after the fetus is delivered, so it's a baby, the umbil 10:44 ical 10:44 artery and umbilical vein and the ductus vanosis will actually disappear or 10:48 change to become 10:49 ligaments and the patent frame in a violin and ductus arteriosus will close up 10:55 preventing 10:56 the right to left shunt we saw. 10:59 I hope this video, I hope you enjoyed this video, thank you for watching.
