If you're seeing this message, it means we're having trouble loading external resources on our website.

如果你被网页过滤器挡住,请确保域名*.kastatic.org*.kasandbox.org 没有被阻止.



访问我们的健康和医药内容(http://www.khanacademy.org/science/healthcare-and-medicine)或MCAT相关内容(http://www.khanacademy.org/test-prep/mcat) 。 这些视频不提供医疗建议,仅供教学目的。这些视频不能替代专业医学建议、诊断或治疗。如有情况及疑问,请寻找正规医疗机构。请勿因可汗学院视频内容,无视医嘱,延误病情。 Nauroz Syed 创建




okay so I want to start off with a scale so so this is a scale a time scale and on on this end is before pregnancy and on this end is after pregnancy and then in the middle is the 20-week point of pregnancy and I want to use this scale to show you how the different pregnancy related hypertensive disorders are split up because they're split up according to when the hypertension occurs and also according to how severe it is so starting on on this end if let's say a woman has had high blood pressure for several years before she became pregnant or if she's found out to have high blood pressure before 20 weeks into her pregnancy then we say that she has she has chronic she has chronic or or pre-existing chronic or pre-existing hypertension so her hypertension has nothing to do with pregnancy because she either had it before she became pregnant or before the 20-week point into her pregnancy and this 20-week point is important because before it sort of in the early stages of pregnancy pregnancy reduces blood pressure so if a woman is hypertensive before the 20-week point then the cause of her hypertension has nothing to do with the pregnancy now if instead she's found to have high blood pressure after the 20-week point in her pregnancy we say that she has gestational she is just a tional hypertension right and I'm just gonna abbreviate hypertension as HTN throughout this video or save a lot of time or or hypertension related to her pregnancy that's what gestational hypertension it and typically gestational hypertension usually should resolve within 12 weeks of giving birth if it doesn't then chances are that the woman probably had high blood pressure before ever becoming pregnant but that we didn't find it sort of in the earlier stages of pregnancy because of that physiologic lowering of blood pressure that we were talking about that occurs early on in so I guess you can say that these two conditions chronic hypertension and gestational hypertension are sort of the milder forms of hypertension so now let's talk about the more serious hypertensive disorders which would have to be preeclampsia pre pre e clamp SIA which is kind of spelled weird preeclampsia and eclampsia preeclampsia and eclampsia so preeclampsia refers to when a woman develops high blood pressure after 20 weeks into the pregnancy so kind of just like gestational hypertension but along with a few other features so in addition to the high blood pressure there's also protein spilling into the urine or proteinuria protein proteinuria so so protein in the urine or there's some other form of end organ damage and I'm gonna go through exactly what that means in just a bit but there is some other form of and organ damage okay so preeclampsia refers to this constellation of high blood pressure proteinuria and end organ damage and eclampsia is when a woman with preeclampsia developed seizures all right so when a woman with preeclampsia develop seizures that's called eclampsia all right so it's all good to know the definition of preeclampsia but why does it happen in the first place well for as much as we don't know about this disease we're pretty certain that a lot of it has to do with the abnormal development of the blood vessels of the placenta early on in the course of the pregnancy so the blood vessels in the placenta just don't develop correctly now if you remember during the formation of the placenta the trophoblast cells of the embryo which which this is the embryo right and these green cells on the outside are the trophoblast the trophoblast invade through the decidua which is what the endometrium is called during pregnancy and they also in way through part of the myometrium and they do this the the trophoblast invade through the deciduous so that they can access and and infiltrate the spiral arteries which are the terminal branches of the uterine artery so they're the arteries that supply the uterus so the infiltrate the spiral arteries to get access to all of that oxygenated blood that's inside them and that's how the placenta forms into this bed where where blood exchange between mom and fetus can occur it's because of this first step of the trophoblast invading into the spiral arteries now in order for this to happen successfully I I guess you could take two things really really have to take place two things have to happen firstly the trophoblasts have to be pretty aggressive in their infiltration they really have to dig into the decidua and secondly the spiral arteries have to remodel themselves they have to go from being these narrow thick walled blood vessels to to sort of being these large kind of tortuous vascular channels that allow a large amount of blood to flow through them so both things have to happen and we think that preeclampsia occurs when they don't so the trophoblast do a bad job of digging into the decidua and and the spiral arteries just don't change enough to allow for the increased blood flow so let's sort of take a step back and look at the big picture if the placenta can't gain good access to the spiral arteries what that means is a poor oxygen supply to the placenta which becomes more and more of an issue as the woman gets further into her pregnancy and the fetus and the placenta require increasing amounts of blood and an oxygen so the shortage in oxygen supply makes the surrounding cells of the placenta really angry that's a really common theme in the human body when cells don't get enough oxygen they get angry and they release molecules usually inflammatory molecules and that's exactly what happens here the placenta releases several factors that enter blood stream and and the factors start altering the way her circulatory system works specifically the factors start damaging the cells that line the inside of the blood vessels the endothelial cells so so if this is a blood vessel kind of we're looking at it head-on right there's a cross-section of a blood vessel we're talking about these cells on the inside these really thin cells called the endothelial cells that line the inside of the blood vessels these cells are the target of those factors that are released by the placenta these are the cells that get damaged and the damage of the endothelial cells leads to those characteristic signs and symptoms of preeclampsia so for example when the endothelial cells are damaged they lose the ability to control the tone of the blood vessels so it's harder it becomes harder for the blood vessels to relax and that's what leads to the high blood pressure the blood vessels aren't able to relax that's why you end up with hypertension and the factor is released by the placenta also cause the endothelial cells to become more leaky right and these leaky blood vessels allow protein to escape from them and so when that leakiness occurs in the blood vessels of the kidney let's say and protein meats out from the glomerular capillaries you end up with protein in your urine or protein urea which is one of the hallmarks of preeclampsia and throughout the rest of the body when protein escapes from the blood vessels into the into the surrounding tissues right and if you remember anything about starlings forces I know I'm asking you to dig pretty deep with this one you'll remember that wherever protein goes water goes so water follows the protein into the tissues and you end up with edema or swelling throughout the body so swelling in the face and the hands and and really swelling outside of what you see in normal pregnancy and the blood vessels in pretty much any organ can be affected leading to whole body signs and symptoms so for example you can have headaches you can see headaches seizures you see headaches seizures and and also visual symptoms so you can see visual symptoms from the dysfunction of the blood vessels in the brain you can also have epigastric pain right so pain in kind of that upper middle region of the belly and elevated liver enzymes elevated liver enzymes from dysfunction in the liver and you can also have fetal growth restriction so the fetus isn't growing enough from dysfunction of the blood vessels in the placenta so that what I meant by organ damage in the beginning of this video also another key point that I'd like to make is that the endothelial cells when they're damaged they can release their own factors so the factors they release promote clotting leading to clots throughout the entire body and as you can imagine that becomes its own separate huge issue now the diagnosis of preeclampsia involves looking for all of these features that I just talked about so in order to make the diagnosis a woman needs to have high blood pressure so so a systolic blood pressure more than 140 a diastolic blood pressure more than 90 that's the general definition of hypertension and she has to have one of the following criteria she either has to have evidence of proteinuria or she has to have some evidence of end organ damage so she could have elevated liver enzymes that indicate liver dysfunction or she could have an increased creatinine which alludes to kidney damage or decreased platelets which hint clot formation any sign of end organ damage will make this diagnosis and if you've ever spent much time on an OB gun floor in a hospital you know that we screen for this disorder pretty aggressively because preeclampsia can have some really serious complications it can lead to placental abruption it can lead to lead to a liver hematoma or rupture it can also lead to thing called disseminated intravascular coagulation which really just refers to clot forming in the vessels all throughout the body it can also lead to stroke and even lead to the need for mechanical ventilation so it's really serious it can be a really serious disorder so how do you cure the seemingly serious disease well really delivery is the only cure which makes sense since the placenta is the source of all of these factors that are damaging mom's vascular system so removal of the placenta should cure the disease and it does delivery of the placenta always results in complete resolution of the signs and symptoms of preeclampsia now of course it's important to consider whether the fetus is mature enough to survive the delivery right so for that reason if a woman is past 37 weeks into her pregnancy then we usually proceed with delivery if the mom has preeclampsia regardless of how how severe it is if the pregnancy however has not yet reached 37 weeks then we usually only deliver if the preeclampsia is severe now one last point that I'd like to make eclampsia or seizures in a woman who has preeclampsia is one of the most feared complications of preeclampsia and the greatest risk for eclampsia is just before delivery during labor and 24 hours after delivery so for that reason every woman with preeclampsia is started on magnesium sulfate every woman with preeclampsia started on magnesium sulfate which is an antiepileptic agent or or an agent that that prevents / terminates seizures and the magnesium is given during labor and has continued for 24 hours postpartum sort of to prevent those seizures from happening and it's also important to manage the hypertension you can't just leave the woman with high blood pressures while she's pregnant so we can use drugs such as hydralazine drugs such as hydralazine and and labetalol and labetalol so hydralazine and Lybia you all are safe antihypertensives to use in pregnancy all right so those are some details about a pretty feared complication of pregnancy preeclampsia