0:00 In this video, we're going to look at the hormones that change through 0:16 pregnancy, but 0:18 mainly we will focus on the hormones and the physiology of parturition. 0:27 So we have to begin where it all began with fertilization, where the sperm 0:33 meets the egg. 0:34 Then together they form a zygote. 0:36 The zygote divides like cells, and they are cells, and they just keep dividing 0:42 continuously, 0:43 forming a cluster of cells called known now as the blastocyst. 0:50 The blastocyst is what will implant into the uterus, the uterine wall, and 0:56 following implantation, 0:58 the cells within the blastocyst that make up the blastocyst will undergo gran 1:04 ulation. 1:04 Essentially through this process, cells will differentiate and form unique cell 1:09 lines, 1:10 which then forms the fetus itself. 1:15 This whole process occurs in the first trimester of pregnancy, which is the 1:20 first three months 1:21 of pregnancy. 1:24 We will now look at the changes in female hormones during the first, second, 1:29 and third trimesis. 1:33 And after this, we will briefly discuss what they mean. 1:36 However again, this video is only stating what is occurring and won't go into 1:40 too much detail, 1:42 because this video will mainly focus on parturition. 1:47 So here I am drawing a graph with hormone concentration on the y-axis and the 1:52 number 1:52 of months during pregnancy on the x-axis. 1:57 So we have one month, and then we have three, six, nine months. 2:02 The nine months is typically where parturition takes place, the giving birth. 2:08 Now an important hormone produced by the embryo and soon the placenta is beta- 2:15 HCG, which stands 2:16 for beta-human chorionic unetotropin. 2:20 Now this hormone is produced by the placenta and peaks about week seven, and 2:25 then it just 2:26 falls down. 2:27 Beta-HCG is produced by the placenta in order to keep the corpus luteum alive. 2:39 The corpus luteum is a dead follicle in the ovaries, and because it is being 2:43 kept alive 2:44 by, thanks to beta-HCG, the corpus luteum is able to continuously produce two 2:49 important 2:50 hormones, which are estrogen and progesterone. 2:55 This all occurs in the first three months of pregnancy, the first trimester. 3:03 In the second trimester, which is between months three to six in pregnancy, the 3:08 fetus, 3:09 of course, will keep growing, beta-HCG, as I mentioned, are peaked at week 3:14 seven and then 3:15 just drops down, but it is still being produced by the placenta. 3:21 By the second trimester, estrogen and progesterone levels still continuously 3:27 increase, because 3:28 it is still being produced by the ovaries. 3:33 But the placenta is also taking over this role and begins producing estrogen 3:37 and progesterone 3:38 as well. 3:45 By the third trimester, which is months six to nine in pregnancy, the placenta 3:50 plays 3:51 the main role in producing the hormones. 3:54 It doesn't really produce any more beta-HCG, because it is now producing a lot 3:59 of estrogen 4:00 and progesterone itself. 4:02 Now importantly, when week 40 hits, or basically the ninth month hits, 4:09 basically when the baby 4:11 wants to come out, all these hormones will drop. 4:15 Estrogen, progesterone, and beta-HCG's drop, and doesn't get produced no more. 4:20 This is in order to allow the uterus to contract and let the baby out 4:25 essentially. 4:27 This process is known as parturition. 4:33 Parturition, as the dictionary describes it, is the act or process of giving 4:38 birth, childbirth. 4:43 And now we will focus on parturition, and the hormones and physiology behind it 4:50 . 4:50 So here I am drawing a pregnant woman whose water just broke and is in labor, 4:55 about to 4:55 give birth. 4:57 Some important organs and structures we need to know, the brain here, we can 5:02 find an endocrine 5:03 gland called the hypothalamus. 5:06 And below the hypothalamus, we have the pituitary gland, but we are going to 5:11 mainly focus on 5:12 the posterior pituitary gland. 5:18 Then here we have the placenta and uterus, and here of course is the baby. 5:24 Here is the baby's brain, it's kidneys. 5:27 Above the kidney, we have to note the adrenal glands, which is important in the 5:31 physiology 5:32 of parturition. 5:38 Now it is important to understand before we get into this diagram that 5:42 throughout pregnancy 5:44 in the first, second and third trimester when estrogen and progesterone levels 5:49 were rising, 5:52 these hormones were actually preparing the mother for labor. 5:58 You see estrogen from the ovaries and the placenta increases oxytocin receptors 6:04 in the 6:05 uterus, and we will talk about oxytocin, but it is essentially an important 6:10 hormone for 6:11 uterine contraction. 6:14 Progesterone also is being produced throughout pregnancy, and it results in the 6:23 relaxation 6:24 of smooth muscles, which inhibits essentially uterine contraction during 6:28 pregnancy. 6:29 This is important because we don't want the uterus to contract during pregnancy 6:34 as the 6:34 baby is not ready to leave the uterus just yet. 6:39 Okay, now let's just look at parturition in a step-by-step process. 6:50 So firstly, the fetal stress when the fetus wants to leave the womb will 6:56 stimulate corticotropin 6:58 hormone release, which is also known as adenocorticotropin hormone. 7:04 Or ACTH, and it's produced by the anterior pituitary gland. 7:10 And this hormone will stimulate cortisol release from the adrenal glands. 7:16 So here we have the adrenal glands that produce cortisol. 7:21 So two, we have cortisol release. 7:24 So what does cortisol do? 7:26 Well cortisol affects the placenta, mainly it causes three things. 7:32 It decreases progesterone production from the placenta. 7:36 It decreases estrogen production from the placenta, but it increases prostag 7:41 landin production 7:43 in the placenta. 7:44 So this is why in the month nine we see just a decrease in progesterone and 7:49 estrogen remember. 7:51 But then we have an increase in prostaglandin. 7:53 What does this mean? 7:55 Well prostaglandin is a molecule that actually is just found throughout the 7:59 body, but in 8:00 this case it causes the uterus to contract, and thus helping the baby leave the 8:07 uterus. 8:08 So, and then four, so as the baby is sort of pushing against the pushing out, 8:15 this causes 8:16 uterine and the cervix to stretch, and thereby stimulating some sensory nerve 8:21 fibers around 8:22 the area. 8:24 The sensory nerve fibers that are being stimulated will stimulate oxytocin 8:30 production from the 8:31 hypothalamus. 8:32 So here as you can see it's signaling to the hypothalamus to produce oxytocin. 8:41 Oxytocin produced by the hypothalamus will be stored actually by in the 8:45 posterior pituitary 8:46 gland. 8:49 And then seven here I wrote, the posterior pituitary will then release oxytocin 8:53 . 8:53 So oxytocin is released from the posterior pituitary. 8:56 What does oxytocin do? 8:58 Well oxytocin causes two main things. 9:00 It causes the uterus to contract, thus helping the baby basically leave the 9:07 uterus, but also 9:09 stimulates the production of prostaglandins. 9:13 So it stimulates the uterus to make more prostaglandins, which again causes the 9:18 uterus 9:18 to contract. 9:20 And this whole cycle actually just continues because the uterus is contracting. 9:25 The baby's head pushes against the cervix and pushes out thereby stimulating 9:32 the stretch 9:33 receptors. 9:34 And then the stimulation of the stretch receptors will stimulate the hypothal 9:38 amus to produce 9:39 more oxytocin. 9:40 And the whole cycle just continues. 9:42 But essentially after some time the uterus will contract, keep contracting, 9:46 keep contracting 9:47 until the baby will leave the uterus and essentially be born. 9:54 So I hope you enjoyed this video on the physiology of parturition as well as 9:58 the hormones that 9:58 we looked at throughout pregnancy, mainly beta-HCG, estrogen and progesterone. 10:05 And as well as during parturition we noted that oxytocin and prostaglandins are 10:10 very 10:10 important. 10:11 So thanks for watching.
