chapter 29 lecture two is zygote to implantation in the beginning when the egg is fertilized the first thing that happens is it undergoes rapid mitosis this is called cleavage and it goes from two cells to four cells to eight cells and so forth notice that the cells originally the egg is this size and then the cells that are taking up the space are getting progressively smaller these cells that are produced are called blastomeres and when you have success of cleavage you end up with this structure called a morula morula is a solid mass of cells this is happening as the egg is moving to be overdraft so here you can see elastomeres now this still has the Zona pellucida around it the corona radiata is gone so day one day two it's four cells by day four it's the solid mass of cells 32 cells so it moves through the uterine tube toward the uterus enters into the uterine cavity as it enters into the uterine cavity it's exposed to something called uterine milk and uterine milk has a lot of glycoproteins in it and it also is what causes excuse me the morula should start to differentiate and remember differentiation means to become more specialized so some of these cells are going to become outer layer excuse me the outer layer of cells called the trophoblast some of them will be will be Inner Cell Mass and then there'll be a space in between that's filled with fluid and this is this base is called the blastocele the Inner Cell mass is what's eventually going to become the embryo and the trophoblast is going to become the um embryonic contribution to the placenta so we have the Inner Cell Mass trophoblast on the outside and the blast to seal now the blastocyst is free in the cavity of the uterus for about two to four days then it attaches to the uterine wall um the attachment is called implantation and derophoplast has two distinct layers the syncio trophoblast this cretenzymes because it it doesn't just attach to the wall it actually Burrows into the wall by digesting through the endometrium and then the cytotrophoblast that is going to be the embryo the trophoblast secretes human chorionic gonadotropin or HCG HCG remember is the feedback mechanism that keeps that corpus luteum alive so that it keeps pumping out progesterone and other hormones and the progesterone is going to um help maintain the uterine lining so that it doesn't Slough off so here you can see the blast desist there's that Inner Cell Mass and it sits down on the side of the endometrium and then starts digesting through it so the Synthesia trophoblast is in here and these cells release enzymes and then misses the cytotrophoblast and then we have the um Inner Cell Mass after implantation the endometrium it's known as the decidua and it has three regions decidua Visalus decidua capsularis and decidua parietales but bastalis is between the chorion and the stratum basalus in the uterus and that's the maternal part of this placenta the decidua capsularis covers the embryo and it's between the embryo and the uterine cavity and the decidua parietales lines the areas that are not involved egg topic pregnancies refer to the development of an embryo or fetus outside the uterine cavity now most of these are going to occur in the uterine too but some can be in the ovaries themselves the abdomen uterine cervix or broad ligaments remember that when the oocyte when ovulation occurs it is released into the pelvic cavity and so pregnancy can occur in the pelvic cavity if the sperm reached the oocyte before it gets into the uterine tube common causes of egg topic pregnancy or blockages and we saw with some of the STDs that they can cause scarring in the uterine tube that blocks the egg from being able to travel through it symptoms Miss menstrual cycles bleeding acute pain women used to die from ectopic pregnancy all the time um now not as many women die you figure this this fertilized egg is going to start to grow and as it's growing in this tube this tube is not elastic enough to accommodate um the growing embryo and so it ruptures and then you have internal bleeding things like that uh twice as common in smokers because nicotine paralyzes the Cilia and depending on the location of the ectopic pregnancy it can be life-threatening particularly if it's in the tube itself placenta previa um the placenta is implanted near or covering the US of the cervix remember the OS is the opening this occurs in one to 250 live births and it can lead to spontaneous abortion which remembers miscarriage premature birth or increased maternal mortality major symptom is sudden painless bright red vaginal bleeding in the third trimester and if um they know that the placenta previa has happened they prefer to deliver through cesarean section the goals for lecture two are Define cleavage blastocyst morula trophoblast Inner Cell mask blastocial sensitiatrophoblast cytotrophoblast implantation uterine milk deciduous decidua capsularis decidua parietales ectopic pregnancy and placenta previa