Embryo Development (003) 2nd Week, 10/15/2020 PDF

(003) 2nd WEEK OF DEVELOPMENT DR. PEREDA │ 10/15/2020 OUTLINE I. 2nd Week of Development A. Day 8 B. Day 9 C. Days 11 and 12 D. Day 13 II. Nota Bene (T...

(003) 2nd WEEK OF DEVELOPMENT DR. PEREDA │ 10/15/2020 OUTLINE I. 2nd Week of Development A. Day 8 B. Day 9 C. Days 11 and 12 D. Day 13 II. Nota Bene (Take Note) I. 2ND WEEK OF DEVELOPMENT A. Day 8  Blastocyst partially embedded in endometrial stroma  Trophoblast differentiated into two layers: 1. inner layer of monucleated cells, the cytotrophoblast 2. outer layer, the syncytiotrophoblast  Embryoblast of inner cell mass differentiates into 2 layers: 1. hypoblast layer adjacent to blastocyst FIGURE 1 A 7.5—day human blastocyst, partially embedded in the cavity endometrial stroma. The trophoblast consists of an inner layer with 2. epiblast layer adjacent to amniotic cavity mononuclear cells, the cytotrophoblast, and an outer layer without distinct cell boundaries, the syncytiotrophoblast. The embryoblast is Together, the epiblast and hypoblast form the bilaminar disc. formed by the epiblast and hypoblast layers. The amniotic cavity The epiblast cells lining the amniotic cavity, which is adjacent to your appears as a small cleft. cytotrophoblast, are called your amnioblast. At the beginning of the second week, the blastocyst is partially embedded in the endometrial stroma. The trophoblast differentiates B. Day 9 into (1) an inner, actively proliferating layer, the cytotrophoblast, and  Blastocyst more deeply embedded in (2) an outer layer, the syncytiotrophoblast, which erodes maternal endometrium tissues.  Trophoblast shows progress in development, vacuoles appear, fuse forming large lacunae, this Implantation occurs at the end of the first week. Trophoblast cells phase is known as the lacunar stage. invade the epithelium and underlying endometrial stroma with the help of proteolytic enzymes. Implantation may also occur outside the By day 9, lacunae develop in the syncytiotrophoblast. Subsequently, uterus, such as in the rectouterine pouch, on the mesentery, in the maternal sinusoids are eroded by the syncytiotrophoblast, maternal uterine tube, or in the ovary (ectopic pregnancies). blood enters the lacunar network. PREPARED AND EDITED BY: TRANS GROUP 3  (003) 2nd WEEK OF DEVELOPMENT DR. PEREDA │ 10/15/2020 Figure 1.1. A 9-day human blastocyst. The syncytiotrophoblast Figure 1.2. Human blastocyst of approximately 12 days. The shows a large number of lacunae. Flat cells form exocoelomic trophoblastic lacunae at the embryonic pole are in open membrane. The bilaminar disc consists of a layer of columnar connection with maternal sinusoids in the endometrial stroma. epiblast cells and a layer of cuboidal hypoblast cells. The original Extraembryonic mesoderm proliferates and fills the space between surface defect is closed by a fibrin coagulum. the exocoelomic membrane and the inner aspect of the trophoblast. The vacuoles and cavities in between the somatic and C. Days 11 and 12  Blastocyst completely embedded in endometrium splanchnic membrane extraembryonic cavity (later on will be  Maternal blood begins to flow through the called the chorion cavity/chorionic cavity). trophoblastic system, establishing the uteroplacental circulation. D. Day 13  Extraembryonic mesoderm splits into 2 layers:  Surface defect in endometrium healed 1. Somatic - membrane lining  Bleeding occurs at implantation site as a result of cytotrophoblast increased blood flow into the lacunar spaces, 2. Splanchnic - lining near blastocyst occurs near the 28th day of menstrual cycle. (exocoelomic) cavity; future yolk sac  Ovulation occurs on the 14th day. So if implantation occurs, it would be either on the 12th or 13th day from the day of ovulation. Meaning, it occurs on Day 26 or 27, near the 28th day. If there is bleeding at those times, it is more likely implantation bleeding, not abortion or menstruation This information can be used as basis for counting the last menstrual period of implantation.  Hypoblast produces additional cells, which is the secondary yolk sac or definitive yolk sac  Extraembryonic coelom expands forming chorionic cavity  Connecting stalk with development of blood vessels will be the umbilical cord.  During this time, extraembryonic membrane is continuous, lining the cytotrophoblast, it only uses the extraembryonic cavity (yolk sac) area going to your blastocyst. The one that closes the connecting stalk is the future umbilical cord. Aside PREPARED AND EDITED BY: TRANS GROUP 3  (003) 2nd WEEK OF DEVELOPMENT DR. PEREDA │ 10/15/2020 from the formation of extraembryonic membranes II. NOTA BENE or mesodermic layer, you also form two cavities: chorionic cavity and amniotic cavity. Figure 2.0 Drawing showing the role of the hypothalamus and pituitary gland in regulating the ovarian cycle. Under the influence of GnRH from the hypothalamus, the pituitary releases the gonadotropins, FSH, and LH. Follicles are stimulated to grow by FSH and to mature by FSH and LH. Ovulation occurs when concentrations of LH surge to high levels. LH also promotes development of the corpus luteum. 1, primordial follicle; 2, growing follicle; 3, vesicular follicle; 4, mature vesicular (Graafian) follicle. - Take note: this is ovarian cycle in parallel with pituitary hormones during growing of follicles in ovarian cycle, the FSH are the one responsible for growing of follicles with the formation of theca cells/follicular cells with your with FSH Figure 1.3 A 13-day human blastocyst. Trophoblastic estrogen is produced. And with the estrogen, stimulating the lacunae are present at the embryonic as well as the abembryonic pituitary gland which produces LH which stimulates the ovary to pole, and the uteroplacental circulation has begun. Note the primary proceed to ovulation. LH also produces corpus luteum which villi and the extraembryonic coelom or chorionic cavity. The responsible for the production of progesterone and prepares the secondary yolk sac is entirely lined with endoderm. endometrium of possible pregnancy if fertilization takes place. When fertilization takes place, the sperm enters to cervix, The second week of development is known uterus, travels to uterus going to the fallopian tube going into as the week of 2’s: the ampulla where the oocyte is waiting and that is when fertilization takes place. 1. The trophoblast differentiates into two layers: the cytotrophoblast and syncytiotrophoblast. 2. The embryoblast forms two layers: the epiblast and hypoblast. 3. The extraembryonic mesoderm splits into two layers: the somatic and splanchnic layers. 4. Two cavities form: the amniotic and yolk sac cavities. - This is your endometrium on your start implantation there is still a gap wherein your entire blastocyst is embedded and you can see that at the area where in the blastocyst will soon be formed, there is plenty of blood coming from the endometrium. If there is plenty of blood coming from the mother, there will be a spill of blood both coming from the mother and the Figure 2.1 A. Primordial follicle. B. Growing follicle. C. Vesicular placenta that is what you called heteroplacental circulation or implantation follicle. Every day from the pool of primordial follicles leaking. A, some begin to develop into growing follicles B, and this growth is independent of FSH. Then, as the cycle progresses, FSH secretion recruits growing follicles to begin development into vesicular (antral) follicles. C. During the last few days of maturation of vesicular follicles, estrogens, produced by follicular PREPARED AND EDITED BY: TRANS GROUP 3  (003) 2nd WEEK OF DEVELOPMENT DR. PEREDA │ 10/15/2020 and thecal cells, stimulate increased production of LH by the pituitary gland (Fig. 2.0), and this hormone causes the follicle to enter the mature vesicular (Graafian) stage, to complete meiosis I, and to enter meiosis II, where it is arrested in metaphase approximately 3 hours before ovulation. FIGURE 2.4 A. Scanning electrón micrograph of sperm binding to the zona pellucida. B. The three phases of oocyte penetration. In phase 1, spermatozoa pass through the corona radiata barrier; in phase 2, one or more spermatozoa penetrate the zona pellucida; and in phase 3, one spermatozoon penetrates the oocyte membrane while losing its own plasma membrane. Inset shows normal spermatocyte with acrosomal head cap. FIGURE 2.2 A. Mature vesicular follicle bulging at the ovarían - These are the three phases of fertilization: (1) penetration of surface. B. Ovulation. The oocyte, in metaphase of meiosis II, is corona radiata, (2) penetration of zona pellucida (3) penetration discharged from the ovary together with a large number of of the membranes of oocyte and sperm cell. But before cumulus oophorus cells. Follicular cells remaining inside the fertilization takes place, the sperm should first be capacitated, collapsed follicle differentiate into lutein cells. C. Corpus luteum. which is the head of the sperm covered with the acrosome, the Note the large size of the corpus luteum, caused by hypertrophy acrosome is covered with a protein membrane. For it to be and accumulation of lipid in granulosa and theca interna cells. capacitated the glycoprotein of the acrosome should be first The remaining cavity of the follicle is filled with fibrin. removed. So that this can penetrate the corona radiata and after penetrating of this it can now penetrate the zona pellucida, the zona pellucida together with the proteins and the enzymes released by the zona pellucida so that the sperm can penetrate the zona pellucida. - Once the zona pellucida is penetrated by the sperm, it cannot be longer penetrated by other sperms. The sperm can now penetrate the membrane of oocyte, what happens inside the oocyte is the formation of secondary meiotic division, after, there will be formation now of male and female protocytes and the head of the sperm and the tail will now differentiate. It can now determine first, it can now restore the diploid number of 46, 23 from male and 23 from female. Second, it can now determine the sexuality of an individual. XY-male and XX-female. Third is the formation of incision of cleavage, followed by the formation of zygote. FIGURE 2.3 Relation of fimbriae and ovary. Fimbriae collect the oocyte and sweep it into the uterine tube. FIGURE 2.5 Development of the zygote from the two-cell stage to the late mórula stage. The two-cell stage is reached approximately 30 hours after fertilization; the four-cell stage is reached at approximately 40 hours: the 12- to 16-cell stage is reached at approximately 3 days; and the late mórula stage is reached at approximately 4 days. During this period, blastomeres are surrounded by the zona pellucida, which disappears at the end of the fourth day. PREPARED AND EDITED BY: TRANS GROUP 3  (003) 2nd WEEK OF DEVELOPMENT DR. PEREDA │ 10/15/2020 - Cleavage starts at formation of 2 cells, the 4 cells, then 16 progesterone, which prepare the endometrium for implantation, which is called “blastomere” then the morula is formed, it is still if implantation occurs the developing blastocysts begins to lined by zona pellucida, as they mature, fluids enter inside and produce human chorionic gonadotropin (Hcg) and rescues the they will form into blastocyst. It will separate into two: the inner corpus luteum, thus maintining progesterone production. FSH = cell mass is the future embryoblast and embryo. The outer one follicle-stimulating hormone; LH= luteinizing hormone. will be the trophoblast which is the future placenta and the one at the middle is the blastocyst cavity. This is the layer of This is the endometrial cycle, ovarian cycle, pituitary and steroids trophoblast that will 1s start to embed in endometrium. This is hormones. The relevance is soon the female wants to have pregnancy the last part of 1st week and the first part of 2 nd week of but she is not able to then you can check first semen analysis of the development. male then if its normal, then check for the female if she is ovulating, if during ovulation part, you can see if the LH is high that causes ovulation. If the LH is not high, the female is not ovulating. Then you can give pituitary hormones, (e.g. Clomiphene) that contains combination of LH and FSH that can stimulate the female to grow eggs. Menstrual cycle have three phases: (1) follicular phase, (2) luteal phase and (3) menstrual phase During the follicular phase the FSH stimulates the follicles to grow and prepares the endometrium. It is also when estrogen is high and on the FIGURE 2.6 A. Section of a 107-cell human blastocyst showing 14th day the female goes to ovulation. It is the LH that goes high and inner cell mass and trophoblast cells. B. Schematic progesterone starts to increase during ovulation. The with LH the representation of a human blastocyst recovered from the uterine corpus luteum is high that produces progesterone, if there is no cavity at approximately 4.5 days. Blue, inner cell mass or pregnancy the corpus luteum will degenerate and the layers of embryoblast; green, trophoblast. C. Schematic representaron of endometrium, the basal layer has blood vessels, at the middle is a blastocyst at the sixth day of development showing trophoblast spongy layer, and above is compact layer wherein the blastocysts will cells at the embryonic pole of the blastocyst penetrating the be implanted if fertilization takes place. But if there is no fertilization uterine mucosa. The human blastocyst begins to penetrate the it is at the level of the compact and spongy layer will degenerate and uterine mucosa by the sixth day of development. the female will menstruate, if this happens, it is the basal layer which has its own vascular that will degenerate. If conception occurs, it will undergo the same phases, the follicular again the ovulation, but then corpus luteum if there is fertilization, progesterone will continue to go high the same with HCH which is called the corpus luteum of pregnancy. The compact and spongy layer will go on the secretory phase, there will be no degeneration. TEST YOURSELF 1. What is noticeable in the 2nd week of development? 2. What two cavities are formed from mesoderm? 3. What produces HCG (Human Chorionic Gonadotropin)? 4. What are the three phases of the menstrual cycle? 5. On what day does your 2nd week of development start? 6. The trophoblast differentiates into two layers. What are these? ANSWERS 1. Implantation bleeding 2. Somatic and Splanchnic 3. Syncytiotrophoblast 4. Follicular phase, luteal phase, menstrual phase 5. Day 8 FIGURE 3.0 Gonadotropin control of the ovarian endometrial 6. Cytotrophoblast, syncytiotrophoblast cycles. The ovarian-endometrial cycle have been structured as a 28-day cycle. The follicular phase (days 1-14) is characterized by rising estrogen levels, endometrial thickening, and selection of the dominant “ovulatory” follicle. During the luteal phase (days 14-21), the corpus lutuem (CL) produces estrogen and PREPARED AND EDITED BY: TRANS GROUP 3