[EMBRYO]LEC_002-FIRST_WEEK_OF_DEVELOPMENT.pdf

(002) 1ST WEEK OF DEVELOPMENT DR. LAPAZ L. PEREDO | 10/08/2020 OUTLINE  Under the influence of GnRH from the hypothalamus, the...

(002) 1ST WEEK OF DEVELOPMENT DR. LAPAZ L. PEREDO | 10/08/2020 OUTLINE  Under the influence of GnRH from the hypothalamus, the pituitary releases the gonadotropins, FSH and LH. Follicles I. OVERVIEW are stimulated to grow by FSH and to mature by FSH and LH. II. OVULATION FSH is not necessary to to promote development of Primordial Follicle into Primary Follicle, but without it, the Primary  Step 1 Follicles die. III. FERTILIZATION  Ovulation occurs when concentrations of LH surge to high  Step 2 levels. LH surge causes (1) elevation of concentrations of maturation-promoting factor which causes oocyte to complete  Step 3 meiosis I and initiate Meiosis II (2) Stimulates production of IV. IMPLANTATION Progesterone (3) Causes Follicular Rupture and Ovulation. LH also promotes development of the corpus luteum.  Step 4  Stages of Implantation V. TEST YOURSELF VI. REFERENCE I. OVERVIEW  Ovulation – one of the ovaries release a mature egg  Fertilization – when the sperm cells from male combine with a mature egg to form a fertilized egg  Implantation – when the fertilized egg lodges itself into the Figure 2. Illustration showing the A. Primordial follicle. B. Growing follicle. endometrial lining of the uterus C. Vesicular follicle.  Hypothalamus controls the sexual cycles by producing  Every day from the pool of primordial follicles, some begin to Gonadotropin-releasing hormone, which acts on pituitary develop into growing follicles, and this growth is independent gland, which secrets gonadotropin hormones. The of FSH. Then, as the cycle progresses, FSH secretion recruits hormones Luteinizing hormone and follicle stimulating growing follicles to begin development into vesicular (antral) hormone, stimulate and controls cyclic changes in the follicles. ovary.  During the last few days of maturation of vesicular follicles, estrogens, produced by follicular and thecal cells, stimulate II. OVULATION increased production of LH by the pituitary gland [Fig. 1], and this hormone causes the follicle to enter the mature vesicular STEP 1 [Graafian] stage, to complete meiosis I, and to enter meiosis II,  Making the egg and sperm where it is arrested in metaphase approximately 3 hours  Male testes produce new sperm cells a day before ovulation.  Egg is only released at a time, once per menstrual cycle  Sperm cells stick around for 3-4 days  Eggs are more short-lived, surviving only around 24 hours after ovulation  Overall, fertile window is only the day of ovulation and the several days leading up to it Figure 3. Illustration showing the A. Mature vesicular follicle. B. Ovulation. C. Corpus luteum.  During ovulation, the oocyte, in meta- phase of meiosis II, is discharged from the ovary together with a large number of cumulus oophorus cells. Follicular cells remaining inside the collapsed follicle differentiate into lutein cells.  The large size of the corpus luteum is caused by hypertrophy and accumulation of lipid in granulosa and theca interna cells. The remaining cavity of the follicle is filled with fibrin. Figure 1. Drawing showing the role of the hypothalamus, and pituitary gland in regulating the ovarian cycle. 1, primordial follicle; 2, growing vesicle; 3, vesicular follicle; 4, mature vesicular [Graafian] follicle. PREPARED AND EDITED BY: LIMBAUAN, J., LIVED, R., LOCQUIAO, C., LOPEZ, F., PADILLA, A., PADOLINA, J., PALAGANAS, B., PANG-AG, L  (002) 1ST WEEK OF DEVELOPMENT DR. LAPAZ L. PEREDO | 10/08/2020  The high concentration of LH causes increase in  Spermatozoa are not able to fertilize the oocyte prostaglandin which causes muscular contractions in the immediately. ovarian wall. These contractions extrude the oocyte - It must first undergo Capacitation (removal of the together with its surrounding granulosa cells from the glycoprotein coat and seminal plasma membrane that cumulus oophorus cells. Some of the cumulus oophorus surrounds the acrosomal region of the spermatozoa in cells rearrange themselves around the zona pellucida to the uterine tube) and Acrosome Reaction (release of form the zona radiata. enzymes occurring after the binding to the Zona  After ovulation, granulosa cells remaining in the wall of pellucida, induced by zona proteins) the ruptured follicle are vascularized. Under the influence of LH, these cells develop a yellowish pigment and change into lutein cells which forms the corpus luteum. Figure 5. The three phases of oocyte penetration.  Phases of Fertilization (Fig. 5) o Phase 1: Penetration of the Corona radiata o Phase 2: Penetration of Zona pellucida (the release of Acrosomal enzyme, Acrosin, allows sperm to penetrate the Zona Pellucida). When a Figure 4. Relation of fimbriae and ovary. sperm becomes in contact with the oocyte surface, it causes the release of Cortical Oocyte  The oocyte is carried to the fallopian tube by the Granules which: (1) changes the permeability of sweeping motion of the fimbriae and by motion of the cilia the oocyte membrane (becomes impermeable to from the epithelial lining. Once it is in the fallopian tube, other spermatozoa) and (2) Zona pellucida alters the cumulus cells withdraw their cytoplasmic processes its structure and composition to prevent sperm from the zona pellucida and lose contact with the oocyte. binding and penetration (zona reaction). Once the oocyte is on the fallopian tube, it is propelled by o Phase 3: Fusion of the Oocyte and Sperm Cell peristaltic muscular contractions of the fallopian tube and Membranes. Once the spermatozoon has by the cilia. entered the oocyte, egg creates three responses:  If fertilization does not occur, the corpus luteum will (1) cortical and zona reaction (to prevent shrink because of the degeneration of lutein cells or polyspermy), (2) resumption of the second luteolysis and it forms a fibrotic scar tissue called the meiotic division (formation of second polar body, corpus albicans. definitive oocyte, and the arrangement of  If the oocyte is fertilized, degeneration of the corpus chromosomes to form the female pronucleus), luteum is prevented by human chorionic Gonadotropin and (3) metabolic activation of the egg (activating (hcG) which is secreted by the syncitiotrophoblast of factor is probably carried by the spermatozoon). the developing embryo. Corpus luteum continues to grow, forming the corpus luteum of pregnancy (corpus  As the spermatozoon moves closer to the female luteum graviditalis). pronucleus, its nucleus becomes swollen, forming the male pronucleus (tail detaches and degenerates). III. FERTILIZATION  Results of Fertilization STEP 2 o Restoration of the diploid number of  Fertilization: Sperm released in ejaculation travel through chromosomes (half from the mother and half the cervix and into the uterus where they make way to the from the father) fallopian tube where the egg lies in wait o Determination of sex  The process of fertilization occurs in the ampullary region of o Initiation of cleavage the fallopian tube. - Movement of the sperm from the cervix to the Fallopian tube is caused by the muscular contractions of the Uterus and very little by the propulsion of the sperm. PREPARED AND EDITED BY: LIMBAUAN, J., LIVED, R., LOCQUIAO, C., LOPEZ, F., PADILLA, A., PADOLINA, J., PALAGANAS, B., PANG-AG, L  (002) 1ST WEEK OF DEVELOPMENT DR. LAPAZ L. PEREDO | 10/08/2020 Figure 6. Development of the zygote from the two-cell stage to the late morula stage.  The two-celled zygote (reached approximately 30 hours after fertilization) undergoes a series of cleavage division, forming blastomeres.  The four-cell stage is reached at approximately 40 hours.  After the 3rd cleavage, they compact (through compaction held Figure 8. Changes in the uterine mucosa correlated with those in the by tight junctions), segregating inner cells from outer cells. ovary.  Three days after fertilization, 16-cell morula is formed, with  Implantation of the blastocyst has caused development of a inner cell mass (inner cells) and outer cell mass (surrounding large corpus luteum of pregnancy. Secretory activity of the cells). endometrium increases gradually due to large amounts of  After 4 days, late morula stage is reached and blastomeres progesterone produced by the corpus luteum of pregnancy. are surrounded by the zona pellucida, which disappears at the end of the fourth day.  Inner cell mass → tissues of embryo proper  Outer cell mass → trophoblast → placenta  As morula enters the uterine cavity, fluid penetrates to the intercellular spaces of the inner cell mass, forming the blastocele (morula → blastocyst). Figure 7. B. Schematic representation of a human blastocyst at approximately 4.5 days. Blue, inner cell mass or embryoblast; green, trophoblast. C. Schematic representation of a blastocyst at the sixth day of development. STEP 3  Fertilization to implantation  In fertilization, 1 sperm is eventually able to make it through Figure 9. Changes in the uterine mucosa [endometrium] and corresponding changes in the ovary during a regular menstrual cycle and combine with the egg to form a zygote without fertilization.  The fertilized egg begins to divide into clamp of cells as it travels through the fallopian towards the uterus  After 4-6 days of cell division, it matures into a IV. IMPLANTATION STEP 4 BLASTOCYST, and its ready to implant into the uterus  Zygote multiplies several times to BLASTOCYST  Blastocyst implants into the uterine lining (uterine cavity)  Implantation happens around the 7th day after fertilization  Blastocyst begins to wedge itself into the endometrial lining of the uterus – this takes about 5 days to complete  After implantation, cell division begins to specialize, forming what will become the embryo’s body and the placenta  Fertilized egg (BLASTOCYST) attached to the lining of the uterus to grow and develop. PREPARED AND EDITED BY: LIMBAUAN, J., LIVED, R., LOCQUIAO, C., LOPEZ, F., PADILLA, A., PADOLINA, J., PALAGANAS, B., PANG-AG, L  (002) 1ST WEEK OF DEVELOPMENT DR. LAPAZ L. PEREDO | 10/08/2020  Happens a week after ovulation, in an early stage of pregnancy, V. TEST YOURSELF and an entirely a natural process 1. All of the statements are true EXCEPT:  Most cases, it takes place around 9 days after ovulation, but A. Sperm cells stick around for 3-4 days sometimes it can occur as early as 7 days or as late as 12 days B. Eggs are more long-lived than sperm cells, surviving only around 24 hours after ovulation STAGES OF IMPLANTATION C. Male testes produce new sperm cells a day  1st Stage – embryo attaches to the uterine wall D. Egg is only released at a time, once per menstrual (endometrium), embryo is about 5-6 days old – Adplantation. cycle  2nd Stage – fertilized egg penetrates the uterine wall, so it is secured in the uterus, adhesion of the blastocyst to the 2. Stimulate and control cyclic changes in the ovary: endometrium A. Growth Hormone Releasing Hormone and Luteinizing  3rd Stage – embryo embeds deeply inside the uterine wall, Hormone ovum located in the endometrial cavity, endometrium grows, B. Follicle-Stimulating Hormone and Luteinizing Hormone cavity wrapped better C. Gonadotrophin-Releasing hormone D. Follicle-Stimulating Hormone and Human chorionic gonadotropin hormone 3. Luteinizing Hormone surge causes all of the following EXCEPT: A. Luteinization B. Ovulation C. Follicular Rupture D. Capacitation 4. As the vesicular (Graafian) stage enters Meiosis II, it becomes: A. Arrested in metaphase approximately 3 hours before ovulation. B. Arrested in anaphase approximately 4 hours before ovulation. C. Arrested in metaphase exactly 2 hours after ovulation. D. Arrested in anaphase approximately 2 hours after ovulation. 5. This shrinks if the fertilization does not occur because of the degeneration of Lutein Cells and it will form a fibrotic scar tissue. A. Corpus Albicans B. Corpus Delicit C. Corpus Callosum D. Corpus Luteum 6. What is the correct sequence of phases of fertilization? Figure 10. Illustration of the changes in a woman’s body during the I. Penetration of Zona pellucida menstrual cycle. II. Penetration of Corona radiate III. Fusion of Oocyte and Sperm Cell  Uterus at Time of Implantation A. I, II, III o Uterus mucosa is in secretory phase (coiled uterine B. III, I, II glands and arteries, and succulent tissues). C. II, I, III o Three distinct layers of the endometrium becomes D. D. II, III, I recognizable: (1) superficial compact layer, (2) intermediate spongy layer, and (3) thin basal layer. 7. Which of the following is NOT true about the development of the zygote from two cell stage to late morula stage? I. The two-cell stage is reached approximately 24 hours after fertilization II. The four-cell stage is reached at approximately 40 hours III. The 12- to 16-cell stage is reached at approximately 3 days IV. The late morula stage is reached at approximately 4 days V. Zona pellucida disappears at the end of the fifth day. PREPARED AND EDITED BY: LIMBAUAN, J., LIVED, R., LOCQUIAO, C., LOPEZ, F., PADILLA, A., PADOLINA, J., PALAGANAS, B., PANG-AG, L  (002) 1ST WEEK OF DEVELOPMENT DR. LAPAZ L. PEREDO | 10/08/2020 A. I and V B. II, III and V C. I, II and III D. I, III and IV 8. Where does implantation of blastocyst occur? A. Fimbriae B. Uterine lining C. Placenta D. Ampulla 9. What is the term for the removal of glycoprotein coat and seminal plasma membrane that surrounds the acrosomal region of spermatozoa? A. Acrosome reaction B. Implantation C. Capacitation D. Hypertrophy 10. At what stage of implantation does Adplantation occur? A. 1st stage B. 2nd stage C. 3rd stage D. 4th stage ANSWERS: 1.B. ; 2.B. ; 3.D. ; 4.A. ; 5.D. ; 6.C. ; 7.A. ; 8.B. ; 9.C. ; 10.A. VI. REFERENCE 1. Mescher, A. L. (2016). Junqueira’s Basic Histology Text and Atlas (14th Ed.). McGraw-Hill Education. 2. Sadler, T. W., & Langman, J. (2012). Langman's Medical Embryology (12th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. PREPARED AND EDITED BY: LIMBAUAN, J., LIVED, R., LOCQUIAO, C., LOPEZ, F., PADILLA, A., PADOLINA, J., PALAGANAS, B., PANG-AG, L