Human Embryology: Fertilization and Implantation PDF

Human Embryology Fertilization & Implantation Dr. Y. D. Kolambage Lecturer, Department of Anatomy, Faculty of Medicine, Sabaragamuwa University of Sri Lanka. ...

Human Embryology Fertilization & Implantation Dr. Y. D. Kolambage Lecturer, Department of Anatomy, Faculty of Medicine, Sabaragamuwa University of Sri Lanka.  Stages in human development Gametogenesis ovum + sperm weeks Fertilisation 1 Dividing zygote / Implantation. 2 Cell division 3 Bilaminar disc Period of Cell growth Embryo Trilaminar disc Differentiation 4 Most vulnerable folding of embryo to period Cell death 8 development of organs and systems formation of placenta 9 Period of foetus Primarily increase in size and complexity To 40 These stages can be assessed by ultrasonography Birth Neonate - Infant - Child – Adolescent Adult ~Fertilization~  Learning Outcomes At the end of this lecture, you should be able to: 1. state the site of fertilisation. 2. list the mechanisms responsible for transport of spermatozoa to site of fertilization. 3. describe the main events associated with fertilization. 4. list the main results of fertilisation. 5. describe the problems associated with fertilization 6. list some of the assisted reproductive techniques ❑What is fertilisation? ❑What is the usual site of fertilisation? ❑What are the results of fertilisation?  WHAT ? The process by which male and female gametes fuse WHERE ? Ampullary region of the Fallopian Tube WHEN ? Within 24 hours of ovulation  How does the sperm move ? Contraction of vaginal & uterine muscles Active swimming movements towards the ovum What are the essential events ? Capacitation Acrosomal reaction  CAPACITATION Removal of the glycoprotein coat & seminal plasma proteins from the plasma membrane that overlies the acrosomal region of the spermatozoa  ACROSOMAL REACTION The release of enzymes needed to penetrate the zona pellucida, including acrosin- and trypsin-like substances Hyaluronidase Acrosin  Response Of The Ovum As soon as the spermatozoon has entered the oocyte: Cortical and zonal reactions. Resumption and completion of the second meiotic division. Metabolic activation of the egg  Female Male Pro nucleus Pro nucleus (n) (n) Pronuclear stage of the fertilized oocyte Growth & DNA Replication Fusion of Pronuclei  ZYGOTE Fertilized ovum after fusion of male and female pronuclei.  Results of Fertilisation Restoration of diploid number of chromosomes. Determination of sex of embryo. X + X ➔ XX =Female X + Y ➔ XY = Male Initiation of cleavage. Beginning of life? First Week of Development ~Implantation~  Learning Outcomes At the end of this lecturer you should be able to: 1. list the changes in the fertilized ovum prior to implantation 2. define the blastocyst, inner cell mass and trophoblast 3. describe the process of implantation 4. list the abnormal sites of implantation and the possible clinical complications Following Fertilisation… 2 cell zygote  1. Cleavage of Zygote WHAT ? A series of mitotic divisions in the zygote WHEN ? From the time of the 2 cell zygote WHERE ? As the zygote travels down the fallopian tube  SPECIAL FEATURES It subdivides the zygote without increasing its size. Each division occur about 20 hours apart. Produces several generations of cells called BLASTOMERES. Become smaller with each cleavage division.  Initially blastomeres are loosely arranged After 3rd Cleavage Blastomeres maximise their contact with each other and form a compact ball of cells held together by tight junctions COMPACTION inner cells segregates from outer cells  MORULA Outer cell mass Inner cell mass Trophoblast Embryoblast 16 Cell Placenta Embryo  Fluid penetrate through Zona Pellucida into the inter cellular spaces between cells of the inner cell mass They gradually become confluent and form a single cavity BLASTOCELE / BLASTOCYST CAVITY  2. Blastocyst Formation Blastocele Inner cell mass Outer cell mass Embryo Placenta BLASTOCYST Blastocyst Zona Pellucida HATCHING At the end of the 4TH DAY Two celled zygote divides (mitosis) Day 3-4 form Blastomeres Morula enters uterine cavity ZP degenerates Day 6 Day 4-5 Implantation Cavity appears in morula - Blastocyst ▪Inner cell mass ▪Outer cell mass  IMPLANTATION Process of attachment and invasion of the endometrium by the blastocyst (From Day 06 to 09) Trophoblast Blastocyst attaches itself to endometrium – on Day 06 Trophoblast has invasive properties, so it invades endometrial stroma. Uterus at Time of Implantation Increase in the vasculature Formation of endometrial glands  TROPHOBLAST (Syncytiotrophoblast) hCG Corpus Luteum Progesterone (Until the end of 4th month) Maintenance of pregnancy  Sites of Implantation NORMAL SITE Posterior Wall Abdominal Interstitial Tubal Internal OS Ovarian Cervical ECTOPIC SITES  Ectopic Pregnancy Questions? Thank you!