3 fertilizatio implantation 1st2nd week

941 views

Published on

Published in: Technology, Health & Medicine
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
941
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
95
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

3 fertilizatio implantation 1st2nd week

  1. 1. (1)Fertilization : It is the process by which mature male & female gametes fuse to form zygote Normal site - in ampulla of uterine tube.  200 – 300 million of spermatozoa deposit in female genital tract  Out of them 300 – 500 reach the site of fertilization  Out of them only one is needed for fertilization, others help in penetrating the corona radiata 1
  2. 2. (2)Penetration of corona radiata   Capacitation - removal of glycoprotein from acrosome /high motility of sperm without morphologic change Corona radiata cells are dispersed by combined action of sperm (Hyaluronidase ) & tubal mucosal enzymes. 2
  3. 3. (3)Penetration of Zona pellucida –  It is penetrated by sperm with the aid of enzyme released by the inner acrosomal membrane, (acrosin)  Zona reaction - Impermeability to other sperm by lysosomal enzymes of 2nd Oocyte 3
  4. 4. (4)Fusion of oocyte –sperm cell membrane  Leaving behind plasma membrane, head & tail enter the cytoplasm of oocyte The Egg responds in 3 ways  Cortical & Zonal reaction  Resumption of 2nd meiotic division  Metabolic activation on the egg 4
  5. 5. (5)Pronucleus formation  Female – after fusion of cell membrane oocyte completes its 2 nd meitotic division. One of the 2 daughter cell forms the pronucleus  Male Nucleus from the head of the sperm becomes swollen to form pronucleus  DNA replication – This occurs in both Pronuclei  Mitosis – Pronuclei meet, their nuclear membrane dissapear & chromosomes arranged in distinct manner for mitosis 5
  6. 6.  (6)Results of fertilization  restoration of the diploid number of chromosomes  new combination of chromosomes  primary sex determination  initiation of cleavage 6
  7. 7. (7)Cleavage  zygote -->  2-cell stage(blastomeres) -->  16-cells(morula) -->  Blastocyst Blastomere  Each of the cells results from cleavage of zygote is called Blastomere Morula:  The name of the embryo at the 16 to 32 cell stage. 7
  8. 8. (8)Formation of Blastocyst Morula when it is filled with uterine fluid is called Blastocyst  Morula eners the uterine cavity 60 – 72 hours after fertilization  At the same time fluid enters into the intercellular spaces of inner cell mass through zona pellucida  Intercellular spaces become confluent & finally a single cavity is formed called Blastocoele  At this time zona pellucida dissappears & the zygote is then known as Blastocyst 8
  9. 9. (9)Blastocyst : Parts  Embryoblast:(Forms Embryo) The cells on the inside.  Trophoblast:(Forms Placenta)(Nutrient providing cells) The cells surrounding the outside.  Blastocyst cavity 9
  10. 10. 10
  11. 11. (11)Implantation Process of placement of blastocyst into the wall of the uterus is called implantation (Erode)  Normal Site – Posterior wall of the uterus close to the fundus  initiated 6-7 days after fertilization 11
  12. 12. (12)Mechanism  Uterine mucosa already undergoes several changes (menstrual cycle) to receive blastocyst.  Duing implantation the mucosa is in secretory phase & poseses 3 layers  Polar trophoblast now adhers to the uterine mucosa & starts penetraion into it by eroding the surface(by release of proteolytic enzymes )  By erosion ,trophoblast forms a cavity in the mucosa into which the blastocyst becomes embeded 12
  13. 13. (13)Uterus after the implantation Decidua  After implantation of blastocyst the endometrium is called decidua Decidual Reaction  After implantation the stromal cells of endometrium enlarge become vacuolated & store glycogen & lipid  These changes in stromal cells are called decidual reaction Divisions of decidua  Decidua Basalis – portion where placenta is to be formed  Decidua Capsularis – portion which separates embryo form uterine cavity  Decidua Parietalis – rest part of decidua 13
  14. 14. (14)Formation of germ layers ( Gastrulation)  By day 8, The trophoblast differentiates into:  An inner cytotrophoblast surrounding the blasocyst  An outer layer of proliferating cells syncitiotrophoblast .  The blastocyst is more deeply embeded in the endometrium by day 9, & the penetration defect is closed by fibrin coagulum 14
  15. 15.     (15)Embryoblast splits into 2 layers:  The epiblast (primitive ectoderm)  The hypoblast (primitive endoderm), thus forming the bilaminar germ disc . Within the epiblast, the amniotic cavity develops Epiblast cells adjacent to cytotrophoblast is called amnioblasts Cells at the periphery of the hypoblast migrate over the inner surface of the cytotrophoblast, forming a thin layer called exocoelomic (Heuser’s membrane) , with the blasocyst cavity hence forth called the primary yolk sac (Exocoelomic Cavity) . 15
  16. 16. 16
  17. 17.    Formation of germ layers Exocoelomic membrane prolifates & splits to form 2 extraembryonic mesodermal layres Extraembryonic somatopleuric mesoderm, Extraembryonic splanchnopleuric M. Cavity inbetween – Extraembryonic coelom (chorionic cavity) Maternal sinusoids have grow into the expanding lacunae to supply the developing membrane 17
  18. 18.     Hypoblast produce additional cells that migrate along the inside of exocoelomic membrane . Cells proliferate & form new cavity is known as secondary or definite yolk sac Large portions of Primitive yolk sack are pinches off as exocoelomic cysts The E. mesoderm and 2 two layers of the Trophoblast together form the chorion. It surrounds the embryo and, later, the fetus. 18
  19. 19. By end of 2nd week of development, bilaminar embryonic disc becomes connected to trophoblast by a band of E. mesoderm called the connecting (body) stalk the future umbilical cord.  Slight thickening in the hypoblast region – Prechordal plate The embryo is now a bilaminar disc consisting of the:  Epiblast that forms the floor of the amniotic cavity  Hypoblast that forms the roof of the yolk sac  19
  20. 20.      Implantation begins on approximately day 5 and is completed by the end of the second week Outgrowths from the syncitiotrophoblast invade the deciduas They erode the maternal blood vessels. They become surrounded by trophoblastic lacunae containing maternal blood A utero-placental circulation is established by day 13 20
  21. 21. Placenta  Is a structure by which fetus is attached to mother & gives O2,nutrition to the embryo(fetus) & excretes waste products ,CO2 from fetus to mother Formation Maternal sources  Desua Basalis Fetal sources  Chorion frondosum 21
  22. 22. Chorion frondosum formed by following stages Primary villi  consist of syncitiotrophoblast and cytotrophoblast  day 13 Secondary villi  have a core of extra-embryonic mesoderm  day 16 Tertiary villi  have blood vessels in the mesoderm  day 21 22
  23. 23. Abnormal implantation  Normal implantation: posterior / anterior wall in the body of the uterus.  Ectopic pregnancy/ extra uterine pregnancy  Placenta previa - Atypical placental positioning and attachment within the lower third of uterus, which may cover the cervix in part or fully. 23
  24. 24. 24
  25. 25. 25
  26. 26. 26

×