Fertillisation

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General Embryology

Embryology:
Ø    A  phenomena which occurs before      
      birth
Ø   Three basic events takes palce
Ø    multiplication, differentiation and 
      degeneration.

Gametogenesis
Ø Gametogenesis is maturation of primordial germ cells through meiosis.
Primordial Germ cells,3rd.week:
Spermatogenesis:
Oogenesis

Ø Oogenesis can be divided in three phases:
      i.            A. Prenatal- 7 millions maximum by 5th.
   ii.                                  month.
   ii.            B. Postnatal
iii.            C. Ovulation
Ovulation  & menstrual cycle
Diagram of Uterus.
Ovulation
when ?
What is safe period ?
  Corpus Luteum.
Corpus luteum:
Ø  What is it? a glandular structure.
Ø   Function?  It secrets progesterone.
Ø   Fate:
      a)  Corpus luteum of menstruation.
          ( Corpus albicans)
       b) Corpus luteum of pregnancy.
Mens
•      Cyclic changes in the endometruim, comprising of  menstrual phase( 3-6) days, proliferative phase of (6-14 days, follicular cells- estrogen), secretory phase ( 15- 28 days- Corpus luteum-progesterone) and ischaemic ( premenstrual phase-27-28days).
Fertilization:
Ø    Definitions: It is the process by which the  
     male and female gametes fuse, to form 
     the zygote.
Ø The fertilization process takes approximately 24 hours.
  
Fertilization(Cont.)
Ø   Fertilization is a complex sequence of coordinated molecular events that begins with contact between a sperm and an oocyte
Ø Where ? Occurs normally in the ampulla  
     of the uterine tube
in vitro fertilization:
Ø This fusion can occur within the body (in vivo fertilization) or using the new technologies outside the body (in vitro fertilization).
Ø Transgenic and gene knockout studies in animals have shown that carbohydrate binding molecules and gamete-specific proteins on the surface of the sperms are involved in sperm-egg recognition and their union.
Ø   ? Cloning: Development of  somatic cell.
Modification of the spermatozoa [before it can fertilize the ova]
   A. Capacitation:
Ø It is activation – enzymatic process on the acrosomal cap of the sperm to allow it to penetrate the corona radiata.
Ø Glyoprotein coat and seminal proteins are removed from the cell membrane.
Modification of the spermatozoa( Cont.)
 B.The Acrosomal Reaction:
Ø Occurs after the sperm binds to the zona pellucida.
Ø Binding of the sperm to the zona is facilitated by ZP3 protein and receptors in the sperm cell membrane.
Ø Enzymes – acrosin and trypsin like substance are released to allow the sperm to pass through the zona pellucida.
Phases of fertilization:
Ø Phase 1: penetration of the corona radiata.
    The enzyme hyalurodinase and the movements of the spermatozoa bring this about. Tubal mucosal enzymes also appear to assist the dispersal.
Ø Phase 2: penetration of the zona pellucida.
    The enzymes esterases, acrosin, and neuraminidase appear to cause lysis of the zona pellucida,
Ø  Phase 3: fusion of the oocyte and spermatozoa cell membranes.
 The plasma or cell membranes of the oocyte and sperm fuse and break down at the area of fusion. The head and tail of the sperm enter the cytoplasm of the oocyte, but the sperm's plasma membrane remains behind
Zonal reaction:
  Zonal reaction:  this is to prevent polyspermy [more than one sperm fertilizing a ova] after the first         sperm passes through the zona pellucida.
   The zona undergoes physiochemical changes that prevent        entry of other sperms. This change is brought by lysosomal enzymes released from the   secondary oocyte.
•      The nucleus of the mature ova is called the FEMALE    PRONUCLUEUS.
•      The head of the sperm [nucleus] – MALE PRONUCLEUS.
•      Duplication of DNA in the pronuclei.
•      Disintegration of nuclear membrane.
•      Maternal and paternal chromosomes intermingle  - at metaphase of first mitotic division of the zygote.
Results of fertilization:
Ø Completion of 2nd meiotic division of the ova.
Ø Restoration of diploid number: two haploid  gametes [n] produce a diploid zygote [2n].
Ø Determination of chromosomal sex.
Ø Initiation of cleavage – a series of mitotic cell        divisions within the zygote.
Ø Species variation – the zygote contains a new       combination of chromosomes and genes. Results in variation of the human species  through mingling of maternal and paternal chromosomes.
Contraceptive methods:
Ø A.  Barrier technique:  Condom
Ø B.  Pills: Inhibit ovulation permit
               menstruation
Ø C.  Depo Provera   ( Depo-provera):
                                     IM Injection.
Ø D.  IUD.
Ø E.  Vasectomy and tubal ligation.
Task 2.
   Mention different types contraceptive methods that is available in Nepal.
Implantation
First week!
First week of development
1.Zygote
2.Morula
                  3.Loss of Zona pellucida
4.Implantation
            5.Blastocyst formation
Implantation
Ø  is the process by which the blastocyst embeds itself into the endometrium of the uterus.
Ø The normal site of implantation is usually in the anterior or posterior wall of the body of the uterus.
Ø The endometrium is already prepared for this process - secretory phase of mens.
5.Blastocyst formation
  A.  Inner cell mass. ( Embryoblast)
  B. Outer cell mass. (Trophoblast. )
  C . Blastocyst cavity.
At the end of first  week of development
Summary of the first week
Ø Zygote formation
Ø Cleavage and blastomere
Ø Morula which enters the uterine cavity
Ø Blastocyst- Embryoblast,trophoblast & blastocele
Ø Zona pellucida disintegrates
Ø Emplantation begins

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