First week of development: ovulation and implantation

First week of development: ovulation and implantation

1. Ovarian cycle

   • Controlled by the hypothalamus
     • GnRH
     • Pituitary
       • FSH, LH
   • FSH
     • 15-20 primary follicles
       • When they become atretic they form a corpus atreticum
       • 1 oocyte
     • Maturation of follicular cells (granulosa)
       • Growth differentiation factor 9
         • estrogen production
           • Proliferative phase
             • LH
               • meiosis I is completed, start of meiosis II
                 • Luteinization
                   • Follicular Rupture
                     • Ovulation
                       • Mature vesicular follicle (Graafian)
                         • During meiosis II the stigma appears
                       • Increase of
                       • Corona radiata is formed by cumulus oophorus cells
                       • Corpus Luteum
                         • Granulosa and the theca intone cells are vascularized
                           • LH
                             • Lutein cells
                               • Estrogens and progesterone
                                 • Secretory stage
                         • Corpus albicans
                           • 9 days after ovulation if there is no fertilization
                         • The oocyte is carried into the uterine tube by the fimbriae and the epithelium

2. Fertilization

   • In the ampulla of the uterine tube
   • Before spermatozoa is capable of fertilize the oocyte they go through
     • Capacitation
       • 7 hours
         • Glycoproteins and seminal plasma are removed from the acrosomal region of the spermatozoa
       • Acrosome reaction
         • By zona proteins after binding the zona pellucida
         • 1. Penetration of the corona radiata
           • 2. Penetration of the zona pellucida
             • ZP3
               • Enzymes
                 • Zona reaction
             • 3. Fusion of the membranes (integrins and desintegrins)
               • Egg response
                 • Cortical and zona reaction: prevent polyspermy
                   • Second meiotic division
                     • Metabolic activation of the egg
                       • Formation of the male pronucleus
                         • Diploid number of chromosomes
                           • Determination of sex

3. Cleavage

   • Mitotic divisions
     • Blastomers
     • Morula (16 cells)
       • Inner cell
         • Embryo
       • Outer cell
         • Placenta

4. Blastocyst formation

   • Embryoblast
   • Trophoblast
     • Cells penetrate through the epithelium of the mucosa on the sixth day
       • L selectin (trophoblast) and carbohydrate receptors
       • Integrins, fibronectin and laminin

5. Uterus at time of implantation

   • It has several stages
     • Menstrual
       • Proliferative
         • Secretory
           • The three layers of the endometrium can be seen. Arteries become coiled
         • Estrogen, growth of ovarian follicles and spongy and compact layers
       • If fertilization does not occur blood from the superficial arteries scapes along with pieces of stroma and gland. Only the basal layer is retained.

6. Correlation: The embryo would not be affected by the drugs because it is until day six when the embryo attaches to the mother´s body and as the use of drugs was only one time it would be out of the system at that time.