full description about fertilization

1. TARANJEET KAUR
B.Sc. Nursing

2. APPROXIMATION OF GAMETES
 The semen on intercourse gets deposited deep in
the vagina at the opening of external os of cervix .
 Ovum is picked up by the fimbrae by muscular
/suction/cililary/positive chemotaxis action .
 Life span of ovum is 12-24 hrs whereas that of
sperm is 48-72 hrs.
 It liquefies within 20 minutes & thousands of
sperms swim up through cervical mucous following
3 minutes into the uterine cavity &100 -300 reach
the outer 3rd of fallopian tube within 5 minutes .

3.  Process of fusion of a single spermatozoa
with a mature ovum at ampulla of
fallopian tube to form zygote.
 Objectives are :
 To initiate embryonic development of egg,
 To restore chromosomal number of species

4.  Chemical action of hayluronidase released by acrosomal
cap of sperm head called capacitation causes complete
dissolution of cells of corona radiata .
 Zona pellucida has sperm receptors (ZP1,ZP2,ZP3) only
a single sperm enter ovum by physically drilling a hole ,
proteolytic digestion of pathway.
 Oolema block occurs to prevent further entry of sperms.
 Second Meiotic division of oocyte takes place each
containing haploid number of chromosomes 23 X ,
bigger one is female pronucleus & smaller is 2nd
polar body.
 Head & neck of sperm become male pronucleus
containing haploid number chromosomes (23 X, 23 Y).

6.  1st Meiotic division leads two cell stage
within 24-30 hrs, zygote now called as
blastomeres ,each contain equal volume &
chromosome number.
 Blastomeres continue to divide by binary
division through 4 ,8 ,16 cell stage.
 The morula stage : 16-64 cell stage ,
reaches uterine cavity after 4th day of
fertilization.

7.  On day 4th morula floats in uterine cavity
going through development formation of
200 cells & fluid filled cavity occurs called
blastocyst.
 At one pole of blastocyst there is a
compact mass of cells formed called inner
cell mass.
 A single layer of cells formed around
outside of blastocyst known as
trophoblast.

9. THANK