For a conception to occur male sperm has to unite with (fertilize) the female ovum.
Sperms: The testes continue to produce sperms right from puberty till about age of 60 or so. One cycle of spermatogenesis
(production of sperms) takes three
months. A sperm has two main
components a small head and a large tail. After the sperms are formed, they are transmitted to the epididymis.
The sperms live in the epididymis
up to two weeks depending upon the frequency of sexual activity. They subsequently pass
through vas deferens and reach a sac like structure called seminal vesicles at
the base of the bladder. The sperms
remain in seminal vesicles
till they are ejaculated.
Ejaculation occurs at the time of male orgasm. It consists of rhythmic
contraction of the muscles throughout the reproductive organs of the male, causing the seminal
vesicles to contract and release the seminal fluid containing the sperms in the male urethra. Further contractions of the
muscles make the seminal fluid and the sperms
move down to the urethra for ejaculation at the
opening on the tip of the penis.
The average male ejaculation consists of 4-8 forceful contractions,
ejaculating the seminal fluid from the penis. The
average ejaculate is 3 to 5 ml, containing about 50 to 250 million sperms/ ml. This makes
the total number of sperms ejaculated
150 to 1000 million, with an average of about four hundred million sperms.
Ovulation: the process of production and release of a
mature egg is called Ovulation. During each
menstrual cycle, about two hundred
and fifty premature eggs begin to develop. Of these, only one develops into a mature egg
and is released in the middle of a regular twenty-eight day menstrual cycle. The ovum is normally released about
14 days before the next menstrual
cycle. This egg dies, if not fertilized, and the next menstrual cycle starts after fourteen days.
During development, the egg lies within graffian
follicle, which gradually grows in size and moves toward the surface of the ovary. When
the egg is completely mature it ruptures and releases some amount of fluid along with the
egg in the abdomen. This egg along with the fluid is sucked into the fallopian tube. The cells
that line the graffian follicle change after ovulation
to form a structure known as corpus luteum. The survival of the fertilized egg
during the first fourteen weeks is completely dependent upon level of progesterone
secreted by the corpus luteum.
More about Ovulation
HOW DOES CONCEPTION OCCUR?
When the male sperm
unite with the female egg in the fallopian tube, conception
occurs. At the time of ejaculation, the sperms
are protected by thick and sticky seminal fluid, which liquefies after about 15 20
minutes, making the sperms loose their
protective covering. The secretions of the vagina are acidic. The sperms are sensitive to acids and those
that have not entered the cervix during these 15 to 20
minutes are killed. Most of the sperms
killed are immature, damaged or abnormal and therefore not suitable for conception.
The alkaline secretions of the cervix nourish the sperms that have entered. Also at the
time of the ovulation, secretions of the cervix
become thin, transparent and most suited for the sperms to enter the uterus (cervical mucus). The
sperms take about 45 minutes to travel from cervix, through the uterus and
inside the fallopian
tube. The secretions of the fallopian tube being alkaline and rich in sugar, provide
nourishment to the sperms and help
them survive for about 48 to 72 hours.
If ovulation has
occurred within eighteen hours before the sperms
reach the outer end of the fallopian tube, the
conception occurs as soon as the sperms
reach the egg.
Although only one sperm
unites with the egg, it is necessary to have many sperms in the fallopian tube as the egg is
covered by a thick and sticky material that can only be liquefied by an enzyme carried by
the sperms. Just one sperm cannot carry enough enzymes to
liquefy the covering of the egg. The actual mechanism of how the sperm and egg unite is not clear.
Within first few hours after conception, the male and the female
nuclei, which contain the chromosomes grow in size and move
towards the center of the egg, fusing together to form a single nucleus. Each chromosome consists of a double
strand of a protein called deoxyribonucleic acid or DNA. Soon after the two nuclei join
together to form one single nucleus, it divides into two equal parts. Each of these parts
contains equal portions of the chromosomes of the mother and father.
During the next 72 hours, the entire fertilized cell continues to divide and forms 64
separate cells. At this stage the divided cells are called morula. The process of
division continues for two hundred and sixty six days from conception, by which time, the
process of forming the wide range of tissues in the body is complete.