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Normal Pregnancy

CONCEPTION

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.

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