Reproduction is one of the most fundamental and complex characteristics exhibited by living entities. It is an inherent ability of entities to produce offsprings of their own kind by transferring genetic information which requires mating of the male and female. There are two modes of reproduction – asexual and sexual. In humans, sexual reproduction is observed.
Sexual reproduction is one of the most advanced and significant forms of reproduction exhibited by higher animals and humans. Ovulation takes place every month in females, where the ovary releases an egg. An average menstrual cycle lasts for about 28 days. An egg matures in the ovaries of a woman during the first 14 days of the cycle, which is stimulated by a hormone called the FSH (follicle-stimulating hormone). Another hormone called the estrogen prepares for conception making nutrient-rich and safe bedding for implantation in case of fertilization in the lining of the uterus. When the egg is not fertilized, this lining sheds resulting in menstrual flow.
In the event of copulation, the human male ejaculates the male sex cell or gametes, the sperm present in the semen (fluid containing sperms) swims up into the female reproductive tract through the cervix, towards the uterus to fuse with the egg in the uterine tubes. Egg or oocyte is the female sex cell. The respective sex cells from both the parents contain genetic information which is required to be transmitted to the offspring. These sex cells contain 23 chromosomes each and are haploid in nature. They combine to form the zygote containing 46 chromosomes. When the egg is fertilized by a sperm, conception takes place.
Once the egg is fertilized, it implants itself in the lining of the uterus and hence the inception of pregnancy. The meiotic process in males produces sperms and is called spermatogenesis, while the meiotic process in females produces ova and is called oogenesis. The zygote undergoes cell division through which the zygote divides and multiplies. It becomes a blastocyst as it travels towards the uterus for implantation. The embryo thus implanted matures and grows here and is surrounded by formations which lend nourishment and support throughout the maturation period called the gestation period(typically 9 months in humans).
Through various weeks and stages, different parts of the embryo develop and come to be known as the fetus exhibiting visible and distinct organs. The fetus grows until the walls of the uterus dilate with uterine contractions indicating the termination of pregnancy that ends with labour and hence childbirth or parturition.
Q.1. Why is sterility caused when testes fail to descend into the scrotal sac?
A.1. It leads to sterility as sperms are not formed because the spermatogenic tissues of the testes are destroyed due to high temperatures of the abdomen.
Q.2. What is the significance of the ampullary-isthmic junction?
A.2. It is the site of fertilization in the female genital tract.
Q.3. Which is the enzyme is the sperm acrosome which aids the entry of sperms into the egg?
A.3. The ovum membrane is dissolved by the enzyme hyaluronidase.
Q.4. Name the stage at which the mammalian embryo is embedded in the uterus.
A.4. The blastocyst stage
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