Sexual reproduction is a mode of reproduction where two parents are involved in producing a new individual. Offspring is produced by the fusion of gametes (sex cells) from each parent. Hence, the newly formed individual will be different from parents, both genetically and physically. Human reproduction is an example of sexual reproduction. Before we learn about reproduction in humans, let’s see how human body prepares for reproduction.
As a part of growth, human body undergoes a lot of changes, physically as well as psychologically. The life stage between childhood and adulthood is called adolescence. During adolescence, the rate of growth is much faster. It marks the onset of reproductive phase in boys and girls. The changes which take place in the body during this reproductive phase is called puberty. Puberty commences the sexual maturity in adolescents.
For the purposes of reproduction, the bodies of a male and a female, which have attained puberty, will show secondary sexual characteristics. The changes are faster in girls than boys. Some changes are common in both boys and girls but some are specific to each gender. This is due to the different hormones released by them.
The gonads begin to produce gametes (sperm in male and ovum in female), which are essential for reproduction in humans. Changes in height, increased sweating, oil production, and hair growth in pubic regions and under armpit are some common secondary sexual characteristics.Menstruation, enlargement of mammary glands, ovulation, etc. are the characteristics exhibited only by girls. In boys, the body becomes more muscular; enlargement of the larynx, sperm production, hair growth on the chest, etc. will take place.
Secondary sexual characteristics and all other changes during puberty are due to the secretion of hormones in our body. Thus, the hormones prepare the body before the actual reproduction happens.
Like plants, reproduction in humans also involves fusion of gametes, i.e., sperm fuses with the egg to form a zygote. Male and female gametes are formed in their reproductive system. The male reproductive system is different from the female reproductive system, both in structure and in function.
Male reproductive system
The male gamete, sperm, is produced within the male reproductive system. The male reproductive system consists of the following parts:
- Testicles (testes): A pair of oval-shaped organ masked in a pouch called scrotum. Testes are responsible for the production of the sperms and male hormone, testosterone.
- Vas deferens: The sperms produced in testes are stored in a tube called epididymis. Here the sperms get matured and passed to urethra through the muscular tube called vas deferens.
- Accessory glands: This includes three glands namely, seminal vesicles, prostate gland, and Cowper’s gland. The secretions from the three glands mix to form a fluid called semen. Semen nourishes the sperm, increases the volume and helps in lubrication.
- Penis: Penis is a cylindrical tube which serves as both reproductive organ as well as excretory organ. It delivers sperms into the vagina during sexual intercourse.
Sperms are a small unicellular structure with a head, middle piece, and a tail.
Female reproductive system
Female reproductive system has two functions –
- Production of female gamete called ovum/egg.
- Nourishment and protection of the developing embryo.
The female reproductive system is active before, during and after fertilization as well. It consists of the following parts:
- A pair of ovaries: Ovaries produce and store ovum in them. They also produce a female hormone called estrogen.
- Fallopian tubes (Oviducts): They are the site of fertilization. They connect ovaries with the uterus.
- Uterus: Uterus is the site of development for the embryo.
- Vagina: It is the part which connects cervix to the external female body parts. It is the route for penis during coitus as well as a fetus during delivery.
During puberty, eggs in the ovaries start to mature. One of the ovaries releases the matured ovum in every 28 to 30 days. This is called ovulation.
Reproduction in Humans
The process of fusion of sperm with egg (ovum) to produce zygote is called fertilization. Fertilization is the crucial stage in reproduction in humans.
During coitus, penis ejaculates millions of sperms into the vagina of the woman. Sperm will travel through the uterus to oviducts. At oviduct, one out of million sperms fertilizes the released ovum. The fertilized egg develops into a zygote.
Zygote starts to divide into many cells and develops into an embryo. Embryo moves to the uterus and attaches to the uterus walls. This is called implantation. Implanted embryo eventually develops into a fetus.
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