Reproduction - Class 10th Science
Sexual Reproduction in Humans
Like in all other vertebrate, sexual reproduction is the only means of reproduction in human beings. Human beings are unisexual, i.e., the sexes are separate.
The Male Reproductive System
Puberty is a stage when reproductive organs start functioning and testes start producing sperms. The age of puberty in a human male is 13 – 14 years.
Following organs include in human reproductive system of a man.
Testes, Vasdeferns, scrotum, urethra, epididymis and penis.
Testes
Testes (singular:testis) are the primary sexual organ of males. A pair of oval testes lie inside the scotal sac.
Each testis is composed of a number of coiled tubules called seminiferous tubules. Each seminiferous tubule is lined by the cells of the germinal epithelium, which divide and proliferate to form male gametes, i.e. sperms.
The function of testes is to produce spermsand male hormones- testosterone. The hormone testosterone controls normal growth of the genital organs and also regulates the development of secondary sexual characters.
Scrotum
It is a sac like extension of abdominal cavity containing testes. Besides providing protection to the testes, scrotum regulates the temperature of testes by contraction and relaxation of its muscular wall. The temperature in scrotum is 1–30 C less than the body temperature. This temperature is suitable for the development of sperms.
Epididymis
Epididymis is a pair of long convoluted tubules located in the scrotum. Each epididymis is closely attached to a testis and lies within the scrotal sac. Epididymis serves as a part of the channel through which sperms pass in order to reach the exterior. Epididymis functions to store sperms.
Vas deferens from the lower part of the epididymis emerges out a thick walled tube called vas deferens. It travels from the scrotumto the pelvic cavity. Behind the urinary bladder, it is joined by the seminal vesicle. The vas deferens, along with the seminal vesicle, opens into the ejaculatory duct.
Ejaculatory ducts of the two sides lead into urethra and the junction of the two remains surrounded by the prostate glands.
Urethra
It is a tube of about 20cm in length. Urethra is a common tube through which both urine and sperms are expelled out of the body. The distal part of urethra passes through the penis to open outside.
Penis
Penis is the muscular, erectile copulatory organ of man. It is made of 3 bundles of loose muscles. On being stimulated, the tissues of the penis get filled with blood making the penis erect and firm to discharge sperms. The distal part of the penis is called glans penis. It bears the opening of urethra through which urine and sperms are discharged.
Male accessory reproductive glands
Besides testes, certain other glands are present which remain associated with the male genital tract. These are as follows:
Seminal vesicles
The function of the seminal vesicles is to store sperms and to produce a viscous fluid which stimulates uterine contraction to help sperms move forward into the fallopian tube of female.
Sperm
Sperm is the male gamete. Sperm is a haploid cells formed inside seminiferous tubules in large numbers.
The fluid consisting of sperms suspended in secretions of the accessory reproductive glands is called semen. One milliliter of semen contains about 120 million sperms. The sperms are tiny bodies that consist of mainly genetic material and a long tail that helps them to move towards the female germ cell.
The female reproductive system
Puberty
A human female reaches at puberty usually between the ages of 11–13 years.
The female reproductive system includes the following organs.
(a) A pair of ovaries
(b) Fallopian tube
(c) Uterus
(d) Vagina
Ovaries
Ovaries are the primary sexual organs of a female. Two ovaries are located close to the lateral cavity, one on either side of the uterus. Ovaries serve two important functions. They produce the female sex cell or ova and secrete the sex hormones oestrogen and progesterone.
A matured ovary contains a large number of ova in different stages of development. Ova are produced by the germinal epithelium of ovary. The formation of ova begins in female foetus even before the birth of a baby. At birth, each ovary contains about 2–3 lakhs of immature eggs (primary follicles). After attaining sexual maturity (puberty), the primary follicles of ovary star maturing one by one under the influence of hormones from the pituitary gland. In a woman, one mature ovum is released from either of the ovaries at an interval of 28 days.
A mature ovum is surrounded by nutritive and protective cells and together they are called Graafian follicles. The process of release of ovum from ovary is called ovulation.
Fallopian tubes (oviduct)
These are paired tubes originated from uterus, one on either side. Fallopian tubes are extended up to the ovary of their respective side. The terminal part of fallopian tubes is funnel shaped with finger- like projections called fimbriae lying near the ovary. Fimbriae pick up the ovum released from the ovary and pushes it into the fallopian tube.
Uterus
It is a single, pear- shaped, highly muscular hollow structure present in the pelvic cavity between the urinary bladder and rectum. Development of foetus occurs inside uterus, hence it is also called, womb. The narrow lower part of the uterus is called cervix, which leads into the vagina.
Vagina
It is a tube which is about 7-10 cm. in length. During intercourse, penis is inserted into vagina for the discharge of sperm. Vagina acts as birth canal during child birth (parturition) and also serves as passage for menstrual flow.
Fertilization
Fertilization is internal. The sperms produced in the testes of male are transferred into the vagina of female through penis during the intercourse. Several million sperms are released during a single ejaculation. Fertilization takes place inside the inside the fallopian tube. The ovum released from the ovary during ovulation is swept into the adjacent fallopian tube. An unfertilized egg remains alive for about 24 hours post- ovulation; after that it degenerates. Fertilization must occur within 24 hours of the release of egg from ovary.
Fertilization results in the formation of the single cell called zygote. The zygote then undergoes repeated mitotic division to increase the number of cells in the zygote or embryo.
The embryo gets nutrition from the mother?s blood and special tissue called placenta. This is a disc which is embedded in the uterine wall. The developing embryo will also generate waste substances which can be removed by transferring them into the mother?s blood through the placenta. The development of the child inside the mother?s body takes nine months (270 days). The time taken from fertilization till the birth of a child is called gestation period. The act of delivering a baby is called parturition.
The child is born as a result of rhythmic contractions of the muscles in the uterus.
What happedns when the eggs is not fertilised?
The unfertilized egg lives for about one day. While the ovary release one egg every month. The uterus also prepares itself every month to receive a fertilized egg. Thus its lining becomes thick and spongy. This would be required for nourishing the embryo if the fertilization had taken place. The inner wall of the uterus, (endometrium), which is highly vascular also becomes ready to receive foetus. If a zygote is not formed, the endometrium breaks which causes bleeding through vagina. This mechanism is called menstruation.
Reproductive Health
Reproductive health means a total well being in all aspects of the reproduction, i.e. Physical, emotional, social and behavioural.
There are some aspects included under reproductive health
- Over population; its ill effects and need to check it.
- Knowledge of reproductive organs and sexually transmitted diseases.
- Sex educations and awadreness about reproduction.
- Birth control divices.
- Care of mother and child.