Reproduction : Reproduction is the process by which an organism produces the same species.
Types of reproduction :
(a) Asexual reproduction
(b) Sexual reproduction
(A) Asexual reproduction : This involves the production of animals without any fertilization and zygote formation. This is of following types :
(i) Binary fission : Amoeba, Euglena, Paramecium, Vorticella, Aurelia, etc.
(ii) Multiple fission : Plasmodium, Amoeba, Monocystis etc.
(iii) By budding : Sponges, Hydra, Planarians etc.
(iv) Fragmentation : Hydra, Planarians etc.
(v) Regeneration : Sponges, Hydra, Planarians, some Echinoderms etc.
(B) Sexual reproduction : In this fusion of two different sex gametes of same species forming zygote takes place. This is of following types :
(i) Syngamy : By autogamy (Paramecium), exogamy, anisogamy and isogamy.
(ii) Conjugation : Paramecium involving gene mixing.
(iii) Automixis : Paramecium.
(iv) Endomixis.
(v) Hemixis.
Parthenogenesis : Ova or sperm without fertilization produces the similar animals. This is called parthenogenesis. e.g. bees, hydra, wasp. Parthenogenesis is found in protozoa also.
Reproduction in man
Male reproductive organs : One pair of testes found suspended in the scrotal sac of man. From every testes a duct arises which consists of epididymis and vas deferens opens into ejaculatory duct and urethra. Male reproductive glands are one prostate, two seminal vesicles, two Cowper’s glands and the male intermittent organ is penis.
Testes are attached in the scrotal sac and are extended to abdominal cavity. Both these cavities are communicated by a canal known as inguinal canal. Testes produce the sperms. Sperms alongwith the secretion of prostate, Cowper’s glands and seminal vesicles form the semen.
A fibrous strip arising from anterior end of testis is joined with the dorsal wall of abdominal cavity. This strip alongwith adjoining structures viz. spermatic artery, vein and nerve are called spermatic cord.
Epididymis is the centre of sperm maturation and collection. It is about 6 metres in length. Penis is made up of spongy tissues. Its upper swollen end is called glans penis. Skin which covers glans penis is called prepuce.
Prostate gland : The fluid it secretes is milky white in colour and forms about 15-30% of semen. It gives odour to semen.
Cowper’s glands secret an alkaline liquid which reduces concentration of semen.
About 20-40 crore sperms are ejaculated in semen of which only 80% are live.
Female reproductive organs : One pair of ovaries, oviducal funnels, fallopian tubes, unpaired uterus and vagina are the organs of female reproductive system. The female reproductive glands are Cowper’s glands and perineal glands.
Ovaries are found attached dorsally in the abdominal cavity by the mesodermal tissue which is known as mesovarium. The oviducal funnel are attached to this tissue.
Oogenesis takes place in graafian follicles and forms one ovum and three polar bodies. The menstrual cycle consists of two phases—the proliferative and secretory phases. In the proliferative phase the walls of uterus, fallopian tubes and vagina grow and proliferate. In this phase the graafian follicles grow, mature and secrete the hormone estrogen and lastly the ovum is released from the follicle. In the secretory phase the formation of corpus luteum from the graafian follicles takes place which acts as an endocrine gland and secretes protesterone. The degeneration of corpus luteum marks the end of this phase. The overgrown endometrium breaks and menstruation’s initiation takes place.
The proliferative phase and secretory phase are also known as follicular and luteal phase respectively. Both phases are controlled by estrogen and progestrone respectively. The cyclic changes of these hormones are due to the cyclic changes in the secretion of gonadotropins from the anterior pituitary.
Uterus : Uterus is pear shaped in structure situated in the pelvic region of abdominal cavity. Outer muscular layer of uterus wall is called myometrium and inner endometrium. Lower narrow end of uterus is called cervix: Fallopian tubes open into uterus.
In the walls of vagina bulbourethral glands are found. Their secretion lubricate vagina at the time of coitus. Above the vagina near upper end of labia minora, clitoris is found. It resembles penis in structure.
Fertilisation : When a male mates with a female, sperms are introduced by the male into vagina of the female. The sperm move into the uterus, and then to the oviduct or fallopian tube and one of them fuses with egg, forming a zygote. This process is known as fertilisation.
Artificial insemination : This is the method by which the females of many animals are made pregnant by artificially depositing the sperm in their vagina.
Puberty : It refers to the age after which a person becomes able to produce sperms in the case of males or to undergo menstruation in the case of females.
Precocious puberty : At onset of menstruation cycle at an age earlier than the normal in case of females is known as precocious puberty.
I.U.D. : It is intra-uterine device (IUD) which is placed in the uterus of the female to prevent inplantation of the fertilised ovum.
Mesovarium : The ovaries in females are kept in the position in the abdomen by mesenteries called mesovarium.
Menopause : It is the age after which female (human) does not have the reproductive capacity and menstruation cycle stops. This is generally occured at the age of 45-59. After the menopause the ovarian cycle or menstruation cycle is stopped.
Tubectomy : It is a surgical procedure that involves the removal of a small segment of the oviduct of a female and two cut ends are tied separately.
Vasectomey : This is a surgical method which involoves the removal of a small segment of vas deferns and two cut ends are tied separately with thread.
Gametogenesis : It is the process of sperm formation in the testes and ova formation in ovary. The first process is known as spermatogenesis and the second process is known as oogenesis.
Menstruation : This refers to a series of cyclic changes in the reproductive tract of female.
Estrus cycle : It involves of cyclic changes in the female reproductive system of non-primate mammals.
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