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Reproduction in Animals

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Reproduction in Animals - Lesson Summary

Reproductive phase is the phase in the life of every individual which makes the individual capable of reproducing the offspring. In the early reproductive phase, individuals acquire changes in the body which result in the formation of germ cells. Sperms are male germ cells and eggs are female germ cells. Reproductive phase involves the changes in appearance and size of the bodily organs.

Puberty: It is the time during which there occur sexual and physical changes which allow the transition of a child to an adult. Puberty starts at the beginning of adolescence. The onset of puberty starts much earlier in girls, between 8 and 13 years of age lasts 2 to 4 years. The onset of puberty is marked by physical changes. A child becomes an adolescent. 
  • Different changes in boys include change in the voice, active functioning of sweat and sebaceous glands, growth of facial and body hair, enlargement of penis etc.
  • Different changes in girls include growth of pubic hair, active functioning of sweat and sebaceous glands, menstrual cycle, enlargement of breasts.

Adolescence: It is the period of life between the onset of puberty and reaching adulthood, that is, the period that leads to reproductive maturity. Adolescent is a general term for teenagers of both sexes. Adolescence is the period of life that leads to reproductive maturity, making a person capable of reproduction. 

Male reproductive system:  This system includes a pair of testis, vas deferens and a muscular organ, the penis.
 
a) Testes: Testis is the main reproductive organ in males. A pair of testis is placed in a structure called as scrotum which is located outside the abdominal cavity. At lower temperature maintained by the scrotum, testes produce sperms by the process of spermatogenesis. Sperms are the male gametes possessing a head, body and a tail. Testes also secrete male sex hormones like testosterone to regulate the development of sperms and the secondary sexual characteristicsleading to puberty.

b) Vas deferens: Sperm duct is also known as vas deferens. They are two in number, each one arising from testis placed on either side. They transport sperms into penis. They also collect fluids secreted by different glands. These secretions are rich in proteins to enrich the sperms. Sperms along with these secretions form thick substance called as semen. Semen is conveyed to urethra through which it is discharged outside. Prostate gland and seminal vesicles secrete semen to make the movement of sperms easier.

c) Urethra: Urethra forms a common passage for both the sperm and urine as it is just one tube that connects both the glands – urinary bladder and vas deferens.
d) Penis: It is a part of male reproductive system. Penis is a muscular organ which transfers semen into female reproductive tract. Penis receives both urinary tube and sperm duct and serves as a common transporting organ for urine and semen. It opens out through a small tube called as urethra. Penis is underlined by thin blood vessels which give it continuous supply of blood.

Testes are placed in a structure called as scrotum which is located outside the abdominal cavity. Scrotum helps in keeping the testes at lower temperatures. Testes produce the male gametes known as sperms. Sperms are the male gametes possessing a head, body and a tail. Testosterone is the male sex hormone secreted by the testes. It regulates the development of sperms and the secondary sexual characteristics leading to puberty.  

Female reproductive system:  This system includes a pair of ovaries, a pair of oviducts, uterus and vagina opening out through urethra. 
 
a) Ovary: A pair of ovaries forms the gonads in female. Ovaries are the female sex organs that lie one on either side of the abdominal cavity. Ovaries by the process of oogenesis form eggs or ova which are released as one per month. Ovaries produce two hormones, namely, estrogen and progesterone.Estrogen controls the changes that occur during puberty, like feminine voice, soft skin and development of mammary glands, growth of pubic hair and controls the release of mature eggs.Progesterone controls the uterine changes during menstrual cycle, and helps in the maintenance of pregnancy.

b) Oviducts: A tube like structure arising from each ovary on either side is called as an oviduct. This is also called as fallopian tube. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube.The two oviducts combine and open into an elastic bag-like structureknown as the uterus.

c) Uterus: Uterus is a hollow muscular organ which has the capacity to bear the child. It is otherwise called as womb. Zygote formed after fertilisation in the fallopian tube travels downward by dividing itself continuously to form an embryo. Embryo as it reaches the uterus gets implanted into the wall of the uterus. After fertilisation, female reproductive hormones bring in many changes to the uterus, so as to bear the growing embryo. As the embryo grows, it transforms into foetus. Uterus is the organ which bears the foetus.

d) Vagina: It is the reproductive part situated at the end of the uterus in female reproductive tract. It connects uterus to the outside world. Vagina secretes mucous to keep the tract wet. It opens out through vulva.

Eggs, the female gametes develop inside the ovaries.  One mature egg is released by either of the ovaries per month. Ovaries secrete two hormones namely estrogen and progesterone which bring about secondary sexual characters in females. The egg is carried from the ovary to the uterus through a thin oviduct also known as the fallopian tube. The two oviducts combine and open into an elastic bag-like structure known as the uterus. The uterus opens into vagina through cervix. The uterus helps in the development of the foetus.

Fertilisation: Fertilisation is the fusion of male and female gametes to give rise to a single cell – zygote. Fertilisation can be external fertilisation or internal fertilisation.
  • When male and female gametes unite outside the body, it is called external fertilisation
  • When fertilisation takes place inside the body, it is called internal fertilisation.
  • When fertilisation takes place in a test tube, the offspring are called test tube babies.
  • Fertilisation that takes place outside the human body is in vitro fertilisation.

Zygote:  It is the super cell formed by the fusion of pronuclei of male and female gametes. It  divides repeatedly to form an embryo.

Embryo: It is transformed zygote with a three layers of cells. This  gets embedded in the wall of uterus, part of the female reproductive system.The development of the embryo takes place in the mother’s uterine wall.All parts of the body start developing in an embryo which finally transforms itself into foetus.

Implantation:   Embryo gets implanted in the lining of the uterus for further development. The placenta is a connective tissue established between foetus and the mother.  It provides a large surface area for the nutrients and oxygen to pass from mother to the embryo. It also helps in transporting excretory wastes from embryo to mother.

Menstruation:  The monthly cycle of changes in the ovaries and the lining of uterus resulting in periodic discharge of blood, mucous and cellular debris through vagina in the absence of fertilisation.  This cycle takes place roughly every month and is controlled by ovarian hormones. Menses lasts for two to eight days.

Contraceptive devices :  These are the devices which block the entry of sperm into oviducts thereby preventing the egg from being fertilized. 
  • Condom is a barrier method falling under the category of contraceptive methods. Condoms are available for both males and females. These structures act as barriers which prevent sperm from meeting the ovum. Condoms are made up of thin rubber or latex sheath.
  • The Copper T is a simple intra-uterine device (IUD) made of a flexible, "T" shaped piece of plastic wrapped with a thin copper containing wire. It is a contraceptive device which prevents from getting pregnant. Copper ions prevent pregnancy by inhibiting the movement of sperm as they are toxic to sperm. 
  • Other than this copper T cannot inhibit the action or kill bacteria or viruses which cause different STDs.
  • Vasectomy is the surgical method executed for permanent birth control in males. It is the sterilisation technique by which vas deferens from the testis is cut or tied to prevent the mixing of sperm with the semen ejaculated from the penis. Semen of vasectomised males will not have sperms in them. As semen is devoid of sperms, there occurs no fertilisation of ovum produced by females.
  • Tubectomy is a surgical method performed in females as a birth control method. It is a permanent contraceptive method. Fallopian tubes emerging out of the ovaries on either side are cut and tied. This is a permanent contraceptive method as there occurs no fertilisation in the fallopian tube. Ovum cannot reach the fallopian tube and wait there for the sperm coming to fertilise it.  

Reproductive health: It is a state of physical, emotional, mental and social well-being in relation to sexuality. Reproductive health requires positive approach to sexuality and healthiness of the individuals participating in mating. Reproductive health also refers to the capability of satisfying the partner. It also specifies the ability and freedom to reproduce.

Sexually transmitted diseases:  STD stands for Sexually Transmitted Diseases. These are the diseases which are transmitted from one person to another during the sexual act between two individuals. STDs can be caused by different microorganisms like bacteria, fungi, virus, protozoans etc. STDs can mostly be prevented from transmission from one individual to another by using protective or contraceptive devices. Gonorrhea, Syphillis, AIDS etc are some of the examples of STDs. 

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