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Evolution is one of the Biology Topics that has been debated and studied for centuries, exploring the process by which species change over time.
Development of the Reproductive Organs and Secondary Sex Characteristics
The study of reproductive or sexual organs involving their structure and functions is called reproductive physiology. The phenomenon by which living beings produce offspring of their own kind is called reproduction. It is a process that involves the formation of new individuals of the same kind along with slight genetic, structural, and physiological variations. Living beings reproduce to maintain life and to continue their own race in the universe. By reproduction living beings also increase in number. Human beings are unisexual animals. They perform sexual reproduction by the union of germ cells or gametes produced by male and female individuals separately.
Human reproduction is a form of sexual reproduction, typically involving sexual intercourse between a man and woman resulting in fertilization. Humans are unisexual organisms in which males and females both sexes are separate. Male and female can be distinguished from their external features and sexual dimorphism is also noticed in them.
Each cell in a normal adult male and female possesses 46 chromosomes (44 autosomes + 2 sex chromosomes). These chromosomes exist in pairs (22 pairs of autosomes + 1 pair of sex chromosomes) and are referred to as diploid chromosomes. Sex chromosomes are called X and Y chromosomes. Females possess 44 autosomes plus two X chromosomes (44 + XX) whereas males possess 44 autosomes plus an X and a Y chromosome (44 + XY). The mature male gametes are called sperms and mature female gametes are called ova. As a result of meiosis division the mature sperm and ovum contain half the number of chromosomes i.e., 23 (22 autosomes + 1 sex chromosome). This is called a haploid number. Now when an ovum (22 + X) is fertilized by a sperm containing (22 + X) chromosomes, the resultant zygote will be of female genotype i.e., 44 + XX and diploid in number and when an ovum (22 + X) is fertilized by a sperm containing (22 + Y) chromosomes, the resultant zygote will be of male genotype (44 + XY). Thus during fertilization, haploid cells from each parent united together to form a diploid zygote.
Reproductive System
Those organs which are involved in the process of reproduction, are combined or united to form a system, called the reproductive system. The male reproductive system of humans is located in the male human body, and the female reproductive system is located in the female human body.
Primary and Secondary Sex Organs
These are organs in the body that are involved in the phenomenon of reproduction. They are different in structure and functions for both males and females.
The sex organs are primary and secondary:
1. Primary Sex Organs: Such sex organs produce germ cells. These are
- In male: A pair of testes which produce sperm.
- In females: A pair of ovaries produce an ovum.
2. Secondary Sex Organs: These are sex organs other than the primary sex organs which do not produce germ cells but help in reproduction.
Male secondary sex organs are Epididymis, Vas deferens, Seminal vesicle, Ejaculatory duct, Prostate gland, Cowper’s gland, Urethra, Penis, and Scrotum.
Female secondary sex organs are the Fallopian tubes, Uterus, Bartholin’s gland, Clitoris, Vagina, Vestibule, Mammary glands, Mons pubis, Labia major, and Labia minora.
External Sex Organs
These are sex organs that are viewed externally.
- In males: The scrotum locates the testis, Penis.
- In female: Clitoris, Vagina, Vestibule, Mammary glands.
All other sex organs in both males and females are internal.
Differences between Primary Sex Organs and Secondary Sex Organs:
| Primary Sex Organs | Secondary Sex Organs |
| 1. Primary sex organs produce gametes. | 1. Secondary sex organs do not produce gametes but they are involved in the conduction of gametes. |
| 2. These type of sex organs secret sex hormones. | 2. They do not secrete sex hormones. |
| 3. Primary sex organs in female is the ovary and in male is testes. | 3. Epididymis, vas deferens, penis, prostate, scrotum, etc., are male secondary sex organs and fallopian tube, uterus, mammary glands, etc. are the female secondary sex organs. |
Puberty
Puberty is the time period when the gonads develop both endocrine and gametogenic functions and generally marks the onset of reproductive life (reproductive life starts functioning). The age of onset of puberty lies between 12 and 16 years, but puberty occurs earlier in females than in males, and it ceases in old age.
Changes in Puberty
During puberty, the following 3 types of changes take place.
- Physical Changes: In males, the body becomes more muscular and taller, the appearance of a beard and mustache; voice breaks, and pubic and axillary hairs grow. In females breasts develop, the muscle mass and muscle strength also increases but the increase is far greater in male than in females. Softening of female muscles etc.
- Sexual Changes: The gonads develop in both females and males, producing mature gametes. Mainly the secondary sex characters develop. In females the appearance of breast buds, enlargement of the breast, breast areola begins to elevate and project, menstruation starts, etc. In males, genital development begins, with the enlargement of the penis, and further growth of the testis, penis, and genitalia.
- Mental Changes: Appearance of sexual desire occur in both male and female (opposite sex attracts).
Disorders of Puberty
Disorders of puberty are mainly related to the time of its onset.
Early onset of puberty (precocious puberty), Late onset of puberty (delayed or absent puberty).
1. Precocious Puberty:
It refers to the onset of puberty in a child before the age of 8 years. This type of puberty is mainly seen in girls. The clear cause of this type of puberty was not found. Though it is thought that any damage in the brain (hypothalamus or pituitary) causes pulsatile secretion of gonadotropin-releasing hormone cases the onset of too fast puberty, or precocious puberty. It is also called true puberty or complete puberty.
2. Delayed or Absent Puberty:
In some individuals, there is a failure in the development of accessory sex organs as well as a lack of development of secondary sex characteristics. This condition is called delayed puberty. It is more commonly observed in boys than in girls. Generally, it is a physiological delay, and ultimately child catches up. In some circumstances, puberty is absent even when gonads and other endocrines function normally. This condition in males is called eunuchoidism and in females is called primary amenorrhoea.
Secondary Sex Characters
These are external and internal characteristics that develop during puberty in both males and females between 14-18 years of age.
Male Secondary Sex Characters:
- The body becomes more muscular and the shoulder becomes broad.
- Beard and mustache develop in the face.
- Hairs appear in the axilla, chest, lower abdomen, and pelvic region.
- Penis increases in length and breadth.
- Scrotum becomes pigmented.
- Testes, prostate gland, and Cowper’s gland are enlarged.
- Larynx and vocal cords are increased.
- The voice becomes rough and deep.
- The mind becomes active and aggressive.
- Attraction develops towards the opposite sex (female).
Female Secondary Sex Characters:
- The body becomes soft and attractive due to the deposition of subcutaneous fat.
- Skin becomes thin, soft, and smooth.
- Mammary glands and vagina are enlarged.
- Hairs appear in the axilla, pelvic region, and around the vulva.
- The pelvic region becomes broad.
- The voice becomes high-pitched.
- The onset of menstruation.
- Attraction develops towards the opposite sex (male).