Class 8 Science
Age of Adolescence
Adolescence: Adolescence is the period of life when many changes take place in the body; leading to reproductive maturity. Adolescence begins at around 10 years of age and lasts till 18 or 19 years of age.
Teenage: The years during adolescence period are counted as ‘teen’, .e.g. thirteen, fourteen and fifteen. Hence, this period is also called teenage.
Puberty: The process of changes during adolescence period is called puberty. Beginning of puberty marks the beginning of adolescence. The end of adolescence or puberty marks the completion of reproductive maturity.
Changes at Puberty
- Increase in Height: The most apparent change during puberty is the sudden increase in height. Long bones grow rapidly and hence height of a person increases rapidly during this period. Initially, girls grow faster than boys but ultimately boys are usually taller than girls. The maximum height is attained by 18 years of age.
- Change in Body Shape: The body of a boy becomes more muscular. His shoulders become wide and waist becomes narrow. The body of a girl becomes wider below waist and narrower at shoulder.
- Voice Change: A boy’s voice becomes deep, and the child like voice is first replaced by a hoarse voice. This happens because the voice is said to crack. Gradually, the voice becomes deep. The change in voice happens because voice box in a boy becomes larger. Girl’s voice is usually high pitched.
- Increased Activity of Sweat and Sebaceous Glands: Secretion from sweat and sebaceous glands increases during adolescence. Due to this, some teenagers may suffer from acne and pimples.
- Development of Sex Organs: In boys, testes begin to produce sperms. Testis and penis develop completely. In girls, ovaries enlarge and eggs begin to mature. Ovaries start releasing mature egg.
- Reaching Mental, Intellectual and Emotional Maturity: These changes also have a profound effect on a person’s way of thinking. Teenagers spend more time on thinking than earlier. So many rapid changes in the body may create a sense of insecurity in most of the teenagers. But teenagers should not worry because these are natural changes.
Adam's Apple: Enlargement of voice box is apparent as a prominent protrusion in the neck. This protrusion is called Adam’s apple.
Secondary Sexual Characters
Characters which help in distinguishing a male from a female are called secondary sexual characters. Marked difference between male and female of a species because of apparent physical traits is called sexual dimorphism.
- Secondary Sexual Characters in Boys: Facial hairs, deep voice and hair on chest.
- Secondary Sexual Characters in Girls: Enlargement of breasts and high pitched voice.
- Some common characters in girls and boys: Hair under armpits, hair in pubic region.
Hormonal Control
The changes during this period are controlled by hormones. Hormones are substances secreted by endocrine glands. Hormones play important role in various metabolic activities.
In boys, testis secretes the hormone testosterone. This hormone is responsible for many changes in boys. In girls, ovaries secrete the hormone estrogen. This is responsible for development of breasts.
Action of these hormones is under the control a hormone secreted by pituitary gland. Another hormone from pituitary gland stimulates the maturation of eggs and production of sperms. Endocrine glands are ductless glands; which means that a hormone reaches the target site through bloodstream.
Reproductive Phase of Life in Humans
The reproductive phase begins with the onset of puberty and it happens at around the same age in boys and girls. But reproductive phase in men lasts much longer than in females. Reproductive phase in women lasts till about 50 years of age. Reproductive phase in men lasts even beyond 60 years of age.
Menstruation: In females, one egg is released by either of the ovaries during each month. After that, the uterus develops a thickening to support a foetus to prepare for a possible pregnancy. If fertilization does not take place; egg and thickening in uterus are discarded in small fragments. This results in bleeding through the vagina for some days. The bleeding (through vagina) at the end of menstrual cycle is called menstruation.
Menstrual Cycle: The cycle of events which begin from release of an egg and end in shedding off egg is called menstrual cycle. A menstrual cycle is usually of 28 to 30 days.
Menarche: The first menstrual bleeding in a girl’s life is called menarche. Menarche marks the beginning of puberty in girl.
Menopause: Cessation of menstrual cycle is called menopause. This happens at around 45 – 50 years of age. Menopause marks the end of reproductive phase.