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10. Reaching the Age of Adolescence

This chapter talks about physical and hormonal changes leading upto reproductive maturity

We have learnt in the chapter ‘Reproduction in Animals’, that only after human beings and animals reach a certain age, they can reproduce.

Growing up is a natural and ongoing process in one’s life & growth begins from the day one is born.

10.1 Adolescence

Adolescence is that period of life, when the body undergoes changes, leading to reproductive maturity. It begins around the age of 11 & lasts upto 18 or 19 years of age. As this period covers the ‘teens’, adolescents are also called as ‘Teenagers’.

Puberty is the process of physical changes by which a child’s body becomes an adult and becomes capable of reproduction.

The following changes occur at Puberty

10.1.1 Increase in Height

The most visible change during puberty is the sudden increase in height, as during this time, the long bones, that is, the bones of the arms & the legs elongate & make a person tall. Both boys & girls reach their maximum height by the time they reach the age of 18. The growth rate varies from individual to individual. The maximum height a person will acquire depends on the genes inherited from parents. Adequate nourishment is also required for the bones, muscles & other body parts for growth.

10.1.2 Change in Body Shape

The changes that occur in boys during adolescence is different from the changes occurring in girls.

In boys, the body muscles grow more prominently & their shoulders broaden.

In girls, the region below the waist becomes wider.

10.1.3 Voice Change

There is a noticeable change in the voice of boys during puberty. Their voice begins to crack & becomes deeper over a period of time. It is so because, boys have larger voice bones. The growing voice bon can be noticed as a protruding part of the throat & is called as Adam’s apple. There is no noticeable change in the voice of the girls during puberty.

10.1.4 Increased Activity of Sweat & Sebaceous Glands

During puberty, the secretion of sweat glands & sebaceous glands (oil producing glands) increases. Due to increased activity of sebaceous glands, lots of people get Acne

10.1.5 Development of Sex Organs

At puberty, male sex organs like testes and penis develop completely and the testes also begin to produce sperms. In girls, the ovaries enlarge & eggs begin to mature & ovaries start releasing mature eggs.

10.1.6 Reaching Mental, Intellectual & Emotional Maturity

During this phase, a child goes through many mental and emotional changes. Some of them are listed below

  1. Adolescence is a period of change when a person starts thinking more maturely.
  2. Adolescents are more independent than before.
  3. They become more self-conscious.
  4. Intellectual development takes place & they tend to spend lot of time thinking.
  5. During adolescence, brain has the greatest capacity for learning.
  6. Sometimes, adolescents find it difficult to adjust to the changes happening in their body & mind.

10.2 Secondary Sexual Characters

Secondary Sexual characters are the features which help to distinguish the males from the females.

The following are the secondary sexual characters of males

  1. Facial hair – moustaches & beard
  2. Hair on the chest
  3. Hair under the arms and in the pubic region (surrounding the genitals)

The following are the secondary sexual characters of females

  1. Develop breasts during puberty
  2. Hair under the arms and in the pubic region

10.3 Hormones and Reproduction

The changes at puberty in males and females are triggered by secretion of male and female hormones respectively. Hormones are chemical substances produced by the endocrine glands. Male hormone is called Testosterone and female hormone is called Estrogen

Endocrine glands are such glands that produce their secretions (hormones) directly into the blood rather than through a duct. For example

  1. Pituitary gland
  2. Pancreas
  3. Ovaries
  4. Testes
  5. Thyroid gland

Pituitary gland is small (about 0.5 grams in weight) pea sized gland, present in brain. It secretes various hormones in blood, which stimulate the target sites (testes and ovaries) to secrete their hormones.

Testosterone and Estrogen released by these glands is again released into the blood and reaches the target sites to trigger various body changes such as growth of facial/pubic hair and growth of breasts & mammary (milk producing) glands.

10.4 Reproductive Phase in Humans

Adolescents become capable of reproduction when their testes & ovaries begin to produce gametes. The capability for maturation & production of gametes lasts for a much longer time in males than in females.

10.4.1 Reproduction phase in Females

The reproduction phase of females starts at puberty (at the age of 10-12 years) & generally lasts till the age of approx 45-50 years.

Menarche – The first menstrual flow in females begins at puberty and is called menarche. Once started, menstruation occurs once in about 28-30 days.

Menopause – The stopping of menstrual cycle is called as Menopause. Menopause occurs at the age of 45-50 years.

Menstrual Cycle consists of the following phases. This cycle repeats every 28 days.

Duration Activity
Days 1 to 7 Menstruation
Days 8 to 11 The lining of the uterus (womb) thickens in preparation of the egg
Day 14 Ovulation of egg
Days 18 to 25 If fertilization has not taken place, the uterine lining will start fading
Days 26 to 28 The uterine lining detaches leading to menstruation


10.4.2 Chromosomes and Sex of the baby

Gametes (egg and sperm) contain thread-like structures called chromosomes, which contain genetic material. Both egg and sperm have 23 pairs of chromosomes. Out of these, 2 chromosomes determine the sex of the zygote. These are called X and Y chromosomes.

Eggs have 2 X chromosomes while sperms contain 1 X and 1 Y chromosome. When an egg is fertilized by a sperm, the resultant zygote may contain

  • 1 X chromosome from egg + 1 X chromosome from sperm. This would result in the zygote being a female
  • 1 X chromosome from egg + 1 Y chromosome from sperm. This would result in the zygote being a male

In both the above cases, it is the variation of the chromosome contributed by the sperm that results in different sex of the child.

10.5Endocrine glands and Hormones

There are multiple endocrine glands in human body and have different functions. In addition to Ovaries and Testes, the following are the other important glands

Gland Hormone Relevance
Pituitary gland Various hormones The hormones released by Pituitary gland are responsible for
  • Stimulating testes & ovaries to produce their hormones
  • Stimulating Thyroid & Adrenal gland to secrete their hormones
  • Secreting Growth Hormones which are necessary for the normal growth of a person
Pancreas Pancreas is a gland present below the chest and produces a hormone called Insulin Insulin regulates the metabolism of fat and carbohydrates in the body. Lack of sufficient insulin causes Diabetes
Thyroid gland Thyroid gland is present in the throat and produces a hormone Thyroxine Thyroxine is responsible for regulation of metabolism in cells. Improper functioning of Thyroid gland can lead to a disease called Goitre. This causes thyroid glands to enlarge
Adrenal gland Adrenal Glands are present near the kidneys and produce Adrenaline Adrenaline increases the heart rate, contracts blood vessels, dilates air passages and mobilize body’s resources in response to stress (anger, danger, worry etc)

Hormones are present in animals as well. Metamorphosis (change from Larva to adult) in insects is controlled by insect hormones.

In Frog, the metamorphosis is controlled by hormone thyroxine, which is produced by Thyroid. Thyroxine production requires the presence of Iodine in water. If the water, in which the tadpoles are growing, does not contain sufficient Iodine, the tadpoles cannot become Adults.

10.6Reproductive Health

Every individual needs to have a well balanced diet for physical & mental well being. However, during adolescence, the need for a well balanced is more because the body is growing.

10.6.1 Nutritional Needs during Adolescence

The diet of an adolescent has to be a well balanced diet which includes proteins from all the food groups like dal, vegetable, roti/rice. Fruits also provide nourishment. Milk is a balanced food in itself. Iron builds blood & iron rich food such as leafy vegetables, jaggery, meat and amla are good for adolescents.

10.6.2 Personal Hygiene

As sweat glands are more active in adolescents, all body parts should be washed & cleaned every day. If hygiene is not maintained, there may be chances of catching bacterial infections.

10.6.3 Physical Exercise

All young boys & girls should play outdoor games as it keeps the body fit & healthy.

10.6.4 Drugs

During adolescence, the body & mind are very active and it is a part of growing up. Sometimes, adolescents feel confused & insecure. During this period of insecurity, if someone suggests to try Drugs, as they give relief, do not believe them & say ‘No’ to drugs as they are addictive.

10.6.5 HIV & AIDS

HIV (Human Immunodeficiency Virus) is a dangerous virus which causes AIDS (Acquired Deficiency Syndrome). There is currently no cure for this disease. It gets transmitted by the following ways

  1. Sexual contact with an HIV positive person
  2. Transfer of infected blood or sharing of syringes contaminated with infected blood
  3. From infected mother to an infant at birth
  4. From infected mother to an infant through breast milk