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Revision Notes on Reaching the Age of Adolescence

Adolescence and Puberty

  • Animals, as well as human beings, can reproduce only after a certain age or time period in their lives after growing up into an adult.

  • This is because of changes in hormones in their bodies that make them capable of reproduction.

What is adolescence?

  • It is a time period in life when the body leads to reproductive maturity and experiences some changes.

  • This time period may vary in different individuals.

  • The adolescence period includes the teenage and therefore adolescents are often called Teenagers as well.

Adolescent Period in  Begins at age around  Ends at age around 
Boys  11 years  18 or 19 years 
Girls  10 or 11 years  18 or 19 years 

 Time Periods in Human Life

Figure 1: Time Periods in Human Life

What is puberty?

  • Puberty is the time period in life when animals and human beings become capable of reproduction.

  • The changes that occur in the body during the adolescent age are an indication that an individual is reaching puberty.

Changes at puberty

What changes occur in humans at puberty?

Changes Explanation

The height increases suddenly

  • The bones of the legs in the arms of a person start to grow longer and hence a person becomes taller in the puberty age.

  • This increase in height occurs until the age of 18 in both boys and girls.

  • However, it is observed that girls grow faster than boys initially.

Change in the shape of the body

  • As boys and girls enter into the time period of puberty their body shapes start to change.

  • The boys generally experience a change in chest and shoulders as they become wider.

  • In girls, the area below the waist becomes wider.

  • However, the changes in boys and girls are different because the muscle growth in boys is higher than that in girls.

Change in voice

  • A change in voice is accomplished as the body hits puberty, especially in boys.

  • The voice box or the larynx develops in boys.

  • It can also be seen as an enlarged part of the throat in boys and is named as Adam's Apple.

  • Boys also experience a hoarse voice for some time due to the changes in the larynx.

  • The larynx in girls, on the other hand, is not visible because of its smaller size.

Increased sweat and oil production in the skin

  • There are sweat glands and oil glands (called sebaceous glands) present in our bodies which start secreting more oil and sweat during the puberty age.

  • Many times girls and boys get acne and pimples on the face during the excess secretion of these glands.

Development of sex organs

  • By the time girls and boys hit puberty the reproductive organs are developed completely.

  • In males, the sperm production begins.

  • In females, the size of the ovaries increases and it starts releasing the eggs.

Mental, emotional and intellectual maturity

  • During the adolescent age, the brain has the maximum learning power.

  • The way of thinking of individuals starts to change.

  • It is also observed that girls and boys start feeling self-conscious.

  • They may also feel a little uncomfortable and insecure due to sudden changes in the body. However, all these changes are completely normal.

Adam's Apple in Boys

Figure 2: Adam's Apple in Boys

What happens due to a sudden increase in height of adolescents?

  • It may not happen that all the parts of the body would grow at the same rate in this age.

  • Hence, sometimes the legs and arms of teenagers appear oversized or not in proportion with respect to their bodies.

  • But with time everything comes in proportion.

Why height of family members is generally similar?

  • The height of a person is a characteristic that they receive from their parents.

  • Hence, in general, the height of a person is similar to the height of a family member.

  • But it is also recommended that adolescents should eat a proper diet which is rich in vitamins, minerals and other nutrients that can help in their growth.

What are secondary sexual characters?

  • At puberty, some changes occur in both males and females that distinguish them from each other. The features that develop in them are called Secondary Sexual Characters.

  • In boys some secondary sexual characters are:

    • facial hair growth

    • growth of hair on the chest, under the arms and pubic area

  • Some secondary sexual characteristics in girls are:

    • development of breasts

    • the growth of hair under the arms and the pubic area

How the changes in the human body occur at the time of puberty?

What are hormones?

There are endocrine glands present in humans with secrete chemical substances in the body is called the Hormones. These chemical substances are responsible for changes in the human body at the time of puberty.

The hormones act as messengers and are responsible for transporting signals for one cell to another.  Hence they evoke responses from various organs of the body and tissues. Hormones have certain properties or characteristics such as:

  • They are secreted by the endocrine glands.

  • They circulate in the body fluids.

  • They are responsible for regulating the behaviour of the target cells.

  • They cause long term effects in the body like change in behaviour, change in growth, development of organs, puberty menopause etc.

  • Hormones are secreted in limited quantities from time to time whenever they are required by the body.

  • Different glands present in the body are responsible for secretion of different hormones.

  • The nervous system regulates the flow of hormones in the body. 

The endocrine glands are also called Ductless Glands because they secrete the hormones directly into the blood. In males, the testes secrete the male hormones or the testosterone. In females, the ovaries secrete the female hormones or the estrogen.

The Endocrine Glands in Humans

Figure 3: The Endocrine Glands in Humans

What are pituitary glands?

There are pituitary glands present in the body switch control the production of the hormones by endocrine glands in both males as well as females.

Role of hormones in initiating the Reproductive Function

The part of the body for which a particular hormone is meant is called the Target Site. The endocrine glands secrete the hormones in the blood and it reaches the target site. Then the target site response accordingly.

Hormones initiate puberty

Figure 4: Hormones initiate puberty

Reproductive Phase of Life in Humans

The ability of production of gametes in humans last until certain time period only. This time period varies between males and females.

Reproductive Phase in Females

  • It begins from the age of 10 to 12 years and lasts until the age of 45 to 50 years.

  • When females hit puberty, the eggs or ova start getting mature.

  • One of the ovaries then releases the mature ovum around 28 to 30 days.

  • The wall of the uterus at this time, when the egg is released, becomes thick to hold the egg in case if fertilization occurs and the egg develops.

  • When the fertilization does not take place, the lining of the uterus sheds along with the egg and the blood vessels.

  • This results in menstruation or bleeding in females.

  • The first menstrual flow occurs at puberty and is called the Menarche.

  • When the menstrual flow stops, it is termed as Menopause.

  • The whole menstrual cycle occurs because of female hormones.

Determining the Sex of the Baby

  • We know that there are 23 pairs of chromosomes present inside the nucleus of every human cell.

  • These chromosomes have a thread-like structure and they always occur in pairs.

  • The chromosomes help in determining the sex of the child.

  • Out of the 23 pairs of chromosomes, 2 of them are sex chromosomes called X and Y.

  • Females have two X chromosomes and males have one X and one Y chromosome.

  • The gametes contain only one set of chromosomes that is either an X or a Y.

  • The egg of the female contains an X chromosome always.

  • However, the sperm can contain only one of the X and Y chromosomes.

  • So if the sperm that contains a Y chromosome fertilizes with the egg which contains the X chromosome, the zygote develops into a male.

  • On the other hand, if the sperm contains an X chromosome and fertilizers with the egg which contains X chromosome, the zygote develops into a female.

  • Hence the sex of the child depends upon the chromosomes of the father and not the mother.

Determination of Sex in Humans

Figure 5: Determination of Sex in Humans

Hormones other than Sex Hormones

Other endocrine glands that are present in the human body are:

Glands Hormones Location and Function




It is found at the front of the neck, between the windpipes.
It has a brownish-red color and secretes a collection of hormones called as Thyroid Hormones.
The thyroid hormone controls the rate of metabolism in body
Lack of Thyroxine results in Goitre



Insulin, Glucagon

The Pancreas is almost a 6 inch long gland located behind the stomach.
It produces digestive enzymes, glucagon and insulin. 
The insulin maintains glucose level in the blood.
The glucagon prevents the insulin levels from getting too low in the body.
The insulin activates when the blood glucose levels are high while the glucagon activates when the blood sugar levels are low.
Lack of insulin in body leads to diabetes




Adrenal glands have a size almost of a walnut and are located above the kidneys.
They secrete more that 150 hormones in the human body for various purposes.
Adrenaline helps in managing stress  as it increases the blood sugar levels, dilates the pupils, increases the heart rate, enhances the blood supply to the muscles
It also maintains a balance of salt in the blood.

Pituitary gland

Pituitary gland

Growth hormone

The pituitary gland has a size as small as pea and is located inside the skull.
It is also called as the master gland as it controls the function of all other glands.
It also secretes prolactin that simulates the production of milk.
The growth hormone is responsible for the growth of a person.




The parathyroid glands are located behind the thyroid glands.
The parathormone maintains the level of calcium in the body.
If they produce excess of hormones it can lead to severe effects such as kidney stones and brittle bones.

Pineal Gland

Pineal Gland


It is also known as the Third Eye, and is located between the two halves of the brain.
The Melatonin is responsible for the working of the internal clock of the body. This means it influences the cardiac rhythm or the sleep-wake cycle of the body.

Role of hormones in completing the life history of insects and frogs

  • Insects like silk moths and some animals like frogs undergo the process of metamorphosis which results in drastic changes in their bodies.

  • The insect hormones control the process of metamorphosis in the insects.

  • In frogs, thyroid releases thyroxine which controls the process of metamorphosis in them.

  • The thyroxine only produces with the help of iodine that is present in the water.

  • If there is a lack of iodine in water the tadpoles would never turn into adult frogs.

Reproductive Health

Factors that lead to overall well being in adolescents:

Reproductive Health in Adolescents

Figure 6: Reproductive Health in Adolescents

1. Nutritional Health of Adolescents

  • The adolescent age requires a balanced diet which is rich in nutrients such as proteins and carbohydrates along with vitamins and essential minerals.

  • This is needed because the bodies of adolescents are changing and developing at a rapid rate at this time.

  • Healthy and nutrition-rich diets are essential for their right growth.

  • Also, they should avoid foods such as chips, soft drinks and soda as they have low nutritional value.

Food Item Major Nutrient Function

Pulses and nuts


Growth, repair of body cells.

Oranges and amla


Keep the body healthy by providing resistance.

Sugar and roti


Provide energy



Provide energy


Vitamins and minerals

keep the body healthy and disease free.

2. Personal Hygiene

Personal hygiene also plays a role in maintaining the mental and physical well being of adolescents. Here are a few ways they can maintain their personal hygiene:

  • Having bath daily as the sweat glands and the oil glands secrete high amounts of sweat and oil in the skin which can lead to bad odour.

  • Maintaining cleanliness of the body as there can be chances of getting a bacterial infection otherwise.

  • Females should take note of the menstrual cycle and prepare themselves accordingly.

3. Physical Exercise

  • Exercising not only keep the body fit but also helps in relieving stress and maintaining mental well being.

  • Therefore, adolescents should indulge in sports, exercises, walking, cycling and other physical activities.

4. Say “No” to Drugs

  • Adolescent age incorporates different changes in the mind and body of the individual.

  • As a result, the adolescents may feel a little uneasy sometimes.

  • However, they should understand that this is natural and they should not be worried about it.

  • But many times the adolescents are fooled by others by saying that taking drugs would bring relief to them.

  • They should always say NO to that as taking drugs can be dangerous for their health.

  • Drugs should be taken only if a doctor prescribed them otherwise not.

  • This is because the drugs are addictive and once a person takes them they feel like taking them again and again.

  • As a result, the mental and physical health of the person starts getting affected due to drugs.

  • Also, taking drugs through syringes can cause AIDS (Acquired Immunodeficiency Disease).

  • This disease is caused by a hazardous virus that can get transmitted from an infected person to another through the use of same syringes.

  • Along with this, it can transmit through sexual contact or from the infected mother's milk.


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