Growing is a natural process. Growth begins from birth. But upon crossing the age of 10 or 11, there is a sudden noticeable spurt in growth. The changes taking place in the body are part of the growing-up process. The period of life, when the body undergoes changes, leading to reproductive maturity is called �adolescence�.

The adolescence period begins at around 11 years of age and lasts up to 18 or 19 years of age. This period covers the �teens� (13-19 years of age). The adolescent is also called a �teenager�.

The period of adolescence varies from person to person. In girls, it may begin a year or two earlier than the boys. The Human body undergoes several changes during adolescence. These changes mark the onset of �puberty�. The most important change that marks puberty is that the boys and girls become capable of reproduction. Puberty ends when an adolescent reaches reproduction maturity.

Changes at puberty

We know that the period of life, around the age of 11 to 18-19 years is called as adolescence period. This period is also known as puberty. The onset of puberty is marked by many changes. In this blog, we will discuss the changes occurring in the body during puberty.

Changes during puberty:-

Increase in height during puberty there is a sudden increase in height. The bones of the arms and of the legs elongate, making a person tall. Initially, the growth rate of girls is faster than boys, but till about 18 years of age, both attain their maximum height.

The rate of growth in height may vary in different individuals: Some may grow suddenly at puberty and then slow down, while others may grow gradually. Sometimes the arms and legs or hands and feet of adolescents look oversized and out of proportion with the body but soon other parts catch up and results in a proportionate body.

Generally, height depends on the genes inherited from parents; therefore, the height of an individual is more or less similar to that of family members.

Change in body shape: Next important change is the change in the body shape During this age: - In boys, shoulders generally broaden out and in girls, the region below the waist becomes wider. In boys, muscles growth is more prominent than muscle growth in girls.

Voice change: In puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes which can be seen as a protruding part of the throat called Adam�s apple and the boys develop a deep voice. Sometimes the nucleus of the growing voice box goes out of control and the voice becomes hoarse. After few days the voice becomes normal. In girls the size of the voice box is small, so it is not visible from outside and therefore girls have pitched voices.

Increased activity of sweat and Sebaceous glands: During puberty, the secretion of sweat glands and sebaceous glands (oil glands) increases. Because of the increased activity of these glands, lots of teenagers develop acne and pimples on the face.

Development of sex organs: The most important change which marks puberty is that the boys and the girls become capable of reproduction and puberty ends when an adolescent reaches reproductive maturity.

During puberty, male sex organs like the testes and the penis develop completely and the testes begin to produce sperms. In girls, the ovaries enlarge, and also eggs begin to mature. Reaching mental, intellectual, and emotional maturity-

Adolescence is also a period during which there is a change in a person�s way of thinking
�    They become more independent.
�    More self-conscious.
�    Their intellectual development takes place.
�    They spend considerable time thinking.

Sometimes, an adolescent may feel insecure while trying to adjust to the changes in the body and the mind. These changes are a natural part of growing up.

Reproductive phase of life in Human Beings

We know that adolescence is the period of life, during which the body undergoes many physical changes leading to reproductive maturity, during which the testes and ovaries begin to produce gametes. In females, the reproductive phase of life begins at puberty (10-12 years of age) and generally lasts till 45-50 years of age.

The ova begin to mature with the onset of puberty. An ovum matures and is released by one of the ovaries once in about 28-30 days. During this period, the wall of the uterus becomes thick so as to receive the egg.

In case the egg gets fertilized, it begins to develop and this results in pregnancy. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which are called �menstruation�.

Menstruation occurs once in about 28-30 days. The first menstrual flow begins at puberty and is termed as �menarche�. Menstrual cycle is controlled by hormones.

It includes �
�    Maturation of egg
�    The released egg
�    Thickening of the uterine wall and its breakdown if pregnancy does not occur.
�    In case, the egg gets fertilized it begins to divide and then gets embedded in the uterus for further development.

Around 45-50 years of age, the menstrual cycle stops and the stoppage of menstruation is termed as menopause. The capacity of maturation and production of gametes lasts for a much longer time in males than in females.

Secondary Sexual Characteristics

We know that during adolescence (i.e. between 11 to 18-19 years of age) the body undergoes many changes. Although the changes do happen in the body, some of them are observable while some are not. The most important change which marks adolescence is that boys and girls become capable of reproduction.

Testes in males and ovaries in females become functional. Much other body changes also occur which help to distinguish males from females; these are called secondary sexual characters.

Some of the secondary sexual characteristics are-
�    In girls, breasts begin to develop. The region below the waist becomes wider.
�    In boys, facial hairs i.e. mustaches and beards begin to grow. Boys grow with broader shoulders and wider chests.

These changes are controlled by hormones i.e. the chemical substances which are secreted by endocrine glands.

Role of Hormones in initiating reproduction

We know that during adolescence the body undergoes many changes which lead to reproductive maturity. These changes which occur during adolescence are controlled by some chemical substances also known as hormones. These hormones are the secretions of ductless glands i.e. endocrine glands.

There are many endocrine glands in our body that directly release hormones into the bloodstream. Through the bloodstream, these hormones reach the destination body part called the �target site� and the target site responds to these hormones.

The Pituitary gland, testes, and ovaries are some of the examples of endocrine glands. The pituitary gland initiates the release of sex hormones released by testes and ovaries. During the onset of puberty, testes start releasing male hormones like testosterone.

This hormone leads to several changes in boys, the changes which distinguish males from females. Similarly, during the onset of puberty in girls, ovaries start releasing female hormones like estrogen which leads to the development of the breasts.

Milk secreting glands or mammary glands develop inside the breasts. So we see that hormones are responsible for initiating reproductive functions. Thus we can say that the onset of puberty is controlled by hormones.

Role of Hormones in completing the life history of insects

We know that hormones which are the chemical secretions of endocrine glands are responsible for the sexual characteristics of human beings. It is these hormones that mature ova in females and leads to the production of sperms in males. Do hormones play any significant role in the life cycle of insects and frogs as well? 

These are the major stages in the life cycle of the silk moth in which the structure varies a lot from caterpillar to adult. These changes are called metamorphosis. Metamorphosis in insects is controlled by insect hormones.

Also, in the life cycle of a frog, a tadpole passes certain stages to become a frog. This is also an example of metamorphosis. In frogs, it is controlled by a hormone known as thyroxin, secreted by the thyroid gland.

Production of thyroxin requires iodine. If the water in which the tadpoles are growing does not contain a sufficient amount of iodine then these tadpoles cannot become adults. So we see Hormones play an important role in the life cycle of insects and frogs as well.

Read More: Reproductive Health And Adolescence: Reproduction In Animals