Introduction To Adolescence

Humans are capable of reproduction after they reach a certain age. This period of life, when the body undergoes changes leading to reproductive maturity, is called adolescence.

Adolescence typically begins around the age of 11 and lasts until about 19 years of age. This period covers the teenage years (13 to 19), hence adolescents are often referred to as teenagers. In girls, adolescence may start a year or two earlier than in boys.

The changes occurring during adolescence mark the transition from childhood to adulthood. The most noticeable changes that occur are collectively known as puberty.

Changes At Puberty

Puberty brings about a series of physical, mental, and emotional changes as an individual matures reproductively.

Increase In Height

One of the most visible changes during puberty is a sudden and rapid increase in height. The long bones of the arms and legs lengthen, causing a person to grow taller. Initially, girls often grow faster than boys, but by approximately 18 years old, most individuals reach their maximum height.

The rate and timing of growth spurts can vary significantly from person to person. Some individuals may experience a rapid surge in height followed by slower growth, while others may grow more gradually.

An individual's eventual height is largely influenced by the genes inherited from their parents, making height a hereditary trait similar among family members. Proper nutrition during these crucial growth years is very important to ensure bones, muscles, and other body parts develop adequately.

The table below shows the average percentage of full height reached by boys and girls at different ages. These figures are averages, and individual growth rates can differ.

Age in Years	% of full height (Boys)	% of full height (Girls)
8	72%	77%
9	75%	81%
10	78%	84%
11	81%	88%
12	84%	91%
13	88%	95%
14	92%	98%
15	95%	99%
16	98%	99.5%
17	99%	100%
18	100%	100%

Using this table, one can estimate the probable full height an individual will reach. If a person's current height and age are known, their full height can be calculated using the formula:

$\text{Full Height (cm)} = \left( \frac{\text{Present height (cm)}}{\text{% of full height at this age}} \right) \times 100$

For example, a 9-year-old boy who is $120$ cm tall is likely to reach approximately $\left( \frac{120}{75} \right) \times 100 = 160$ cm when he reaches full height.

Sometimes, during rapid growth, parts of the body like arms, legs, hands, or feet may grow disproportionately large compared to the rest of the body, but the other parts usually catch up over time, resulting in a more balanced physique.

Change In Body Shape

Significant changes in body shape occur during puberty, differing between boys and girls.

• In boys, the shoulders tend to broaden, and the chest becomes wider. Muscles also develop more prominently compared to girls.
• In girls, the region below the waist becomes wider.

Voice Change

The voice often changes during puberty, especially in boys. The voice box, or larynx, starts to grow larger.

• In boys, the growing larynx can become visible externally as a bulging part of the throat, known as the Adam's apple. This enlargement leads to a deeper voice. Sometimes, the voice muscles may become temporarily uncontrolled, causing the voice to crack or become hoarse for a few days or weeks before settling into a deeper tone.
• In girls, the larynx is smaller and usually not visible from the outside. Girls generally develop a high-pitched voice.

Increased Activity Of Sweat And Sebaceous Glands

During puberty, the activity of sweat glands and sebaceous glands (oil glands) in the skin increases significantly. This heightened activity can lead to increased sweating and oily skin, often resulting in acne and pimples in many adolescents.

Unlike endocrine glands which release hormones directly into the bloodstream, sweat, oil, and salivary glands release their secretions through ducts.

Development Of Sex Organs

At the onset of puberty, the primary sex organs develop completely and become functional.

• In males, the testes and penis fully develop, and the testes begin to produce male gametes, called sperms.
• In females, the ovaries enlarge, and the eggs within them start to mature. The ovaries also begin releasing mature eggs periodically.

Reaching Mental, Intellectual And Emotional Maturity

Adolescence is a period of significant changes in thinking and emotional development. Adolescents tend to become more independent and more aware of themselves (self-conscious). Their intellectual capabilities grow, and they often spend more time thinking and contemplating.

This phase is generally considered a period when the brain is highly capable of learning. However, the rapid physical and mental changes can sometimes lead to feelings of insecurity or confusion as adolescents adjust. It is important to understand that these changes are a normal and natural part of growing up.

Secondary Sexual Characters

Apart from the changes in the primary sex organs, puberty also brings about visible characteristics that help distinguish males from females. These features, which appear during adolescence but are not directly involved in reproduction, are called secondary sexual characters.

Examples of secondary sexual characters:

• In girls: Development of breasts, hair growth under the arms and in the pubic region.
• In boys: Growth of facial hair (moustache and beard), development of hair on the chest, hair growth under the arms and in the pubic region.

The appearance of secondary sexual characters signifies the beginning of the reproductive phase of life, when an individual becomes biologically capable of reproduction.

Role Of Hormones In Initiating Reproductive Function

The numerous changes that occur during adolescence are regulated and controlled by chemical substances called hormones. Hormones are secretions produced by specialised glands called endocrine glands or ductless glands, as they release their secretions directly into the bloodstream.

Hormones travel through the bloodstream to specific parts of the body called target sites. The target site then responds to the presence of the hormone.

Several endocrine glands are involved in initiating and controlling reproductive function:

• Pituitary Gland: This gland is often referred to as the "master gland" because it produces many hormones, including hormones that stimulate other endocrine glands. The pituitary gland secretes hormones that trigger the testes to produce male hormones and the ovaries to produce female hormones. It also produces a growth hormone essential for normal physical growth.
• Testes: Stimulated by pituitary hormones, the testes start producing the primary male hormone, testosterone, at the onset of puberty. Testosterone is responsible for the development of secondary sexual characters in boys, such as facial hair growth, deepening of voice, and muscle development.
• Ovaries: Also stimulated by pituitary hormones, the ovaries begin producing the primary female hormone, estrogen, once puberty is reached in girls. Estrogen causes the development of breasts and the maturation of eggs. Milk-secreting glands (mammary glands) develop inside the breasts under hormonal influence.

Thus, the initiation of puberty and the maturation of reproductive parts are orchestrated by hormones, primarily controlled by the pituitary gland and the sex hormones (testosterone and estrogen) produced by the testes and ovaries, respectively.

Reproductive Phase Of Life In Humans

Humans become capable of reproduction once puberty is attained, and the testes and ovaries start producing gametes.

In males, the capacity to produce mature gametes (sperms) and reproduce continues for a relatively longer period compared to females.

In females, the reproductive phase of life begins at puberty, usually between 10 and 12 years of age, with the onset of menstruation. This first menstrual flow is called menarche.

During the reproductive phase, typically once every 28 to 30 days, one ovum (egg) matures and is released by one of the ovaries. Simultaneously, the wall of the uterus thickens and becomes prepared to receive the fertilised egg.

If fertilisation occurs, the fertilised egg (zygote) begins to divide and implants itself in the thickened uterine wall, leading to pregnancy. The embryo then develops further in the uterus.

If the egg is not fertilised, the released egg, along with the thickened lining of the uterus and associated blood vessels, is shed from the body. This shedding results in bleeding in women, a process known as menstruation. Menstruation occurs approximately once every 28 to 30 days.

The menstrual cycle is a recurring process controlled by hormones, involving the maturation and release of an egg, thickening of the uterine lining, and its breakdown if pregnancy does not happen.

The reproductive phase in females generally lasts until around the age of 45 to 50 years. At this age, the menstrual cycle stops permanently, which is called menopause.

Initially, menstrual cycles might be irregular and may take some time to establish a regular pattern.

How Is The Sex Of The Baby Determined?

Boy Or Girl?

The biological sex of a baby is determined at the time of fertilisation. The instructions for determining sex are contained within the chromosomes present in the fertilised egg (zygote).

Human cells have 23 pairs of chromosomes in their nucleus. One pair consists of sex chromosomes, designated as X and Y.

• A female has two X chromosomes (XX).
• A male has one X chromosome and one Y chromosome (XY).

Gametes (sperms and eggs) are haploid, meaning they contain only one set of chromosomes.

• An unfertilised egg always contains one X chromosome.
• Sperms, however, are of two types: half the sperms carry an X chromosome, and the other half carry a Y chromosome.

When a sperm fuses with an egg during fertilisation, the resulting zygote receives one chromosome from the sperm and one from the egg to form a pair of sex chromosomes.

• If a sperm carrying an X chromosome fertilises the egg (which always carries X), the zygote will have XX sex chromosomes, and the baby will develop as a female.
• If a sperm carrying a Y chromosome fertilises the egg (which always carries X), the zygote will have XY sex chromosomes, and the baby will develop as a male.

Therefore, the sex of the baby is determined by the type of sperm (X or Y) that fertilises the egg. This means the father, through his sperm, determines the sex of the child, not the mother. Blaming the mother for the sex of the baby is scientifically incorrect and unfair.

Hormones Other Than Sex Hormones

Besides the sex hormones and the pituitary hormones that control them, other endocrine glands in the body also produce hormones that regulate various functions, some of which indirectly relate to growth and well-being during adolescence.

Other important endocrine glands include:

• Thyroid Gland: Located in the neck, it produces thyroxine hormone, which regulates metabolism. Deficiency of thyroxine can cause goitre, characterised by a swollen throat. Thyroxine production requires iodine, highlighting the importance of iodised salt in the diet.
• Pancreas: This gland produces insulin, a hormone essential for regulating blood sugar levels. Insufficient insulin production leads to diabetes.
• Adrenal Glands: Located on top of the kidneys, adrenal glands secrete hormones that help maintain the body's salt balance in the blood. They also produce adrenalin (also known as epinephrine), the "fight or flight" hormone, which helps the body cope with stress, fear, anger, or excitement by preparing it for rapid action.

The activity of glands like the thyroid and adrenals is often regulated by hormones secreted by the pituitary gland, demonstrating the interconnectedness of the endocrine system.

Role Of Hormones In Completing The Life History Of Insects And Frogs

Hormones also play a crucial role in the life cycles of animals other than humans, particularly in processes involving drastic transformations from larva to adult, known as metamorphosis.

• Insects undergo metamorphosis which is controlled by specific insect hormones.
• In frogs, the transformation from tadpole (larva) to adult frog involves metamorphosis controlled by the hormone thyroxine, produced by the thyroid gland. The production of thyroxine in tadpoles requires the presence of iodine in the water they live in. If water lacks sufficient iodine, tadpoles may not be able to produce enough thyroxine and thus may not complete their metamorphosis into adult frogs.

Reproductive Health

Overall health encompasses both physical and mental well-being. Maintaining good health requires a balanced diet, personal hygiene, and adequate physical exercise throughout life. During adolescence, as the body undergoes rapid growth and changes, these aspects become even more critical.

Nutritional Needs Of The Adolescents

Adolescence is a period of intense growth, requiring careful attention to diet. A balanced diet is essential, providing all necessary nutrients – proteins, carbohydrates, fats, vitamins, and minerals – in appropriate amounts.

Traditional balanced meals, like Indian meals consisting of cereals (roti/rice for energy), pulses/dal (for proteins necessary for growth), and vegetables, are suitable. Milk is a naturally balanced food, and fruits also provide essential nutrients.

Iron is particularly important during adolescence, as it helps build blood. Iron-rich foods include leafy vegetables, jaggery, meat, citrus fruits, and Indian gooseberry (amla).

While convenient, processed foods like chips, packed snacks, noodles, and burgers often lack adequate nutritional value and should not replace regular, balanced meals.

Personal Hygiene

Maintaining personal cleanliness is crucial, especially for teenagers, whose sweat glands are more active, potentially causing body odour. Daily bathing and thoroughly washing all body parts are necessary to prevent bacterial infections.

Girls need to pay extra attention to hygiene during menstruation. Keeping track of the menstrual cycle and using clean sanitary products (like sanitary napkins or clean cloth pads), changing them regularly (every 4-5 hours or as needed), is important for health and comfort.

Physical Exercise

Engaging in physical activities like walking, running, or playing outdoor games in fresh air helps keep the body fit and healthy. Regular exercise is beneficial for the overall well-being of adolescents.

Say “No” To Drugs

Adolescence involves normal physical and mental changes, and it's important not to feel confused or insecure during this phase. It is critical to avoid drugs unless specifically prescribed by a doctor for medical reasons.

Drugs are highly addictive. Trying them even once can create a strong urge to use them repeatedly, leading to dependence. Drugs are severely harmful to health and can ruin one's life and happiness in the long run.

Awareness about diseases like AIDS, caused by the HIV virus, is also important. HIV can spread through sharing syringes used for injecting drugs, from an infected mother to her child during pregnancy, childbirth, or breastfeeding, and through sexual contact with an infected person.

Adolescent Pregnancy

In many countries, including India, there is a minimum legal age for marriage (currently 18 for girls and 21 for boys in India). This legal age is set partly because individuals, particularly teenage girls, may not be physically or mentally prepared for the responsibilities of marriage and parenthood.

Early marriage and motherhood can lead to health issues for both the young mother and her child. It also limits educational and employment opportunities for young women and can cause significant emotional and mental stress due to the unpreparedness for parental responsibilities.

Myths, Taboos, Do’s And Don’ts

Based on scientific understanding of reproduction and adolescent changes, it is important to differentiate between facts and common misconceptions or myths. Many taboos and wrong notions exist surrounding the changes experienced by adolescents.

Examples of common myths that should be disregarded:

• The belief that a girl can become pregnant by just looking at boys during menstruation.
• The incorrect notion that the mother is solely responsible for determining the sex of her child. (As learned, the father's sperm determines sex).
• The taboo that girls should not be allowed to work in the kitchen or participate in certain activities during menstruation.

As informed adolescents, it is important to rely on scientific facts, challenge myths, and discuss these topics openly and responsibly.

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