CBSE Class 8 Biology – 10. Puberty and Adolescence (Notes)

STAGE OF LIFE:   Infancy(0-2years), Childhood (3-12), Adolescence (13- 19) , Adulthood (20-40) Old age(above 40years)

Adolescence:-The period of life when many changes from leading to reproductive                               maturity take place in the bodyis called adolescence.

Adolescence begins at around 10 years of age and lasts till 18 or 19 years of age.

Adolescents are also called as teenagers as teen age period.

The period of adolescence varies from person to person. In girls, adolescence may begin one or two years earlier than boys.

Teenage:- The number of years during adolescence period are counted as ‘teen’, .Eg:  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.

NOTE:-Puberty is the stage when a boy or girl attains sexual maturity. This means that sex organs start developing in both boys and girls. Boys start producing sperms and girls start producing eggs.

Changes at Puberty
Increase in Height	Change in Body Shape	Voice Change	Development of Sex Organs
Reaching Mental, Intellectual and Emotional Maturity		Increased Activity of Sweat and Sebaceous Glands

1. 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.Que:-Height of an individual is more or less similar to that of some family member. Why? Ans:-Height of an individual is more or less similar to parents because height depends on the genes inherited from parents.
2. 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.
3. Voice Change: –At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice boxes in boys can be seen as a protruding part of the throat called Adam’s apple. In girls, the larynx is hardly visible from the outside because of its small size.Generally, girl have a high pitched voice, whereas boys have a deep.
4. 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 (muhasa) and pimples.
5. Development of Sex Organs: –In boys, testes begin to produce sperms. Testis and penis                                  develop completely. The testes also begin to produce sperms.                       In girls, ovaries enlarge and eggs begin to mature. Ovaries start releasing mature egg.
6. Reaching Mental, Intellectual and Emotional Maturity: –Mental growth:-Thinking skill develops.Emotional growth: – Emotional changes cause the young person to look at friend and family in new ways.Interest in the opposite sex and desire for closeness arise.                                              Social growth: – Developing personal identity, forming more mature relationship with peers of both sexes. Developing independence and preparing for career.
7. Secondary Sexual Characters:-Characters which help to distinguish the male from the          female are called secondary sexual characters.

Sexual dimorphism:-    Marked difference between male and female of a species because of           apparent physical traits is called sexual dimorphism.

Secondary Sexual Characters in Boys:Widening of shoulders.                                                                                                                                 Deep voice. Appearance of bread and moustachesand hair on chest.                                                                   Growth of sex organs(testes and penis)

Secondary Sexual Characters in Girls:                                                                   Widening of pelvis and hips.                                                                          Enlargement of mammary gland(breasts)                                                                       High pitched voice.Maturation of secondary sex organs like fallopian tube, uterus.

Some common /similar Secondary Sexualcharacters in girls and boys: Hair under armpits, hair in pubic area. Increase activity of sweet and sebaceous glands. Darkening in skin colour of the genital area.

                                               Hormones:                                                                                Hormones are the chemical substances secreted by endocrine glands for        proper functioning taking place during adolescence in the human body.
In males, at the beginning of puberty, the hormone or testosterone begins to get released by the testes. And this results in some changes in boys like the growth of facial hair, deep voice and hair on chest.
In females, ovaries start to produce the female hormone or estrogen which results in breasts development on reaching puberty. Also, milk secreting glands or mammary glands development takes place inside the breasts.

The production of these hormones is under the control of another hormone secreted from an    endocrine gland called pituitary gland. 

The testes and ovaries secrete sex hormones. These sex hormones are controlled by the hormones secreted from the pituitary gland. The pituitary secretes many hormones, one of which makes ova mature in the ovaries and sperms form in the testes.

The onset of puberty is controlled by hormones

                                          Humans Reproductive Phase:                                                                         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:  The ending of menstrual cycle is called menopause. This happens at around 45 – 50 years of age. Menopause marks the end of reproductive phase.

                       Sex Determination
                                                  Will it be a Boy or Girl?
Gender of a child is dependent on the combination of chromosomes taking place in the zygote. In human beings, normally a cell has 46 chromosomes, i.e. 23 pairs of chromosomes. Out of these 46 chromosomes, 22 pairs are identical. But chromosomes in the 23rd pair may be same or different.
There are two kinds of chromosomes in 23rd pair. They are known as X and Y chromosomes. The last pair (i.e. 23^rd) in a male has XY combination, while in case of female it has XX combination.
1. Birth of girl will take place when a sperm with X chromosome fertilizes the egg.
2. Birth of boy will take place when a sperm with Y chromosome fertilizes the egg.

                                         Hormones Other Than Sex Hormones:                                                            Sex hormones are not the only hormones responsible for changes during adolescence. There are few other hormones that act in the background.

Position of Endocrine Glands in the Human body

 

Gland
Endocrine glands (ductless , secretes secretions directly into the blood)	Exocrine glands(ducts to expel their material)
Pituitary gland Thyroid gland Parathyroid gland Thymus gland Adrenal gland Pancreas Testis Ovary	Salivary glands(contains amylase to help soften our food) Bile-making glands of liver Part of the pancreas                  ( secretes pancreatic enzymes into the duodenum of the small intestine) Prostate gland (helps propel seminal fluid during ejaculation) Gastric glands (digests our food) Sweat glands (removes heat from the body)

Exocrine glands: -Those glands that have ducts to expel their material onto an epithelial                                           surface rather than the bloodstream are called exocrine glands.

This external surface can be our skin.

Endocrine glands: -Those glands that are ductless which secretes there secretions directly into the blood are called endocrine glands.

Its hormone reaches the target site through blood.

The Endocrine glands are:-

Thyroid gland: –It is located in front of neck below the larynx and secretes thyroxine hormone.                                                             

Function

Hypo secretion of thyroxine hormone results in the formation of swelling in the neck which is called goitre.

Thyroxine hormone regulates the rate of metabolism and also effects the general growth of body.                                                                                                                                  Parathyroid gland:-There are two pairs of parathyroid glands one pair of each side of         thyroid gland.

Function

They secrete a hormone that increases calcium level in the blood.

Pituitary gland: –

It is the small gland like a pea and is located at the base of brain.

It is directly controlled by the hypothalamus.

Pituitary gland secretes growth hormone which is necessary for the normal growth of     person.

Hypersecretion of growth hormone causes gigantism while its hyposecretion causes  dwarfism

Pancreas:-Pancreas is located below the stomach and it has both exocrine and endocrine             part,so it is also called mixed gland or heterocrine gland.      

Function

It secretes insulin hormone which regulate the sugar level in blood.

 The pancreas also releases digestive enzymes that break down protein, fats, and carbohydrates in our food.

Hyposecretion of insulin form pancreas causes diabetes because insulin regulates the glucose in the blood. Lake of insulin results in excess glucose(sugar) in the blood, which comes out through urine. This is one of the symptoms of diabetes.

Thymus gland:- It is located between our lungs in the chest. It is only active until puberty                            commences.

Function

It produces a hormone called lymphocyte in children. It is functional in children and gradually it disappears in adults.

It secretes hormones important for puberty and a healthy immune system.

Adrenal gland:- Adrenal gland are two in number. Each gland is located on each kidney                              like a cap.

Function

Adrenal gland secretes the hormone adrenalin which is also called the stress hormone.

It helps the body to adjust to stress such as anger, worry or embarrassment.

 Adrenalin hormone  maintain the salt and water balance of the body.

It regulates the blood pressure, and also prepares the body to meet emergencies and to be ready to fight.            

Testis(in males):-The primary sex organs and located in scrotum of male                                   Function

Male hormone or testosterone is released by the testes which controls the development of male sexual organs and secondary sexual character such as broadening of shoulder, growth of facial hair, public hair and hair in the armpits, hoarseness of voice, etc            

It also helps to produce sperms-the male-gamets-in the testis.

Testosterone promotes sperm production & our sex drive.

Ovary(in females):-In female, there are two ovaries, one on each side of the uterus,                    hanging externally in the lower abdomen.           

Function

The ovary produces a hormone called estrogen and progesterone which which make the breasts develop. Milk secreting glands or mammary glands develop inside the breasts.

Mammary glands secrete milk after the birth of a child.

Estrogen initiates menstruation, and the release of an egg each month.

 The production of estrogen and progesterne hormone under the control of another hormone secreted from an endocrine gland called pituitary gland.

                    Role of Hormone in Completing the Life Cycle of insects and frogs

Insect hormones control the metamorphosis of larva into adult.

Thyroxin controls the metamorphosis of tadpole into frog. If a frog lays eggs in iodine deficient water, the tadpoles will not develop into frogs and will perish.

                                          Reproductive Health

Balanced Diet: Rapid growth during adolescence necessitates balanced diet. A teenager should take adequate amount of carbohydrates, protein, fat, vitamins and minerals in food. One should avoid eating fried food and junk food. Girls need to take lot of iron-rich food because iron is necessary for formation of RBCs.

Personal Hygiene: We have read that sweat and sebaceous glands show increased activity during this period. If proper hygiene is not maintained, it can lead to many skin diseases in adolescents. Girls need to take special care of hygiene during menstrual period.

Physical Exercise: Walking and playing in fresh air keeps the body fit and healthy. All young boys and girls should take walks, exercise and ply outdoor games.

Say ‘NO’ to Drugs: The menace of drugs is spoiling many a life. During adolescence period, one can easily get influenced and carried away by negative stimulations. We need to have a strong will power to say NO to drugs. Addiction to drugs will destroy your career and life.                                              AIDS (Acquired Immuno deficiency syndrome):

       AIDS is a disease which is caused by HIV (Human immune deficiency virues). This virus destroys the natural defence mechanism of the body and makes it susceptible of diseases.

Causes of AIDS:

1. Sharing the needle of the syringe for injecting drugs.
2. Unprotected sex with an infected person.
3. Transfusing blood into the body of a healthy person from an infected person.
4. Infected mother can pass HIV virus through milk to an infant.

How to prevent AIDS:

1. Use disposable syringes.
2. Get blood from registered blood banks for transfusion.
3. Have safe and protected sex.
4. HIV infected mother should not breast feed her baby.