Reaching the Age of Adolescence Summary Class 8 NCERT Summary Chapter 7

Adolescence

• The time period when the body undergoes changes to reach reproductive maturity is known as adolescence.
• It begins around the age of 11 and lasts till about 18 or 19 years of age.
• Adolescence in girls can begin one or two years earlier than boys.

Puberty

• The various changes that occur in the body during adolescence marks the onset of puberty.
• Puberty ends when teenagers attain sexual maturity.
• Changes that take place during puberty

Increase in height

• It is caused by the growth in long bones of the arms and legs.
• Girls grow faster than boys initially but both reach their maximum height by the age of 18 years.

Change in body shape

• Boys develop broader shoulders, wider chests, and prominent muscles.
• In girls the region below the waist becomes wider.

Change in the voice pattern

• Voice box or larynx starts growing during puberty.
• It protrudes in males in the neck region and is called Adam’s apple.
• Boys develop deep low-pitched voice.
• Girls develop high-pitched voice.

Change in activity of sweat and sebaceous glands

• The activity of sweat glands increases during puberty, resulting in production of more sweat.
• The oily secretions from sebaceous glands increase. The accumulation of oil and bacterial action leads to acne problems in teenagers.

Changes in sex organs

• Testes and penis develop completely in boys.
• Testes start producing sperms.
• Ovaries develop completely and start producing eggs in girls.

Change in intellectual level

• The learning capacity of brain increases.
• Intellectual development takes place during adolescence.
• Development of secondary sexual characteristics.

Secondary sexual characteristics in boys

• Appearance of moustaches and beard.
• Appearance of hair on chest.
• Growth of hair in genital area and other parts.

Secondary sexual characteristics in girls

• Increase in breast size
• Growth of hair in the pubic region.

Hormones

• Hormones are chemical secretions that bring about various changes in the body.
• They are produced by endocrine glands.
• These glands release hormones into blood to reach specific target site.
• Production of hormones is under the control of hormones produced from pituitary gland.

Characteristics of hormones

• Hormones act as chemical messengers.
• They are secreted by living cells/tissues or organs called glands.
• They are secreted in very small quantities by glands.
• They act upon specific cells, tissues, or organs called the target sites.
• They are generally slow in action, but have long lasting effects.
• They either accelerate or inhibit a reaction.

Endocrine glands

• Hormones are secreted by endocrine glands such as the pituitary gland, thyroid gland, adrenal gland, pancreas etc.
• Major endocrine glands in humans are
  (i) Pituitary
  (ii) Hypothalamus
  (iii) Pineal
  (iv) Thyroid
  (v) Parathyroid
  (vi) Thymus
  (vii) Pancreas
  (viii) Adrenal
  (ix) Testis in men /ovary in women
• A feedback mechanism (positive and negative) regulates the action of the hormones.

Pituitary gland

• It is a pea sized gland situated at the base of the brain. It secretes a growth hormone (GH).
• It is required for proper body growth.
• The hyposecretion of growth hormone causes a condition called dwarfism.
• The hypersecretion causes gigantism in children and acromegaly in adults.

Thyroid gland

• It is located close to trachea in the neck. It produces a hormone called thyroxine.
• It is required for regulating metabolism in the body.
• The hyposecretion of thyroxine causes hypothyroidism.
• This condition causes abnormalities like simple goitre, myxoedema and cretinism.
• Lack of iodine leads to deficiency of thyroxine, which results in a disease called goitre.
• The excess secretion of thyroxine causes hyperthyroidism. It results in high metabolism, protrusion of the eye balls, high BP, nervous tension, etc.

Parathyroid Gland

• There are four parathyroid glands present on back side of thyroid glands that secrete parathyroid hormone or parathormone (PTH).
• This hormone regulates the level of calcium ions in the bloodstream.
• Excess of parathyroid hormone removes calcium from bones and makes them soft.

Pancreas

• It produces two hormones- Insulin and Glucagon.
• These hormones maintain blood sugar level.
• Deficiency of insulin results in diabetes.

Adrenal Gland

• There are two adrenal glands located one on upper part of each kidney.
• It has two parts- cortex and medulla.
• Cortex secretes the hormones like cortisol that regulates the rate of metabolism.
• The medulla secretes a hormone like adrenaline that prepares the body to face various stressful situations.

Gonads

• It includes testes in males and ovaries in females.
• Male sex hormone is testosterone. It is produced by the testes on the onset of puberty.
• Female sex hormones produced by ovaries are estrogen and progesterone.
• Deficiency of estrogen causes infertility.
• Process of Hormonal Action
• Endocrine glands release their secretions (hormones) into the bloodstream.
• Hormones, on reaching their target site, bring about necessary changes to maintain proper functioning of the body.

Historical background and Discovery of HIV

• The first cases of AIDS were recognized in U.S.A in the year 1981.
• The AIDS virus was first discovered by the team of French scientists lead by Luc Montagnier in1983.
• In 1984, the American virologist named Robert Charles Gallo gave the first report on the virus causing AIDS.
• The name HIV was suggested by the International committee on the nomenclature of viruses.
• In India the firsts AIDS patient was identified in Chennai in the year 1987.
• AIDS or Acquired Immune deficiency syndrome is a viral disease, caused by the deadly virus (HIV).

Structure of HIV

• Human Immunodeficiency virus (HIV) is spherical in shape and contains RNA as its genetic material.
• Externally, the virus is covered by the double layered membrane made up of fatty substances.
• Inside the fatty membrane a core of proteins is found that surrounds the viral RNA along with the enzyme reverse transcriptase.

Transmission of HIV

• Sharing of syringes during drug abuse.
• Unsafe sexual contact.
• Transfusion of infected blood
• From infected mother to her infant through milk.

Prevention of HIV

• Avoid sexual contact with infected persons
• Ensure use of disposable syringes
• Screening blood from blood banks

Tests for detection of HIV

• PCR (Polymerase Chain Reaction)
• ELISA (Enzyme linked Immuno Sorbent Assay)
• Western Blot

Personal health and hygiene in adolescents

• Adolescents should have a balanced diet with right proportions of various nutrients.
• Adolescents should maintain cleanliness to prevent bacterial infections.
• They should indulge in some physical exercises to keep their bodies fit.
• They should avoid the consumption of drugs and alcohol.

Sex determination in humans

• Autosomes: First 22 pairs of chromosomes that do not determine the sex of an individual.
• Sex chromosomes: Last pair of chromosomes, represented as X and Y.
  • Females have two X chromosomes, so can be represented as 44+XX.
  • Males have one X and one Y chromosome, so can be represented as 44+XY.
  • Each gamete receives half of the chromosomes i.e. 22+X or 22+Y.
  • Male gametes have 22 autosomes and either X or Y sex chromosome.
  • Male gametes can be of two types, 22+X or 22+Y.
  • Female gametes can be of only one type, 22+X.
  • Sex of a baby is determined by the type of the male gamete (X or Y) that fuses with the female gamete.