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Class 8, Science, Chapter-7, Lecture-2, Hormone (Notes)

HORMONE:

A chemical substance produced in the body which controls and regulates activities of specific tissue or organ of a living organism is termed as hormone.

ENDOCRINE SYSTEM: 

The collection of ductless glands that produce hormones to control and regulate activities of various tissues or organs of a living organism is called endocrine system.

CHARACTERISTICS OF HORMONES:

  1. They are specific chemical messengers
  2. They are secreted by endocrine glands
  3. They are poured directly into the blood and carried by blood circulation
  4. They act on specific tissue or organs called target organ.

LIST OF ENDOCRINE GLANDS AND HORMONES RELEASED:

Endocrine gland

Hormone released

Role

1. Pineal

Melatonin

Regulates Sleep Cycle.

2. Hypothalamus

Tropic Hormone

Regulates Endocrine System

3. Pituitary
(MASTER GLAND)

Growth Hormone,

Gonadotropic Hormone

Thyroid Stimulating Hormone (TSH)

Controls Growth

Controls secretion of sex hormones

Stimulates the thyroid to release thyroxin

4. Thyroid

Thyroxin

Regulates Basic Metabolism

5. Parathyroid

Parathyroid Hormone

Regulates amount of Phosphorus and Calcium

6. Thymus

Thymosin

Activates Immune System

7. Adrenal

Aldosterone

Adrenalin

Regulates salt balance of body.

Helps to adjust to stress during anger, embarrassment or depression (“Fright, Fight or Flight” action)

8. Pancreas

Insulin

Glucagon

Reduces sugar level

Increases sugar level

9. Ovary

Estrogen and Progesterone

Regulates Female sex organs

10. Testes

Testosterone

Regulates Male sex organ

METAMORPHOSIS:

The biological process of transformation from larva or tadpole to an adult is called metamorphosis.

Hormones involved in Metamorphosis: 

  • Insect Hormones in insects 
  • Thyroxine in amphibian

SEXUALLY TRANSMITTED DISEASES:

An infectious disease which is spread from an infected person to a healthy person by sexual contact is called sexually transmitted disease (STD).

Examples of STD:

  • Bacterial Infections - Gonorrhoea, Syphilis 
  • Viral Infections - Warts, AIDS

Symptom of STD: Burning sensation at urination and urethral discharge

Prevention from STD: Use of condom during sex.

Mode of Transmission of AIDS:

  • From infected mother’s milk to child
  • Through sharing of syringes or Shaving blades
  • Blood transfusion from infected person
  • Sexual contact with infected person