Why is the use of iodized salt advisable?

Iodine is important for the thyroid gland to make thyroxine hormone. Thyroxine regulates carbohydrates, proteins and fat metabolism in the body so as to provide the best balance for growth. If iodine is deficient in the diet, thyroxine cannot be produced and the thyroid gland at the neck swells resulting in a condition called goitre. Use of iodized table-salt can provide the required amount of iodine in the diet.

How does our body respond to emergency situation like fight?

In case of fight (reaction to an emergency situation), adrenal glands release adrenaline into blood. (i) The heart begins to beat faster resulting in supply of more oxygen to the muscles. (ii) The blood to the digestive system and skin is reduced due to the contraction of smooth muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. (iii) The breathing rate increases because of the contraction of the diaphragm and the rib muscles. (iv) All these responses together enable the body to be ready to deal with the situation.

Endocrine Glands

The various endocrine glands in humans are hypothalamus, pituitary gland, thyroid gland, parathyroid glands, pancreas, adrenal glands, ovary (in female) and testis (in males).

• Pituitary gland is also known as 'Master gland' of the body. It is because of the fact that the pituitary gland controls the functioning of most of the endocrine glands.

• Hypothalamus plays an important role in the release of many hormones. For example, when the level of growth hormone is low, the hypothalamus releases growth hormone releasing factor which stimulates the pituitary gland to release growth hormone.

• The gonads i.e., testes and ovary are both endocrine and non-endocrine in function. Their non endocrine function is to produce male and female reproductive cells i.e. sperm and ova respectively.

1.0Endocrine Glands and Their Hormones and Functions

Endocrine Gland	Hormones	Function	Deficiency may cause
Pituitary	Growth Hormone	Regulates growth and development of body	Dwarfism
Pituitary	ADH	Regulates the concentration of urine	Diabetes insipidus
Thyroid Gland (Largest endocrine gland)	Thyroxine	Controls carbohydrate, protein and fat metabolism. It regulates BMR [Basal metabolic rate]	Goitre
Thyroid Gland (Largest endocrine gland)	Thyro-calcitonin	Regulates blood calcium levels
Adrenal gland	Adrenaline	Prepares the body to deal with emergency situations	–
Pancreas	Insulin	Decrease blood sugar levels	Diabetes mellitus
	Glucagon	Increase blood sugar levels
Testes	Testosterone	Causes development of sexual organs and secondary sexual characteristics in males	–
Ovary	Oestrogen	Causes development of sexual organs and secondary sexual characteristics in females	–
Ovary	Progesterone	Maintains pregnancy	–

In animals, chemical coordination is achieved through the agency of hormones which function as chemical messengers or informational molecules. Hormones are secreted in very small amounts by specialized tissues in the body called endocrine glands. These glands are ductless and pour their secretions directly into the blood. Blood transports them to the target tissues/organs. Hormones coordinate the activities of living organisms and also their growth. For example, the pancreas secretes two hormones-insulin and glucagon.

2.0Feedback Mechanism

Feedback mechanism is a regulatory mechanism in which presence of certain level of substance promotes or inhibits its further formation. Hormone regulation is mostly done by feedback mechanism. A good example of negative feedback is the release of the hormone insulin. Insulin is a hormone produced by the pancreas. Insulin is released when the amount of glucose in the blood goes up. It stimulates the target cells to take glucose out of the blood which is utilized in cells during respiration or is stored as glycogen. When cells take up glucose from the blood this makes the glucose level reach to normal state. With the fall in blood glucose level, insulin secretion decreases. This checks the further fall in blood glucose level. So, the negative feedback work to keep the blood glucose level normal.

3.0Also Read

Reproduction	Reproductive Health	Origin of Life On Earth
Human Male Reproductive System	Heredity and Its Variation	Evolution and Classification
Human Female Reproductive System	Mendel's Experiment	Movement in Plants

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