HORMONAL SYSTEM (ENDOCRINE SYSTEM)
In addition to the nervous system, the endocrine system also helps in coordinating the activities of our body.
A group of endocrine glands which produces various hormones forms the endocrine system. It is also known as hormonal system.
The various endocrine glands in human body are – Hypothalamus, Pituitary, Thyroid, Parathyroid, Pancreas, Adrenal, Pineal, Thymus, Testes (in males) and Ovaries (in females).
Gland
Gland is a cell, tissue or an organ which secretes a specific substance in the body.
Hormones
The term ‘hormone‘ was introduced by Bayliss and Starling.
Hormones are the chemical messengers which coordinate the activities of living organisms.
Characteristics
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They are secreted in small amounts by endocrine glands.
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They are poured directly into the blood and carried throughout the body by blood.
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They act on specific tissues or organs known as target organs.
Endocrine glands in human beings
|
S.No. |
Name of Gland |
Hormones |
Functions |
|
1. |
Hypothalamus |
Releasing hormones |
Regulates the secretion of hormones from the pituitary. |
|
2. |
Pituitary |
Growth hormone |
Regulates the development of bones and muscles. |
|
Oxytocin |
Regulates the secretion of milk during lactation and regulates uterine contractions. |
||
|
Vasopressin |
Regulates the water and electrolyte balance in the body. |
||
|
Prolactin |
Regulates the function of mammary gland. |
||
|
Trophic Hormones |
Regulates the secretion of hormones from other endocrine glands like thyroid, adrenal, ovary and testis. |
||
|
3. |
Thyroid |
Thyroxin |
Regulates the metabolism of carbohydrates, fat and proteins in the body. |
|
Calcitonin |
Controls calcium and phosphorus balance. |
||
|
4. |
Parathyroid |
Parathormone (PTH) |
Regulates calcium and phosphorus balance in the blood. |
|
5. |
Adrenal |
Corticoids
|
Regulates carbohydrate, fat and protein metabolism and maintains electrolyte balance. |
|
Adrenaline |
Regulates heart rate, breathing rate, blood pressure and carbohydrate metabolism. |
||
|
6. |
Pancreas |
Insulin |
Lowers the blood sugar level |
|
Glucagon |
Increases the blood sugar level |
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|
7. |
Testes |
Testosterone |
Regulates the development of male reproductive organs and accessory sexual characters like beard, moustache, etc. |
|
8. |
Ovaries |
Estrogen
|
Regulates the development of female reproductive organs and accessory sexual characters like development of mammary gland. |
|
Progesterone |
Maintenance of Pregnancy. |
Some interesting hormones and their role
(a) Adrenaline as an ‘Emergency Hormone’:
Adrenaline hormone is usually secreted in small amounts but when a person is under stress like he is frightened, it is secreted in large amounts. It prepares the body for action as it speeds up heart beat and breathing, raises the blood pressure and allows more glucose to go into the blood to give us a lot of energy to combat the stress situation.
This happens as follows : When the heart beats faster, it supplies more O2 to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and rib muscles. All these responses together enable the animal body to be ready to deal with the situation.
(b) Growth Hormone:
Growth hormone is one of the hormones secreted by pituitary gland. This regulates the growth and development of the body.
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If there is deficiency of this hormone in childhood, it leads to Dwarfism.
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If there is excess of this hormone in childhood, it leads to Gigantism.
(c) Thyroxin:
Thyroid gland secretes the hormone Thyroxin. Iodine is essential for the synthesis of Thyroxin by the thyroid gland. So, if iodine is deficient in our diet, less thyroxin hormone is there leading to a disease called Goitre. The main symptom of goitre is that neck of the person becomes swollen due to enlargement of thyroid gland. That is why it is advised to take iodised salt in the diet so as to prevent goitre.
(d) Insulin:
Insulin hormone, produced by pancreas functions to lower the sugar level of the blood. If it is not secreted in proper amounts, the sugar level in the blood rises causing Diabetes. Then, people suffering from diabetes are advised to take less sugar in diet. They might be taking injections of insulin as a part of treatment.
Feedback Mechanism
It is important that hormones should be secreted in precise quantities because both excess or deficiency of hormones has an harmful effect on the body. So we need a mechanism through which this is to be done. The timing and amount of hormone released by various glands are controlled by ‘Feedback mechanism’ which is inbuilt in our body.
For e.g. When we eat a carbohydrate rich meal, the sugar level of the blood rises. It is detected by the cells of pancreas, which respond by producing and secreting more insulin into the blood. In this way, blood glucose level is brought back to normal.
And if the blood sugar level falls below normal, insulin secretion by pancreas decreases automatically.
FEEDBACK CONTROL OF BLOOD GLUCOSE LEVEL