In the previous section, you have studied about nervous system, which plays a major role in maintaining control and coordination of the body parts. Besides nervous system, the endocrine system and g also plays a central role in maintaining control and coordination.
The endocrine system of the body is formed by endocrine glands of the body. These are ductless glands and their secretions are called hormones. These hormones play a central role in maintaining coordination.
Hormones
Hormones are the chemical secretions that are produced by various endocrine glands of the body. Hormones are the messengers of information.They have following remarkable features:Important Features of Hormones
- Hormones are organic compounds, which are produced by endocrine glands.
- Hormones are required in secretion).
- Hormones exert their effect always in remote areas (area, which is far away from the place of their minute quantity.
- Hormones are transported with the help of blood stream.
- Hormones have low molecular weights.
- Hormones may accelerate and inhibit a metabolic (physiological) process.
- Hormones get destroyed (or consumed) after their function. Thus a hormone can not be reused.
- Hormones may or may not be proteineous.
Differences between Hormones and Enzymes
Hormones
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Enzymes
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Hormones are secreted by endocrine glands
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Enzymes are secreted by exocrine glands
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Hormones may be a protein, steroid or tyrosin derivative
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Enzymes are always protein in nature
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Hormones get consumed during the reaction
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Enzymes are not consumed during the reaction
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Hormones mainly act as primary messenger
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Enzymes mainly act as bio-catalyst
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hormones work in an area which is far away from the site of their secreted
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Enzymes work in the same area where they are of their are secretion
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Endocrine Glands In Human Beings
- These glands are ductless glands.
- Due to the absence of the duct, their secretions are poured into the nearby blood vessels (i.e., into blood stream).
- These glands secrete hormones only.
- These glands together form the endocrine system of the body.
- Example : Pituitary glands, thyroid gland, endocrine part of the pancreas, adrenal gland, gonad (testes and ovary) etc.
Pituitary Gland (Hypophyseal Gland)
- It is a pea-sized small gland, attached to hypothalamus of brain by a stalk.
- Pituitary is also called as master gland because it directly or indirectly controls the other endocrine glands of the body.
- Pituitary gland has three regions:
- (i) adenohypophysis (anterior part)
- (ii) neurohypophys (posterior part)
- (iii) pars intermedia (middle part).
Growth hormone is very important. It promotes the growth of all tissues of the body.
Its deficiency in growing children may result in dwarfism (i.e. the child becomes a dwarf). Its excessive secretion in children may cause gigantism (the child becomes extremely tall in size).
Vasopressin (ADH) regulates the amount of urine formation. Oxytocin helps in the birth of a baby in a pregnant woman and also helps in the secretion of milk from mammary glands (after the baby's birth).
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Thyroid Gland
- The thyroid gland is the largest endocrine gland.
- It plays an important role in the metabolism of the body.
- Thyroid is located in the throat region. It is a bilobed gland.
- The hormones secreted by thyroid gland are : thyroxin and calcitonin.
- Thyroxin increases the rate of metabolic reactions in the body. It regulates the metabolism of carbohydrates, proteins and fats. It provides the best balance for the growth of the body.
- Iodine is very important for the formation of this hormone. So deficiency of iodine can cause poor growth of the body. In these situations, the neck becomes swollen. This is called goitre.
- Calcitonin helps to regulate the calcium level in blood.
Parathyroid Glands
- Human beings contain 4 parathyroid glands (2 pairs).
- These are very small in size and are present embedded in the thyroid gland.
- The hormone secreted by parathyroid gland is parathormone or PTH, which along with calcitonin, regulates the level of calcium and phosphorus in the body.
Adrenal or Suprarenal Glands
- Adrenal glands are also called supra-renal glands or "Glands of emergency.
- These are located at the top (anterior apex) of each kidney.
- Each adrenal gland consists of an outer cortex and an inner medulla. Both these portions behave as separate glands and secrete distinct hormones.
- Adrenal cortex secretes mineralocorticoids and glucocorticoids which regulate electrolyte balance and carbohydrate metabolism.
- Adrenal medulla secretes two important hormones: (a) Noradrenaline and (b) Adrenaline.
- Noradrenaline causes increased activity of the heart, inhibition of gastrointestinal tract, dilation of the pupils of the eyes etc.
- Adrenaline is secreted mainly at the time of emergency (sudden stress, anger, shock, emotions etc.). Therefore, it is also known as emergency hormone.
Adrenalin : Emergency Hormone
Adrenalin is very important hormone, secreted from adrenal gland. This hormone prepares the body under emergency/scary conditions (sudden stress, fear. anger, shock, emotions etc.). Under these conditions, the adrenalin is secreted from the adrenal gland and it is mixed directly into the blood. Adrenalin acts on many tissues of the body including heart. It increases heart-beat to pump the blood faster to different organs of the body, especially skeletal muscles. The blood supply to digestive organs and skin is reduced. This supply is diverted to brain and skeletal muscles. Adrenalin also causes an increase in the activity of diaphragm and rib muscles to increase the breathing rate. All these changes together prepare the body to deal with the emergency situation. In the way, endocrine system and hormones are also very important in maintaining control and coordination within the body.Pancreas
- It is a mixed gland, i.e., it has both endocrine as well as exocrine activity.
- It is located below the stomach in the loop of duodenum.
- Pancreas secretes two important hormones-Insulin and glucagon.
- Insulin converts excess of glucose into glycogen in liver and thereby reduces the level of glucose the blood. Its deficiency increases the level of blood glucose. The excess of glucose may be passed with urine. This condition is called diabetes mellitus (or simply diabetes).
- Glucagon works in opposite direction. It increases the level of blood glucose by converting glyeog into glucose (when there is low glucose level in the blood).
Sex Hormones
These are called sex hormones, because these are different in male and female. These hormones are secreted after the age of 10 - 12 years. This is called puberty age. After puberty age, the sudden secretion of these hormones cause many changes in the body.Male sex hormones are secreted by testes. The principal male sex hormone is testosterone. Testosterone promotes the growth and development of male secondary sex organs during and after puberty. Testosterone also stimulates the formation of sperms. It is responsible for muscular development, beard and moustache development and voice cracking.
Two important female sex hormones are : (a) oestrogens and (b) progesterone. Oestrogens stimulate the development of female secondary sexual characters during puberty and maintain them. Oestrogen directly influence the growth of breasts and help in oogenesis (formation of ovum or female gamete). These hormones also promote deepening of the voice (high pitch) and shyness in behaviour.
Progesterone also helps in the maturation of secondary sexual characters. It also promotes pregnancy related changes in a pregnant woman.
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