Ray was a member of Science Olympiad, participates in science and health writing competitions, and studied at a sci-tech school.
What Is the Endocrine System?
The endocrine system is the collection of glands in our body that produce hormones that regulate growth, tissue function, reproduction, and metabolism. The presence of fine tubes, or ducts, is a characteristic common to all endocrine glands. These fine tubes are where secretions pass.
Another group of glands in our body are those which do not have ducts. Hence, they are called ductless glands. They go directly into the bloodstreams. The secretions diffuse from the secreting cells through the walls of the blood vessels into the blood. The secretions of ductless glands are called hormones.
Hormones are special protein substances that are present in small quantities in the body. They bring about changes in cells or tissues which are referred to as their targets. The effect of a hormone may be an increased activity or a decreased activity of the target cells. It may also be just plain maintenance of cells.
Among lower animals such as insects, crustaceans, mollusks, and amphibians, hormones have been found to regulate growth and development from egg to adult. Metamorphosis is the term for the development from egg to adult.
A series of researches have revealed that invertebrate hormones differ from vertebrate hormones both in chemical composition and in function. Our present knowledge of hormones in lower animals is still very limited, and further research on this field of study is encouraged.
The figure below shows the different endocrine glands of our body. How do the hormones produced by the glands affect the functioning of our bodies?
3a. Adrenal Cortex
Cortin, Cortisone, Sex Hormones
3a. Adrenal Medulla
5. Beta Cells of Islets of Langerhans
8a. Hypophysis - Adenohypophysis
Growth hormone, Thyrotropic hormone, Follicle-stimulating hormone (FSH), Protactin, Adrenocorticotropic hormone (ACTH)
8b. Hypophysis - Neuro Phypophysis
10. Stomach Upper Intestine
Thyroxin is produced by the thyroid glands to regulate the growth of the body and oxidation in the cells. A very important component of thyroxin is iodine. If iodine is lacking in your diet, your thyroid glands begin to enlarge. This is a case of simple goiter.
When thyroxin is produced in small amounts, that person suffers from hypothyroidism. The word "hypo" means abnormal deficiency. This disorder is characterized by the slow beating of the heart and a low metabolic rate. The person is sluggish, and his movement is very slow.
Sometimes too much thyroxin is produced because of the overactivity of the thyroid gland. The overproduction of thyroxin in a person's body is said to be hyperthyroidism. The prefix "hyper" means abnormal excess. A person suffering from hyperthyroidism has a high metabolic rate.
Oxygen is used up at a fast rate to cope with the high rate of chemical reaction in the cells. A hyperthyroid person is highly nervous and irritable. In most cases, enlargement of the thyroid glands is accompanied by the bulging of the eyeballs. This case is called an exophthalmic goiter.
A hyperthyroid person may be treated with radioactive iodine to destroy overactive tissues of the thyroid gland. Sometimes removal of a portion of the thyroid gland is resorted to.
Functions of Thyroxin
- Thyroxin controls metabolic rate.
- Thyroxin controls physical growth.
- Thyroxin controls mental growth.
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The parathormone hormone is produced by the parathyroid glands. It regulates the amount of calcium and phosphorus in the blood. It controls the deposition of calcium salts in the bones and teeth. Insufficient parathormone in the body results in uncontrolled twitching and spasms of muscles.
This is a painful experience, it may be treated with calcium or parathormone extract. Excess parathormone causes a high concentration of calcium in the blood. Calcium is removed from the bones. The bones lose their firmness and become deformed by the weight of the body. The spine or vertebral column becomes abnormally curved.
Function of Parathormone
- Parathormone regulates the amount of calcium in the blood.
There are two adrenal glands, one on top of each kidney. The adrenal gland is divided into two parts: an inner part, called the adrenal medulla, and an outer part called the adrenal cortex. The adrenal medulla secretes the hormones adrenaline and noradrenaline.
During an emergency, a fire, for instance, adrenaline is released by the gland causing many body changes, which enable a person to cope with the emergency conditions. The rate of heartbeat is increased. Additional blood sugar is released from the liver into the bloodstream. The arteries of the heart, liver, brain, and muscles become wider.
Hence, more blood sugar and oxygen are supplied to these organs. As a result, a person becomes unusually strong during an emergency. For instance, a man can easily lift a big dining table all by himself during a fire.
Adrenaline also causes the blood to clot easily. Because of these effects of adrenaline, it is known as the "emergency hormone." Adrenaline is released into the blood also when a person is angry or frightened.
The other hormone produced by the adrenal medulla is noradrenaline. It is responsible for the constriction of blood vessels. As many as 40 hormones are produced by the adrenal cortex so that once the cortex is decreased, death follows within a short time.
Functions of Hormones of Adrenal Cortex
- Cortin regulates sodium, calcium, and water balance of the blood.
- Cortisone maintains carbohydrates, fat.
- Cortisone maintains protein metabolism.
- Cortisone promotes the health of connective tissues.
- Sex Hormones influence the development of secondary sex characteristics.
Functions of Hormones of Adrenal Medulla
- Adrenaline hastens the release of glucose into the blood.
- Adrenaline increases the rate of heartbeat.
- Adrenaline increases blood pressure.
- Noradrenaline controls blood vessels.
4. Insulin and Glucagon
Insulin is a hormone secreted by a group of cells in the pancreas known as the Islets of Langerhans. Insulin controls the transformation of the simple sugar glucose into glycogen, an insoluble carbohydrate stored in the liver and muscles.
Insulin, therefore, lowers the amount of sugar in the blood. When the body does not have enough insulin, the blood sugar level increases, and glucose appears even in the urine. This condition is known as diabetes.
Another hormone produced by the pancreas is glucagon. This hormone tends to raise the amount of sugar in the blood by changing liver glycogen into glucose. That is, when more energy is needed by the cells, the body changes glycogen in the liver into glucose.
You can see here that the effects of insulin and glucagon are the opposite. The secretion of the two must be balanced for the body to have just the right amount of sugar in the blood. The average concentration of blood sugar is 60 to 120 milligrams per 100 milliliters of whole blood.
Functions of Hormones of Pancreas
- Glucagon controls the transformation of liver glycogen into blood glucose.
- Insulin controls the transformation of blood glucose into liver glycogen.
5. Androgen and Estrogen
Two groups of hormones are primarily responsible for the development of secondary sex characteristics—androgen and estrogen. Androgen is produced by the male sex gland or testis, while estrogen is produced by the female sex gland or ovary. The secondary sex characteristics begin to show during the age of adolescence, which is at 12 to 16 years of age.
The principal androgen is testosterone. Testosterone is responsible for the male secondary sex characteristics such as muscular body build, deep voice, and growth of hair in certain regions of the body such as the face, chest legs, and arms. The female secondary sex characteristics are the development of mammary glands and rounded contours.
Functions of Hormones of Sex Glands
- Estrogen controls female secondary sex characteristics.
- Androgen controls male secondary sex characteristics.
6. Hormones of Hypophysis
The hypophysis or pituitary gland is a ductless gland located below the brain. This gland has two parts—adenohypophysis and neurohypophysis. The hormones of the adenohypophysis are responsible for the development and maintenance of a structure, and activity of other ductless glands.
Among the glands regulated by the hormones of the adenohypophysis are the thyroid, adrenal, and sex glands. Modern researches have shown that even the pancreas and the parathyroid are regulated by hypophysis. One hormone produced by the adenohypophysis is responsible for body growth.
It is referred to as a growth hormone. Lack of this hormone results in a dwarf, or midget. An oversecretion of it results in a giant.
The neurohypophysis secretes the hormones vasopressin and oxytocin. Vasopressin controls the elimination of water by the kidneys. When the body does not have enough vasopressin, it eliminates large amounts of dilute urine. Oxytocin controls blood pressure and stimulates the smooth muscles of the uterus.
Functions of Hormones of Adenohypophysis
- Growth hormone regulates the growth of the skeleton.
- The thyrotropic hormone regulates the activity of the thyroid.
- Follicle-stimulating hormone (FSH) regulates follicle formation in the ovary.
- Follicle-stimulating hormone (FSH) regulates sperm formation in testis.
- Prolactin stimulates mammary glands to secrete milk.
- Adrenocorticotropic hormone (ACTH) regulates activity to the adrenal cortex.
Functions of Hormones of Neurophypophysis
- Vasopressin controls the elimination of water by the kidneys.
- Oxytocin controls the contraction of the smooth muscles of the uterus.
- The thymus hormone controls the formation of antibodies.
- Gastrin stimulates the secretion of gastric juice by gastric glands.
- Secretin stimulates pancreatic juice by pancreatic glands.
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