One of the most fascinating Biology Topics is the study of genetics and how traits are passed down through generations.
Endocrine System: What is it, Functions and Organs
A group of endocrine glands that produces various hormones is called an endocrine system. The endocrine system is also called the hormonal system. We will now discuss the endocrine system in humans in detail.
In addition to the nervous system, the endocrine system also helps in coordinating the activities of our body. The endocrine system in our body consists of a number of glands (or tissues) that make, store, and release chemicals called hormones. There are a large number of endocrine glands in the human body. The endocrine glands present in the human body are the Pineal gland; Hypothalamus gland; Pituitary gland; Thyroid gland; Parathyroid glands; Thymus; Pancreas; Adrenal glands; Testes (only in males) and Ovaries (only in females). The positions of all these endocrine glands in the human body are shown in Figure. The endocrine glands are located in different parts of the body. As we can see from the Figure, the endocrine glands are located in the head, neck, and trunk of our body.
The positions of endocrine glands in the human body.
Different endocrine glands make different types of hormones that act on different organs of our body. The working of endocrine glands is controlled by our nervous system. The hormones produced by endocrine glands act as messengers between the nervous system and the organs of our body. We will now take the example of adrenal glands to show how the endocrine system (or hormonal system) coordinates our body activities.
There are two adrenal glands in our body, one on top of each kidney (see Figure). The adrenal glands make adrenaline hormones. The adrenaline hormone prepares our body to function at maximum efficiency during emergency situations like danger, anger, excitement, etc. This happens as follows: When we are faced with a dangerous situation (like being chased by a ferocious dog), then our nervous system stimulates the adrenal glands to secrete more adrenaline hormones into our blood. This adrenaline hormone increases our ‘heart beats’, ‘breathing rate’, ‘and blood flow into muscles and causes the liver ‘to put more stored glucose into our blood’.
All these actions of adrenaline hormones produce a lot of energy in our body very, very quickly. And this energy helps us to run away very fast from the dog to save ourselves. In this way, the adrenaline hormone prepares our body to run away very fast from a frightening object. Similarly, it is the adrenaline hormone that prepares our body to fight an enemy (say, a burglar in our house) by providing us with a lot of energy in a very short time. A lot of adrenaline hormone is also secreted by adrenal glands when we are ‘angry’ or ‘excited’. The rapid output of energy thus caused helps us to cope with these extreme emotional situations.
It is the adrenaline hormone (secreted by adrenal glands) that has prepared the body of this person to run away very fast from a ferocious dog.
Complete coordination in the human body is achieved by the nervous system and endocrine system working together. The main centres in the body for the coordination of the two systems of control (the nervous system and the endocrine system) are the hypothalamus and the pituitary gland. The hypothalamus plays an important role in collecting information from other regions of the brain and from blood vessels passing through it. This information is passed on to the pituitary gland which by its own secretions, directly or indirectly, regulates the activities of all other endocrine glands.
The hormones are involved in the regulation of several functions in the human body like growth, metabolic activities, and reproduction. We will now give the names of the endocrine glands, the hormones released by these glands, and the functions of these hormones in the human body. Please note that the pineal gland which is present in the brain has no known function. The pineal gland is supposed to be a vestigial organ (Vestigial organs are those organs that no longer function). Let us discuss the other endocrine glands now.
The Hypothalamus gland is present in the brain. Hypothalamus produces ‘releasing hormones’ and ‘inhibitory hormones’. The function of the hypothalamus is to regulate the secretions of hormones from the pituitary gland. That is hypothalamus controls the pituitary hormones.
2. Pituitary Gland
The pituitary gland is present just below the brain. The pituitary gland secretes a number of hormones. One of the hormones secreted by the pituitary gland is growth hormone (or human growth hormone). The growth hormone controls the growth of the human body. For example, growth hormone controls the development of bones and muscles. A person having a deficiency of growth hormone in childhood remains very short and becomes a dwarf. On the other hand, a person having too much growth hormone becomes very tall (or a giant) (see Figure).
An improperly functioning pituitary gland can produce either too little or too much growth hormone. Too little growth hormone makes a person dwarf whereas too much growth hormone makes a person a giant.
If a person does not get enough iodine from diet or drinking water, the thyroid gland cannot make sufficient thyroxine hormone. Due to the deficiency of thyroxine hormone, the thyroid gland in the neck enlarges, causing the neck to swell too much. This condition is called goiter. Please note the swollen neck of the woman shown in the above picture. She is suffering from goiter disease.
Iodized salt can provide all the iodine needed by the thyroid gland to make sufficient thyroxine hormone for our body so that goiter does not develop.
3. Thyroid Gland
The thyroid gland is attached to the windpipe in our body. The thyroid gland makes a hormone called thyroxine (which contains iodine). The function of the thyroxine hormone is to control the rate of metabolism of carbohydrates, fats, and proteins in the body. Iodine is necessary for the making of thyroxine hormone by the thyroid gland, therefore, a deficiency of iodine in the diet can cause a deficiency of thyroxine hormone in the body. The deficiency of iodine in the diet of a person produces less thyroxine hormone and causes a disease known as goiter.
The main symptom of goiter is that the neck of the person appears to be swollen (due to the enlargement of the thyroid gland located in the neck). People are advised to use cooking food so as to prevent goiter disease. This can be explained as follows: Iodine is required by the thyroid gland to make thyroxine hormone. Iodized salt contains the appropriate amount of iodine compounds (such as potassium iodide). Iodized salt can provide all the iodine needed by the thyroid gland to make sufficient thyroxine for our body (see Figure 49). Since there will be no deficiency of thyroxine in the body, goiter cannot develop.
4. Parathyroid Glands
There are four small parathyroid glands that are embedded in the thyroid gland. Parathyroid glands secrete a hormone called parathormone. The function of the parathormone hormone is to regulate calcium and phosphate levels in the blood.
5. Thymus Gland
The Thymus gland lies in the lower part of the neck and upper part of the chest. The Thymus gland secretes thymus hormone which plays a role in the development of the immune system of the body. The Thymus gland is large in young children but shrinks after puberty (or sexual maturity).
The pancreas is just below the stomach in the body. Pancreas secretes the hormone called insulin. The function of the insulin hormone is to lower the blood sugar level (or blood glucose level). The deficiency of insulin hormone in the body causes a disease known as diabetes. Diabetes disease is characterized by large quantities of sugar in the blood (and even urine). The insulin hormone controls the metabolism of sugar. If, due to some reason, the pancreas does not produce and secrete a sufficient amount of insulin into the blood, then the sugar level in the blood rises. The high sugar level in the blood can cause many harmful effects on the body of a person. A person having a high sugar level in the blood (or diabetes) is called a diabetic. Diabetic persons are advised by doctors to take less sugar in their diet. Common diabetes can be controlled by controlling diet, reducing weight, doing regular physical exercise, and taking medicines. Persons having severe diabetes are treated by giving injections of insulin.
This bottle contains insulin (in the form of a colloidal solution).
Insulin solution is filled in a syringe through the injection needle.
A child suffering from diabetes is being given an insulin injection.
7. Adrenal Glands
There are two adrenal glands which are located on the top of two kidneys (see Figure). The adrenal glands secrete adrenaline hormones. The function of the adrenaline hormone is to regulate heart rate, breathing rate, blood pressure, and carbohydrate metabolism. Adrenaline hormone is secreted in small amounts all the time but in large amounts when a person is frightened or excited. When adrenaline is secreted in large amounts it prepares our body for action (see Figure). It speeds up heartbeat and breathing, raises blood pressure, and allows more glucose (carbohydrate) to go into the blood to give us a lot of energy quickly to fight or fight (run away). Adrenal glands are often called ‘glands of emergency’.
The two adrenal glands are located on the top of two kidneys in our body. They make and secrete adrenaline hormones.
This picture shows how the adrenaline hormone prepares the body for action.
Testes are glands that are present only in males (men). Testes make male sex hormones called testosterone. The function of the testosterone hormone is to control the development of male sex organs and male features such as a deeper voice, mustache, beard, and more body hair (than females). All these changes caused by testosterone are associated with male puberty which boys attain at the age of 13 to 14 years. The testes also make the male gametes called sperms.
Ovaries are glands that are present only in females (women). Ovaries make two female sex hormones called estrogen and progesterone. The function of the estrogen hormone is to control the development of female sex organs, and female features such as feminine voice, soft skin, and mammary glands (breasts). All these changes caused by oestrogen are associated with female puberty which girls attain at the age of 10 to 12 years. The function of the progesterone hormone is to control the uterus changes in the menstrual cycle. It also helps in the maintenance of pregnancy. The ovaries also make the female gametes called ova (or eggs).
The excess or deficiency of hormones has a harmful effect on our bodies. For example, the deficiency of insulin hormone results in a disease called diabetes whereas excess of insulin in the body can lead to coma. So, it is necessary that the hormones are secreted by the glands in our body in precise quantities which are required for the normal functioning of the body. This means that there should be some ‘mechanism’ to regulate the production and release of hormones in the body. The timing and amount of hormones released by various glands are controlled by the ‘feedback mechanism’ which is in-built in our body.
For example, if the sugar level in the blood rises too much, they are detected by the cells of the pancreas which respond by producing and secreting more insulin into the blood. And as the blood sugar falls to a certain level, the secretion of insulin is reduced automatically. Before we end this discussion we would like to give a comparison of the nervous system and endocrine system (or hormonal system) for the control and coordination in humans (and other higher animals).
|Nervous System||Endocrine System (Hormonal System)|
|1. Made of neurons (nerve cells)||1. Made of secretory cells (or glands)|
|2. Messages transmitted in the form of electrical impulses||2. Messages transmitted in the form of chemicals called hormones|
|3. Messages transmitted along nerve fibers||3. Messages transmitted through bloodstream|
|4. Messages travel very quickly||4. Messages travel more slowly|
|5. Effect of the message usually lasts for a very short while||5. Effect of the message usually lasts longer|