Write in brief about the hormones other than sex hormones?
Sex Hormone – An Overview
We have just discussed two sex hormones called testosterone and estrogen. Testosterone hormone is secreted by endocrine glands called ‘testes’ (which are found only in males) whereas estrogen hormone is secreted by endocrine glands called ‘ovaries’ (which are found only in females).
There are many hormones other than sex hormones. Some of the important hormones (other than sex hormones) are : Growth hormones, Thyroxine, Insulin and Adrenaline. Growth hormone is secreted by pituitary gland ; thyroxine hormone is secreted by thyroid gland ; insulin hormone is secreted by pancreas; whereas adrenaline hormone is secreted by adrenal glands. Pituitary gland, thyroid gland, pancreas and adrenal glands are found in both, males as well as females. The positions of major endocrine glands in the human body are shown in Figure. We will now describe the functions of the hormones (other than sex hormones) secreted by various endocrine glands.
1. Pituitary Gland (or Pituitary)
Pituitary is an endocrine gland. Pituitary gland is attached to the base of the brain (see Figure). The pituitary gland secretes a number of hormones. One of the hormones secreted by pituitary gland is the growth hormone (or human growth hormone). The growth hormone controls the growth of the human body (like the growth of bones and muscles). Proper amount of growth hormone is necessary for the normal growth of the body. A person having the 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).
Pituitary gland is the most important endocrine gland in the body. Pituitary gland is called ‘master gland’ because many of the hormones which it secretes control the functioning of other endocrine glands in the body. For example, pituitary gland secretes hormones that make other endocrine glands such as testes, ovaries, thyroid gland, and adrenal glands to secrete their hormones. In other words, the testes, ovaries, thyroid gland and adrenal glands secrete their hormones when they receive orders from the pituitary gland through its hormones.
2. Thyroid Gland (or Thyroid)
Thyroid is a large endocrine gland in the neck. It is attached to the wind pipe in our body (see Figure). Thyroid gland makes a hormone called thyroxine (which contains iodine).
Thyroid gland secretes its hormone (thyroxine) when it receives instructions from the pituitary gland through its hormones.
Thyroxine hormone controls the rate of body’s metabolism (the chemical processes which occur continuously in human body to maintain life). Thyroid gland needs a constant supply of iodine in order to produce thyroxine hormone. This iodine normally comes from the diet we eat. Since iodine is necessary for the making of thyroxine hormone, therefore, a deficiency of iodine in the diet can cause a deficiency of thyroxine hormone in the body.
The deficiency of thyroxine hormone causes a disease known as goitre. Since the deficiency of thyroxine hormone is caused by a deficiency of iodine in the diet, so we can also say that the deficiency of iodine in the body causes a disease known as goitre. The main symptom of goitre disease is that the neck of the person suffering from goitre appears to be swollen (see Figure).
The person appears to have a big and bulging neck. Goitre is a disease of the thyroid gland. If people do not have enough iodine in their diet, they will get goitre disease caused by the lack of thyroxine hormone in the body. People are advised to use iodised salt for cooking food so as to prevent goitre disease. Iodised salt contains appropriate amount of iodine compounds (such as potassium iodide). Iodised salt can provide all the iodine needed by thyroid gland to make sufficient thyroxine hormone for our body. Since there will be no deficiency of thyroxine hormone in the body, goitre cannot develop. So, the importance of consuming iodised salt is that it prevents goitre disease.
Pancreas acts as an endocrine gland as well as an exocrine gland. Pancreas is just below the stomach in our body (see Figure). Pancreas secretes the hormone called insulin. The function of insulin hormone is to lower the blood sugar level (or blood glucose level). Deficiency of insulin hormone in the body causes a disease known as diabetes. Diabetes disease is characterised by large quantities of sugar in the blood (and even urine). The insulin hormone controls the metabolism of sugar.
If, due to some reason, pancreas does not produce and secrete sufficient amount of insulin into blood, then the sugar level in the blood rises. The high sugar level in the blood can cause many harmful effects to the body of a person. The person having high sugar level in 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. The persons having severe diabetes are treated by giving injections of insulin.
4. Adrenal Glands (or Adrenals)
Adrenals are endocrine glands. There are two adrenal glands in our body which are located on the top of two kidneys (see Figure 11). The adrenal glands produce adrenaline hormone (Adrenaline is also written as adrenalin). The adrenaline hormone prepares our body to function at maximum efficiency during emergency situations (like danger, fear, shock, surprise, anger or excitement, etc.) This happens as follows: When we are faced with a dangerous situation (say, like being chased by a ferocious dog), then the adrenal glands secrete more adrenaline hormone into our blood.
This adrenaline hormone speeds up the heartbeat, increases breathing rate, raises blood pressure, and causes liver to release more stored glucose into the blood. All these actions of adrenaline hormone 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 function at maximum efficiency during the emergency situation of being chased by a ferocious dog.
It is also the adrenaline hormone which prepares our body to fight an enemy (say, a burglar in our house) by providing 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.
The adrenal glands also produce and secrete another hormone called ‘aldosterone’. The aldosterone hormone secreted by adrenal glands maintains the correct salt balance in the blood. The adrenals (or adrenal glands) secrete their hormones when they receive instructions from the pituitary gland through its hormones. We will now discuss the role of hormones in completing the life history of frogs and insects.
Role of Hormones in Completing the Life History of Frogs And Insects
We have already studied the life history of frog. In a frog, the tadpole (or larva) hatched from the eggs passes through certain stages to become a frog. The change from tadpole (or larva) to the adult frog is called metamorphosis. In a frog, metamorphosis is brought about by thyroxine hormone (produced by the thyroid gland). The production of thyroxine hormone requires the presence of iodine in water. So, if the pond water in which the tadpoles are growing does not contain sufficient iodine to make enough thyroxine hormone, there will be deficiency of thyroxine hormone due to which tadpoles cannot undergo metamorphosis and hence cannot become adult frogs.
It is not only the frogs which require thyroxine hormone to complete their life history, in fact, all the amphibians need thyroxine hormone to undergo metamorphosis and change from larvae into adults.
We have also studied the life history of a silk moth. The caterpillar (or larva) has to pass through various stages and undergo metamorphosis to become an adult silk moth. Silk moth is a kind of insect. There are a large number of other insects too. All the insects undergo metamorphosis to change from larvae to adult forms. The process of metamorphosis in insects (such as silk moth) is controlled by insect hormones. In other words, the change from larva to adult insects during metamorphosis is brought about by insect hormones (which are made in their endocrine glands).