The endocrine system

Besides the nervous system, the other system which controls and coordinates many of the body’s activities is the endocrine system. This consists of several glands, called the endocrine glands. These glands secrete chemical messengers, or special chemicals that carry messages to particular organs or tissues.

Also called hormones, these chemicals are released directly into the blood stream, unlike the secretions of other glands, which are transported though vessels or ducts. This is why the endocrine glands are called ductless glands. Hormones are released in response to both external and international stimuli.

Each endocrine gland secretes specific hormones or specific purpose, as we shall see in this section.

Pituitary gland

This is small round gland situated at the base of the brain and is linked with the hypothalamus. It is the most important gland of the endocrine system as it secretes many hormones which control the functioning of other endocrine glands. For this reason, it is known as the master gland.

One of the most important secretions of the pituitary gland is the growth hormone. This promotes the growth of bones and muscles during early lie. If too much of this hormone is secreted, there is excessive growth. This condition is called gigantism. If the secretion is below normal, the person’s growth is stunted, a condition called dwarfism.

The pituitary gland also controls the growth controls the growth and functioning of the thyroid gland. It secretes another hormone which influences the production of sperms and the maturing of ova. Its other functions include controlling the secretion of milk by the mammary glands.

Thyroid gland

This large gland is located in the throat, near the larynx. The main hormone it secretes is thyroxin, which is iodine –contain protein. This hormone controls the general metabolic functioning of the body, especially the rate at which energy is produced and oxygen consumed. Thyroxin is also necessary or normal physical growth and development.

Excessive secretion of thyroxin is called hyperthyroidism. This raises the general metabolism of the body and as a result stored fats are converted into energy too fast. A person with this condition suffers from high blood pressure and loss of weight, and may become overactive. Insufficient secretion of thyroxin is called hypothyroidism. This causes sluggishness and gain of weight. Since it slows down metabolic activity, it retards growth and mental development in children. Another symptom is the swelling of the thyroid gland. This is called goiter, which may also occur if one’s diet lacks iodine.

Parathyroid glands

These are four small glands located right behind the thyroid gland. The hormone secreted by these, called parathoromone, helps maintain the level of calcium in the blood. Our blood needs a certain level of calcium to facilities muscular activity, among other things.

Adrenal glands

There are two adrenal glands, one attached to each kidney. They produce a hormone called adrenaline. This hormone is secreted when a person is in danger, under severe stress, fearful or angry. In general, the adrenal glands come into action to prepare the body for emergencies by getting it to supply more energy. Adrenaline increases the heartbeat and the rate of respiration, and also raises the blood pressure.

Pancreas

The pancreas, as you know, is digestive organ located in the stomach. However, it contains clusters of endocrine cells. These clusters are called the islets of Langerhans. The most important hormone produced by these I insulin. Insulin regulates the level f glucose in the blood. It converts excess glucose to glycogen, which is stored in the liver. People whose pancreas does not secrete enough insulin suffer from a condition called diabetes. The level of glucose in the blood increases and the extra glucose in excreted along with urine.

Reproductive organs

As you know, apart from producing sperms, the tests also produce testosterone, the male sex hormone. Testosterone is involved in the development of secondary sexual characters in males once they attain puberty.

The ovaries secrete a female sex hormone called Oestrogen. The secretion of Oestrogen starts once a girl attains puberty. Oestrogen produces the secondary sexual characters and also prepares the body for pregnancy. Progesterone is another hormone secreted by the ovary. It brings about changes in the body of a pregnant woman.