There are some special tissues in our body called endocrine glands that secrete chemical substances called hormones. These hormones help in coordinating the activities of living organisms and their growth. Following are the characteristics of hormones:
A gland secretes a specific substance in the body. There are two types of glands. They are:
i) Exocrine glands
ii) Endocrine glands
Exocrine glands are the glands that secrete its product into a duct. For example salivary gland secretes the saliva into the salivary duct.
Endocrine glands are the glands that secrete its product directly into blood. There are no ducts in endocrine glands. The chemical substance secreted by endocrine glands is called hormone. These hormones travel through blood and act on the concerned body part. Hormones are a kind of chemical messengers.
There are glands which have both exocrine and endocrine functions. Pancreas, testes and ovary perform both exocrine and endocrine functions. For example, pancreas acts as an endocrine gland and secretes insulin. It also acts as exocrine gland and secretes pancreatic juice into pancreatic duct.
The Endocrine System
Endocrine system also helps in coordinating the activities of our body. The endocrine glands present in our body are pineal gland, hypothalamus gland, pituitary gland, thyroid gland, parathyroid gland, thymus, pancreas, adrenal gland, testes and ovaries. The nervous system controls the working of endocrine glands. The hormones act as messenger between nervous system and organs of the body.
Hypothalamus and pituitary gland are main centres for the coordination of nervous system and endocrine system. Hypothalamus helps in collecting information from the regions of brain and from blood vessels passing through it. The information is then passed on to pituitary gland which by its secretions regulates the activities of all other endocrine glands. In human body hormones help in the growth, metabolic activities and reproduction.
This gland is present in brain and produces releasing hormone and inhibitory hormone. Hypothalamus regulates the secretions of hormone from pituitary gland.
This gland is present just below the brain and secretes number of hormones. One of the hormones secreted by pituitary gland is growth hormone. This growth hormone controls the development of bones and muscles. Person having deficiency of growth hormone becomes very short and the person having too much growth hormone becomes very tall.
Thyroid gland is attached to the wind pipe and makes a hormone called thyroxin which contains iodine. Function of this hormone is to control the rate of metabolism of carbohydrates, fats and proteins in the body. Deficiency of iodine in diet can cause deficiency of thyroxin hormone in the body. This causes a disease called goitre.
There are four parathyroid glands which are embedded in the thyroid gland. Parathyroid gland secretes a hormone called parathormone which helps to regulate calcium and phosphate levels in the blood.
This gland is present in the lower part of neck and upper part of chest. Thymus gland secretes thymus hormone which helps in the development of immune system of the body.
This hormone is present just below the stomach and secretes hormone called insulin. The function of insulin is to lower the blood sugar level. Deficiency of insulin hormone causes a disease called diabetes. A person having diabetes has large quantities of sugar in the blood.
There are adrenal glands are located at the top of two kidneys. This gland secretes adrenal hormone which regulates heart rate, breathing rate, blood pressure and carbohydrate metabolism. This hormone is secreted in large amounts when the person is excited or frightened. This gland is also called glands of emergency.
This gland is present only in males and makes male sex hormones called testosterone. The testosterone controls the development of male sex organs and male features such as deeper voice, moustache, beard, etc.
This gland is present in females only make female sex hormone called oestrogen and progesterone. Oestrogen helps in controlling the development of female sex organs and female features such as feminine voice, soft skin and mammary glands. The progesterone hormone controls the uterus changes in menstrual cycle. It helps in maintenance of pregnancy.
The excess or deficiency of hormones has harmful effect on our body. So in order to control and regulate the production and release of hormones in the body there is feedback mechanism which is in-built in our body.