Chapter 11.
Endocrine system
Many of the activities of the body are controlled by the nervous system. One of the characteristics of the nervous system is rapid response. On the other hand, the endocrine system exercises control over many body functions in a slower manner and for long period of time.
The endocrine system controls the rate of metabolism, growth, and the formation of temperament and character. The endocrine system is made up of organs that are often called ductless organs or glands. The endocrine system produces or assists in the production of special chemicals of substances called hormones.
A hormone is a chemical messenger secreted by the ductless gland that reaches its destination by traveling in the bloodstream. The hormone has the power to influence the activity of the other distant organs. Some organs have many functions, and are included in the endocrine system because of the production of hormones. An example of this is the pancreas.
The pancreas produces insulin that passes into the blood. The pancreas also produces pancreatic juice used in digestion that reached the duodenum by the pancreatic duct. Some hormones, as such as adrenaline, have immediate action while others, such as the pituitary growth hormone, exercise influence over many years.
The most important glands in the endocrine system are: the pituitary gland, front and back lobes; the thyroid gland; the adrenal glands; the sex glands, also called gonads; the insulin secreting cells of the pancreas.
The pituitary gland is situated and the base of the brain, and is known as the master gland. It is about 1 cm in diameter and is attached to the brain by short stalk just behind the optic chiasma (intersection of the optic nerves).
Growth hormone is just one of the many hormones secreted by the pituitary gland, which also produces hormones that control the functioning of the thyroid gland, the development of the sex glands, the function of the adrenal glands, menstruation, milk formation in pregnant women and fat and sugar metabolism.
The thyroid gland is situated in the lower part of the neck. It receives a bountiful blood supply. Some of the functions of the thyroid gland are to control the body’s metabolism rate, the irritability of the nervous system, keeping hair shiny and in good condition, and the storage of iodine. It also affects physical growth and mental development.
The adrenal glands are two small, yellowish colored bodies about 1 inch long, situated at the top of each kidney. The functions of the adrenal glands are essential to life. The outer section (adrenal cortex) of the gland secretes a number of hormones: aldosterone, glucocorticoids (cortisone and cortisol), sex hormones (androgens and estrogens). The inner section (medulla) of the adrenal gland secretes epinephrine (adrenaline) and norepinephrine.
The sex glands are the ovaries (producing estrogen and progesterone) and the testes (which produce testosterone). Both of these glands produce hormones that affect the reproductive cycles of males and females.
Certain cells in the pancreas produce insulin, which assists in the metabolism of carbohydrates and starchy foods, such as bread, pasta, rice and sugar. A lack of insulin produces a condition known as diabetes mellitus.
Please watch the following videos:
- Endocrine gland hormone review | Endocrine system physiology | NCLEX-RN | Khan Academy (about 12 minutes)
- The Endocrine System (about 14 minutes)
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