The following excerpts are taken from various parts of ‘Medical Question and Answer Book’, Reader’s Digest, Sydney, Auckland, 2010. “The body communicates with, and controls, its many parts by means of two major systems, the nervous system and the endocrine system.
“Every second of our lives, the brain receives, processes and acts on information. Even while we are asleep, scientists estimate, the brain receives and sends out about 50 million messages per second.But the brain doesn’t work alone: it relies on our sense organs for reports from the outside world; and it needs a means of communicating with the rest of the body. This is where the nerves come in. Through the spinal cord and the vast network of branching nerves that make up the peripheral nervous system, nerve impulses pass back and forth between the brain and every part of the body. These crucial messages not only keep us alive, but enable us to feel, think, remember and carry out acts as ‘simple’ as raising a hand, or as complex as writing a poem.
“The organs called glands that form the endocrine system do the job of regulating other organs and tissues by secreting into the blood stream chemical liquids (messengers) known as hormones. Growth and development, sexual activity, responses to stress and injury, ability to convert food into energy, even the symmetry of a woman’s figure and the hair on a man’s chest – all are under the influence of these hormones. The most important of the endocrine system glands are the pituitary, thyroid, parathyroid, adrenals, pancreas and sex glands – the ovaries in females and the testes in males.
“In addition, the part of the brain called the hypothalamus, plays a crucial role in the operation of the endocrine system. The pituitary gland nestles just below the brain, is about the size and shape of a pea and is a very important part of the endocrine system. The hormones it secretes operate both directly on body tissues and, indirectly, by triggering and regulating the hormone production of other glands. One pituitary hormone (growth hormone), for example, causes a child’s bones and soft tissues to increase in size. Another (thyroid stimulating hormone or TSH) regulates metabolism by stimulating the thyroid glands. Such pituitary hormones as follicle-stimulating hormone, luteinizing hormone and prolactin, all help to determine sexual characteristics and control reproduction, while adrenocorticotroic hormone (ACTH) causes the adrenal glands to release their vital hormones.
“More recent discoveries in endocrinology have revealed that the pituitary is not the body’s master gland. It is itself controlled by the hypothalamus, a part of the brain that lies directly above it (as mentioned earlier). The hypothalamus is constantly bombarded with information in the form of nerve impulses about the condition of the body; when it senses the need for action, it secretes chemical substances, known as releasing factors and inhibiting factors, which trickle down to the pituitary gland and stimulate or inhibit the release of hormones stored in the gland.
“These hormones then work to control the body’s growth and development and many of its functions. The role of the hypothalamus in modulating the pituitary shows how closely the nervous system works with the endocrine system to keep the body functioning.
“The hypothalamus also makes two hormones called oxytocin and vasopressin; these travel down special cell pathways to the pituitary, which in turn stores and releases the hormones as needed. Oxytocin stimulates muscle contractions during childbirth, while vasopressin helps to keep blood pressure up by constricting blood vessels and by causing the body to retain fluids.”
The two hormones that play a crucial role in the pre-menstrual, menstrual and post-menstrual periods in a woman’s life are oestrogen and progesterone. The hormone oestrogen stimulates the release of eggs. As soon as a woman’s supply of eggs has run out, oestrogen levels start to go down. Progesterone’s main function is to prepare a woman’s womb for possible impregnation. This hormone also helps to protect the endometrium (the lining of the uterus).
Artificial oestrogen substitutes are made from horse urine or plants. Artificial progesterone is made from yams and soybean. These two hormones, made from natural products, have exactly the same characteristics as those produced by the human body.
In my next column I will go into greater detail on the influence of these hormones on pre-menstrual, menstrual and post-menstrual health and behaviour of women and the current availability of treatment.
To be continued
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